Review and Enhancement of a 1979 Review of Weather Modification

Oh, yeah, baby!  1979!  The Sex Pistols with Johnny Rotten and punk bands like Black Flag were on the rise! 

My belated review of “Weather Modification” has to be done, IMO:  i.e., corrections and comments, to complete a peer-reviewed article that was published in the journal, Reviews of Geophysics and Space Physics, using literature available to the authors at the time of the article was submitted/published that they omitted or didn’t know about.  

As an aside, omitting stuff happens a LOT in the domain of “weather modification/cloud seeding.”  A recent example, to go into a minor rant, was in the peer-reviewed article by Benjamini et al. 2023 (J. Appl. Meteor. and Climate)  who reported a null result of randomized cloud seeding in Israel.  Benjamini et al.  could not bring themselves to cite my 1995 article with Prof. Peter V. Hobbs (same journal), that concluded cloud seeding increases previously reported by Israeli scientists at the Hebrew University of Jerusalem were illusory.  Thus, there was no reason to think cloud seeding would work in another randomized experiment.  Sure, it’s painful for them to cite my work, but still….same old same old; omit, omit, omit.  Science is not always what you think it should be!

As an expert in some elements that are addressed in the 1979  article, I am happy to be able to improve and clarify it for readers of historic material, should they find it,  before the Grim Reaper drops by.  Here is the full article, which overall is quite good, except for those areas I am intimately familiar with:

A review and enhancement of the “weather modification” review by Grant and Cotton_1979_one column

I am quite candid about WHY I am doing a series of these “reviews and enhancements” of historic material as you will read above.  I tend to get carried away, and so all the minutiae I discuss might be “painful,” too.  I do my best, though.

Sincerely,

Art

A Review and Enhancement of “A Critical Assessment of Glaciogenic Seeding of Convective Clouds for Rainfall Enhancement”

I submitted a long “review and enhancement” on this article by Dr. Bernard A. Silverman’s 2001 massive (14,000 word) review article in the Bulletin of the American Meteorological Society (BAMS) in March 2002.  My “Comments” were too long, the Bulletin editor said, and so it never even went to peer review.  And, he was right, it was too long.

Silverman’s long review article is here.  It’s well worth reading and there is much we agreed on in those days,  if anyone cares:

2001 Silverman Critical assessment 2001ocr

Most of my “review and enhancement” of Silverman’s excellent, unbiased article despite his pro-cloud seeding stance, concerns the Israeli clouds and cloud seeding experiments.  I am an expert in that domain, having spent 11 weeks in Israel in 1986 studying their clouds, rain and sounding data with the full cooperation of the Israel Meteorological Service.  The ensuing article was published in the J. Roy. Meteor. Soc. in 1988.  The gist of it:  the clouds of Israel were not being described correctly by the leaders of cloud the seeding experiments at the Hebrew University of Jerusalem.  They described them as plump with cloud seeding potential when they were not.

In the early 1990s,  I re-analyzed the Israel-1 and Israel-2 randomized experiments along with my co-author, Peter V. Hobbs, director of the Cloud and Aerosol Research Group at the University of Washington, Seattle.  The article, which concluded that there had been no cloud seeding induced increases in rain in these experiments,  was published in the J. Appl. Meteor. in 1995.  Several cloud seeding-centric scientists commented on that paper in 1997 along with our “Replies.”

When I saw Dr. Silverman’s 2001 article and that he had misdescribed some of my own work, I went into a controlled rage of objectivity (haha),  as scientists do from time to time,  and decided to write a “Comment.”  But, as I added more and more material, my  “Comment” became an article in itself, even a “novella” of sorts.    Eventually those 2002  “Comments” led to a full blown article:  “The Rise and Fall of Cloud Seeding in Israel,” that manuscript submitted in 2017 and rejected by BAMS in 2019 (J. R. Fleming, private communication) after two split reviews.  BAMS did not allow me to respond to the comments of the two reviewers or revise my manuscript.

Well, after all these years, I just re-read my critique of Silverman’s 2001 article and thought it had some merit for those of you interested in 1) cloud seeding, 2) Israel.    So, here it is, as it was submitted with a couple of minor corrections and an update.  Caution:  the subject of scientific misconduct is broached. That didn’t help me in 2002, either, but I’ve left it in anyway.

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  1. Introduction

Silverman (2001, hereafter S01) is to be commended for attempting the prodigious task of making sense of all of the randomized cloud seeding experiments targeting cumuliform clouds during the past 40 years.  In large measure he has succeeded and made a significant contribution to the field of weather modification.  Still, some comments and clarifications are needed .

In his historical overview of cloud seeding, S01 should have mentioned the great effort that an independent agency, the U. S. Weather Bureau (USWB), made in attempting to replicate the early and often spectacular claims of seeding successes that began to appear in the late 1940s (e.g., Kraus and Squires 1947).  The USWB (i.e., Coons et al. 1949; Coons and Gunn 1951) seeded dozens of summertime cumuliform clouds in Ohio and along the U. S. Gulf Coast that were similar to clouds in several of the projects examined by S01 with up to “60 lbs of dry ice per mile.”

They found no evidence of any particular seeding effect.

On the contrary, USWB observers found that the turrets usually dissipated or settled back in altitude after they had been seeded.

The USWB scientists also made an unexpected and important discovery: ice was already forming in clouds with tops as warm as –6°C before they had seeded them.  The occurrence of ice was at far higher temperatures than was expected from ground ice nucleus concentration measurements on which seeding hypotheses were based.  Those ground measurements suggested that ice would not form until clouds reached temperatures of –15° to –20°C.  This stunning USWB observation was to be confirmed in more sophisticated aircraft measurements more than ten years later in Missouri during Project Whitetop (Koenig 1963).

The USWB’s independent seeding trials that showed little evidence of seeding having affected rain on the ground, crude as it was, stands tall today relative to the same conclusions about the seeding of cumulus clouds reached by S01 50 years later.

  1. Why weren’t seeding effects produced in the projects reviewed?

One would think that we know how to seed clouds successfully with indisputable scientific evidence for more rain on the ground after more than 50 years of attempting to do so.  However, the production of seeding effects in rainfall on the ground have been preempted by three crucial cloud factors, particularly so in the projects examined by S01:  1) Due to the relatively warm cloud bases in the projects he examined, natural ice forms in, or can be expected to form, in the targeted clouds either within or soon after their summits ascend above –5° to –10°C, the temperature range where seeding might take place; 2) the formation of ice crystals is vastly increased in the temperature range of –2.5° to –8°C in clouds with warm bases once ice has formed due to an explosion of ice splinters and fragments caused by secondary ice-forming mechanisms associated with large drops; and 3) perhaps most surprising to the Bulletin reader: we don’t yet know what the true concentrations of ice particles are in clouds today due to past instrument limitations that have only recently been overcome.

Today’s knowledge concerning ice in clouds has been limited because of our inability to reliably measure ice crystals smaller than about 100 mm in maximum dimension.  Thus, published concentrations, even as high as they have been, have had to necessarily omit the contribution of very small ice crystals to the total in the cumulus clouds that have been sampled (e.g., Koenig 1963; Rangno and Hobbs 1991, 1994; Levin et al. 1996).  Early measurements with a new probe capable of measuring these small ice crystals suggest that the total ice crystal concentrations in clouds will be several times higher than previously thought (e.g., Lawson and Jenson 1998).  Hence we are once again on the verge of learning what the USWB did more than 50 years ago: there is more natural ice in clouds than we imagined.

Therefore, the seeding experiments discussed by S01 were, in a sense, premature since the experimenters had made, and perhaps unavoidably, erroneously low estimates of the amount of natural ice that formed in clouds.  In essence, they were pouring water into a river without knowing whether there was a flood already in progress.

This fact has been demonstrated by Stith et al. (2002) who found little liquid water in tropical cumuli above the –12°C level and but “traces” of liquid water by –18°C.  The clouds studied by Stith et al. represent the kinds of clouds seeded in several of the projects reassessed by S01, those in tropical regions with warm cloud bases and moderate updrafts.  The liquid water in the clouds studied by Stith et al. had been consumed by the explosive natural ice formation taking place in rising turrets at temperatures before they reached the –12°C level and that were glaciated by –18°C.

  1. Project Whitetop

 Project Whitetop (Braham 1979) still remains as one of the most important, enigmatic, and well designed of all the randomized cloud seeding experiments carried out to this day and it was surprising that it was not mentioned by S01.  It was worthy of discussion because of its design and results, and because of the seeding method employed, which probably constituted its only major design flaw.

  1. What made Project Whitetop so special?

Project Whitetop had the three critical attributes that characterize sound experimental design:  the experiment was 1) randomized, 2) the target area and the specific rain gauges for evaluation purposes were identified before the experiment began, and 3) the results were evaluated contractually by those removed from the conduct of the experiment, the institution carrying it out, and the evaluators had no vested interests in cloud seeding.[1]  The importance of these attributes in the conduct and evaluation of cloud seeding experiments cannot be overemphasized.  We do not know from S01 which, if any of his reviewed experiments, had these essential design attributes.

Project Whitetop stirred great interest and controversy when the initial analyses following its conclusion suggested strong decreases in rainfall had been produced by cloud seeding over a wide area (e.g., Lovasich et al. 1969).  Later analyses, however, found that rain was also less on seeded days over wide areas upwind of the seeding line as well and subsequently, most scientists now believe that the random draw was uneven and produced a false negative (Type II statistical error or “unlucky draw”) and seeding actually produced a null result overall (Braham 1979).

What went wrong in Project Whitetop?  First, just as the USWB scientists had found in similar clouds more than 10 years earlier, natural ice was forming in the Project Whitetop clouds at shockingly high cloud top temperatures, between –5° and –10°C, and clouds glaciated (turned completely to ice) with great rapidity (Koenig 1963; Braham 1964). Without doubt,  “ice multiplication” as this phenomenon was later dubbed by Hobbs (1969), seriously compromised the chances of creating more rain on the ground through cloud seeding.  This is because the purpose of the seeding was to create more ice in clouds that were (erroneously) believed by the experimenters to have little ice.

The warm-based Missouri clouds, like those projects in tropical settings discussed by S01, and also like those in Israel, produce copious quantities of large drops (>23 mm diameter) and even precipitation-sized drops (>200 mm diameter) as they ascend past the freezing level, making them ultra-ripe for the onset of various natural ice multiplication mechanisms (e.g., Hallet and Mossop 1974; Mossop 1985; Hobbs and Alkezweeny 1968).  In themselves, these mechanisms can produce effects similar to those produced by cloud seeding (Rangno and Hobbs 1991, 1994).

  1. Were the clouds seeded effectively in the experiments reviewed?

Again, Project Whitetop has something to say about the projects assessed by S01.  Project Whitetop had, in retrospect, a key design flaw: the seeding method used. Instead of injecting the seeding agent into updraft regions of clouds upwind or over the target as would be done today, the three aircraft used in this experiment dispensed it in lines about 50-km long upwind of the target at a height that was just below the bases of the cumulus clouds that might have been forming in the area.  Suitable cumulus clouds (building ones with, or about to have supercooled tops) with updrafts above the aircraft as they dispensed silver iodide was not a criterion for releasing the seeding agent in Project Whitetop.

Whether the silver iodide released by the aircraft in Project Whitetop ever got into suitable clouds, whether it did so at the right locations upwind or in the target, and in what concentrations if it did, was never established.  In fact, the “patrol” seeding, as it is sometimes called, appeared to be relatively ineffective from the ground measurements of ice nuclei concentrations that were made downwind in the target (Bouqard 1963).

Thus, a crucial link in the chain of events in the seeding process in Project Whitetop was completely missing.  The method of seeding suggests another reason why results of Project Whitetop were doubtful; the seeding hypothesis itself may never have been fully tested.

The questionable seeding method used in Project Whitetop was similar to the one that was adopted in the first experiment in Israel that was begun at about the same time as Whitetop, and this in turn affected the choice of seeding method used in the Puglia experiment (List et al. 1999) that S01 discussed.  Patrol seeding was used in the Puglia experiment because it appeared to the Puglia design team that the first experiment in Israel had been a statistical success, and they wished to replicate exactly in their own experiment the seeding methodology that had apparently brought success in Israel.  Whether, in fact, the first experiment in Israel was a success is now subject to doubt on several accounts (e.g., Rangno and Hobbs 1995, 1997a,b.)

The assumptions about dispersion made by the Project Whitetop design team also represents one of several recurring themes in cloud seeding experiments: an exaggerated view of dispersion, an accompanying lack of dispersion measurements prior to cloud seeding experiments, and an underestimate of the natural ice concentrations in the clouds to be seeded.

  1. The two randomized seeding experiments in Israel

The two randomized experiments carried out in Israel deserve special attention beyond that given by S01 because of their importance for a number of years in convincing the scientific community, even the most skeptical scientists, that randomized cloud seeding experiments had finally produced a measurable result (e.g., Mason 1980, 1982; Kerr 1982; Silverman 1986; Dennis 1989; Young 1993; Cotton and Pielke 1995).  Indeed, many have believed that they were the onlyexperiments in cloud seeding that had demonstrated a seeding success among all those that have been conducted. In this context, S01 must be admired for his ability to move from one who has previously validated the results of the experiments in Israel to one who now believes as the author does that they did not prove cloud seeding effectiveness after all. However, some descriptions by S01 of the Rangno and Hobbs (1995, hereafter RH95) reexamination of these experiments are incomplete and require further discussion.

First, why did the experiments in Israel have such great credibility as successes to such a wide audience?  This was because they seemed to have had, for a time anyway, all of the requisites for unambiguous scientific credibility: a sound design that included randomization, a choice of evenly spaced rain gauges (at least in the first experiment) that was limited to all of the gauges in a pre-existing recording rain gauge network, an apparent confirmation of a statistically significant result in a follow-up confirmatory experiment, and a sound cloud microstructural basis for believing that the statistical successes reported were achievable because the clouds were so deficient in ice.

For example, the experimenters reported over a period of many years that the clouds in Israel achieved rather great depths and low cloud top temperatures (to –21°C) while producing little ice or precipitation (i.e., Gagin and Neumann 1974, 1976, 1981; Gagin 1975, 1980, 1981, 1986, hereafter GN74, GN76, GN81 and G75, G80, G81, and G86, respectively).  This left a wide window (–12° to –21° C) for seeding to initiate ice and precipitation in those clouds.  The higher temperature mentioned above demarcated the highest temperature at which appreciable concentrations of the silver iodide seeding crystals would have begun to nucleate and the lower temperature where it was reported that the natural ice concentrations were high enough that seeding was not required to boost ice content.

With cloud bases regularly at 800 m or so above sea level at 5-9°C (GN74, G75), this meant, according to these reports, that there was a large population of non-precipitating or barely precipitating clouds moving into Israel from the Mediterranean Sea that were as much as several kilometers deep.  Furthermore, in support of this picture, the effects of seeding, according to the experimenters, had been in duration of rainfall, not in intensity (G86), a fact compatible with the kind of seeding done.  From these many reports, it all made sense to outside scientists.

It will surprise and trouble many readers who do not follow the cloud seeding literature closely that the reporting of the results of the experiments by those who conducted them was not apropos according to normal scientific expectations.  This unfortunate element of these experiments, which necessarily impacts the reliability of the body of literature about them, is discussed in Section e.

  1. Seeding logistics and heterogeneities in the two experiments in Israel

Perhaps because the patrol method of seeding described in Section 4 had just been adopted by the United States in its major test of seeding in Project Whitetop, the experimenters in Israel, about to embark on their own major seeding trial at about the same time (in the late winter of 1960-1961), also chose this method.  In fact, patrol seeding was used almost exclusively in the six years of the first experiment (National Academy of Sciences 1973, GN74).[2]

However, the experimenters in Israel used a seeding track that was 65-75 km long, or about 15-25 km longer than the one used in Project Whitetop (Gabriel 1967).  Moreover, they had but a single twin-engine aircraft available to them to seed a longer experimental period over which rainfall was to be evaluated for seeding effects, a 24 h day vs. Project Whitetop’s 14 h experimental period.  Most remarkably, seeding by this method was carried out for an average of only about 4 h of the 24 h experimental day and yet still seemed to have produced statistically significant results (Gabriel 1967; Wurtele 1971; GN74).   The precipitation climatology of Israel, that makes this an astonishing fact, was discussed by RH95.

 Not surprisingly, the experimenters themselves came to realize the inadequacy of coverage of the 4 h per day of patrol seeding by a single aircraft in the first experiment.   When their second experiment began in the fall of 1969, they had added no less than 42 ground generators and a second aircraft with aircrews to man them 24 h a day (National Academy of Sciences 1973).

These new and greatly extended sources of seeding in the second experiment constituted an enormous heterogeneity in seeding coverage in the amount of seeding material released, and a shift in the methodology between the two experiments from solely airborne seeding to mainly ground seeding supplemented by airborne seeding.  Yet, implausibly, according to the partial statistical reports of the experimenters, the enormous increase in seeding and the shift in methodology produced virtually the same seeding result as in the first experiment, a 13% increase in rainfall in the North target (e.g., GN81) compared with the 15% overall increase in both targets of the first experiment when only seeding 4 h per day took place.

  1. The cloud microstructure of Israel does not make a case for seeding having produced statistically significant results in the experiments

A second factor that makes it implausible that the 4 h of seeding produced the statistical results reported in the first experiment, or effects in the second is that the clouds of the eastern Mediterranean are, in fact, largely unsuitable for seeding due to high concentrations of ice and the onset of ice at slightly supercooled cloud top temperatures (e.g., Rangno 1988; Rangno and Hobbs 1988, 1995, 1997a,b; Levin et al. 1996).

However, S01 stated that a “fraction” of the clouds of Israel do not correspond to those required for seeding to be effective.   S01, by using the phrase “a fraction of” the clouds may have been “unsuitable” for seeding, presumably means that some of the clouds making landfall on the Israeli coastline where they were to be seeded already contained high natural ice crystal concentrations and thus had no seeding potential, or had tops that were too warm for seeding to be effective, or were stratiform in nature with no updrafts below them to draw the seeding material upward as was noted in RH95.

However, the word “fraction”, as used by S01, is ambiguous and may inadvertently mislead Bulletin readers by suggesting that it means  “a small amount of.”

In fact, it would be a rare day in which high ice concentrations are not observed in mature and aging cumuliform clouds with tops  >–14°C.  Levin et al. (1996) gathered ice concentrations in clouds with tops warmer than about –14°C on several rather ordinary shower days in Israel and found tens to hundreds per liter in those clouds. The author directs the reader to papers that discuss the cloud microstructure of Israel (Rangno 1988, 2000; Rangno and Hobbs 1988, 1995, 1997a,b).

       2.  The stratifications of seeding effects by the cloud top temperatures in the second experiment are unreliable

S01 repeats the cloud top temperature stratifications that were reported on numerous occasions by the experimenters as having strongly partitioned seeding effects in the second experiment.  The experimenters reported, for example, that the maximum seeding effect in the second experiment was a 46% increase in rainfall compared with control days when the cloud top temperature was in the range of  –15° to –21°C (e.g., GN81).

However, the cloud top temperature stratifications by the experimenters are unreliable for several reasons and should not be quoted (RH95).  Also, in view of the tens to hundreds per liter ice particle concentrations found in the clouds of Israel with tops warmer than about –14°C on rather ordinary showery day situations (Levin et al. 1996), combined with the discovery that rain routinely falls from clouds with tops warmer than –10°C (Rangno 1988), it is no longer scientifically credible that the strongest seeding effect was produced in clouds that had top temperatures between –15° and –21°C where excessive natural ice crystal concentrations already exist.

       3.  Discussion of statistical issues:   Israel-1

S01 stated that RH95 concluded that the results of the first experiment were due to a false positive or Type I statistical error based solely on evidence reported by Wurtele (1971).   RH95 performed a “cradle to grave” analysis of the first experiment and several significant factors, besides the fact that the greatest apparent seeding effect was in a region that was avoided by the seeding aircraft, led us to our conclusion. We direct the reader to our paper and subsequent discussions of this issue (Rangno and Hobbs 1995, 1997a, 1997b; Rosenfeld 1997).

On the other hand, S01 himself offers no explanation in his evaluation of the first experiment about why the statistical significance was highest in the little-seeded Buffer Zone (BZ) that lay between the two targets.  In ignoring this fact S01 does not heed the same large “red flag” that should have raised skepticism about the statistically significant results in the first experiment more than thirty years ago.

No less than the chief meteorologist for the first experiment[3] stated, with notable candor in Wurtele (1971), that the BZ could only have been seeded 5-10% of the time, a conclusion sustained in RH95.  Moreover, GN74, themselves puzzling over this same statistical anomaly in the BZ, concluded that relying on a seeding argument for the BZ anomaly was weak (though they did it anyway) since the statistical significance in the BZ also accrued on seeded days in which the lone seeding aircraft did not even fly!

It would be interesting to learn what knowledge S01 has developed to refute these assessments by the experimenters themselves.       

      b.   Israel 2

Two Type I statistical errors in a row (lucky draws) is a slim possibility as some have noted concerning RH95.  However, two false positives in a row did not occur in the Israeli experiments when the same crossover scheme was used to evaluate both of them as was called for in the a priori design (Gabriel and Rosenfeld 1990, Silverman 2001).

Second, when using the South target gauges as the control for the North target area, as was also specified in the a priori design (e.g., GN74), a null result for the second experiment was produced again (Gabriel and Rosenfeld 1990; RH95).

However, in a third design component of the second experiment, a statistically significant result was evinced when a few rain gauges in a coastal plain upwind of the North target area were used to assess seeding effects in the target (GN81).  The statistical significance so obtained in the third of the three design evaluation components comprises the second statistically significant result in a row that S01 refers to.  Are you following me, reader?

At first glance, perhaps the achievement of any statistical significance in even one of the three design components is an impressive result even if it is outweighed by two null results (both of which went unreported at the time).

However, in a wider analysis than that performed by the experimenters, or by Gabriel and Rosenfeld (1990), RH95 found comparable or even heavier rain that fell on the seeded days in the North target area also fell over a wide region in and outside of northern Israel; namely, in central and southern Lebanon, western Jordan, and in Israel south of the North target area including Jerusalem itself!  Ironically, the experimenters had their offices in Jerusalem and were somehow oblivious to the heavy rain they were receiving when they seeded the North target area some 100 km to the north.

The single exception to this regional pattern of markedly heavier rain on North target area seeded days was in the coastal plain upwind of the North target area that had been pre-selected as a control zone.

The widespread regional pattern of bias in rainfall discovered by RH95 on North target seeded days suggests to meteorologists that the random draw was flawed or compromised by a bias in the weather systems that favored heavier rain over a synoptic scale region on North target area seeded days.

The second point that weakens the statistical significance obtained in the North target area is that those conducting the experiment did not specify the rain gauges for the evaluation prior to the experiment contrary to good scientific design (e.g., Court 1960).  Not naming gauges, or not using all of the established gauges in post analysis allows for “cherry-picking” of those gauges to find whatever result one wanted to find[4].

           c. The delayed reporting of statistical results and other actions by the experimenters constituted scientific misconduct and therefore the body of work by those researchers is inherently compromised

 S01 should be applauded for his valiant attempt in his review to ferret out the misleading reports of statistical significance.  However, there is a far more important test of the reliability of published results that S01 did not consider: if demonstrable scientific misconduct occurs in the reporting of results, then no publication by the wayward author(s) before or after this time can be considered reliable and they should not be quoted.

But what is “scientific misconduct”?

“Drug Maker Admits That It Concealed Tests Which Showed Flaws.”

“The Warner-Lambert Company, one of the nation’s largest drug companies, pleaded guilty yesterday to criminal charges and agreed to pay a $10 million fine for hiding from the Food and Drug Administration faulty manufacturing processes used for several drugs….”

                                                                                                –New York Times,  p1, 29 November 1995

Most readers can recognize egregious scientific misconduct such as concealing data that impact and change the conclusions of an experiment in which only favorable and therefore, deceptive results are published,  as described in the newspaper story above.

Misconduct also occurs when researchers conceal for many years the results of new experiments that contradict those of their previously published “successful” experiments on which the scientific community and public have depended upon.

Misconduct can also be understood to have occurred when a researcher denies access to his “lab” to bonafide workers in his field who have come to study and validate his unique long-published results, results that only his lab in all the world have produced with the “equipment” he has used.

We can all recognize these acts as contrary to the values of science and its pursuit of  truth.  An action such as the latter is particularly odious when the researcher’s much ballyhooed results are later shown to be wholly fictitious.

Very regrettably, all three acts of misconduct occurred in the cloud seeding experiments in Israel.  It is a matter of record that the experimenters chose to conceal the negative statistical results that accrued in the randomly seeded South target area of Israel-2 from the time that experiment ended in the spring of 1975 until 1990. These omitted statistical results, when incorporated into the mandated crossover evaluation of that experiment, resulted in a null (-2%) seeding effect (Gabriel and Rosenfeld 1990).[5]  Thus, the complete second experiment had not replicated the results of Israel-1 as Silverman (2001) also concludes but had been widely believed based on the experimenters’ partial reports limited to the North target area (e.g.,  Tukey et al. 1978, Kerr 1982; Silverman 1986).

The experimenters also chose to conceal from their colleagues the ongoing results of a third randomized cloud seeding experiment, Israel-3, that was taking place in central and southern Israel.  This experiment began in the fall of 1975 and ended in 1994.  The random seeding in this experiment suggested year after year that seeding was having no effect or possibly decreasing the rainfall in the target (e.g., Rosenfeld and Farbstein 1992; Rosenfeld 1998).  The first interim results of the third randomized experiment were not mentioned until 1992, 17 years after it had begun.  This reporting behavior is in contrast to the positive reports that were issued in journals part way through the first and second experiments by Gabriel 1967 and GN74 when the effects of seeding were indicated to be positive.

In summary, during 24 consecutive years of randomized seeding in the south target  in Israel-2 and -3 combined, had less rainfall (about 10%) on seeded days than on the control days.   This contrary knowledge was hidden from the scientific community for more than 15 years.  The original authors of the partial reports passed away before these concealed results were, or could be, reported in journals for the outside community to evaluate.

No one can doubt that the crucial negative statistical results of seeding described above in Israel-2 and -3, would have raised many questions, and should have been made known om a timely manner, first of all, to the experimenters’ own countrymen, to the outside scientific community as a whole, and especially to the scientific community in Jordan downwind of central and southern Israel that might have been impacted by the remote possibility of having their rainfall decreased.

In a third example of misconduct, this writer, known to the leader of the Israeli experiments as a skeptic[6] of the cloud microstructure reports that he had been publishing in journals, was denied access to the experimenters’ two radars during rainy spells to examine the heights (and temperatures) of precipitating clouds during his 11-week visit to Israel in early 1986.  One of the radars, a vertically pointing X-band or 3-cm wavelength radar, was located near the offices of the experimenters at a satellite office of the Hebrew University of Jerusalem.  The second, a C-band or 5.5-cm wavelength radar, was located on the grounds of Ben Gurion Airport to which this writer bicycled to from Tel Aviv for a meeting with the leader of these experiments who forbade him to go there during storms due to “airport security.”

From the rawinsonde data analyzed by me in 1988, and from the airborne data of Levin et al. 1996 we now know why the experimenters did this.

It doesn’t seem possible to conjure up the magnitude of incompetence required on the part of the experimenters to misinterpret so many cloud measurements over so many years from the many measurement sources they had at their disposal:  their own radars, satellite thermal imagery which they used routinely for forecasting cloud seeding opportunities and in their research reports (e.g., Rosenfeld 1980; G80), their own aircraft that for two rainy seasons skimmed the tops of clouds over their vertically pointing radar at Jerusalem (e.g., G80).   And, of course, they also had the Israel Meteorological Service (IMS) rawinsonde profiles launched up to four times a day from Bet Dagan (near Tel Aviv )from which it could be discerned that the clouds were not as they were describing them.

In view of these documentable instances of misconduct by the experimenters, none of the publications regarding cloud seeding, or its potential in Israel or elsewhere by those who participated in these acts, can be considered reliable.  Such publications should not be quoted until the full story concerning the actions of the experimenters is revealed.   Of particular interest is the original list of random decisions for Israel-2 due to the extreme one-sided nature of that draw on seeded days (Gabriel and Rosenfeld 1990).  We need to be sure that the list wasn’t compromised when heavy rain was forecast by the Israel Meteorological Service.  From experience in commercial projects, I know that it’s satisfying to say when someone asks that you seeded when heavy rain falls.

  1. But why discuss misconduct in science? Won’t a discussion of, or a finding of “misconduct” diminish public support of science?  And won’t that, in turn, lessen the job opportunities that we workers in science might have?

In fact, from our own narrow purview, it could be (and will be by some) argued that we should never discuss or even mention misconduct in any area of science.  Rather, we should promote the thought that as scientists, we are not like other people, but, in fact, are superior to them and never do anything wrong or fraudulent because of our training like other people.  Sarcasm here.

Of course, we must not only discuss but eradicate misconduct from our ranks or others will.  And, yes, it is likely that there will be some erosion of public support for cloud seeding in the face of reports of misconduct in that field.  Someone may indeed lose his job.

But from a larger viewpoint, it is an outrage to not consider the question of whether scientific misconduct occurred that resulted in misspent tens of millions of public dollars.

Most worrisome, there are no guarantees that this will not happen again. We do not know, for example, if more data relative to cloud seeding or cloud microstructure are being concealed or consciously misanalyzed by this same group in ongoing efforts to justify what now appears to be a dubious operational cloud seeding program begun by the Israeli government in 1975 that was based on the experimenters’ partial statistical reports of seeding success and descriptions of  fictitious clouds.

Update: Due to the re-analysis of the Israeli experiments in 1995, and the subsequent journal exchanges in 1997, a panel was formed by the Israeli government to independently examine the results operational cloud seeding of the Sea of Galilee (Lake Kinneret) that began with the winter of 1975-76.  The panel found no  viable evidence that cloud seeding had increased runoff into the Sea of Galilee over a 27 year period (Kessler et al. 2006, Sharon et al. 2008).  Israel-4 ended with a null result after seven seasons of randomized seeding (Benjamini et al. 2023).

A reputational dark cloud will hang over the group from which these acts originated until the details are fully known and the data in these papers verified.  An independent panel of inquiry into these matters, while time consuming, can only benefit all parties by lifting this dark cloud so that we can move ahead.

On the other hand, the field of cloud seeding is unique in the atmospheric sciences.  Its past charlatans, quacks, and even misguided, self-deceived but sincere scientists who made ludicrous claims about seeding effects, have been well documented throughout its history (e.g., Fleming 2010).  In the early days of modern cloud seeding we had the USWB with their aircraft and their independent scientists (e.g., Coons and Gunn 1951) to invalidate some of the outrageous claims being made.

Today, it seems, we have only the peer-review process to ensure that the truth is told.  And, from the many reversals of published findings of major, even widely accepted experiment results, some once seen as having “proved” cloud seeding as evaluated by our best scientists (e.g., National Academy of Sciences 1973), we can conclude that peer-review is but a thin “firewall” indeed against this type of more subtle quackery.

Workers in weather modification today, like S01, with their own continuing silence on the matter of the omitted, crucial statistical results of the experiments conducted in Israel, are exhibiting an eerie tolerance for a pernicious kind of science reporting in journals on cloud seeding that, from this author’s viewpoint, threatens to destroy this field altogether.

 

REFERENCES

Benjamini, Y, A.,  Givati, P.,  Khain, Y. Levi, D. Rosenfeld, U. Shamir, A. Siegel, A. Zipori, B. Ziv, and D. M. Steinberg, 2023:  The Israel 4 Cloud Seeding Experiment: Primary Results.   J. Appl. Meteor. Climate, 62, 317-327.  https://doi.org/10.1175/JAMC-D-22-0077.1

Bouqard, A. D., 1963: Ice nucleus concentrations at the ground.  J. Atmos. Sci., 20, 386-391.

Braham, R. R., Jr., 1964: What is the role of ice in summer rain-showers?  J. Atmos. Sci., 21, 640-646.

_______________., 1979:  Field experimentation in weather modification.  J. Amer. Stat.

        Assoc., 74, 57-68.

Coons, R. D., E. L. Jones, and R. Gunn, 1949: Artificial production of precipitation.  Third Partial Report: Orographic Stratiform Clouds–California, 1949.  Fourth Partial Report: Cumuliform Clouds–Gulf States, 1949.  U. S. Weather Bureau Res. Paper No. 33, Government Printing Office, Washington, 46 pp.

_________, and R. Gunn, 1951: Relation of artificial cloud modification to the production of precipitation.  Compendium of Meteorology.  Amer. Meteor. Soc., 235-241.

Cotton, W. R., and R. A. Pielke, 1995: Human Impacts on Weather and Climate, 2nd edition, Cambridge University Press, 288 pp.

Court, A., 1960: Evaluation of cloud seeding trials.  J. Irrig. and Drainage Div., Proc. Am. Soc. Civ. Eng., 86, No. IR 1, 121-126.

Dennis, A. S., 1989: Editorial to the A. Gagin memorial issue. J. Appl. Meteor., 28, 1013.

Fleming, J. R., 2010:  Fixing the Sky:  The Checkered History of Weather and Climate Control.  Columbia University Press,  306pp.

Gabriel, K. R., 1967: The Israeli artificial rainfall stimulation experiment: statistical evaluation for the period 1961–1965.  Proceedings, Fifth Berkeley Symposium on Mathematical Statistics and Probability, Vol. 5, L. M. LeCam and J. Neyman, eds., University of California Press, 91–113.

_______, and D. Rosenfeld, 1990: The second Israeli rainfall stimulation experiment: analysis of rainfall on both target areas.  J. Appl. Meteor., 29, 1055–1067.

Gagin, A., 1975: The ice phase in winter continental cumulus clouds.  J. Atmos. Sci., 32, 1604–1614.

________, 1980:  The relationship between the depth of cumuliform clouds and their raindrop characteristics.  J. Res. Atmos., 14, 409-422.

_______, 1981:  The Israeli rainfall enhancement experiments. A physical overview. J. Wea. Modif., 13, 1–13.

________., 1986: Evaluation of “static” and “dynamic” seeding concepts through analyses of Israeli II and FACE-2 experiments. In Precipitation Enhancement–A Scientific Challenge, Meteor. Monog., 21, No. 43, Amer. Meteor. Soc., 63-70.

_______, and J. Neumann, 1974: Rain stimulation and cloud physics in Israel. Weather and Climate Modification, W. N. Hess, Ed., John Wiley and Sons, 454–494.

________., and J. Neumann, 1976: The second Israeli cloud seeding experiment–the effect of seeding on varying cloud populations. Proc. II WMO Sci. Conf. Weather Modification, Boulder, WMO Geneva, 195-204.

_______, and _________, 1981: The second Israeli randomized cloud seeding experiment: evaluation of results.  J. Appl. Meteor., 20, 1301–1311.

Hallett, J., and S. C. Mossop, 1974: Production of secondary ice particles during the riming process. Nature, 249, 26-28.

Hobbs, P. V., 1969:  Ice multiplication in clouds.  J. Atmos. Sci., 26, 315-318.

__________., and A. J. Alkezweeny, 1968:  The fragmentation of freezing water droplets in free fall.  J. Atmos. Sci., 25, 881-888.

Kerr, R. A., 1982: Cloud seeding: one success in 35 years.  Science, 217, 519–522.

Kessler, A., A. Cohen, D. Sharon, 2006:  Analysis of the cloud seeding in northern Israel. A report submitted to the Israel Hydrology Institute and the Israel Water Management of the Ministry of Infrastructure, In Hebrew with an English abstract). 117pp.  No doi.

Koenig, L. R., 1963:  The glaciating behavior of small cumulonimbus clouds.  J. Atmos. Sci., 20, 29-47.

Kraus, E. B., and P. A. Squires, 1947:  Experiments on the stimulation of clouds to produce rain.  Nature, 159, 489-492.

Lawson, R. P., and T. L. Jensen, 1998: Improved microphysical measurements in mixed phase clouds. Preprints, Conf. Cloud Phys., Everett, WA, Amer. Meteor. Soc. 451-454.

Levin, Z., E. Ganor, and V. Gladstein, 1996: The effects of desert particles coated with sulfate on rain formation in the eastern Mediterranean.  J. Appl. Meteor., 35, 1511-1523.

List, R., K. R. Gabriel, B. A. Silverman, Z. Levin, and T. Karacoastas, 1999:  The rain enhancement experiment in Puglia, Italy:  statistical evaluation.  J. Appl. Meteor. 38, 281-289.

Lovasich, J. L., J. Neyman, E. L. Scott, and J. A. Smith, 1969: Wind directions aloft and effects of seeding on precipitation in the Whitetop experiment.  Proceedings, National Acad. Sci., 64, 810-817.

Mason, B. J., 1980:  A review of three long-term cloud-seeding experiments.  Meteor. Mag., 109, 335-344.

___________, 1982:  Personal reflections on 35 years of cloud seeding.  Contemp. Phys., 23, 311-327.

Mossop, S. C., 1985: Secondary ice particle production during rime growth:  the effect of drop size distribution and rimer velocity.  Quart. J. Roy. Met. Soc., 111, 1113-1124.

National Academy of Sciences, 1973: Weather Modification: Progress and Problems. T. F. Malone, ed., 258 pp. (Available from the National Research Council, Washington, D. C.)

Rangno, A. L., 1988: Rain from clouds with tops warmer than –10°C. Quart J. Roy. Meteor. Soc., 114, 495-513.

___________, 2000:  Comments on “A review of cloud seeding experiments to enhance precipitation and some new prospects.” Bull. Amer. Meteor. Soc., 81, 583-585.

____________, and P. V. Hobbs, 1988: Criteria for the development of significant concentrations of ice particles in cumulus clouds. Atmos. Res., 22, 1-13.

_____________, and __________, 1991: Ice particle concentrations and precipitation development in small polar maritime cumuliform clouds. Quart. J. Roy. Met. Soc., 117, 207-241.

___________, and __________, 1994:  Ice particle concentrations and precipitation development in small continental cumuliform clouds. Quart. J. Roy. Meteor. Soc., 120, 573-601.

___________,  and P. V. Hobbs, 1995: A new look at the Israeli cloud seeding experiments.  J. Appl. Meteor., 34, 1169-1193.

___________, and _________, 1997a: Reply to Rosenfeld.  J. Appl. Meteor., 36, 272-276.

___________, and _________, 1997b: Comprehensive Reply to Rosenfeld. Cloud and Aerosol Research Group, Department of Atmospheric Sciences, University of Washington, 25 pp.

Rosenfeld, D., 1980:  Characteristics of rain cloud systems in Israel derived from radar and satellite images.  M. S. Thesis, The Hebrew University of Jerusalem, Israel, 129 pp. (Available from the Department of Geosciences, Hebrew University of Jerusalem, Israel)

___________, 1997: Comment on “Reanalysis of the Israeli Cloud Seeding Experiments.” J. Appl. Meteor., 36, 260-271.

___________, 1998: The third Israeli randomized cloud seeding experiment in the south: evaluation of the results and review of all three experiments. Preprints, 14th Conf. on Planned and Inadvertent Wea. Modif., Everett, Amer. Meteor. Soc. 565-568.

___________., and H. Farbstein, 1992: Possible influence of desert dust on seedability of clouds in Israel. J. Appl. Meteor., 31, 722-731.

Sharon, D., A. Kessler, A. Cohen, and E. Doveh, 2008:  The history and recent revision of Israel’s cloud seeding program.  Isr. J. Earth Sci., 57, 65-69.     https://DOI.org/10.1560/IJES.57.1.65.

Silverman, B. A., 1986: Static mode seeding of summer cumuli–a review. In Precipitation Enhancement–A Scientific Challenge, Meteor. Monog., 21, No. 43, 7-20.

_____________, 2001:  A critical assessment of glaciogenic seeding of convective clouds for rainfall enhancement.  Bull. Amer. Meteor. Soc., 82, 903-923.

Stith, J. L., J. E. Dye, A. Bansemer, A. J. Heymsfield, C. A. Grainger, W. A. Petersen, and R. Cifelli, 2002:  Microphysical observations of tropical clouds.   J. Appl. Meteor., 41, 97-117.

Turkey,  J. W.,  D. R. Brillinger, and L. V. Jones, 1978b: Report of the Statistical Task Force to the Weather Modification Advisory Board, Vol. II.  U. S. Government Printing Office, pE-3.

Young, K. C., 1993: Microphysical Processes in Clouds.  Oxford University Press, 335-336.

Wurtele, Z. S., 1971: Analysis of the Israeli cloud seeding experiment by means of concomitant meteorological variables. J. Appl. Meteor., 10, 1185-1192.

Footnotes

[1] The University of California Statistical Laboratory under the direction of Jerzey Neyman.

[2] Four ground generators were located in hilly terrain in the extreme northeast portion of the country.

[3] The Chief Meteorologist for the seeding experiments in Israel was misidentified by Wurtele (1971) as a meteorologist with the Israel Meteorological Service.

[4] Rangno and Hobbs (1995) used a subset of rain gauges that whose data were routinely published in monthly or annual summaries by the Israel Meteorological Service and therefore, were “pre-selected” by the Israel Meteorological Service, an agency not affiliated with the seeding experiments.

5 Even then, these “full” statistical results for the second crossover seeding experiment were not published in a vacuum; but only after the leader of the experiments passed away in 1987, and after a letter-writing campaign to Israeli government offices by the former Chief Meteorologist of the experiments urging the experimenters to publish the full results.

[6] My July 1983 submitted article,  asserting that rain was falling from clouds with tops much warmer than could be accounted for by the experimenters’ cloud descriptions was rejected by J. Climate  Appl. Meteor. in 1983 (B. A. Silverman, co-chief Editor, private communication.)  Moreover, the leader of the experiments in Israel had provided a lengthy and perhaps pivotal negative review of that paper (A. Gagin, 1984, private communication.)

The Catalina, AZ, 2023-24 Water Year

Check it out.  We’re still having generally greater totals than we had during those many droughty years of the late 1990s to about 2012 that caused so much speculation about longterm permanent drought here due to global warming (later rephrased to “climate change” after a hiatus in global warming that began around 1999 and lasted more than a decade).    The red line is a quadratic fit to the data.  Let’s hope those greater WY totals of late continue despite overall gradual warming over this whole period.

The Catalina WY record happened to begin in 1977-78 right at the beginning of one of the wettest few years in hundreds of years in the Southwest generally as seen in tree ring records.  The overall Arizona statewide average (unfortunately presented by calendar years by NOAA) doesn’t show much going on over the past 100 years, see lower graphic through 2022, the latest year available.

Catalina Cool Season (October-May) Was Slightly Above Average

Here’s a long term graph with a curve fit of the Catalina October through May precipitation beginning in 1977.

The Catalina record begins with an extraordinary wet spell in 1977-78 through the early 1980s, augmented by El Niñoes and possibly the Pinatubo eruption in the early 1990s. The initial wet spell was  associated with a shift in the so-called “Pacific Decadal Oscillation.”  The red line is a polynomial fit to the data.  It seems to suggest a recovery is underway from the overall drier winters of the early 2000s despite the 2020-21 Oct-May drought.  Will a recovery continue?  Is it real?

A New Decadal Climate Oscillation Detected in Past Data a Long Time Ago? A Fool’s Journey? Namias Reacts

Purpose of this post of ancient, unfinished work with the humorous title:  Could it inspire someone to continue it in a more sophisticated way than I have?

Named climate/weather influencing  “oscillations” have become so numerous in the scientific literature (e.g., Atlantic Meridional Oscillation, Arctic Oscillation, Pacific Decadal Oscillation, El Niño-Southern Oscillation, Atlantic Oscillation, Quasi-Biennial Oscillation, Madden-Julian Oscillation, etc.)  one is tempted to ask humorously, “Doesn’t everyone have one?”

Well, I do, but this research is incomplete.  And it may ne bogus, illusory; it seems to lead to a dead end.  Still, “we” journey on, hoping these early findings, incomplete as they are and needing to be updated, will nevertheless bring someone a Nobel Prize in meteorology.  (Also still waiting for some kind of science prize or medal from Israel for the work I’ve done there in exposing faulty cloud seeding results and descriptions of non-existent clouds supposedly ripe with seeding potential (Rangno and Hobbs 1995, Rangno 1988).  But, as the Prunes sang, I had too much to dream last night.

https://youtu.be/-xRRT92Fpgs

Let us begin this story from the beginning.  Let us explore how a gigantic amount of work, consuming work, really,  thousands of hours of personal effort, can lead to a dead end. Maybe.

The oscillation story begins in an undergraduate  climatology class I took at San Jose State College in the late 1960s.  Each of us was assigned to do a climate research project.  I chose to do something on Los Angeles Civic Center rainfall, something I had been charting since childhood.  I graphed the days with measurable rain over the period of record for the Civic Center  going back to the 1877-78 “rain season.”  In California, the period of July 1 through June 30 is deemed the “rain season.”  That was the way rainfall data were presented in the newspapers.  The California “rain season” is similar to the water year precipitation totals widely used in the western US for the period of October 1 through September 30.  If you are a meteorologist in the West, the calendar year is generally eschewed in place of rain season or water year since the latter capture the character of whole winters and better account for snowpacks in mountains.

I saw an interesting phenomenon in the plot of days with measurable rain; there appeared to be an “instability”; a jump to much wetter conditions after a decades long trend of declining days with measurable rain. After reaching what appeared to a minimum of days with measurable rain, there was a  sudden jump in the next season to one having considerably more than the average.  But, it wasn’t just one season that had many more days with rain!  It was most of the next ten rain seasons that had above average days with rain.  This had happened in my plot on three occasions; the season following 1903-04, the season following 1933-34, and lastly, the season following 1976-77.  Namely, it wasn’t just a one-shot wonder, a season long singularity.

I was EXCITED!  So excited I eventually sent my Los Angeles Civic Center plot to a famous professor of climate and weather at Scripps Institution of Oceanography, Prof. Jerome Namias. I had read his papers in the Monthly Weather Review.  (I had begun subscribing to this journal when I was 13 years old. By this time I had seen that these same three jumps had occurred at San Luis Obispo, Santa Barbara, and San Diego.  There was no evidence of this phenomenon at San Francisco; it faded to the north.

If you’re a Los Angeles or Southern California “precipophile” like me, you might well guess immediately why I wasn’t so much interested in rain totals as with days with measurable rain.  A couple of huge storms can hide the character of a whole rain season, but the character of a rain season would be called out by days with rain.  An extreme example:  on New Year’s Eve, December 1933 into New Year’s Day, 1934, Los Angeles received it’s greatest 24 h rainfall:  7.36 inches!  Approximately half fell in December 1933 and a little more than half in January 1934.   The season’s rainfall total that year was 14.64 inches, or just about average.  HOWEVER, the DAYS with rain was two standard deviations below average! That’s “what done it” for me, that extraordinary rain day and why rain totals might hide the real character of a winter’s rain season.

Naturally, there is pretty high correlation between the days with measurable rain and the season’s total.  But from day one, I was convinced that the days with measurable rain was a better indicator of circulation changes over the years while rain amounts added “noise.”  Here is the correlation between rain amounts and days with rain for Los Angeles Civic Center:

Professor Jerome Namias seemed to be excited, too.  Here is his reply to my graph of LA rain frequency over the period of record.

Here’s the plot that started it all and that Namias and Stidd found interesting.  It didn’t look like “white noise.”

By the time I corresponded with Professor Namias, I had been hired as the Assistant Project Forecaster for the nation’s largest randomized orographic cloud seeding experiment, the Colorado River Basin Pilot Project.   I was living in Durango, CO, where the project’s headquarters were as I continued my research on a possible oscillation.

I was hoping that my work would eventually qualify as a Master’s Thesis from the meteorology department at San Jose State College (despite poor grades in grad school).  As an aside to the reader: I had no business whatsoever in being in grad school taking classes like “numerical methods,” “advanced hydrodynamics.” etc.  But I loved my campus life in those days of campus trash cans set on fire to protest the war, album protest rock, the marches, the demonstrations, the be-ins, the draft card burnings, to pinch a quote from National Lampoon’s “Bob Dylan’s Golden Protest” parody:

Over the next couple of years I added to my Los Angeles dataset with ones from San Francisco, San Luis Obispo, Santa Barbara, and San Diego.  These stations all had records that went back even earlier than the one at Los Angeles.  All but San Francisco, whose record exhibited what one might call, “white noise,” exhibited the trend I had seen in the Los Angeles record!  It was amazing to see.

Below is a running, 3-season average for SLO, SBA, LAC, and SAN through the early 1980s.  Sadly, I was not paying attention when scanning this original diagram and parts are not shown here, such as the abscissa comprised of the rain seasons.  The ordinate is the number of days with measurable rain at these four stations with a running mean of 3 seasons of those totals.  It ends with the 1981-82 season, far right.  For those in the know, the following season,  1982-83 featured a giant El Niño and that, combined with whatever was going on in what I was charting,  produced numbers of days off the chart!  I was so happy!  The Great Salt Lake was about to overflow, too, from this incredible wet spell that accompanied the shift to a more frequently rainy regime.

Since the rain at these locations is associated with cold troughs in the wintertime westerlies, I imagined that the circumpolar westerlies gradually retracted over the years, then hit some kind of tipping point and sprung back to more a more southerly latitude before beginning the same slow retraction over decades.

In the 1950s and 1960s,  the Los Angeles forecast office used the 564 decameter geopotential height contour as a divider of rain; heights at or below that contour was where the rain was and no rain was the rule for heights greater than the 564 decameter contour.   This key contour was used as an aid in forecasting rain as troughs approached and entered California.

The last shift to wetter conditions I found happened after the 1976-77 rain season.  With the 1977-78 rain season, it became much more frequently rainy along the central and Southern California coast for most of the next seven years.

My California rainfall study ended a few years into this transition to wetter conditions due to two elements:  1) NOAA had stopped publishing the “Daily Series, Synoptic Weather Maps, Part 1, Northern Hemisphere Sea-Level and 500 mb Charts and 2) I got very upset over the misleading cloud seeding literature that was being published in journals and jumped ship into reanalyzing previously published cloud seeding literature for most of the rest of my career almost solely on my own time (e.g., Rangno 1979, Hobbs and Rangno 1979, Rangno and Hobbs 1995).

The NOAA surface and 500 mb charts were important because that’s what I had used to track cyclones across the Pacific for five winter seasons before and after a “shift.”   I wasn’t able to do a set of tracks before and after the 1977-78 shift.  It was interesting that about 20 years later, the 1977-78 shift I was studying was discovered as the, “Pacific Decadal Oscillation”  (Wallace et al. 1994).

By the 1973-74 rain season I was so sure a prolonged shift to wetter conditions in the SW was on the doorstep that I was writing to the LA Times science writer, George Getz, the BuRec’s PR person, Hunter Holloway (the BuRec was the sponsor of the cloud seeding experiment I worked on), and to the Durango Herald about this coming shift to wetter conditions.

I was a little too early; the downward trend continued through the 1976-77 winter.  Here’s an example of those writings, one an audacious, self-written “news release” that follows the letter to Mr. Holloway shown here:

The reason I posted the letter above is to PROVE that I really was anticipating “The Shift” BEFORE it happened:

The additional research I carried out went far beyond the rain day graphs:

Pacific cyclone tracks before and after a “shift,”

NH average sea level pressures before and after a shift.

Here are the sea level maps for the 1930s, before and after a shift that occurred with the 1934-35 rain season.  For those not acquainted with the synoptic charts of that 1930s era it was something of a golden age of ship reports before they disappeared on these maps during World War II.  Thus northern hemisphere sea-level pressure and cyclone tracks changes could be reliably charted.

A graphically obtained “delta” map of sea-level pressure changes before and after a shift comprises the third graphic.   Not much can be seen to have happened when looking at these average maps for whole December through March seasons due to having  semi-permanent pressure systems like the low in the Gulf of Alaska, and the “Pacific High.”  I deemed looking at cyclone tracks (the following graphics) as far more useful.  Nevertheless, these are never-before-seen-or-done maps by anyone but me.  Enjoy:

Strangely believe it, the greatest sea level changes were in the domain of the Arctic Oscillation; in the North Atlantic, Greenland and England.  Whodda thunk it?  Not much change in the Pac and West, as expected due to persistent pressure fields even in these extremely frequent days with rain and those with many fewer ones.  I honestly did not know what to make of this change.  Do you?  If not, let’s keep moving….

Before doing the sea level pressure maps, I had charted cyclone centers across the central Pacific to the Rockies for the same winter (Dec-Mar) periods as was done above.  These charts were much more illuminating concerning the shift that happened in days with rain in central and Southern California:

First, the cyclone track “densities” of the five low frequency days with measurable rain winters preceding the shift.  A strong channeling of cyclones was seen during these winters from the lower latitudes of the central Pacific into the Gulf of Alaska and into southern British Columbia to a lesser degree.  This suggests the geographically anchored Asia/western Pacific Ocean jet exit had extruded farther east and into the central Pacific.  (Upper-level maps are not available for this period.). This was to resemble what happened in the low rain frequency seasons of the early and mid-1970s that preceded another shift.

In the figure below are the tracks following the “shift” to higher frequency rain day occurrences in central and Southern California.  The channeling is gone and what appears to be a standard distribution of low centers has replaced it.  Cyclones that developed in the western Pacific moved northeast into the Aleutians relatively close to Japan rather than scooting across the lower latitudes of the central Pacific.  The difference between these two maps is shown in the final map below this one.

The Delta Cyclone Density Map (pardon the skew):

Many more low centers tracked across the extreme eastern Pacific into California and into the Great Basin low pressure cyclogenesis zone in the lee of the Sierras.  This map is more illustrative than the sea-level pressure maps of those changes that happened after the shift to wetter conditions .

Questions:  Did channeled cyclones disrupt the sea surface enough to cause temperature anomalies in real time or later?  Were the El Niños that followed in the late 1930s and early 1940s in part triggered by the lower latitude cyclones racing across the central Pacific? Was this a global change such that Western Europe and northwest Africa saw a shift to wetter conditions after the ones noted in central and Southern California?  Data were not available for this period of study (1930s) except in the Middle East for Jerusalem, Israel.  There was no indication of a long period of decreasing days with measurable followed by a sudden and prolonged shift to more frequently rainy days.

My favorite answer to, “What caused this shift when someone asked was based on the work of E. N. Lorenz at MIT.   Professor Lorenz is famous for bringing our attention to chaos theory where small initial changes in starting conditions can lead to huge differences later.  Today, this concept is used to improve forecasts by introducing minor changes in initial data in the models from that observed to see how much difference results in the model predictions.

There need not be an external cause for climate shifts, he wrote.  It may just that systems shift in and out of favorite modal types without an external  forcing.  Thus, the best answer for what caused the shift I think I detected was, of course, “nothing.”  See Lorenz (1968, Climate Determinism) in the Amer. Meteor. Soc. Monograph Vol. 8, No. 30, on,  “The Causes of Climate Change.”   Strangely believe it, there are no papers on CO2 in this Amer. Meteor. Soc. monograph!   Mauna Loa measurements of C02 had just begun and so there was no awareness of how it was steadily increasing over the years.

——-

Work to be done?

Bringing the days with measurable rain plots up to date, storm tracks in the 1970s, and investigate whether the 564 decameter geopotential height contour shows a global expansion after the 1970s shift after hemispheric geopotential heights became available (beginning in the mid-1940s).   Or is the shift to a high rain frequency along the central and Southern California coast a local phenomenon where a mean upper-level trough recurrs along the West Coast for years at a time?  In a cursory check recently, there seems to be no clear recurrence of the prior three shifts in days with rain.  Boo.

And lastly, one must ask, is what I have done a “scientific mirage,” and expression used by Foster and Huber (1997) to denote illusory science?

I would like the answer to be a sudden global expansion of the polar westerlies (shown in the average hemispheric latitude of the 564 500 hPa geopotential height contour that accompanies a shift, something like the “Bond Cycles” observed in historic ice core data:  a “reset,” if you will, after a long, long period of withdrawing ever so gradually over the decades.  Perhaps our gradually shifting climate to a warmer one has done something to interfere with this “shift” phenomenon?

An obstacle that arose in later years was that climate station at Cal Poly, San Luis Obispo. whose record started in 1868,  started having missing monthly data that never showed up in the “Delayed Data” section in NOAA’s Climatological Data in the June and December issues.   Eventually, NOAA dropped even having a “Delayed Data” segment in the June and December issues!   Boo on that!  Santa Barbara, whose record also went back into the 1860s, too, had missing months that never were reported.  I remember how discouraged I was when these events happened and thought about giving up.  How can stations whose records go back into the 1860s (!) suddenly have incomplete records where observers don’t file reports with NOAA?  Where was the California State Climatologist?  Asleep at the wheel, I suppose.

Maybe you, one of my two readers, will take this research up to see if it goes anywhere?

Sincerely, Art “I’m dreaming” Rangno.   :

Caveat:  My grad advisers at San Jose State and a professor at the U of WA were unimpressed with these works.

A Review of the Israeli Cloud Seeding Experience in the Context of the 2023 Israel 4 Null Primary Result

PROLOGUE

I have written an extensive,  “comment” and “enhancement” of an article by Benjamini et al.  published in the in J. Appl. Meteor.  in January 2023.  The article was about the results of a fourth randomized Israeli cloud seeding experiment, Israel-4.   My “comments” and “enhancement” of Benjamini et al. (2023) posted below would never be published in an Amer. Meteor. Soc. journal.  The words are too strong.  So, I am going this route, a blog post.

Evidence for such a contentious assertion?  Prior experience.

I submitted a paper on the history of Israeli cloud seeding in 2018.  The journal, the Bull. Amer. Meteor. Soc. (BAMS) got but two reviews:  “Accept, important paper, minor revisions” by one Israeli scientist, and the second review, an outright “reject” in  a long review by an Israeli seeding partisan who signed his review. The chief editor of BAMS did not allow me  to revise my manuscript where needed (minor corrections),  nor rebut  the many specious comments by the seeding partisan.

Why is this behavior by the chief editor of BAMS outrageous and in non-compliance with our science ideals?

Replying to the comments of reviewers of manuscripts following peer-review is standard procedure in science after which a final decision on publication is then reached by the editor based on the responses of the author and the revisions made in the submitted manuscript.  This is exactly the process that Prof. Dave Schultz, Chief Editor of the Amer. Meteor. Soc. journal, The Monthly Weather Review,  and I are going through right now with a cloud seeding manuscript on the Colorado River Basin Pilot Project sub omitted to the AMS’ J. Appl. Meteor. and Climate (as of January 2024).

As an acknowledged expert on Israeli clouds, weather, and cloud seeding (e.g., Rangno 1988, Rangno and Hobbs 1995a), I deemed this refusal by the BAMS Chief Editor to allow me to respond to the comments of the two reviewers the sign of a corrupted journal process within the Amer. Meteor. Soc.:  Certain stories about failed science are not to be told, especially if they involve a country people have strong feelings about, as in this case.   My 2018 history describes unimaginably inadequate peer-reviews of the original published reports, those describing ripe for  seeding  clouds and the cloud seeding statistical “successes” that were all scientific mirages crafted by cloud seeding partisans.

The manuscript below has the same elements as the 2018 submission thus guaranteeing its rejection by a partisan AMS leadership.  But I feel strongly that certain things need to be said, and questions asked, to stop seeding partisans in Israel from costing their country so much in wasted cloud seeding efforts as they have over so many decades.  Sound implausible?  Read on…..

Despite what might be considered some “harsh” language at times, I consider myself a friend of Israel and donate to the American-Israeli Cooperative Enterprise, an organization that regularly counters the negative descriptions of Israel in much of the media today in their “Myth vs. Facts” segments.

=========THE MANUSCRIPT==========

ABSTRACT

The result of a fourth long-term randomized cloud seeding experiment in Israel, Israel-4, has been reported by Benjamini et al. 2023.  The seven-season randomized cloud seeding experiment ended in 2020 with a non-statistically significant result on rainfall (a suggested increase in rain of 1.8%).  This review puts the results of Israel-4 in the context of prior independent reanalyses of Israel-1 and -2,  reanalyses that can be said to have anticipated a null result of both the Israel-4 experiment and the lack of evidence that rain had been increased in the 30 plus years of the operational cloud seeding program targeting the Lake Kinneret (Sea of Galilee) watershed discovered in 2006 by an independent panel of Israeli experts.  The published literature that overturned the reports of success in the first two experiments, Israel-1 and Israel-2, was omitted by Benjamini et al., and thus, misled readers concerning those first two experiments.

The lack of cloud seeding success in Israel can be attributed to unsuitable clouds for seeding purposes, ones that form prolific concentrations of natural ice at relatively slight to moderate supercoolings which preclude seeding successes using glaciogenic seeding agents.

The phenomenon of “one-sided citing,” practiced by Benjamini et al. via the omission of relevant contrary literature is addressed.   Several corrections to and enhancements of the Benjamini et al. article are also included.

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  1. Introduction and Background

The results of the first two randomized crossover cloud seeding experiments in Israel, Israel-1 and Israel-2, discussed recently by Benjamini et al. 2023, as well as the descriptions of “ripe for seeding” clouds in Israel by the seeding experimenters, had an important role in the history of cloud seeding.   For many years it appeared that the viability of cloud seeding to have produced economically important amounts of rain had been established in those two “crossover” experiments conducted by scientists at the Hebrew University of Jerusalem (HUJ) (e.g., Kerr 1982, Mason 1982, Dennis 1989).  In descriptions of the first two benchmark experiments, ones that created the scientific consensus described above, Benjamini et al.  (2023, hereafter, “B23,”) do not tell the whole story in their history of cloud seeding in Israel that preceded their evaluation of Israel-4.

This review is meant to fill in the gaps for the reader left by B23 about those first two experiments that had so much practical impact.  For example, the Israel National Water Authority (INWA) began a several decades-long operational cloud seeding of the watersheds around Lake Kinneret (aka, Sea of Galilee) based on the seemingly favorable results of Israel-1 and those in the “confirmatory” Israel-2 experiment that followed (Gabriel 1967a; b; Neumann et al. 1967; Wurtele 1971; Gagin and Neumann 1974; 1976).  The INWA began seeding Lake Kinneret’s watersheds in November through April, beginning with the 1975/76, the winter season that immediately followed the end of Israel-2.

The statistical results of Israel-1 and -2 were backed by several cloud microstructure reports over the years that underpinned the idea that rain could be increased substantially by seeding Israel’s clouds (e.g., Gagin 1975, 1981, 1986, Gagin and Neumann 1974, 1976, 1981).  These reports caused Science magazine’s reporter, Richard Kerr,  to proclaim in 1982 that those first two Israeli experiments constituted the “One success in 35 years” of cloud seeding experimentation.  Kerr (1982) also wrote:

The Israeli II1 data must still be reanalyzed by other statisticians, but most researchers are also impressed that the results make so much physical sense.  The clouds that Gagin and Neumann hypothesized would be most susceptible to seeding did indeed produce the most additional rain after seeding.”

These statements are compatible with the history that B23 have provided, but it was to be far from the end of the “story.”

Fifteen years after Israel-2 had been completed it was learned that the random seeding of the south target clouds of Israel-2, a crossover experiment as Israel-1 had been, produced the indication that cloud seeding had decreased rainfall by a substantial amount, 15% (Gabriel and Rosenfeld 1990)2.  Gagin and Neumann (1981), however, had claimed that the random seeding that took place in the south target was “non-experimental” and so did not report the results of random seeding there.  No one challenged this claim. 

Until 1981 the result of seeding in the south target seeding had been described as “inconclusive” (Gagin and Neumann 1976), and prior to that, by (Gagin and Neumann 1974) after the first two seasons of Israel-2, that seeding had resulted in a seed/no seed average rainfall fraction in the south target that was “less than 1,” suggesting rain might have been decreased on seeded days.

However, the crossover evaluation of seeding in Israel-2 was not reported until Gabriel and Rosenfeld (1990)2.  The design document, approved by the Israeli Rain Committee and completed before Israel-2 began had, however, mandated a crossover evaluation (Silverman 2001) as had been done for Israel-1.  Nowhere did Gagin (1981) or Gagin and Neumann (1974, 1976, 1981) explain why they did not perform the mandated crossover evaluation of Israel-2.

Instead of Israel-2 crossover evaluation replicating Israel-1, where seeding appeared to have increased rainfall by about 15% when the data from both targets was combined (e.g., Wurtele 1971), the crossover evaluation of Israel-2 indicated a slight decrease in rainfall of 2% (not statistically significant).  Thus, Israel-2 had not replicated Israel-1 in an important way.

But results of Israel-2 were complex, as noted by Gabriel and Rosenfeld (1990) and left questions that they could not resolve.  The most revealing statement in Gabriel and Rosenfeld (1990) in reporting the “full” results of Israel-2 was this enigma (my italics and bold font):

There is a surprising contradiction between this finding and those of the analyses of Tables 4-17.  The difference occurs because the historical comparison of Table 18 ignores the unusually high south precipitation on north-seeded days (as well as the north precipitation on south-seeded days).  In other words, it is what happened when there was no seeding that causes the differences between the two analyses. The different choice of “control” days for the south, whether all the rainy days of 1949-60 or the north-seeded days of 1969-75, is what crucially affects the comparison.  If such large differences-of a magnitude of several standard errors and clearly significant by the usual statistical criteria-occur by chance, then chance operates in unexpected ways on precipitation and historical comparisons become highly suspect (see also Gabriel and Petrondas 1983). Otherwise, one would need to explain why there was so much more rain in the south when the north was being seeded; as of now, no explanation is available, especially as the prevailing wind direction is from the southwest.”

A “Type I statistical error,” the “good draw,” in Israel-2, heavy rains that affected both targets on north target seeded days3, was there for all to see if they wanted to.

Thus, a severe blow to the idea of randomizing cloud seeding experiments occurred in Israel-2 due to the exceptional random draw described by Gagin and Rosenfeld (1990).  Randomization could produce wildly unrepresentative results in which slight, but important, rain increases due to seeding could be forever hidden.

The null result of the combined targets in Israel-2 was due to an apparent decrease in rainfall on seeded days in the south target (~15%) that canceled out apparent increases in rainfall (~13%) in the north target.   Despite the new result and the many questions it raised, the INWA continued the commercial-like seeding of the Lake Kinneret watersheds during the winter rain seasons for more than 20 years after Gabriel and Rosenfeld’s (1990) disclosure of the “full” results of Israel-2.

The continuation of seeding of Lake Kinneret watersheds in northern Israel by the INWA despite the Israel-2 null result may have been due to the hypothesis put forward by Rosenfeld and Farbstein (1992)4; “dust/haze” had interfered with seeding in Israel -2 by creating high natural ice particle concentrations in supercooled clouds and that the presence of “dust/haze” even resulted in collisions with coalescence-formed rain (“the warm rain” process) that does not require the ice phase.  These cloud attributes, they concluded, meant there could be no increases in rainfall due to cloud seeding in the south target nor in the north target when dust/haze was present.  Without “dust/haze,” Rosenfeld and Farbstein argued, the clouds of Israel were as ripe as ever for cloud seeding.

2).    The Motivation for a Reanalysis of Israel-1 and Israel-2

The publication and the hypothesis of Rosenfeld and Farbstein (1992) formed the motivation for the Rangno and Hobbs 1995, hereafter RH95a) reanalyses of Israel-1 and -2.  This writer had spent 11 winter weeks in Israel in 1986 studying the rain-producing characteristics of Israeli clouds and felt Rosenfeld and Farbstein’s hypothesis had little credibility;  a full independent review of Israel-1 and -2 was needed as had been suggested in Science magazine (Kerr 1982).  And it would be done by someone who knew the clouds and weather of Israel (Rangno 1983, rejected by the J. Appl. Meteor.; Rangno (1988), Rangno and Hobbs (1988, hereafter, RH88).

I am also experienced in exposing suspect cloud seeding claims in the published literature (e.g., Hobbs and Rangno 1978, 1979, Rangno 1979, 1986, Rangno and Hobbs 1980a, b, 1981, 1987, 1993, 1995b).  By the time I began reanalyzing the Israeli experiments in 1992 I had also logged more than 400 flights for the University of Washington’s Cloud and Aerosol Group in studies that mostly concerned ice crystaldevelopment in slightly supercooled clouds in polar air masses similar to those that affect Israel (Rangno and Hobbs 1983, 1991, 1994, Hobbs and Rangno 1985, 1990).

3).   The results of the Rangno and Hobbs (1995) benchmark reanalyses of Israel-1 and Israel-2 that went uncited by B23

RH95 concluded that neither Israel-1 nor Israel-2 had produced bona fide increases in rain on seeded days, contradicting the HUJ experimenters’ reports and those contained in B23 that cloud seeding had increased rain in each of these experiments.  The conclusions of RH95 were given support by Silverman (2001) and later, for Israel-2, by Levin et al. (2010).

Moreover, in R88 it was strongly indicated that the “ripe for seeding” clouds described repeatedly by the experimenters (e.g., Gagin and Neumann 1974, 1976, 1981, Gagin 1975, 1981, 1986) did not exist.   The findings in R88 concerning shallow clouds that rained was not news to Israel Meteorological Service forecasters with whom I spoke nor to the Israeli experiments’ “Chief Meteorologist,” Mr. Karl Rosner.  Mr. Rosner wrote to me in 1987 that, “sometimes heavy rain fell from clouds with tops at -8°C.”  Thus, in contrast to the many HUJ experimenters’ reports cited previously, it was widely known by weather forecasters in Israel that rain fell regularly from clouds with tops >-10°C (~3-4 km thick clouds) as was documented in R88.

The HUJ experimenters had also reported, contrary to the above,  that many clouds with radar measured tops between -15°C and -21°C did not precipitate naturally due to a lack of ice in them or that precipitation formed by “warm rain” (collisions with coalescence) process (e.g., Gagin 1981, 1986) did not occur.  Those non-precipitating clouds in this low radar top temperature range were responsible for extra-large increases (46%) in rain on seeded days  (Gagin and Neumann 1981, Gagin and Gabriel 1987).

Seeding, they also reported, had no effect on naturally precipitating clouds, a finding compatible with the “static” seeding method carried out by the HUJ experimenters where small amounts of the seeding agent,  silver iodide are released.   Namely, when seeding took place, it rained for more hours on seeded days than on control days, but it did not rain harder.

B23 also refer to the Israel-2 low radar top temperature partition as having been associated with increases in rain.

(Questions)

Is it possible that Israeli weather forecasters and the “chief meteorologist” of the Israeli cloud seeding experiments had a better idea of which clouds rained in Israel than those whose research careers at the HUJ depended on reliable assessments of their own clouds and their cloud seeding potential?   Ans.  Probably not.

Why?

This writer, while welcomed at the Israel Meteorological Service in January 1986, was denied access to the seeding experimenters’ radar on the grounds of Ben Gurion AP to obtain echo heights  by the leader of the Israeli experiments, Prof. A. Gagin.  He insisted in our meeting that my monitoring of top heights would only confirm his cloud reports; that it took deep and very cold-topped clouds to rain in Israel.

It was also learned during January 1986 at about this same time that no less than six attempts had been proposed by outside groups to do airborne studies of the seemingly unique clouds of Israel, as shown in RH88, ones that had responded so well to cloud seeding (Personal communication, Prof. Gabor Vali, University of Wyoming, 31 January 1986).  Every one of those attempts to study Israeli clouds had been blocked.

Why?  And by whom?

  1. More about Rangno and Hobbs (1995): the most controversial and commented on paper ever published in an Amer. Meteor. Soc. journal and the unusual strategy used by the editor in choosing reviewers

 In a moment of brilliance (in retrospect), the editor for our journal manuscript, L. Randall Koenig, chose three reviewers who would be sure to reject the RH95a manuscript and its negative findings concerning cloud seeding.  But at the same time, Koenig realized that there would be no easy pass on it; no stone would go unturned by the reviewers, and our findings would be severely tested.  In fact, RH95 was significantly better for having cloud seeding partisans, H. Orville, W. Woodley, and D. Rosenfeld, review it (all signed their reviews).

Editor Koenig, himself an expert on weather modification and cloud microphysics (e.g., Koenig 1963, 1977, 1984), was also steeped in the long record of frequent mischief by those in the cloud seeding domain, weighed the arguments of the reviewers and the modifications of RH95a that reflected the reviewers’ criticisms:  He made the choice to publish RH95a.

It took courage for Editor Koenig to do that and recognizing who he felt had the better arguments.  In RH95a were the first two independent re-analyses of Israel-1 and Israel-2, as had been recommended years earlier in Kerr (1982) but ones that were clearly not going to take place.   How many other papers in our journals would be the improved and bogus claims eliminated if editors used the strategy of of Koenig and were as informed about the topic of the manuscript?

Perhaps due to the size of the ox being gored, our paper drew comments by the reviewers of our manuscript and others (1997a, b, c, d, e).   The number of journal pages involved in “Comments” and “Replies” on a single article is still a record for an Amer. Meteor. Soc. journal.   We draw particular attention to our “Replies” to the many, as we showed, specious “Comments” of Dr. Rosenfeld in RH97a and RH97b, and a B23 co-author.

Let the reader decide where truth lies.  We urge the reader to carefully review RH95a and our replies for the considerable evidence we present that the Israel-1 and Israel-2 experiments were both mirages of cloud seeding successes, contrary to the assertions in B23.

  1. Israel-3: enhancing B23’s description

B23 describe the results of the longest randomized cloud seeding experiment ever conducted, Israel-3 (1975-1995), a single target experiment.  However, they omit informing the reader that the remarkable “inconclusive” result was a suggested 9% decrease in rainfall on seeded days compared to non-seeded days (Rosenfeld 1998).  By omitting the sign of the null result, B23 left the reader to speculate on what the sign of the “null” result was.  The suggestion of a decrease in rain on seeded days again points to clouds naturally form precipitation very efficiently in Israel.  With the result of Israel -3 in hand, the reader would now learn, with Israel-2 (Gabriel and Rosenfeld 1990), that over a period of 25 plus years (Israel-2 and Israel-3 combined) decreases in rainfall due to seeding were suggested in central and southern Israel by cloud seeding!

  1. Rectifying B23’s statement concerning operational seeding

B23 state the increase in rainfall during the operational seeding, 1975/76 winter to 1990 reported by Nirel and Rosenfeld (1995) was “6-11%.”  In the abstract of the quoted article, the authors state that rainfall due to cloud seeding was increased by 6%, not “6-11%.”  This same increase in rain (6%) was also quoted by Sharon et al. (2008).

Moreover, the 6% increase in rain (said to be statistically significant by Nirel and Rosenfeld 1995) was not confirmed by Kessler et al. (2006) in their independent evaluation of operational seeding through the same period.  The independent panel reported 4.8% suggested rain enhancement over the same period evaluated by Nirel and Rosenfeld (Figure 1). 

Figure 1. The results of operational seeding on the watersheds of Lake Kinneret (aka, Sea of Galilee) as reported by Kessler et al. 2006.  (a) is that result of seeding on rainfall reported by Nirel and Rosenfeld (1995), b-d are the results found for various periods, including the very same era evaluated by Nirel and Rosenfeld (1995)5.

  1. What triggered the formation of an independent panel to evaluate cloud seeding?

The panel was created after RH95a was published and then followed by extensive journal exchanges by RH97a, b, c, d, e, in “Replies” to various “Comments” in 1997.  The INWA was then inspired to form an independent panel of experts due to these exchanges to evaluate what they were getting from the operational seeding of Lake Kinneret’s (aka, Sea of Galilee) watersheds rather than relying on the evaluations by the seeding promoters at the HUJ (e.g., Nirel and Rosenfeld 1995).  The results found by the panel are shown in Figure 1.

Should the lack of seeding results after 1990 shown in Figure 1 surprise?  I don’t think so.  This sequence of optimistic claims by seeding experimenters concerning their own experiments followed by reanalyses by external skeptics that find the original claims were “scientific mirages” (Foster and Huber 1997, Judging Science) is a pathology within the cloud seeding realm that has dogged it since its earliest days (e.g., Brier and Enger 1952, versus MacCready 1952).

In view of Figure 1, one must ask, “What if there had been no RH95a”?

We suspect that not citing our independent re-analyses of Israel-1 and Israel-2, Silverman’s (2001) conclusions concerning the first two Israeli experiments, and Wurtele (1971) who first drew the attention to a major red flag in Israel-1, combined with the fact that the HUJ experimenters failed to even understand the precipitating nature of their own clouds for decades with all the tools at their command, all pose monumental science embarrassments for Israel, their scientists, and for the prestigious HUJ from which the faulty reports emanated.

Can there be other reasons for not citing the work of external, foreign workers who overturned benchmark experimental science by the home country’s scientists?

  1. Did the background airborne microphysical measurements that preceded Israel-4 justify a new experiment?

B23 cite Freud et al. (2015) as having demonstrated cloud seeding potential in the mountainous north region of Israel through a series of airborne flights; but did it support the idea of strong cloud seeding potential as B23 assert?

No.

I was not asked to review Freud et al. 2015, as one might have expected given my background.  Nevertheless, I carried out a post publication “comprehensive review” that can be found under 2017 here.

Freud et al. 2015 was a “Jekyll and Hyde” read; some of the best reporting by the HUJ’s cloud seeding unit was contained in it.  But it also contained misleading statements.  My recommendation after reading what I considered to be a strongly biased study that was going to mislead the INWA concerning cloud seeding potential: “Don’t do a cloud seeding experiment in northern Israel based on the research of Freud et al. (2015)!”

 As the INWA could have suspected, Freud et al. (2015) would not be the first time that cloud seeding researchers at the HUJ had misled the INWA about the clouds of Israel being filled with cloud seeding potential.  My conclusion regarding the false picture of “abundant” cloud seeding potential in the northern mountains of Israel painted by Freud et al. 2015 was, in essence, affirmed post facto by the “primary” results of Israel 4.  The “abundant” cloud seeding potential in northern Israel described by Freud et al. (2015) was not realized or was imaginary to begin with.

A caveat on airborne sampling:  One can “lie” with aircraft measurements by sampling only newly risen turrets and avoiding those that are maturing or in aged states with appreciable ice particle concentrations.  Gagin and Neumann (1974), for example, stated that they chose only newly risen turrets, narrow ones at that, and flew research flights on mostly dry days, and those choices misled them and the rest of the scientific community regarding the microstructure of Israeli clouds and their cloud seeding potential.  Significant rain days in Israel are comprised of large complexes of convective clouds in various stages of development, “tangled masses,” as they were described by Neumann et al. (1967).  To their credit, Freud et al. informed the reader that they sampled only newly risen turrets when reporting the low (<2 per liter) modal ice particle concentrations in those turrets.

Freud et al.’s measurements could not have been more incompatible with uncited by B23 measurements of Levin (1992: 1994; Levin et al. 1996).  Tens to hundreds per liter of ice particles were found in six flights on four days in clouds having tops >-13°C.   Freud et al. 2015 could not bring themselves to inform their readers of similar high ice particle­­­ concentrations that they likely encountered during their 27 flights (that is, if they did not deliberately avoid those high ice particle concentration regions).  Freud et al. 2015, therefore, may be a first in the evaluation of cloud seeding potential in which measurements of ice particle concentrations in mature and aging clouds were not reported; the absence of such data made their entire report unreliable.

One of the B23 co-authors (DR) has claimed that ice particle measurements measured in their airborne research were “unreasonably high” in Israeli clouds due to probe caused shattering of ice crystals and thus weren’t reliable.  D. Axisa, a representative of the manufacturer, Droplet Measurement Systems, of the CAPS probe used by Freud et al. (2015) stated that this statement was false: “They could have reported accurate ice particle concentrations if they had wanted to.” Dr. Axisa is a former president of the Weather Modification Assoc.  It seems likely that HUJ researchers are once again withholding vital information on the clouds of Israel6.

  1. What do we know about cloud seeding in Israel today?

 What we know today is that if careful, skeptical and independent analyses of Israel-1 and Israel-2 experiments and equally careful evaluations of the clouds of Israel had been done in the first place by independent Israeli scientists or ones outside Israel that are non-partisan cloud seeding scientists (as was carried out by RH95a, R88, and by Silverman 2001), there would not have been 30 plus years of wasted operational cloud as would be found by independent evaluators in the decades ahead (Kessler et al. 2006, Sharon et al. 2008).  Fortunately, we need not guess whether those 10s of millions of dollars were wasted on the seeding of Lake Kinneret watersheds.  They were.   Inexplicably, the INWA drove through the “stop sign” presented by Kessler et al. (2006) and commercially seeded around Lake Kinneret for another seven years after this report came out according to B23.

  1. Why hasn’t cloud seeding worked In Israel?

 Answer:  too much natural ice formation in clouds.

B23 failed to mention that the “ripe-for-seeding” cloud foundation for the statistical results of Israel-1 and Israel-2 no longer exists.  The mythical clouds described by HUJ researchers were critical in the acceptance of the Israeli cloud seeding rain increases by the scientific community, as quoted in Kerr (1982) earlier and by Dennis (1989).

A review of the Israeli cloud microstructure shows that they are “ripe,” but not for cloud seeding, but for an explosion of ice as the tops ascend to temperatures below -5°C and age.  In most cases, precipitation-sized drops have already formed when the Israeli cloud ascend through this level (Gagin and Neumann 1974, Figure 13.4), and the concentration of cloud droplets exceeding the Hallett-Mossop riming-splintering criterion of >23 µm diameter can be inferred to be copious in that -2.5° to -8°C temperature zone.  Furthermore, there is an enhancement of the H-M process when droplets <13 µm are present (Goldsmith et al. 1976, Mossop 1985) and such drops would be present in the semi-polluted air masses; initially, shallow cold layers diluted by the warming of the Mediterranean Sea to depths of 3-9 km on shower/thunderstorm days by the time they reach Israel under cold polar troughs.

Without the “ripe for seeding” clouds, ones with great seeding potential to cloud top temperatures as low as -21°C as described by Gagin and Neumann (1976, 1981 and Gagin 1981), there can be no viable increases in rainfall due to cloud seeding.  This does not mean that some small, slightly supercooled clouds can’t be seeded to make small amounts of rain as noted by the HUJ researchers, Gagin and Neumann (1981), and by Sharon et al. (2008).  However, those small amounts weren’t deemed viable for a cloud seeding operations.

  1. The nature of the reporting of the experiments by the HUJ cloud seeding researchers

 The omission of the south target result (Gagin and Neumann 1976, 1981) was tantamount to the cancer researcher who only reports on the 50 mice his treatment cured while not reporting on the 50 mice that died from the same treatment.  This kind of behavior in virtually every field but weather modification/cloud seeding, would be termed, “scientific misconduct,” specifically of a type called, “falsification” when data are omitted or adjusted (Ben-Yehuda and Oliver-Lumerman 2017, Fraud and Misconduct in Research)6.  Inexplicably, Prof. K. Ruben Gabriel, the Israeli cloud seeding statistician, acquiesced in this omission as a reviewer of Gagin and Neumann’s 1981 paper in which this critical omission occurred.

Moreover, reporting the apparent negative effect on rainfall in the south target of Israel-2 would have raised numerous questions about the clouds of Israel:   How could seeding Israeli clouds, described as being filled with great seeding potential as had been repeatedly described by the HUJ researchers, have resulted in what appeared to be a large decrease in rainfall in the south target on seeded days?  Cloud tops in the south target in Israel average higher temperatures than those in the north (e.g., GN74; RH95a) making findings of decreased rainfall due to cloud seeding (as Rosenfeld 1989, Rosenfeld and Farbstein 1992 suggested) even harder to explain.

Moreover, while interim “positive” reports of cloud seeding increases in rain emanated from the HUJ during Israel-1 and Israel-2, HUJ researchers clearly felt differently about reporting indications of rain decreases in Israel-2 and Israel-3.   For example, the scientific community was not informed of the suggestion of decreased rain due to clouds seeding in Israel-3 by the HUJ experimenters until 17 years after randomized seeding had begun (Rosenfeld and Farbstein 1992).  Is this what the HUJ stands for?  This chronology demonstrates a pattern that HUJ experimenters have had reporting suggestions of decreased rainfall or null results due to cloud seeding and in correcting their flawed cloud microstructure reports to the scientific community and to their countrymen in the years prior to B23.

Moreover when “good draws” or null results are suggested, the HUJ researchers reach for the magic bag to explain why “cloud seeding did it,” not nature.  For example, when the Israel-1 chief meteorologist provided a plume analysis that the buffer zone (BZ) of Israel-1 could not have been appreciably contaminated by inadvertent seeding (a conclusion also supported by Neumann et al. 1967),  Gagin and Neumann (1974), however, countered with an opposite explanation; the BZ had surely been contaminated on Center seeded days.  The reason and data behind these two different explanations for the difference in the two plume analyses was not given except in general unsatisfactory terms.

When a Type I error and massive “good draw” affected the north seeded days of Israel-2 that also brought heavy rain to the south target, the crossover null result was then explained as due to “dust/haze” that produced different cloud microstructures when present in each target, first proposed by Rosenfeld (1989) in an HUJ report.

When RH95a showed that the results of seeding on the coast of Israel in Israel-1 were too close to the cloud base seeding release point to have resulted in rain practically falling on top on the seeding aircraft that flew in a line along the coast, Rosenfeld (1997) wrote a magical explanation filled with conjectures, one requiring nine steps to be fulfilled to explain the troublesome indication of rain increases in the BZ and in the coastal zone on Center seeded days.  Please see my extended “Reply,” p11, to the hypothesis of Rosenfeld (1997) at:

http://carg.atmos.washington.edu/sys/research/archive/1997_comments_seeding.pdf.

When the independent panel, Kessler et al. 2002, could find no viable increases in rain in the seeding of the Lake Kinneret watersheds in their interim report, the HUJ seeding team then asserted that “air pollution” was suddenly( after 1990) decreasing rain as much as cloud seeding was increasing it (Givati and Rosenfeld (2005).  One might ask, “what happened to ‘dust/haze’”?

Ice crystal concentrations measured in Israeli clouds by our best instruments are “unreasonably high” according to B23 co-author, Rosenfeld (private communication, 2018).  Rosenfeld’s statement, however, contrasts with that of Droplet Measurement Technologies (DMT), the manufacturer of the Cloud, Aerosol and Precipitation Spectrometer (CAPS) probe used by the HUJ researchers:  “They could have reported accurate ice particle concentrations if they had wanted to” (D. Axisa, DMT scientist, personal communication, 2018).

With the certainty of dust/haze days and incoming Israeli shower clouds affected by “sea spray” as Freud et al. 2015 described on shower days during the time the HUJ experimenters were flying their research aircraft in the early 1970s, monitoring storms with their radars, or examining rawinsondes during rain spells, we can conclude confidently that the lack of reporting on shallow precipitating clouds that occurred regularly in Israel is one of the more inexplicable and troubling aspects in the reporting of the Israeli cloud seeding experiments.

Deepening this enigma is that for two winter seasons in the late 1970s, the experimenters measured the depth of raining clouds with a vertically pointed 3-cm wavelength radar with research aircraft overflights to verify accuracy (Gagin 1980).  Dr. Rosenfeld, a B23 co-author who studied clouds and radar imagery at this time, is the sole living person who can tell us what happened (Rosenfeld 1980, master’s thesis).  One must necessarily ask if the HUJ experimenters discovered clouds they “didn’t like,” and withheld that information from us as they did the results of seeding in the south target of Israel-2?  Without conjuring up a stupefying degree of incompetence, it seems likely.

It is not science that we are dealing with concerning the reporting by the HUJ cloud seeding researchers.  There will ALWAYS be another problem that prevented seeding from working and if only corrected, seeding will work, as we are sure to learn when the inevitable “secondary” results of Israel-4 are published.

Will I be given a chance to review an Israeli cloud seeding manuscript as an expert in Israeli clouds, weather, and cloud seeding?  It seems unlikely with the journal atmosphere we have today.

  1. The on-going journal problem of “one-sided citing” as seen in B23; the equivalent of today’s “cancel culture” 

The omission of the work by myself and with Prof. Peter V. Hobbs was shocking to see in B23 since all the B23 authors knew of this work.  In human terms, external skeptics from a foreign country that expose faulty science in another country are not going to be exactly welcomed (or apparently cited) by that’s country’s scientists when a scientific embarrassment unfolds, as has happened in Israel concerning cloud seeding.  While this may seem like an outlandish claim, what happened could be interpreted as tinged with nationalism has previously been shown to obfuscate science (Broad and Wade 1982, p114).

For journal readers who are used to “one-sided citing” in partisan media, our scientific journals are supposed to be immune from these acts due to a peer-review “filter” that is supposed to eliminate this practice before an article reaches the publication stage.

        a).  Why do authors, like B23, tell only one side of the story?

In the words of Ben-Yehuda and Oliver-Lumerman (2017) of the HUJ,  such deceptions are, “…a deliberate attempt to create a false reality, persuade audiences that these realities are valid, and enjoy the benefits that accompany scientific revelations, whether those of prestige, money, reputation, or power….”  The effect of one-sided citing on journal readers is well expressed in the U. S. Federal Trade Commission’s (FTC) statement on consumer fraud:

“Certain elements undergird all deception casesFirst, there must be a representation, omission or practice that is likely to mislead the consumer [journal reader].”

For the reader, one-sided citing, if it is not obvious, is purposefully done by authors to hide results that they do not want you to see.  In effect, B23 performed the same act as Gagin and Neumann (1981) did when the latter authors did not report the results of random seeding of the south target of Israel-2, results that they did not want the world to see, and results that would have raised so many questions.

Regrettably, one-sided citing (a form of deception) is widely observed in Amer. Meteor. Soc. journals and in J. Weather Modification articles on cloud seeding/weather modification:

https://cloud-maven.com/journal-citing-practices-in-a-controversial-domain-cloud-seeding/

B23 practiced one-sided citing (defined by Schultz 2009) in their article concerning the Israel-1 and Israel-2 experiments.  Inexplicably, our groundbreaking work (e.g., R88, RH88, who pointed out how anomalous the Israeli cloud reports were compared to other clouds, and RH95a) went uncited by B23.   Our work, in toto, can be said to have anticipated the both the null result of decades of operational seeding of Lake Kinneret (Kessler et al. 2006, Sharon et al. 2008) and the null “primary” result of Israel-4 reported by B23.

B23 repeatedly misled/deceived readers, the “consumers” of journal science, concerning Israel-1 and Israel-2.   If there is something different than what was done by B23 than what is described by the FTC above its not apparent.

Nor did B23 cite Wurtele (1971), Silverman (2001) or mention the critical airborne cloud measurements by one of Israel’s own leading scientists, Levin 1992, 1994, and Levin et al. 1996).  The latter measurements were the first cloud ice measurements in Israel since Gagin (1975).  Those new, independently acquired cloud ice measurements supported the conclusions in R88, RH88, and those in RH95a, all which contravened the many HUJ experimenters’ fictitious reports of “ripe for seeding” clouds whose tops could ascend to ~-20°C without precipitating.

Later measurements of cloud properties via satellite would also confirm the independent cloud measurements and assessments; that the clouds of Israel formed precipitation far more readily and at much higher cloud top temperatures (Ramanathan et al. 2001) than the HUJ experimenters could discern over many decades.

In 2015, the HUJ cloud researchers discovered that “sea spray” in the Mediterranean makes the cumuliform clouds invading Israel precipitate more efficiently and at the high cloud top temperatures like those reported in R88 (Freud et al. 2015).  We can be quite sure that Mediterranean Sea spray has been occurring and affecting clouds that move into Israel for millions of years, and of course, did so during the 1970s when the HUJ scientists were performing their aircraft and radar cloud studies.  Yet, they could not detect, or did not report, on those clouds that would have erased most of their seeding potential.

The shame of one-sided citing in B23 is that the authors could have added a single sentence following their repeated claims of rain increases in Israel-1 and -2:  “However, these results, and the cloud reports that gave the statistical results credibility, have been questioned/overturned,” followed by a string of citations.

But B23 could not bring themselves to do that.

          b) Why should we care about one-sided citing?

 Knowledgeable readers of a specific topic like this writer will know that an article has been skewed to deliberately mislead readers due to omissions of contrary findings that go against what the authors assert.  But less informed readers will not know, and their knowledge will be truncated regarding an important public policy, as when their state or local government considers a­­­­ cloud seeding program.  They will want to know the unabridged findings about the Israeli experiences as a tale of caution about accepting claims by promoters of seeding that have not been closely scrutinized by outside experts.

Moreover, “one-sided citing” sullies the reputations of all the authors even those who may not have agreed with doing it, and likewise sullies the reputations of institutions represented by the authors who practice it by suggesting that those institutions do not uphold standard science practices by those who work there.   It also damages the authors whose work goes uncited since one’s impact in science is measured by citation metrics.  Finally, even the journal in which one-sided citing occurs can be considered to have been damaged since unreliable findings have been published in it.

Nevertheless, it would appear that reviewers, editors, and journal management do not care so much about this issue.  No statement in our Amer. Meteor. Soc. ethics statement addresses the question of the pernicious practice of one-sided citing as seen in B23.  Its intellectually dishonest to omit relevant findings for your science audience just because you don’t like them

              c) Who’s responsible for “one-sided” citing in        journals?

 “One-sided” citing, specifically as observed in B23, is due to poor peer reviews of manuscripts by seeding partisans or reviewers ignorant of the literature they are supposed to know.   However, it is also due to those that do know the literature but do not get those manuscripts to review.  For example, even though I would be deemed an expert on Israeli clouds, weather, cloud seeding, and on cloud microstructure, I was inexplicably not asked to review a manuscript in my specialty; that by B23 which would have made these comments unnecessary.

The reviewers of B23 manuscript were either ignorant of the literature they were supposed to be knowledgeable about or were cloud seeding partisans that also desired that the “other side” of the story for Israel-1 and Israel-2, as represented in the peer-reviewed literature by R88, RH88, RH95a, RH97a, b, c, d, e, Silverman (2001), Wurtele (1971) and Levin’s cloud measurements (e.g., Levin et al. 1996),  be hidden from the journal readers.

At the top of the “responsibility pyramid” for one sided citing in journal articles, however, must reside the editor of the journal who chose the reviewers that allowed this to happen.  Whomever this was at the J. Appl. Meteor. Climate, should not be allowed to be an editor who disburses cloud seeding manuscripts again.

        d) Concluding remarks on one-sided citing

 While all the B23 authors are technically responsible for its misleading content, one suspects some were likely “drug along” by stronger author personalities or authors who have funding power over them.  As is done in Geophys. Res. Letts., the actual contributions of each author to this article should have been listed so we can truly know who was responsible for providing one-sided histories for Israel-1 and Israel-2 and other misleading statements.

We know, too, seeding partisans at the HUJ that have cost their own country so much will not let the “primary” null result of B23 stand; there will be “secondary” and “tertiary” stratifications of Israel-4 data perhaps designed to mislead the INWA into another randomized cloud seeding experiment or to resume operational seeding of Lake Kinneret.

It will be critical that if a new experiment is conducted at the behest of the HUJ seeding partisans, that outside, independent experts conduct it!  It is also critical that prior to a new experiment that new airborne measurements of the clouds of Israel also be undertaken by outside, independent and experienced researchers in view of the problems that researchers at the HUJ have had over several decades, right up to today,  in reporting ice particle concentrations in their clouds and their clouds’ actual seeding potential.

The major question we must now confront to avoid further science mischief by HUJ cloud seeding researchers, is how was it that they were not aware of the natural state of their clouds, namely, that clouds with tops warmer than -10°C that regularly rained, a finding that seriously limits cloud seeding potential?   To date, no explanation has been put forward.  And what evidence will they skew or miss in a likewise manner in the inevitable Israel-4, “secondary” results article?

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Lastly, a note of scientific etiquette for B23 and young researchers: B23 cite the work of French et al. (2018) in demonstrating cloud seeding efficacy via the use of mm-wavelength radar.

The first use of mm-wavelength radar of the type used by French et al. (2018) was used by the Cloud and Aerosol Group at the University of Washington in a “proof of concept” experiment (Hobbs et al. 1981).  Scientific etiquette means citing those that went first (Schultz 2009)   Thus, a citation to the Hobbs et al. (1981) article should have preceded that of French et al. 2018)8.   Our experiment proved that cloud seeding works in limited situations as in those described by French et al. (2018).

=================FOOTNOTES=====================

1The Israeli experiments have had several names over their history.  We use the latest terms for them here, e.g., Israel-1, etc.

2Pressure was applied in 1986 on the HUJ researchers by the Israeli experiments’, “Chief Meteorologist,” Mr. Karl Rosner, who began a letter writing campaign to have the important results of seeding in the south target published by Prof. Gagin.  Mr. Rosner told Professor Hobbs and myself in a Seattle visit that he felt that Prof. Gagin’s co-author, Jehuda Neumann, was “drug along” as a co-author of Gagin’s papers.

3This author believes that it is critical that a certified copy of the list of random decisions for Israel-2 be compared against those days used in the experiment.  The remarkably unlikely random draw described by Gabriel and Rosenfeld (1990) could be explained if the original list was violated by the experimenters: draws were made and assigned to  “seed” days when heavy storms were forecast.

4Rosenfeld (1989) in an unpublished HUJ report argued that the divergent apparent effects of cloud seeding were real.

5The findings of Kessler et al.  were challenged by seeding partisans at the HUJ and who claimed that “air pollution” had decreased rain as much as cloud seeding had increased it after 1990.  While this was a convenient explanation, it was not found credible by many subsequent independent investigators, including by Kessler et al. (2006).

6Ben-Yehuda and Oliver-Lumerman’s 2020 book, Fraud and Misconduct in Research, should be required reading for B23.  Ben-Yehuda and Oliver-Lummerman are professors at the HUJ.

7I suggested the use of our vertically pointed, mm-wavelength radar for cloud seeding use to Prof. Larry Radke and Peter Hobbs, after seeing virga signatures pass overhead of that radar, realizing that creating lines of seeding in supercooled cloud layers that passed over such a radar could prove the viability of cloud seeding in a new way.  I also carried out this experiment as flight scientist/meteorologist in the seeding/monitoring aircraft.  However, I was not credited for this idea by Prof. Hobbs in the Science article.

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Review of a published assessment of Israeli cloud seeding potential in support of the Israel-4 cloud seeding experiment

After pasting my incredibly LONG review of this article in this space, I realized it was too long for a blog, so will just put a link here where that strange person who would want to read it will find it.  I’m following in the paths of F. A. Gifford and Fred Sanders, of whom it was said their reviews were sometimes LONGER than the manuscripts they were reviewing!

Review of Freud et al 2015 (monograph sized)

Below is my pathetic attempt to put my review into a viable/readable blog that I will be working on to “clean up”, add figures from the original and “other”.  So look for changes as time goes by.  I don’t expect the pdf to change.   The figures are in the pdf above, btw.

A continuing theme of reviews like this is, as in other cases,  I was not asked to review this manuscript in my expertise before publication, even though I was known by the authors as an expert on Israeli clouds, weather, and cloud seeding.  Perhaps the editor of this journal,  who chose the reviewers did not know???   Right now, its “Ready, Fire, Aim” to quote a book title describing the premature publication of this blog.

Oh, that Israel-4 cloud seeding experiment?!    The result of the seven season randomized experiment was published by Benjamini et al. (2023, J. Appl. Meteor.).  The “primary” evaluation found no viable increase in precipitation due to cloud seeding, in agreement with my 2017 review of this cloud seeding potential paper and all my prior work on Israeli clouds (Rangno 1988, Quart J. Roy. Meteor. Soc.) and cloud seeding (Rangno and Hobbs 1995, J. Appl. Meteor.)

Cloud seeding potential was grossly exaggerated by Freud et al. (2015).  I wanted to scream to the Israel National Water Authority, “Don’t do a cloud seeding experiment based on these findings!”  But, it was too late.

==================================================================================================

A comprehensive review of

“Cloud microphysical background for the Israeli-4 cloud seeding experiment”

by Freud, E., H. Koussevitsky,  T. Goren and D. Rosenfeld,

(the article which is reviewed below was published in 2015 by Atmospheric Research)

with a recap of the Hebrew University of Jerusalem’s cloud seeding experiments

as seen by a long-time observer (me)

  1. A. L. Rangno[1]

Opening remarks

“What is scientific knowledge? When is it reliable?”, ask Kenneth Foster and Peter Huber (1997), in “Judging Science:  Scientific Knowledge and the Federal Courts”, MIT Press.  “Scientific knowledge” might be considered anything published in a peer-reviewed journal.  Having passed the peer review “filter” gives, or should give, that which appears in a peer-reviewed journal particular reliability on which our scientific knowledge grows.

Much of this review addresses the second question raised by Foster and Huber, the reliability of published science. Implicitly, this review also addresses the quality of the peer-review “filter” in the cloud seeding domain:  “Has it improved since the 1960s through 1980s when hundreds of pages of faulty cloud seeding claims concerning experiments in Colorado and Israel were published, ones that misled our best scientists?”  In this review of a recently published paper, we must answer, “No.”

In this review[2], we examine the reporting of current and past research by researchers at one of the world’s great universities, the Hebrew University of Jerusalem (HUJ). The researchers at the HUJ in the article to be examined are reporting in a domain of science particularly susceptible to controversy, cloud seeding (e.g., Changnon and Lambright 1990); a field of study afflicted by a quasi-religious “confirmation biases”, and polarization that have corrupted it repeatedly.

Moreover, can the contents in articles published in peer-reviewed journals always be trusted in the polarized domain of cloud seeding with so much at stake for experimenters who report on their own work (jobs, prestige, confirmation of a priori beliefs, etc)?  And, it is experimental work that is unlikely to have attempts at independent replication, our best safeguard against faulty claims, due to the high cost of field experiments.  There may be no more vulnerable field to corruptive influences than cloud seeding due to these factors.

Conversely, pressure arises when you can’t find more rain on your cloud seeding experiment’s seeded days; you may be deemed a failure by others who KNOW that seeding worked.   You may lose funding and your job since you found no response.  This is because the value of a carefully conducted cloud seeding experiment with no viable proof of a seeding effect is undervalued.  These factors converge to produce repeated false “happy” results in cloud seeding publications.

The idea of making it rain or snow on command, as it were, has corrupted many a good scientist since the earliest modern days of this field when Schaeffer dropped dry ice in a layer of Altocumulus clouds in 1946)[3].    The controversy largely results from reports of cloud seeding successes (precipitation increases) by the original experimenters whose findings are subsequently overturned by independent scientists “upon closer inspection” in re-analyses.  This cycle of reverses has gone on since Brier and Enger (1952) right through the era of randomized experiments (e.g., Levin et al. 2010)!   Randomization apparently did not remove experimenter bias.   The Israeli experiments have been subject to this rise and fall cycle.

In Freud et al. (2015)—hereafter, F2015, this rise and fall cycle in the Israeli experiments conducted by the HUJ-CSG is not explained as candidly as it should have been for their Atmospheric Research ( AR) readers and funders, thus prompting this review.  This review scrutinizes all aspects of the F2015 paper which apparently led to additional cloud seeding in Israel.   Because  F2015 was also part of a proposal to the Israel National Water Authority (INWA), it is also reviewed with more rigor for that reason.  Proposals are written by “Party A” to extract monies from “Party B”;  it’s a sales pitch.  When this is done, one might find that Party A has painted a rosier scene for possible accomplishments (his “product”) than is viable for Party B.  In droughty times, it’s always the cloud seeding salesman that wins.  And it’s a win situation for funders who want to show constituents that they are doing something about a drought.

The review of F2015 is organized by topics.   It also contains a “corrective history” of cloud seeding in Israel since Israeli 1.   The history is based on the hope that it will be useful to potential future reviewers of  manuscripts in cloud seeding that might emanate from the HUJ’s “cloud seeding group” (hereafter, “HUJ-CSG”;  referring to those HUJ authors over the decades that have authored or co-authored papers on cloud seeding).  This history may also be of interest to young graduate students within the HUJ science department who may not be informed about it.

Much of this critique of F2015 is due to the authors’ incomplete and misleading descriptions of prior cloud seeding results reported by the HUJ in the abstract and “Introduction” segments.  The former chief editor of Science magazine says it all:

The difficulty is that positive claims are sometimes made against a background of    unrevealed negative results.” 

—————– Donald Kennedy, 2004 Science editorial:  “The Old File Drawer Problem.”

The word “independent” is highlighted in this review due to the remarkable number of times that outside, independent researchers, when examining the findings published by the HUJ-CSG in peer-reviewed journals, beginning with Rangno (1988-hereafter R88), could not substantiate or reversed them.   This may give the HUJ-CSG the unenviable reputation as a frequent producer of published, but “unreliable, irreproducible” results.  The primary reason is that the HUJ-CSG publishes ambiguous results but describes them as though they were “in concrete”, hiding the ambiguities in their findings that others bring out later.  What should be troubling is that there are likely more ambiguities in HUJ-CSG publications hidden in what appear to be solid findings that have not yet been examined by independent researchers.

HUJ are you listening?

“One-sided citing” is often practiced by the HUJ-CSG, and is seen again in F2015.  Those instances are called out in this review.   “One-sided citing” has recently been condemned in the American Meteorological Society book, Eloquent Science, by David Schultz (2009).  Here’s what Schultz had to say about one-sided citing:

“One-sided reviews of the literature that ignore alternative points of view, however, can be easily recognized by the audience, leading to a discrediting of your work as being biased and potentially offending the neglected authors (who might also be your reviewers!).”  (Yep, me!)

Moreover, there is material damage to your fellow scientists when they are not cited when they should be, as by the HUJ-CSG in this and other cloud seeding articles.  The impact in one’s field; promotions, awards, impact and status, is usually determined by an impact metric, such as the number of citations of your work.

Too, there is implicit damage to the reputation of the home department and institution from which one-sided citing emanates.

HUJ, are you listening?   After all, “the Hebrew University of Jerusalem is Israel’s premier academic and research institution,” as the HUJ states on its web page.  Thus, it should be held to a high standard of research reporting.   The HUJ should be appropriately troubled to read what it finds here.

It is strongly recommended that the HUJ-CSG authors read Schultz’ book, and also that a course in scientific writing and ethics be taught at the HUJ.  (Perhaps many research institutions involved in cloud seeding research would benefit from such courses.)

One-sided citing in F2015 also demonstrates a poor AR peer review process prior to publication, perhaps by seeding partisans (“one-sided reviewing”?)  The obvious poor peer review of this article in the manuscript stage is a further reason why I have troubled to spend time doing a “comprehensive” , “no-stone-unturned” review.

———————–Organization of the Review——————

1)  Overall assessment of this paper and its claims about cloud seeding potential in northern Israel.

2) Who should be assessing seeding potential in Israel?  Ans.  Not the HUJ-CSG, as told by their history.

3)  The shifting cloud microstructure reports over the decades from the HUJ-CSG: how did it go so           wrong in the first place?  (Ans.  “We don’t know yet.”)

4)  The wrongful scientific consensus on Israeli cloud seeding:  how did it go so wrong?

Ans.  Inadequate peer-reviews,  insufficient skepticism and too much trust on the part of scientists reviewing manuscripts on cloud seeding.

5)  A mandated list of publically-available data from the F2015 field program described in this paper,       and why (see above remarks).

6)  “Filling in the blanks”:  Correcting F2015’s incomplete descriptions of Israeli 1, 2, and 3, and operational seeding  (in separate, titled “modules.”)

7) If you want to go further:  the remainder of the original article, absent the abstract and Introduction sections follows in black type with “inline” reviewer’s comments following highlighted statements.

8) After the References follows reviewer’s disclaimers, baggage, conflicts of interest, a prior convictions about cloud seeding, and his background that qualifies him for this review, etc., items that should always be mentioned.

Line numbers have been added so that rebuttals or support for this review can be easily accomplished.

I don’t apologize for the length of this review.  After all, reviews are intended to prevent faulty science from reaching the pages of journals, and help authors in explain their work.   It didn’t happen under AR prior to the publication of F2015.

The excessive length?   The HUJ-CSG has “earned it”; it can’t be trusted in the seeding domain under its current leadership IMO.  If this sounds overly provocative, or even outrageous, read on:

“It didn’t come out of a vacuum[4].”

This review is virtually identical to the one I would have done for AR for F2015 and the HUJ-CSG’s accompanying proposal for Israeli-4 to the INWA if I had been asked.  In polarized research environments, reviews of manuscripts by must be especially intense, every sentence checked for accuracy, every claim suspect until clearly proven;  the discovery of omissions of critical data called out and discussed as in this review.  F2015 encapsulates all that is right and wrong with the HUJ-CSG cloud seeding literature.

The decision from here on the manuscript version of this article would have been:

“Accept, but ONLY upon the authors fulfilling the required major revisions, posting mandated data online, and implementing corrections to their partial descriptions of prior work.”

As a proposal to initiate the Israeli-4 randomized experiment?

“Reject.”

There is insufficient evidence to guarantee a successful outcome.  I review F2015 as a proposal that I myself would be asked to pay for (as an Israeli citizen will be doing).

This “review” will contain compliments and condemnations.   Expect to get mad at someone, maybe me.  The language is sometimes blunt, and the question of misconduct is raised[5].

  1. Overall assessment of F2015

 

This article, due to its “Jeckyl-Hyde” properties, presents a unique review challenge; some of the best conscientious scientific writing by the HUJ-CSG is in this very article; the kind of writing marked by caveats and qualifications made in a circumspect manner.

On the positive side, too, it was pleasant and unexpected to read in F2015 that the HUJ-CSG has finally agreed with long standing work, first published by R88, that the Israeli clouds are overall unsuitable for seeding with silver iodide due to their propensity to form precipitation/ice readily.  This finding was re-iterated in Rangno and Hobbs (1995-herafter RH95).   Due to an oversight, or small-mindedness, however, F2015 do not cite the original altruistic work.

In contrast to the positive writing mentioned, there are elements of writing in this paper that cast a dark shadow on the authors, their home institutions, and ultimately, the journal that their article appeared in, AR.   Partial, and therefore, misleading descriptions of the prior Israeli experiments are found in several places, along with omissions of important references to work that was critical of HUJ-CSG findings, thus representing a stunningly “gorgeous” exhibition of “one-sided citing” in F2015, as is often practiced by the HUJ-CSG.

Nonetheless, the HUJ-CSG’s idea that inland clouds reforming over the Golan Heights/Mt. Hermon region might have seeding potential has merit and is worthy of further investigations and corroboration and expansion of the results in this paper by independent groups before any seeding takes place.

Viable seeding potential in the Golan region, however,  is not demonstrated in this paper, as will be shown in subsequent commentaries.

Factors to consider in the extreme northern Israel seeding scenario:  Cloud tops in northern Israel are usually significantly colder than those in the central and southern regions of Israel (Gagin and Neumann 1974, hereafter GN74; RH95).

GN74 reported modal radar tops on rain days in the north target of Israeli 2 near -19°C, whereas in the south target of Israeli 2, they were -16°C.  GN74 (written in 1972) in preliminary analyses, used those temperature differences to explain why seeding was seemingly effective in the north target (more activation of AgI), but not in the south target due to less activation of AgI[6].

Today, however, due to R88, Levin 1992, 1994, and Levin et al 1996, hereafter L929496, and in F2015, we know thatboth cloud top temperatures given in GN74 would be associated with high ice particle concentrations as turrets mature; they would be highly unsuitable for seeding, a situation this reviewer feels would extend into the Golan on many, if not most, storm days.

3)  Who should evaluate cloud seeding potential in the Golan?  Not the HUJ-CSG

Perhaps the most surprising and troubling aspect of F2015  is that the assessment of seeding potential in the Golan is being undertaken by HUJ-CSG; “troubling” due to that organization’s prior reporting history in that domain, i.e., its inability to detect (or hid) the nature of Israel’s clouds for decades with so many tools at its disposal, and the inherent conflict of interest such a new study represents.

Philosopher George Santayana said it: “Those who cannot remember the past are condemned to repeat it.”

Moreover, if the present “background” paper by F2015 is the primary reason why a new randomized cloud seeding experiment, Israeli-4,  was undertaken, then yes, the failed past of the HUJ-CSG’s seeding experiments (Israeli 1, 2 and 3) will be repeated providing that Israeli-4 is evaluated by independent, non-HUJ statisticians and scientists divested of cloud seeding interests!

The evaluation of the clouds in this article in AR is not complete enough to provide confidence that seeding is going to increase rain by an economically worthwhile amount in the Golan.   A new randomized experiment, or operational seeding, both appear to this reviewer to be unwise or at least, premature undertakings in spite of Israel’s urgent water needs.  Cloud seeding “salesmen” are drawn to drought like bees to a jar of spilled honey.  Funders, too, are anxious to open their tills to show their constituents that they are doing something about drought.  It’s a win-win situation for both.  Thankfully, the INWA in a burst of courage, went “randomized” and not into direct operational seeding based on the HUJ-CSG claims.

The sad history of the HUJ-CSG reporting in the cloud seeding domain is reprised for the reader or reviewer who is/was likely unaware of it so that the faults in F2015 can be seen in the context of  “damage control.”   These faults also represent “baggage” carried by the HUJ-CSG and their efforts to recoup the HUJ-CSG’s damaged credibility when they re-write and minimize key elements of that seeding history in F2015.

What “baggage”, you ask?

What if the HUJ-CSG knew for decades that the seeding operations started by the INWA after Israeli 2 in 1975 and  costing millions over the following 30 plus years were actually targeting inappropriate, highly efficiently precipitating clouds rolling in off the Med with little or no seeding effect likely?

What alternative would that group have other than posting one unreliable finding after another that seeding had worked anyway on such clouds?

Is it really possible for the HUJ-CSG to acknowledge error and cover up of that cloud knowledge as likely happened and apologize to the INWA and to the people of Israel?    Absent that apology, the HUJ-CSG group should be terminated IMO.

The appearance of F2015 showed that the HUJ-CSG has yet one more chance (after Israeli 1,2, 3, and in their evaluations of operational seeding) to skew findings to impress an apparently still naïve INWA and their countrymen about  seeding potential in the Golan.

This is the perfect example of the “fox guarding the hen house,” analogous to the Phelps-Dodge Mining Corporation being solely responsible for the environmental impact statement of its next mine.  That Phelps-Dodge assessment could be right; but it would never be trusted as such without outside,  independent confirmation.

Why doesn’t the INWA recognize this inherent, and, obvious to all familiar with the history of seeding in Israel, HUJ-CSG conflict of interest?

Why weren’t outside,  independent groups, such as the University of Wyoming, Stratton Park Engineering Company, NCAR, Droplet Measurement Technologies, Tel Aviv University, etc., brought in by the INWA to make this assessment?  The people of Israel and their media should be asking this question.   The HUJ-CSG forfeited its right to do such an assessment decades ago due to their incompetence in assessing their clouds.

Lastly, because of our experiences with the HUJ-CSG and the unreliability factor in their cloud seeding publications, I URGE that  INWA  have outside, independent groups experienced in airborne work collect data and report on the seeding potential of Israeli clouds in conjunction with critical supporting ground measurements of the nature of ice crystals and precipitation at Mt. Hermon as a next step before experimentation begins. (OK, I’m late to the party, but that’s what I would have recommended to the INWA).

 

  1. The shifting sands of the HUJ-CSG cloud microstructure reports over the decades and their shifting implications on cloud seeding

The essential question that should be asked by all of us is, “Why did it take so long for HUJ-CSG to discover the true nature of their highly efficiently precipitating clouds, given all the tools they’ve had available to them since the later 1970s? The tools at their disposal included multiple radars, including a vertically-pointed 3-cm one (Gagin 1980), aircraft, IMS rawinsondes, and the skill of the IMS forecasters who were well aware of the efficiency (shallowness) of Israeli clouds when they begin to precipitate[7].  And this information was there in plain sight for all of us (e.g., GN74, Fig 13.4, GN76, Figs. 2 and 3, Druyan and Sant 1978).

The inability of the HUJ-CSG to detect the nature of their clouds can be either seen as an example of astounding incompetence or one of investigable misconduct if those within the HUJ-CSG knew that their clouds were not as they described them in journals so many times; but, rather, hid that knowledge from their peers and the INWA to keep their jobs, their seeding programs, and misbegotten prestige intact.

Donald Kennedy (2003), in another Science editorial on research fraud:

In the real instances of research misconduct we know about in biology and physics, the motive appears to have been career enhancement, pure and simple. It is, after all, a competitive world, and the incentive to gain reputation can be powerful. But other motives may appear in those social sciences that bear upon major policy issues.”  (Always was and always will be—reviewer’s comment)

 

You decide.

The reason why the Israeli government is now attempting to once again see if the clouds of Israel can be made to produce economically useful amounts of water via seeding is because none of the prior Israeli experiments produced credible rainfall increases due to seeding.  And that due to the unsuitable clouds for seeding.

5) The false scientific consensus on cloud seeding created by the HUJ-  CSG

 That the HUJ-CSG could not discover the true nature of their clouds until recently, and did not report results of experiments in a timely manner[8], also produced an erroneous “consensus” view in the science community that cloud seeding had been “proven”in Israel (e,g, Tukey et al. 1978, Mason 1980, 1982, Kerr 1982, American Meteorological Society 1984, Dennis 1989, World Meteorological Organization 1992, Young 1993).

So what?

A wrongful consensus damages all of science!   This false “consensus” was published in numerous textbooks, and in countless popular articles along the lines of, “Israelis make it rain in the desert.” Who will retroactively correct those statements?

  1. Mandated publically-available data requirements from the F2015 cloud sampling program

Due to the past history of much-published, but faulty, cloud seeding research by the HUJ-CSG,  this reviewer would have mandated prior to publication of F2015 and before any cloud seeding experimentation took place, that the HUJ-CSG provide the following critical data online so that the wider community of experts could have evaluated the findings in F2015.  These should be provided at this time:

1) A table of flight data with dates and times of flights, linked to synoptic maps and satellite imagery for those flight days, and the ability to access flight videos from this program.

2)  A table detailing some of the microstructural measurements, following Hobbs and Rangno (1985), Table 1:

  1. a) maximum ice particle concentrations found in each sampling zone on each day over widths of                         of 300 m and 1-km,
  2. b) cloud top temperatures and heights of sampled clouds
  3. c)cloud base temperatures and heights of sampled clouds
  4. d)flight level temperature at which sample was obtained,
  5. e) height of the sample below cloud top,
  6. f) widths[9] near cloud top of the clouds that were sampled,
  7. g) average and maximum liquid water content in each “study” cloud,
  8. h) sizes of droplets <13 µm diameter and >23 µm diameter within the H-M temperature zone of                        -2.5° to -8° C  clouds,
  9. i) Large size tail of the FSSP droplet spectrum (“threshold diameter”, after Hobbs and Rangno 1985)
  10. j) average and maximum droplet concentrations in study clouds,
  11. k) estimate of stage that the cloud was in when sampled
  12. l)results of any ground work in the Golan/Mt. Hermon
  13. m) back trajectories for flight sampling times over the Mediterranean Sea, and over the Golan

The mandated data elements for outside researchers to examine may seem like an undue burden to the HUJ-CSG since some of these require care to obtain.  But these requirements have to be put in the perspective of how much the prior erroneous and incomplete reports by the HUJ-CSG cost not only the people of Israel in ineffective cloud seeding but also by neighboring Arab countries that undertook similar ineffective seeding operations, and finally, by the cost of the failed attempted replication of the ersatz Israeli results in Italy (List et al. 1999).

  1. a) The Israeli 1 experiment as described by F2015 and the counter evidence to that description; “filling in the blanks”

F2015 Abstract:  “These clouds were seeded….producing statistically-significant positive effects…”

This partial description of results for the first two experiments in the authors’ abstract should have been removed by the prior reviewers.  Right from the start the HUJ-CSG authors began misleading less-informed AR readers, some of whom will likely not go beyond the abstract.

There are MANY reasons why the Israeli 1 rain increase results are suspect, all known by the authors of F2015.  They deflected the full story about those reasons to, “positive effects.”  We reprise those reasons why no one any longer believes that Israeli 1 nor Israeli 2, have credibility as successes in rain production for AR readers who might have taken the faulty abstract prima facie:

Prior to the appearance of F2015 in ARINDEPENDENT  assessments (this cannot be overstressed) of  the statistical results of seeding in Israel  found them questionable at best  (RH95, Silverman 2001[10], Levin et al 2010, 2011, the latter in reply to Ben-Zvi et al 2011).   Those independent assessments are strongly supported by clouds that we now know are unsuitable for seeding due to the copious natural formation of ice at modest supercoolings.  Indeed, the Israeli clouds have never been suitable for seeding in spite of the numerous published reports by the HUJ-CSG to the contrary.

Conversely, it was those erroneous ultra “ripe-for-seeding” cloud descriptions by the HUJ-CSG in the 1970s and 1980s that gave the statistical results of the Israeli 1 and 2 experiments credibility; that seeding really had increased rain (e.g. Kerr 1982, Mason 1982, Dennis 1989).

Thus, the F2015 authors cannot reasonably believe that actual rainfall increases occurred in Israeli 1 and 2 although they inform the AR reader of “positive effects” in the abstract.  Seeding clouds whose high natural efficiency to form ice is as high as that anywhere in the world, cannot lead to statistically-significant results in a “static-style” cloud seeding experiments, as the Israeli experiments were.

Gagin (1986):

“While it is important to record the effects of seeding on rainfall at the ground, the statistical evaluation of this parameter alone cannot constitute an acceptable result of a successful seeding effect.”   Q. E. D.    End of story.

Turning our attention specifically to Israeli 1 and why the indications of rain increases are no longer credible:

1) The clouds of Israel have been found largely unsuitable for seeding as the HUJ-CSG themselves finally have discovered and now report in F2015, in agreement with several other studies, initially by R88.  If there are no suitable clouds for seeding, then statistical results cannot be due to seeding effects, but rather must be due to “lucky” random draws, or other mischief such as omitting data, post-facto cherry-picking controls, etc.

It is worthwhile to reprise another GN74 statement concerning statistical results without a cloud foundation, a well-known principle within the weather modification community:

“…no statistical evaluation will be of real value unless these results are substantiated by detailed physical considerations.”   

It’s the clouds that drive the credibility of the statistical results, not the other way around.

2) Evidence for a Type I statistical error in Israeli 1 was reported by the Chief Meteorologist of that experiment, Mr. Karl Rosner,  who pointed out to Wurtele (1971) that the region that exhibited the highest statistical significance on Center seeded days,  the “buffer zone” (BZ) between the two targets, could barely have been seeded (“5-10%” of the time).  The HUJ seeding unit did not give this “red flag” enough attention; that is, they did not attempt to reconcile the wind analysis by Shimbursky (in GN74) with their own Chief Forecaster Rosner’s evaluation.   In contrast to their Chief Meteorologist’s view, they considered the BZ inadvertently seeded (GN74).

Let us also quote Neumann et al. (1967) on the BZ issue:

“An acceptable and unbiased way of omitting most unsuitable days was to restrict the analysis to the 327 rainy days, defined as days with some precipitation in the buffer zone by the Mediterranean, a location where rainfall is unlikely ever to have been affected by seeding in either experimental area.”

 

3) The BZ seeding issue was examined independently and in more detail by Rangno and Hobbs (1995-hereafter RH95).  In RH95 was concluded, based on their wind analysis when rain was falling in Israel (when seeding would have been expected to be taking place) that it would take a very bad pilot to have inadvertently seeded the BZ when instructed not to do so.  This conclusion due to the very narrow low-level wind envelope concurrent with rain in Israel.

The Shimbursky wind analysis in GN74, on the other hand,  had only a once-a-day IMS rawin launches, which may or may not have been associated with clouds and rain, and thus, could not address the direction of winds solely coincident with rain falling in Israel at the time of the launch as did RH95.

4) Additional evidence for a Type 1 error in Israeli 1 was presented in RH95 due to more rain on seeded days in the immediate coastal zone of Israel over which the seeding aircraft virtually flew, a conclusion that was reached earlier by Neumann et al 1967, also due to logistical considerations.  Quoting Neumann et al (1967):

“After some 2 1/2 seasons of operational seeding experience, it was noticed that flying was effectively limited in such a way as to affect only the interior parts of the two areas.”

 

Gabriel (1967:

 It was claimed that the seeding plane generally did not fly outside visual contact with the coastline so that there could have been no seeding effect near the coast; hence a 10 km

wide coastal strip must have been unaffected.

 

Gabriel and Baras (1970)

The second modification was suggested in 1963 in view of the actual flight patterns of the seeding plane. It seemed that seeding could only effectively reach the interior parts of the two areas and that analysis should therefore be restricted to these sub-areas.

Rosenfeld (1997) in a series of grand speculations concerning Israeli 1, offered an alternative to RH95 and those by the experimenters:  he argued that some of the airborne-released AgI dispersed downward from the initial releases in the southwesterly or westerly flow, was eventually into in a thin offshore flowing layer near the ground.  That portion of the plume, Rosenfeld conjectured,  then went  offshore, was ingested by seedable clouds (which we know do not exist; never did) at the right distance upwind for the AgI to rise up into the those offshore clouds, nucleate at appropriate levels (usually above 3.5 km ASL),  grow into precipitation-sized particles that fell out just in time on the Israeli coast, thus “explaining” the indications of a bias in storms (more rain on Center seeded days on the Israeli coast).

Whew.  Irving Langmuir comes to mind….

On Rosenfeld’s behalf, there is an occasional offshore flowing shallow layer during less vigorous synoptic rain situations, and one largely confined to early morning hours.  But, Rosenfeld provided no statistics on how often that shallow offshore flow occurred while seeding was taking place in Israeli 1.

5) Too little seeding (an average of but 4 h per day and only about a kilogram of AgI, Gabriel 1967) was carried out and dispersed in Israeli 1.   RH95 demonstrated that the area claimed to have had increased rainfall (under the seeding line, sidewind, downwind, in the target) was not commensurate with the amount of seeding material released in Israeli 1, a conclusdion reinforced by unsuitable-for-seeding clouds (R88, F2015).

6) The line seeding carried out by a single aircraft flying 75 km up and down the Israeli coastline was deemed ineffective by RH95 in having seeded enough clouds to have produced an effect; more rigorously corroborated in later modeling studies by Levin et al. 1997.[1]

 

  1. b)  The Israeli 2 experiment as described in F2015 and the counter evidence to that description; filling in more blanks

In Israeli 2, the HUJ-CSG, realizing the poor seeding strategy it had used in Israeli 1, added a second aircraft, and 42 ground generators in Israeli 2 (NRC-NAS, Panel on Weather Modification, 1975).  In Israeli 1 there had been but a single aircraft, and four ground generators located in the far NE of Israel (GN74).

The authors omit for the AR reader, the fact that the north “positive” effect in Israeli 2 was found to be  the product of an astoundingly one-sided random draw[2] for heavy storms throughout Israel (Gabriel and Rosenfeld 1990[3]), and also one that affected Lebanon, and Jordan (RH95).   The extraordinary random draw saw the home of HUJ-CSG in the south target experience the most rain of all the stations available to RH95 on north target seeded days!

Ignoring the report of extreme rain in the south target on its control days, those when the north target is being seeded,  Rosenfeld and Farbstein (1992) proposed that dust-haze,  when combined with AgI, had caused overseeding of clouds in the south target; that is, rain had actually been decreased while the north target, having fewer “dust-haze” days, experienced rain increases due to seeding.  This assessment gained wide traction for a time (e.g., Simpson 1990, Presidential Address to the Amer. Meteor. Soc., Young 1993), but like so much HUJ-CSG work, it was unreliable.

Let us quote Gabriel and Rosenfeld (1990) on the rain in the south target:

“Otherwise, one would need to explain why there was so much more rain in the south when the north was being seeded; as of now, no explanation is available, especially as the prevailing wind direction is from the southwest[4].”

Ergo, rain in the south was not “decreased” by seeding, but rather, in no way could seeding overcome the astounding random draw for north seeded days[5].  And, as we expect, the finding of extreme rain in the south target on north seeded days is not mentioned by Rosenfeld and Farbstein.  How could they?

The rain throughout Israel on north target seeded days once again points to efficiently precipitating clouds that are doing just fine without seeding with AgI.

Levin et al 2010 examined Israeli 2 in more detail than did RH95.  They attributed the apparent seeding-induced extra rainfall in the interior of the north target as due to a bias in strong synoptic systems on north target seeded days, one that created a misperception of seeding (see also, Levin et al 2011, reply to Ben-Zvi  et al. 2011).

Ironically, the Levin et al. (2010) findings are strengthened in F2015 when they observed that the intrusion of large aerosols inland from the Mediterranean on windy days in the north increased rain efficiency of inland clouds.

The Israeli 2 experiment had several design options (GN74), the first of which was the “crossover” evaluation, the same evaluation mode as was used in Israeli 1.  The true tragedy of Israeli 2, however, was in the omission of numerical results of random seeding in the crossover scheme, and in the south target by the HUJ-CSG after 1974.  It was an omission that kept the scientific community in the dark about how the full Israeli 2 had actually turned out.

While it is true, as GN81 pointed out, that the larger area of seeding done in the south in Israeli 2 reduced the correlation with the north, thus making seeding effects harder to detect in Israeli 2 compared with the Center/North crossover comparisons in Israeli 1.  Nevertheless, a crossover analysis based on the prior Center target gauges could have been presented with whatever caveats the authors wished to add.  The prior Center target gauges were in zones S1 and S3 of Gabriel  and  Rosenfeld (1990).  However, it is clear from the SAR’s of those regions in Gabriel and Rosenfeld (1990) that the crossover result of  Israeli 2 was not going to replicate Israeli 1.  At this point, if GN81 had done what they should have, they would have displayed that null result, and provided some thoughts on why it had happened.

It took 15 years after Israeli 2 ended, and at that,  spurred by a letter writing campaign begun in the winter of 1986 by the Israeli experiments’ own Chief Meteorologist, Mr. Karl Rosner, to “out” both the crossover results (-2%) and the negative SAR (-15 to -20%) for the south target.  And this was ONLY after the lead HUJ-CSG experimenter passed in 1987.

We have to assume that without Mr. Rosner’s public call for the exposition of the crossover and south target results, they would still be hidden from view within the HUJ-CSG.  Why weren’t authors, Gabriel and Rosenfeld, or others at the HUJ, troubled by this omission over the years after Israeli 2 ended in 1975[6]?  (Ans.  We don’t know why.)  Donald Kennedy does:

The difficulty is that positive claims are sometimes made against a background of    unrevealed negative results.” 

Furthermore, the early reports of a “confirmation” of the results of Israeli 1 due to the partial reporting of an Israeli 2 “success,” limited to the north target in a  target-control evaluation, spurred the decision by the INWA to begin an “operational seeding” program in 1975 (GN76), one that produced no viable results for more than 30 years when evaluated by independent scientists.[7]  And, perhaps, those Israeli 2 partial results also convince the INWA to begin Israeli 3 in the south target of Israeli 2.

Did the INWA know about the south target results of Israeli 2 before they began Israeli 3?  We don’t know what inspired Israeli 3.  INWA, F2015:  please tell us.

Where, too, was the outside cloud seeding community, one that failed to raise post-publication questions about the results of random seeding in the south target of Israeli 2 following GN81? ( I count myself in this oversight…and blame.)   Statistician Jerzy Neyman, who closely monitored cloud seeding publications and had a reputation for commenting on them, would surely have caught the Israeli 2 omissions had he not passed in 1980.   There is a lot of blame to go around.

Not reporting the south target results of Israeli 2, one that superficially suggested decreases in rain on seeded days also suppressed the inevitable questions that would have arisen:  “How could there be a suggestion of decreased rain on seeded days with such ultra “ripe-for-seeding” clouds (with warmer tops than in the north) as had been described by the HUJ-CSG over so many years?

Without doubt, the wheels would have come off the HUJ-CSG’s seeding train with full reporting of Israeli 2 in a timely manner.  And the report in Science that there had only been “one success in 35 years” in cloud seeding (Kerr 1982) would never have occurred.

We reprise the speculation of Gabriel and Rosenfeld (1990) near the end of their statistical analyses, one that was to be confirmed 20 years later by Levin et al. in 2010:

“The most plausible explanation (for the statistical results of Israeli 2) is one of random variation, with the north-seeded days being more rainy inland, especially towards the northern and southern edges of the experimental region.”

 

7  c)  The reported, primary effect of seeding in Israeli 2: duration:  where it stands today (it’s not credible).

Virtually the entire supposed seeding effect claimed in the Israeli 2 experiment was due to a greater duration of rain, not greater intensity  (GN81, Gagin and Gabriel 1987, hereafter, “GG87”).  Seeding with AgI, they reported,  caused cold-topped (-15°C to -21°C),  non-precipitating clouds to precipitate exactly like natural clouds, thus extending the duration of rain on seeded days (north target evaluation only).     The increase in that one temperature range was a whopping 46%, all of it due solely to extended duration caused by seeding!

That duration finding no longer makes sense in the face of highly efficiently precipitating Israeli clouds.   It never really did upon close,  independent inspection.

 

 

7 d) The Israeli 3 experiment:  its delayed reporting, and its significance

The first interim report about the progress of Israeli 3 randomized experiment from the HUJ-CSG was in 1992 (Rosenfeld and Farbstein), 17 years after it began[8].  Decreases in rain were suggested in that experiment year after year.  The final result, reported by Rosenfeld (1998) at conference, was that after 19 winter seasons and nearly 1000 random decisions there was an indication of a decrease in rain of 8% on seeded days (non-statistically significant).

In F2015, the authors, following in the footsteps of GN76, cannot divulge for the AR reader the indication of decreased rain on seeded days in Israeli 3.  Instead they cloak that result, as did GN76 for the Israeli 2 south target, with the correct but carefully chosen word, “inconclusive”.  “Inconclusive” could refer to increases or decreases in rain that are merely not statistically-significant; reporting indications of decreases, even if not statistically significant,  would have raised more interest.

The 8% suggested reduction in rainfall on seeded days after 19 winters and nearly 1000 random decisions were important on two accounts: that 1000 random decisions after 19 winter seasons could lead to a result so far from a null one after so many random draws,  assuming there really was no seeding effect as Rosenfeld (1998) asserted.  IF Rosenfeld and Farbstein (1992) are right about “dust-haze” combined with AgI, then the HUJ-CSG in the conduct of Israeli 2 and 3, combined,  have decreased rain for 25 years in the central and southern parts of Israel.

Israeli 3 also demonstrated that the clouds of Israel are unsuitable for glaciogenic cloud seeding.  There is nothing substantially different between the clouds that affect the central and southern regions of Israel from those that affect the north in terms of microstructural behavior except that the clouds in northern Israel are overall generally colder from top to bottom.  In both regions they glaciate effectively.

And, who would undertake a randomized seeding experiment for 19 years knowing you might have a natural draw so far from zero that can’t even be overcome by an actual 10% seeding-induced increase in rain[9]?   (One wonders about the quality of the random draw again…)

7 e)  Operational seeding:  the descriptions in F2015 and the counter evidence to those descriptions; filling in still more blanks

F2015:  “Subsequently operational seeding in the north of Israel was carried out between 1975 and 2013.”

The above quote by the HUJ-CSG authors’, writing in 2015 in AR, shows that they cannot bring themselves to report that the “operational seeding” program in the north of Israel, as it was originally formulated, was terminated in 2007 (Sharon et al 2008[10]).    We quote Sharon et al. 2008 for the AR reader:

 

“3b. A revision and elaboration of possible future seeding activities

In view of Kessler et al.’s initial finding in Section 2a and the ensuing controversy, a joint forum of the

National Water Authority and other professionals involved, met early in 2007. After 50 years of uninterrupted seeding activities, the forum decided to discontinue the program at the end of that rainy season (April 2007) and instead, consider the initiation of a new updated experiment, Israeli IV.”

Why was the original program terminated by the INWA and its panel[11]?

Answer:  The independent panel of experts (Kessler et al 2002, Kessler et al. 2006, distilled by Sharon et al 2008) could find no additional runoff due to seeding into the target, Lake Kinneret (aka, Sea of Galilee) over the 30 plus years of seeding.  They also found that the small increases (6%) reported by Nirel and Rosenfeld (1994); Rosenfeld and Nirel (1996) could not be substantiated when more data from later years were used.   This null finding for the operational program by Kessler et al. was later corroborated by independent scientists at Tel Aviv University (Levin et al. 2010, 2011, the latter in reply to the comments of Ben-Zvi et al 2011).

At this point, one wonders who the reviewers of an article in the respected journal, AR, were?

How could they let such partial statements and an article absent vital references appear?  One must also assume that the reviewers for AR were woefully ignorant of the history of the Israeli experiments to have allowed the F2015 distortions reach the print stage of a major journal.  Truthfulness and a full exposition of events is not part of the HUJ-CSG’s understanding of how to compose a manuscript for a scientific journal.   Their manuscripts and publications, in essence, need to not just be reviewed, but “policed” for accuracy.

F2015:  “Additional statistical analyses showed that the orographic precipitation responded most sensitively to the seeding experiments (Givati and Rosenfeld 2005).”

F2015 claimed in the above publication, that air pollution had decreased precipitation exactly by the amount that seeding was increasing it in the interior of Israel (thus explaining the lack of operational seeding effects reported by the independent panel).  The finding by Givati and Rosenfeld (2005)

could not be substantiated independently by either (Alpert et al 2008, Halfon et al 2009a[12], b) nor by Levin et al. 2010.   The pollution claim by Givati and Rosenfeld (2005) was found to be ambiguous at best.

 

It is useful to quote Thom (1957) on how Givati and Rosenfeld came up with their “pollution” findings (as was demonstrated by Alpert et al 2008 and Halfon et al 2009):

 

“If one takes the liberty of choosing among minimum distance controls, he can often find any result for seeding that suits his purpose, either positive or negative.”

That the results of operational seeding as reported by the HUJ-CSG could not be validated by independentresearchers on four occasions (Kessler et al 2002, Kessler et al. 2006, Halfon et al 2009, and Levin et al. 2010, 2011 (reply to Ben-Zvi et al) is one of the most important aspects of the seeding history in Israel.

For those who know this story, we again see one-sided citing in this discussion; the HUJ-CSG in F2015 cannot bring themselves to cite those publications, damaging those independent workers, themselves, and whether they realize it or not, their own home institutions.

HUJ, are you listening?  Isn’t it best if you policed the HUJ-CSG publications instead of someone like me doing it after they’re out in print?

  1. A critique of the cloud sampling and its effects on the cloud microstructural properties reported: how unbiased are they?

This discussion will make it clear why F2015 must make videos from their research flights publically available; these are crucial to understanding what they did and how they did it.

Median concentrations in “hard”, newly risen turrets over the Mediterranean, as the authors show in Figure 16 from their Mediterranean cloud targets, produces a bias toward low ice particle concentrations and higher liquid water contents compared to values that would be found as those same clouds as they matured minutes later.   The authors know this.  The authors are to be commended for adding the description of the stage that the Mediterranean clouds were in when they were sampled.   This really helps the experienced reader weight those “medians” in the Figure 16.

But did the authors’ sample “hard” but meteorologically inconsequential, slender, “chimney” Cu as well in Figure 16?  These are ones we know produce little ice/precip compared to their wider brethren even if they are at the SAME cloud top temperature (e.g., Schemenauer and Isaac 1984, Rangno and Hobbs 1991).  Cloud top width, in particular, is an extremely important metric and should be listed in an online supplement by F2015.

Some background on the width issue:  the apparent error of penetrating isolated, likely “chimney” Cumulus with “smooth, hard tops” Cumulus clouds instead of the wider complexes that produce appreciable rain in Israel was one that was made in the original cloud reports coming out of the HUJ-CSG in the 1970s and 1980s (e.g., GN74, GN76, Gagin 1975, 1981).

Due to that sampling strategy, it misled those HUJ-CSG scientists on the ice content in their clouds, and ultimately their journal audiences.  In contrast to those early cloud samples, GG87 reported that the average duration of a shower in Israel was 23 minutes.  With just a 10 ms-1 wind carrying that shower along, that rain would have fallen from a cloud system at least about 13 km long; at least 26 km long if it was carried along in a 20 ms-1 wind!

So, what DID F2015 sample that was relevant to Israeli shower clouds?  We don’t know.  But its critical that we do know.

Another source of bias toward low ice concentrations can result if the authors, in fact,  did sample wider, high ice-producing complexes, but only penetrated the very newest, “hard” turrets in them (typically on the upwind side) in which the explosion of ice had not yet occurred.

Lastly, another critical metric for understanding the quality of the HUJ-CSG authors’ measurements in Fig. 16 is the height of sampling below cloud top.  Sampling too close to cloud top, say, tens of meters instead of a few hundred meters, also leads to a low detection of precipitation-sized particles (and also why Re satellite derivations can mislead in newly risen turrets, and in ice-spewing, supercooled water-topped layer clouds common in orographic settings.  This again reinforces the need for videos of the F2015 study.

  1. The HUJ-CSG’s continuing trouble with ice

The HUJ-CSG has carried out several airborne sampling programs with modern droplet and hydrometeor probes over the past 25 years, beginning in the middle 1990s (Rosenfeld and Lensky 1998).  Further airborne studies were conducted by Lahav and Rosenfeld (2000), Rosenfeld et al. 2001), and by F2015.   Maximum ice particle concentrations and the degree of ice multiplication were not divulged by the HUJ-CSG in any of these publications!

In F2015, we finally have ice particle concentrations!   However, what we get are unsatisfactory-for-seeding-potential, “median” concentrations obtained  in “hard” turrets for those clouds in the Mediterranean.   This prevents us from understanding the “ice life cycle” of Israeli clouds.

Ice particle concentrations, and their origin,  has been one of the continuing mysteries of cloud microstructure (e.g., Mossop 1970, 1985);  in particular,  a primary enigma is how secondary ice forms in clouds with top  temperatures warmer than about -15°C, as occurs prolifically in Israel.    AR readers are likely aware of the 2017 Amer. Meteor. Soc. Monograph  (Field et al.[13]) that focused on the origin of secondary ice and the puzzle it still represents.

Israel is in a region of confluence of various aerosols that affect clouds.  Reports of the degree of ice multiplication from Israel would have surely helped fill in some microstructural blanks in our knowledge.  What a shame the HUJ-CSG can’t address this question in their cloud sampling programs!

Too, where are the droplet spectra and graupel concentrations in the Hallett and Mossop secondary ice-producing temperature zone of -2.5° to -8°C?  Nowhere to be found.    More missing pieces to the knowledge required to understand the clouds of Israel.    Why does it feel like I am reading a paper written in 1968?  The authors could have done better with the “black glove” technique, or a foil sampler (Koenig 1963).

From the reviewer’s experiences in 1986, ice multiplication in the clouds of Israel is rampant.  But, remarkably, only L929496, has addressed this issue in Israel been addressed over the past 43 years since Gagin (1975). The study of ice multiplication, a staple of airborne cloud microstructural studies over the past 60 years (e.g., Mossop et al 1972).  T he HUJ-CSG seems to have trouble since the early 1980s of honoring this standard.

This discussion above begs the question about why F2015 didn’t target mature and dissipating portions of Mediterranean clouds after high ice particle concentrations had formed?  Its inexplicable.  The statement by F2015 that mature, heavily precipitating clouds were avoided due to aircraft safety considerations is not credible to us researchers in airborne studies.  Heavy icing, graupel, hail are found in the younger turrets, not in the maturing ones where icing is subdued due to the formation of high ice particle concentrations that consume the liquid water.

Neither can the HUJ-CSG’s median ice concentrations be compared to the concentrations of ice in Israeli clouds reported by L929496 who was somehow able to sample the high ice-containing regions of Israeli clouds that F2015 found so dangerous.

Specific examples of HUJ-CSG reporting from airborne work over the years since Gagin 1975:

Rosenfeld and Lensky (1998) flying on shower days in pursuit of a comparison between satellite and aircraft measurements of Re, wrote that they  did not carry a 2-DC probe for hydrometeors on their aircraft on the two flights with showers (!).

Lahav and Rosenfeld (2000), in a ten flight sampling program having a 2-DC probe, nevertheless refrained from reporting ice or other hydrometeor concentrations, while titling their paper, “Microphysical Characterizations of the Israeli Clouds from Aircraft and Satellites.”    But that’s not what they did, or, at least reported.  They only reported partial results.  Sound familiar?

Rosenfeld et al. 2001 had a 2-DC on their research aircraft, but once again, refrained from reporting  concentrations of hydrometeors in the clouds they sampled.  What they did report was that there was a “large number”, or that they were” increasing” or “decreasing.”  What’s going on here?  How does such reporting like this make it into a prestigious journal like PNAS?

This reviewer’s guess, from his 1986 Israeli field project, is that the HUJ-CSG has found in those several airborne projects mentioned above that they have an “embarrassment of ice particle riches” and wants to keep those concentrations and the degree of ice multiplication away from AR readers and funders who might consider cloud seeding.   Ice multiplication in clouds has always been considered an impediment to successful “static” glaciogenic cloud seeding (e.g., GN74, Dennis 1980).

Is there another motive by the HUJ-CSG for keeping maximum concentrations from us?  Yes, another critical omission of results by the HUJ-CSG.    To repeat:

The difficulty is that positive claims are sometimes made against a background of       unrevealed negative results.” 

This is why, again, that  independent groups are critical in evaluating seeding potential in Israel!

INWA, are you listening?

Gagin (1975), in support of ripe for cloud seeding clouds, claimed that ice particle concentrations do NOT increase with time.  This finding could have been evaluated, too, at many points in the HUJ-CSG airborne studies.

Even more relevant is that those very same ice-filled clouds over the Mediterranean Sea are going to be swept downwind and into the Golan within ~30-40 min during rainy spells, making it doubly important to have reported those maximum concentrations and followed their evolution downstream in route to the Golan.

In sum, yes, you CAN mislead with an aircraft, even one with a full complement of 21st century cloud microstructure instruments via omission and sampling biases.

The points raised in the foregoing section concerning the airborne sampling carried out by F2015 emphasizes all too well why in-flight videos must be made publically available as they are at the University of Washington and also for a number of other projects at NCAR.

To summarize the dark history of the HUJ-CSG:   over a period of several decades: it misled their own people and the world repeatedly about their clouds, withheld statistical results for Israeli 2 for 15 years, results that would have raised so many questions, delayed for 17 years the reporting of results from the Israeli 3 randomized experiment that, too, would have raised numerous questions.   And under its new leadership, that following the passing of Professor Gagin still can’t seem to publish reliable results about their cloud seeding work, either.  Neither can they fully report on their clouds such basic information as the degree of ice multiplication that Israeli clouds exhibit.

Furthermore, and this may the most telling of all, every paper the HUJ-CSG has published and that has been examined by outside, independent investigators, has been found to be unreliable.  Will more unreliable HUJ-CSG claims be turned up in their literature?  It seems inevitable.

One can predict confidently that in the future the HUJ-CSG will, without major changes to its leadership,  and without a more skeptical INWA concerning the claims coming out of that group, “repeat history.”

——–End of “Commentary” on the F2015 Abstract and Introduction

Following the Abstract and Introduction segments, F2015 improves demonstrably; it is written extremely well in places, representing the best in what we think of as scientific writing.  However, there are still a few lapses and reviewer-required “clarifications” that will be addressed as they appear.  The type in black is that from the original article.

The objective of this paper is to present the available knowledge on  the cloud  properties in northern Israel,  which supported the decision to commence with the Israel-4 experiment, as briefly described above. Section 2 describes thetypical synoptic conditions during the rainy  days  and  the dynamics of the  clouds as they  interact with the sea  and  the topography. Section  3 describes the  methodology of the physical experiment,  the  cloud  physics aircraftinstrumentation,  flight  patterns and  methodology of data analysis. The methodology of supporting satellitemicrophysical retrievals is also given  in this section. The results of the measurements with respect to aerosols and theway they determine the microstructure at cloud base are given  in Section  4.1. The subsequent vertical evolution ofcloud microstructure with height above  cloud  base  and  initiation of rain are described in Section 4.2. The mixed-phase processes and availability of super-cooled cloud water are presented in Section 4.3. Finally, a summary ofthe results and a discussion of the suitability of the clouds over  the Golan  Heights to glaciogenic seeding aregiven  in Section 5.

  1. Synoptic, dynamic and macro-physical considerations

2.1. Meteorological conditions

The  synoptic systems that are  responsible for  more than

90% of the annual precipitation in northern Israel occur  with cyclones passing through the  north-eastern part of the Mediterranean Sea, these cyclones are  referred to as Cyprian Cyclones  (Goldreich, 2003). A rain  event typicallystarts with the passage of a cold  front  followed by  a  thermal low  that develops in  the  cold  air-mass behind thefront   due  to  the relatively warm sea and the lee effect of the Turkish  mountains to the north. An upper trough withrelatively cold  air aloft is associated with the  cyclone,  which increases the thermal instability and  favors  thunderstorm  formation over  the  sea. First precipitation over  land  typically starts with the arrival of the cold front, as the air ahead of it is characterized by dry and often dusty air from the Sahara desert. Fig. 2 shows the synoptic conditions on a typical rainy day in Israel, at the time of the cold front  arrival.  As the winds veer from southerly towesterly, the low-level air  becomes moister and  the cloud-base elevation lowers to a typical level of 500-1000 m (allabsolute heights are given  above  sea  level).  The thermal instability reaches its maximum in the thermal low afterthe passage of the cold front. The average wind speeds are often greater than 10 m/s and they contribute to theorographic component of the precipitation. When the low-pressure system moves to the east the instability is graduallyreduced. However, due to the long trajectory of the cool low-level air over the warm sea the instability and moisture supply supports continued rainfall for another day or two.

Minor:  The IMS refers to periods of rain as “rainy spells.”   This is because they often consist of several consecutive days with recurring showers.  In Israeli 1, there was a period of 17 consecutive days with rain.  The F2015 highlighted sentence might be revised to reflect the occurrence of “rainy spells.”

2.2. Cloud dynamics

Fig. 3 illustrates the cloud and  precipitation characteristics on a typical rainy  day in the  air-mass behind the coldfront.  It is a west–east cross-section across northern Israel,  and  it is based on our  observations and  impressionsfrom  the physical experiment. The schematic figure  is intended to illustrate the main features of the cloud  and  precipitation processes that often  take place  as the air-mass travels eastwards across  the land  and  over themountains.

Figure 3 and its caption:  “…clouds in a typical rain day on northern Israel, as a west-east cross section from the Mediterranean Sea to the Golan Heights.  Rain originates in convective clouds over the sea as graupel and hail.  The sea spray from the rough sea seeds the clouds hygroscopically.  Orographic cloud over the Galilee are often seeded by the remnants of convection.  The clouds evaporate into the Jordan Valley and reform over the Golan Heights.”

This figure is over-simplified, perhaps out of necessity due to the many scenarios that would have to be presented to reflect the several stages in Israeli storms as troughs come and go as documented in the comprehensive satelllit studies by Rosenfeld in 1980, 1982, by Gagin 1981, R88, RH95).

F2015 show a higher level stratiform region extending from a line of convection at the Israeli coast in Figure 3.  However,  it is but one snapshot of an incoming storm, not a semi-permanent pattern as the AR reader might infer.  There are many other scenarios that could have been drawn, which could have been as online supplements to fill in the picture of Israeli rainy days more. Figure 3 is really much closer to a depiction of the coastal convergence zone that tends to develop in the later nighttime and morning hours during lesser onshore flow periods (e.g., Neumann 1951, Goldreich 2003).

Satellite imagery reveals that during major events (lines of convection organized by upper level troughs) clusters of Cumulonimbus clouds and stratiform rain areas barge into Israel en masse.  While the roots of the of convection might be lessened when they move inland in wintertime, as F2015 note,  these mesoscale/synoptic scale systems march across Israel with much of the deep, precipitating cloud system intact.  They do not separate completely, as a rule, into an upper layer and lower layer as shown in Figure 3.   Too, some of the rain that falls is due to aggregates in quasi-stratiform debris clouds.

The Stratocumulus over the hill regions in Figure 3 might be accurate for that specific moment of an approaching storm.  However, drizzle, and mist-like rain (due to collisions with coalescence) often falls from such hill-topping overcast low clouds topping out,  as shown in Figure 3,  at about 3 km ASL[1].   It should have been pointed out that such low clouds, “auto-precipitate.” They frequently top out at temperatures where seeding them would not be effective (> -5°C, e.g.,  R88).

In later winter and spring, shallower Stratocumulus clouds tend to lift off the lower hills as temperature rises during the day, and by later afternoon can sprout into small Cumulonimbus clouds (glaciated clouds) under cold trough situations.  Also, due to the local strengthening of the onshore flow during the afternoons, incoming convection can weaken and may disappear altogether in the coastal divergence zone responding to that strengthening flow.

The deepest clouds in springtime are frequently over the inland hill regions rather than offshore as evidenced by an increase in lightning frequency inland during the late winter and spring.

Minor:  Figure 3 also indicates that the bases of the clouds reforming over the Golan are virtually as low as those on the hills of Galilee.  This seems implausible under the loss of precip water and downslope motions in prevailing westerly flow.  Bases should be higher over the Golan, and probably closer to the freezing level?  Or?

As mentioned in  the  previous section, the  lower troposphere during a typical rainy  day  is quite moist and  unstable due to the relatively warm sea (sea  surface temperature never drops below 17 °C) and colder air aloft(typically below + 2 °C at 850 hPa during the rainier days).

The cycle of Mediterranean Sea temperatures from fall to late winter is significant.   It starts out at around 22°C and descends gradually to 17° C.  Cloud base temperatures, hence, water content in clouds and the propensity to form warm rain and copious ice, also are impacted, likely further reducing seeding opportunities in the warmer fall/early winter period.

This favors the formation of fairly  deep convective clouds over  the sea.  This  is also  why hailstorms and  lighting activity are  more probable near the coastline and less common further inland (Altaratz et al., 2003; Goldreich, 2003).

Lightning activity is about equal over the Mediterranean Sea and inland areas in November and March (Altaratz et al. 2003).   This equality likely extends into April as well.

When these convective clouds move inland, they become separated  from   their main sensible heat and moisturesource and  weaken quickly.

To repeat, the roots of convection may weaken, but these major complexes usually don’t separate with a clear zone between upper and lower clouds as shown in Figure 3; its just one of many scenarios.  F2015 do not support their Figure 3 scenario with frequencies of occurrence during the winter.  How does it compare with the frequencies of other storm scenarios?

However, the moist air that is pushed inland by the strong westerly winds is forced upwards  by   the  topographyof  the  western  Galilee,   and therefore an orographic component is added to the weakening convective  clouds.  The  annual precipitation amount in  the upper Galilee peaks at 1000 mm, as compared to the ~ 600 mm at the coast.

When the air continues eastwards it descends about 800-1000 m to the Jordan (Hula) valley, the clouds, unlessthey are synoptically forced,  tend to dissipate and  break up. This leaves the valley   with  an   annual  precipitation  amount  of  only

~ 500  mm.  This is the  area  where often  visual  flight rules  can apply  and  below-cloud aerosol measurements can  be  made safely.

The slopes of the Golan  Heights force  the air to rise  again and  to produce new  orographic clouds with smallerdroplets.

Check+

The crest  of the Golan Heights rises  gradually from  a height of 400  m  in  the south to  1200  m  in  the  north. Further north, Mount Hermon rises  up to an elevation of 2800  m. The Golan Heights  are   45–70  km  away   (shortest  distance) from   the coastline and  the  clouds there are  normally less  convective than the clouds overthe Galilee and over the sea, because much of the instability is consumed upwind.

 “…normally less convective… ”  True,  except maybe for November  and spring when convection over inland regions is apparently more evenly distributed if lightning occurrences are an indicator (Altaratz et al 2003).  What are the seeding implications of enhanced convection in the Golan?  Do the authors know?  Likely less potential if deeper clouds in the Golan glaciate at modest supercoolings.

The  terrain over  the Golan  Heights is also  less  complex than over  the Galilee  and therefore the flight throughthe  clouds over the  Golan Heights is often relatively smooth. The top of the ridge is only about 10-15  km  downwindfrom  the foothills where the  clouds form. This leaves the clouds little time to  convert their water into precipitationbefore they start to dissipate and lose their water content back to the atmosphere.

We reprise Figure 1 from F2015:  Isn’t the target too small and close from seeding release points for seeding to result in a fallout of precip on it?  Where does the water go in the lee of the Golan, to Syria or into Lake Kinneret?   (This diagram should have had a kilometer scale.)

GN74 estimated 30 min for precip fallout from line seeding, as do F2015.   In the HUJ-CSG publications we find various distances from the aircraft line seeding at which the fallout of seeding-induced precipitation may have occurred, possibly due to variations average wind velocities used .  These ranged from 25-35 km downwind (Gagin and Neumann 1976;  35-50 km  (Gagin 1981); 25-45 km (Gagin and Neumann 1980) ; “about 40 km” (in GG87) to “25-35 km” in F2015.

So which is it?

 And what wind speeds were used in F2015?  And why?  What climo did you use?  The estimate contained in Gagin 1981 (35-50 km) appears to be too great a distance for a precip fallout for this project to be successful except in deep southwest flows.

What are the flight levels of the line seeding aircraft?  Why is this information not in F2015?   This is critical information since if those seeding lines are too low, the seeding material will not reach the necessary heights for nucleation and precip fallout in time to help runoff.  (Perhaps this information is contained in the full proposal?)

How can airborne or ground releases target the region north of the dashed line in Figure 3, including the wettest location, Mt. Hermon, when seeding plumes have to climb to between 700 and 500 mb levels to nucleate effectively and when the primary wind flow is westerly?  In winds even a little north of westerly, it does not appear that seeding is going to be viable in the wettest portion of the Golan unless you get help from Lebanon.

And isn’t the downwash into the Hula Valley going to be detrimental to seeding the Golan?

See the wind rose for 850 mb for those times that rain is falling in Israel from RH95.  It would appear that  many periods of precip  in the north part of the Golan, anyway, will not be able to be seeded efficiently.

Lastly, seeding can reduce upslope precipitation by reducing the degree of riming on upslope precipitation.  Riming is reduced as new, tiny AgI ice crystals form reduce or deplete the upslope supercooled LWC.  The trajectories of ice crystal/snow precipitation are less steep, raised since riming accelerates the downward fall of snow and that will be lessened in seeding.  Will it be made up by more ice crystals?

Ground measurements of precipitation should have been incorporated into the proposal to the INWA or mentioned in F2015 in supporting their contentions about seeding potential in the Golan.

In case there are synoptically-forced or mature clouds above, which survived the  descent to the Jordan (Hula)valley (Fig. 1), they often  precipitate through the orographic clouds and  seed  them naturally from  the top.

What is the frequency of occurrence of this scenario?

The  annual precipitation amount  over   the ridge   increases from  600 mm  in the south to more than 1200  mm  over Mount Hermon to the north, mainly depending on the surface elevation (Goldreich, 2003).

2.3. Aerosol dynamics

The trajectory of the air  mass  that is associated with the Cyprian   Cyclone  passes various regions on  its approach to Israel. Each of these regions leaves  its signature on the aerosol properties. One of the  common features of the warm sector of the approaching low-pressure system is the reduced visibility due to increasing loads ofdesert dust in the air. The winds with the southerly component get stronger as the cold-front comes closer,  lift the dustparticles from  the  surrounding deserts and keep  them airborne. The low-level convergence raises the dust particleshigher up,  so they can  travel greater distances. The dust concentrations are normally higher in central and southern Israel  than in  the  northern part.  This  is due  to  a number of reasons: 1) Northern Israel is farther away  from  the main dust sources; 2)  The  south-westerly flow  ahead of the  cold  front travels some distance over  the south-eastern Mediterranean before arriving to northern Israel, and is occasionally associated with pre-frontal rains   that can wash out  some   of  the  dust particles; and 3) The Israeli deserts in the south, where sand and dust  storms are  common, can  also  contribute to the aerosol population in central and  southern Israel.  After the passage of the cold-front with the arrival of the cool air, the visibility tends to quickly  improve.

Dust particles can  act as cloud  condensation nuclei (CCN) and  may  also  serve   as  natural ice  nuclei   (IN). The  seeding potential of the  clouds is therefore expected to depend on the presence and  the concentrations of thedust particles in  the boundary layer   and   in  the free  troposphere. This  was  the reason, according to  Rosenfeldand  Farbstein (1992), to why they found a positive seeding effect both in northern and  in central Israel when theystratified the experimental data  based on dusty and non-dusty days. Consequentially, one can assume that therelease of silver iodide may have the intended effect of accelerating the precipitation formation only when and  where natural IN supplies are limited and ice does  not readily form in the super-cooled clouds.

Another common and  important aerosol type that is quite abundant when strong westerly winds are prevailing is thesea salt aerosols. The breaking waves and  rough seas trap bubbles of air in the sea water. As the bubbles float backand  reach the surface of the water, they burst the thin film of the seawater and release small  drops into  theatmosphere — the sea spray.  The largest drops may quickly fall back to the sea, but those that stay airborne just 5

long enough have  the chance to remain in the air for a much longer time period as they evaporate and get smaller and  more concentrated. The vertical mixing in the  boundary layer  together with the convergence associated withthe low- pressure system assist  in raising these sea salt particles to the cloud  base  level.  These  fairly coarse and hygroscopic particles are the first to act as CCN and  make the largest droplets in the cloud, which serve  as embryosfor subsequent raindrops.

Concerning “sea spray” and large droplet formation in Israeli clouds:

The discussion of sea spray and bubbles strongly resembles that of Woodcock (1953).  These researchers stand upon the shoulders of Woodcock but do not cite him.  This again points to weak reviewing of the pre-publication manuscript.  We quote Woodcock (1953) below:

 “It is suggested that bursting air bubbles in “white caps” on the open sea are a major source of the salt nuclei, and that a greater portion of the sea surface may act as a source of these particles during average winds than might be judged from the relatively small area usually covered by white caps”.

 

We note with interest that Woodcock was likely wrong in his initial 1953 finding (e.g., Woodcock et al. 1971).Woodcock’s finding that large particles are more numerous on “average wind days” rather than days associated with a large number of whitecaps, supports the occurrence of warm rain on more days than just those with numerous whitecaps and stronger winds in Israel.

More work is needed on this finding by F2015, preferably, again, by independent groups.

L929496 should be cited here.  In Levin’s studies it was found that large CCN comprised of sulfate-coated desert particles led to large droplets in Israeli clouds starting at cloud base.  He did not report on sea surface conditions, however.

————————

However, rather than strong winds and “sea spray”, the occurrence of large droplets in clouds are likely to be modulated by cloud base temperatures and low or moderate droplet concentrations in clouds over Israel and the Mediterranean, with relatively weak cloud base updrafts in which only the largest CCN are activated.

 In an R88 case study, clusters of Cumulus congestus clouds moving in from the Mediterranean Sea on a nearly calm day and produced light rain showers with cloud tops only near 0°C.  Cloud base temperatures on that day were above the average quoted range of 5° to 9°C, about 11°C.

Cloud base temperatures vary substantially in Israel, not only changing as the air mass trajectory changes, but also due to the warm to cool cycle of the eastern Mediterranean from fall to late winter and spring where the temperature can start at 22°C at the start of the rain season,  and ends up at 17°C in mid-late winter.

In RH95, it was noted that cloud base temperatures in Israel varied from 12°C to 5°C.  There would be approximately 40% more water available for condensation with the highest cloud base temperatures compared to the coolest ones, given the average cloud base altitude of about 800 m above sea level.    We note that the authors are aware of this effect of cloud base temperatures, but they do not present those temperatures.

Herut et al. (2000) analyzed the chemical composition of nearly 600  samples of rain  water collected all aroundIsrael during five rainy  seasons. They found that the  sea-salt fraction of the  rainwater composition is influencedmainly by the distance from the Mediterranean Sea, with a decrease from 73% of sea salt fraction in the coastalsamples in the north to 55% in the samples from  the Golan  Heights. They also  reported that the contribution of non-sea-salt precursors to the salinity of the rainwater was much greater in the south due to higher input of continentalcomponents and  lower annual precipitation there.

  1. Methodology of the microphysical measurements

3.1. The research aircraft

A twin-engine turboprop Beechcraft King-Air C90 aircraft was instrumented for the  cloud  physics measurementsduring the rainy seasons (November through April) between 2009 and 2013.  At the start of every  season the airplanewas fitted with the aerosol and cloud-microphysics instrumentation as well as the data acquisition and displayinghardware and software. The entire system was  tested on the ground periodically while the airplane was standing-byready for suitable weather to arrive.

3.2. Instrumentation

For measuring the  concentrations and properties of the aerosols we used  a CPC (condensation particle counter), acloud condensation nuclei (CCN) counter and an aerosol spectrometer.

The CPC (TSI model 3781) is a water-based condensation nuclei counter that measures the total concentrationof particles larger than 6 nm  in diameter, at a 1-Hz  temporal resolution  (Hering  et   al.,  2005).  The   simple design,   fast response and  continuous measurement help  detecting variations  in  aerosol concentrations that could  be  related to the atmospheric thermodynamic structure, pollution sources and/ or aerosol nucleation events. It is aninstrument that is fairly easy to handle and  maintain and  is considered reliable.

The  CCN counter that was  purchased from  Droplet Measurement  Technologies (DMT)  for  the  experiment is  a continuous-flow streamwise thermal-gradient counter (Lance et al., 2006). It measures the concentrations of theparticles that were activated into  small  droplets at  a set super-saturation, as well as the sizes of the activateddroplets. The CCN counter can  measure continuously at  a constant super-saturation or alternatively cycle  thoughuser-defined super-saturations for measuring the CCN spectra. The downside of changing super- saturations is that ittakes a couple of minutes for  the temperatures to stabilize and  the actual super-saturation to settle around the  required super-saturation. This also happens when the sample temperature or the pressure changes due to changes in flight altitude. We were therefore flying most of the time with a constant super-saturation (typically 0.5%), exceptduring the dedicated time for measuring the CCN spectrum at a constant flight level below the cloud base (typicallytwo-thirds of the way from  the  surface to the  cloud  base). The effects  of the  sample pressure on  the  actualsuper-saturations as  well  as  the  temperature changes within the  instrument were accounted for during the  data  analysis and quality control.

During   the rainy   season  of  2009–2010  we   had   a  DMT manufactured

aerosol spectrometer (PCASP-X2) onboard (Tan et al., 2010). As opposed to the CPC and the CCN counter, it does not expose the aerosols to  any  super-saturation, but  actually does  the  opposite; it dries  the  air sample for avoidingaerosol swelling due to absorption of water vapor. The PCASP-X2 measures the diameters and concentrations of aerosolsin the range 100 nm to 10 μm. The instrument was  mounted inside the cabin.  The air intake was  isokinetic only  up  toaerosols of about 2  μm, thus truncating the sampling of much larger aerosol than 2 μm.

            Another  DMT instrument on  the   plane was   the Cloud, Aerosol  and  Precipitation Spectrometer (CAPS)(Baumgardner et al., 2000). It consists of two spectrometers (CAS and CIP) and sensors for measuring thetemperature, relative humidity, static and  dynamic pressures as  well  as  a  hot-wire for  measuring cloud  liquid  water content (LWC). The CAS (Cloud and  Aerosol Spectrometer) measures particles and  droplets at the diameter range of 0.5 to 50 μm. The instrument is mounted on a pylon under the wing  and  measures directly the airstreamfrom  the cloud.  The measured aerosol spectrum is therefore sensitive to the  relative humidity. Accounting for thiseffect  is not  possible without knowing the chemical composition of the  aerosols, so we  mainly used  this  probe as asecond cloud  spectrometer for particles larger than 2 μm, as a backup for the main cloud droplet probe (CDP) and forquality control.

The CDP is a DMT-made cloud droplet spectrometer that measures the concentrations and  sizes of the cloud droplets in the  2–50  μm diameter range (Lance et al., 2010). This range is divided into 30 bins, which are muchnarrower than the bins of the CAS (in the cloud droplet size range). Both probes size each droplet that crosses theirsampling volume, based on the amount of light that is scattered forward when the laser  beam hits the droplet.

The DMT-made Cloud  Imaging Probe  (CIP) (Baumgardner et al.,  2000) provides 2-D  images of  precipitationparticles based on their shading pattern on a 62-element array of photo- diodes. The CIP that has been used hadpointy tips, to minimize error due  to shattering of large  particles, and  a resolution of 15  μm so  the  nominal widthof the array  corresponds to a length of 930 μm. The CIP allows identifying the different habits of the ice particles aswell  as distinguishing them from  rain/ drizzle.  It is not possible to directly derive the mass  of the precipitationparticles when ice is present due to their complex form and sensitivity to their orientation. However, the number concentration of the particles (after software partial removal of splinters from shattered particles) along  with particleimages can be useful  for identifying different microphysical phases in the clouds.

Details of the methodology used to remove “splinters from shattered particles” by F2015 is mandatory due to the HUJ-CSG’s prior excess removal of “splinters” from in-cloud measurements that apparently misled them about ice formation in their clouds (e.g., Gagin 1975).  We also note that F2015 used a 2-DC probe with “pointy-tips” as described by F2015 to minimize artifacts in the first place.

So, to re-iterate something that shouldn’t need to mentioned more than once, “Why can’t F2015 report concentrations of ice particles, beyond the medians Figure 16?”

Other parameters that were being   recorded during the flights were the air temperature, the relative humidity andthe navigation data from the  GPS system.

3.3. Flight patterns and execution

During the four rainy seasons of the physical experiment, 27 research flights  were conducted. Each flight lastedtwo and  a half  to three hours on  average.

How different were the synoptic settings?

A table of dates and times of flights is mandatory as are related synoptic maps (surface and 500 mb maps) preferably those embedded with satellite IR imagery.  IMS, aircraft soundings, and, if available, Beirut rawinsonde profiles, should also be made available.   Radar imagery should also be posted online for these flights.

These will help corroborate the authors’ findings; to insure that cherry-picking of a few particular synoptic regimes hasn’t been done to “improve” the overall apparent magnitude of seeding potential.  (One can observe the lack of trust of the HUJ-CSG on the part of the reviewer here in evaluating seeding potential with the baggage they now carry. Sorry, HUJ.)   If they did select only certain flow regimes, because only a few produce targeting possibilities, they should have stated this.

Fig. 4 displays a typical flight track. The black curved line shows the ground path, while the colored line  isprojected and  colored according to the flight altitude. The numbering relates to the geographical locations that arementioned below.

The take-off was  either from  Sade-Dov  airport in Tel Aviv (denoted as point “1a”  in Fig. 4), or from  Ben-GurionInternational airport which is ~ 20 km to the southeast (point “1b”).  The flight typically started with flying out to theMediterranean Sea at low  level  in order to assess the roughness of the  sea and  to safely measure the aerosolsbelow cloud base (point “2” in Fig. 4). This was followed by profiling the deepest clouds in the region from bottom to top,away from local pollution sources over land, while heading north (to point “3”). The profiling was done either at aconstant climbing rate of ~ 500 ft/min in case the cloud layer was  continuous or  by  flying  horizontally through cloudsand climbing stepwise 500–1000 ft in the cloud-free air, in the case of well-defined convective clouds.  After reaching andsampling the tops of the convective clouds over the sea we were normally able to look  eastwards towards the hilly regions of northern Israel, and  identify new  clouds over  the  Galilee. We would then fly to these clouds and profilethem from their tops to the lowest safety flight level (6000 ft) in a spiral  (point “4”).

We note that the sampling height over the Galilee district is about 3500 feet above the bases of the Mediterranean Sea and coastal clouds.

 Sampling “new” clouds might bias ice concentrations to lower values than actually developed a little later. Perhaps the authors don’t mean “new” in the sense of cloud stage?

The next step  was to descend to below the cloud bases over

the Jordan  valley  between the western and  eastern mountain ranges (i.e.,  between the  Upper   Galilee  mountainsand  the Golan  Heights) in order to measure the aerosols inland.

Heights of cloud bases and temperatures should have been given here; preferably listed in a comprehensive table for all flights and different sampling regions.

This was  either done over  the Hula Valley (point “5a”) or over  the Sea of Galilee (“5b”), depending on the  weatherand/or the  air traffic control directions. The CCN counter was set at this point to cycle through three super-saturations(normally 0.3, 0.6 and 0.9%) for approximately 15 min, while we were flying in circles at a constant altitude, and  tryingto avoid  areas with rain. The third cloud  profile  was  done over  the  Golan  Heights, starting with the cloud basesover the eastern edge of the valley and  above  the  slopes (point “6”).  Due to the proximity of the Syrian  border, therest  of the  climb  over  the crest  was  mostly done either in spiral  ascent or in a number of north–south legs, each  approximately 5 min  long,  perpendicular to the  westerly wind direction, until  reaching the cloud top or the heightwhere the  cloud  was  fully glaciated. At that point we typically started heading back south, unless we had a chance tocomplete another profile   or  measurement that we  were not  able  to  complete earlier. Finally we landed at Herzliyaairport (point “7”).

The maneuvering was reasonable in consideration of the realities of the area.  However, as the authors know, sampling on the upslope side of mountains leads to more LWC and less ice than would be found farther downwind.  Again, is radar coverage of the sampling area on the fight days available?  Did the aircraft have recorded radar imagery?  If so, can it be made available for each zone that sampling took place?  Are there ground hourly precip reports?

3.4. Data analysis  and quality control

The main software onboard the research aircraft for real- time data  acquisition was  PADS (Particle Analysis  and  Display System). PADS has been developed and  is maintained by DMT.  This data  was  subsequently processed byour  own  procedures for merging PADS and non-PADS datasets, extending the analysis from   the   research  aircraftmeasurements,  as  shown  in Section  4.2.

Interesting commentary here on what happens to DMT’s PADS processing package.  What exactly is meant here,  “processed by our own procedures”?  What changes, if any, are made from what PADS puts out?  Does DMT agree with this revision to your software’s output?  These may be harmless, but they should be discussed.

  1. Results and discussion

4.1. Aerosols and cloud base microstructure

The research aircraft was not equipped with instruments to study the chemical composition of the cloud  and  rain  water. However,  we  noticed that often  on  windy days,  after flying through a cloud,  there were white streaks ofsalt left on  the windshield of the aircraft after the evaporation of the  cloud water streamers.  Fig. 5  shows what theaircraft windshield looked like after passing through a cloud over the Sea of Galilee on 3 Feb 2010, as an example.This is one of the expressions of high  salinity of  the  cloud/rain water in  Israel,  as  had  been studied by Herut et al. (2000) and  mentioned in Section  2.3.

Nice photo.

Another  and  more quantitative expression of  the  abundance of sea  spray  is achieved by comparing the  aerosol size distributions  (ASD)  that  were measured by  the PCASP-X2 below cloud   bases   (Fig.  6).

Each  curve   shows a  60-second averaged ASD at elevations between 400 and  700 m. The black, blue and greencurves show the ASD measured on 28 Feb 2010, which was  a fairly windy day (mean wind of 10.3 m/s  at Haifa Port during the flight  time). The sea  was  rough and  full with white caps — and hence we would expect an extensivedischarge of sea  spray.

We note again that Woodcock et al (1971), in later studies of the chemical composition of rain, did not find the expected association between salt in rain.  We would like to see independent confirmation, of course.

 It can  be  seen  that these three curves have  the greatest concentration of super-micron aerosols — even  when the  measurement was  made approximately 45 km inland (the green curve) over  the Hula  Valley. These  largestaerosols are normally the first to activate into droplets at cloud base at rather low super-saturations, as they act as giantCCN (GCCN).

There  were probably more GCCN than what is shown in Fig. 6, but the experimental setup and the inlet of thePCASP-X2 caused the truncation of  the  ASD at  aerosol dry  diameters greater than 2  μm,  as  mentioned in Section 3.2.  However, despite the slight undercounting of the super-micron particles, it may still be useful to lookinto the geographical differences in their concentrations.

          Fig. 7 presents the  statistics of the  concentrations of super- micron (diameter N  1 μm)  aerosols in  the  marine boundary layer and at the foothills of the Golan Heights measured during four  different flights.   The dataset comprises the 60-second averaged PCASP-X2  concentrations measured at  a maximum elevation of 1000 m above  the ground. In-cloud and  noisy measurements were filtered out, so each  box in Fig. 7 is based on  5  to  20  one-minute  averaged aerosol distributions.  The green text  above  the boxes  denotes the mean wind speed and direction that were measured at Haifa Port at the  time  of the flights.

One can see that the last flight (12 Apr 2010) stands out in the  sense that this  was the  only flight where the super-micron particle numbers at the foothills of the Golan Heights were not considerably smaller than in  the marineboundary layer.  On the other three flights  the large aerosol concentrations over the sea  were 2–5  times greaterthan ~ 45 km  inland. The smallest difference and  the greatest inland concentrations (excluding the last flight) wereon 28 Feb 2010 — the day with the strongest winds. This implies that relatively little time was  available for the  large  particle to  settle on  their way  inland. The  greatest difference and  lowest inland concentrations was  on  26  Feb2010, with the weakest winds out of the three earlier flights.

Levin et al. 2010 attributed their finding of synoptic bias that explained the north target results of Israeli 2 to to stronger synoptic systems with strong winds that drove the precip max farther inland.  The authors’ finding seems to support the idea that large, Mediterranean Sea-derived aerosols also played a role in creating an ersatz seeding effect in the interior regions of that experiment.

The  wind speed at  the shore is not the only  factor that determines the absolute concentrations of the super-micron particles  and   certainly not  their  rate   of  removal  through cloud  and  precipitation  processes.Furthermore,  there could be additional sources of super-micron particles, other than sea spray,  such  as desert dustand  local  pollution. The PCAPS-X2 does not distinguish between the different particles, this allows only  aqualitative estimation of their relative contribution to the observed values.

The flight notes and pictures from the flight of 12 Apr 2010 indicate hazy conditions over central and northernIsrael, with desert dust being  the  probable main constituent of the super-micron aerosols. That is also the day withthe weakest winds recorded at the shore and  lowest concentrations of large aerosols near the coast, so the seaspray  production may be the lowest on that day, compared to the three others. Low sea spray production and highregional dust loading can  explain the relatively low concentration of large  aerosols over sea, and  the small differences between the marine boundary layer  and  the foothills of Golan Heights, as were observed on that day(Fig. 7).

What were the offshore cloud droplet concentrations for 12 April 2010?

Both desert dust and sea salt have  the  potential of accelerating the  precipitation formation, but  through different microphysical processes. The sea salt is an efficient CCN/GCCN, which can  produce large  cloud  droplets and drizzle particles, and   hence  speed  up  the warm rain   processes.  The  larger droplets are also more likely tofreeze and accelerate the rate of secondary ice splinter production (Mossop and  Hallett, 1974). Desert dust particles,on the other hand, may not be as effective CCN as sea salt, but they tend to be more efficient ice nuclei that mightmake cloud seeding with silver-iodide redundant  on dusty days. This may be something to account for in operational cloud seeding.

The sub-micron particles contribute much more to the aerosol total number concentrations than the super-micron particles. A large  source of small  aerosols is local  pollution, especially when  the  air-mass travels inland over  densely- populated areas,  such  as in central Israel. This is demonstrated by comparing the blue and green curvesin Fig. 6 with the black curve — all from 28 Feb 2010. The first two curves demonstrate the fairly  low  backgroundaerosol concentrations on that day because the green curve,  despite showing an  inland distribution,  is from  the rather sparsely-populated north. The  black curve,  on  the other hand, shows the aerosol size distribution downwindfrom  the heavily-populated Tel Aviv area  where the concentrations of  both   sub-  and  super-micron particles increase. But it is the sub-micron population that dominates the number concentrations, thus being  responsible fordoubling of the PCASP-X2 concentrations from  ~ 350 cm− 3 over  the sea to~700 cm−3  about 10 km downwind ofTel Aviv.

The remaining three curves in Fig. 6 show the  aerosol size distributions on relatively calm days; one with hazyskies — due to dust that was  transported from  SW (12  Apr  2010) with mean winds of 7 m/s  at Haifa Port; and  one  with no haze  (26

Mar 2010) and  mean winds of only 4 m/s.  The ASD of 26 Mar

2010   (in   purple)  shows  the  least   super-micron  particles despite being  sampled only  5

km  inland.  With  weak winds and calm seas the production of sea spray was very limited, but local air pollutionprobably caused the high  concentrations of the sub-micron particles. The  red  ASD in  Fig. 6, which was measureddownwind from  the heavily industrial area  near Haifa, had  the highest total aerosol concentration of all other ASDs. There were about 1000 cm−3 particles in the 0.1 to 2 μm size  range.  These  particles make the largest partof the  CCN population.

Fig. 8  presents a  comparison  of  two CCN spectra from another flight. The blue curve shows the CCN concentrations at three different super-saturations (nominal 0.3, 0.6 and 0.9%), as measured over  the sea  on  2  Jan 2012  at  ~ 600  m.

What were cloud base heights, if any?  What time of day was this measurement made?  Onshore or offshore flow?  The Bet Dagan sounding nearest the time of the flight should be presented so we know this case is not a fair weather day with the aerosols clamped down by stable layers.  Also, over what distances were these data collected?

 The  CCN concentration at 1% super-saturation is estimated at 360 cm− 3, while the total aerosol concentrationmeasured by the CPC was 700–1000 cm-3. The red  curve,  on the other hand, shows the  higher CCNconcentrations ~ 45 km inland. The low-level winds on  that day  had  a  clear  southerly component,  which could have  brought the pollution from  the industrial area  near Haifa to the Hula  Valley. The CPC concentrations below theclouds were 3000–3500 cm-3  while the CCN concentrations at  1% super-saturation were close  to 2000  cm-3. The  actual cloud base super-saturation was probably lower, as the highest cloud droplet concentrations in that area  barely exceeded 1000  cm-3 on that day.

The cloud drop concentration and size distribution at cloud base are determined primarily by the properties of theaerosol population (concentrations,  sizes  and  chemical composition) as well  as the cloud  base  updraft. GreaterCCN concentrations and  stronger updrafts lead  to nucleation of more and  smaller cloud  droplets at  the cloud  base.

     Fig. 9 shows a comparison between the shapes of  the cloud  droplet size  distributions (DSD) slightly above the cloud  base  for a windy, a hazy  and  a calm day — all over the sea. All DSDs have a mode near 10 μm, a totaldroplet concentration of ~ 120  cm-3  and a liquid  water content of ~ 0.04 g/m3. However, the difference that standsout between the DSDs is the “tail” of the largest droplets. While  on the calm  day  of  26  Mar  2010,  the DSD is quite symmetric around the  mode,  it becomes more and  more skewed with increasing concentrations of super-micron aerosol concentrations (see matching colors in Fig. 6). On the windy day of 28 Feb

2010,  the concentration of the ~ 20 μm cloud  droplets is about an order of magnitude greater than on the calm  day,with the concentrations of the hazy day in between.

Would like to see more November – December data, that period when the Mediterranean Sea temperatures are warmer; cloud bases, too!

A comparison of near cloud-base DSDs of more than 20 clouds sampled during 12 different flights  over theMediterranean Sea and the Golan Heights, is presented in Fig. 10.

There is no separation between windy, hazy  or calm  days  because the emphasis here is on the geographicaldifferences. Because  the cloud  droplet initially grow  (in  diameter) rather quickly,  only clouds within a  hundredmeters from  the  cloud  base  were considered —  as  long  as  the mode of the  volume-weighted distribution wasbelow 10 μm and the mean LWC was between 0.01  and  0.1  g m− 3.  These  filters were applied in  order to avoid  including DSDs from  clouds whose bases  could  not  be documented due to safety and air traffic controlrestrictions, as well  as in order to exclude highly  diluted clouds.  In addition, the cloud   base   altitudes had   to be within 300  m  in  both locations on the  same day.  This is to prevent large  variations in cloud  base  temperatures that determine the  amount of condensable water vapor near the  cloud  base.

Superlative considerations, but where are the ACTUAL cloud base temperatures?  Nowhere to be found!  The reader will want to know what they were to compare with “historical” reports of cloud base temperatures.  Also, without care, low LWC’s and small droplets can be found in clouds with bases that are evaporating upward providing a false indication of where an original base was.  Here’s where flight videos would be helpful to outside researchers evaluating these claims.

          The integrated LWC of the mean cloud  base DSD over  the sea and  over  the Golan  Heights, as indicated inFig. 10, is comparable (0.052 vs. 0.045 g m-3, respectively). This facilitates the comparison of the  shapes of the observed distributions  because it suggests that the  differences in the distance of the compared samples from  the  actual cloud  base  and/or different exposures to entrained cloud-free air,  are  probably not the main contributors to  the   non-overlapping DSDs in  Fig. 10. This  leaves  the different mean aerosol properties and  cloud base updrafts as  the probable causes for  the different DSDs. However,  the  greater instability over  the sea  isexpected to produce stronger updrafts that would result in a larger number of CCN to activate there — assuming acommon CCN spectra. This would shift the blue DSD in Fig. 10 to the left, i.e. to smaller sizes.  But the mode of theblue  DSD is actually ~ 4 μm larger than the  red  DSD (9.0  vs. 4.8 μm). So apparently the different mean aerosolproperties and their resulting CCN spectra, as the example in Fig. 8 shows, are  the  main factors in shaping the mean near cloud  base  DSD.

The droplet number concentrations that corresponds to the DSDs in Fig. 10 are 225 and 480 cm-3 over the sea andthe Golan Heights, respectively.

These are very credible concentrations from the author’s experience in Israel, except on some haze and smoke,  afternoon “fair weather” Cu days (Cu mediocris, even Cu congestus) in the Golan  (where the reviewer was briefly in ‘86),  droplet concentrations would likely be higher than 480 cm-3.

The larger number of activated droplets over the western slopes of the  Golan  Heights results in  the smallerdroplet sizes  near the cloud  bases  there, compared to over the sea.

Furthermore, the  proximity of the  Mediterranean clouds to the  source of the sea  spray  tends to result in a tail  oflarger droplets, as the comparison of the mean near cloud base DSDs in Fig. 10 shows. This is due to the activation ofthe giant CCN there (which are much fewer than the rest  of the CCN). The  90th percentile DSDs in  Fig. 10  (filled   circles   above   the curves) indicate that the cloud base DSD over the Golan Heights can also have a considerabletail of large droplet. This is probably caused by  activated sea  spray,   which has  been transported inland withstrong winds, because the  dust particles, as  discussed above,  are  less efficient as CCN.

Here is another finding about large aerosol particles that supports the Levin et al 2010 reanalysis of Israeli 2 and the finding that strong synoptic situations led to the misperception of a seeding effect in the interior of the north target.

 The largest cloud  drops at the tail of the  DSD have  greater fall speeds than the  smaller cloud droplets,  and  therefore they can  collide  with and  collect the small   droplets and   grow   further.  Those  droplets also  have higher probability of freezing in sub-freezing temperatures and hence help  producing precipitation-sized particles moreeffectively. The clouds over the Golan Heights, however, most often have  a smaller tail and  hence convert theircloud  water into precipitation-sized particles by warm processes less efficiently.

4.2. Vertical evolution  of cloud microstructure

The convection that occurs from synoptically or topographically-induced updrafts raise  the cloud  droplets that nucleate at cloud  base  to higher elevations and  colder temperatures.

This is such a common descriptor combination it’s hardly worth pointing out, but a temperature cannot be warm or cold.  Peter Hobbs:  “A cup of coffee can be warm or cold, but not a temperature.”  A temperature refers to an object that is warm or cold.  It itself, a number, cannot be warm or cold, it tells one aspect of the physical state of an object.

The droplet condensational growth is determined by the number of activated CCN and the height above cloud base(Freud et  al.,  2011). The  rate   of  droplet  coalescence is  determined mainly by droplet size and  is related to the 5th power of cloud drop effective radius (re) (Freud and Rosenfeld, 2012). This rate depends also on cloud  dropletspectrum width and  concentrations. When re exceeds 14 μm rain tends to initiate. This process takes normally a  fewtens   of minutes and  requires that the typical convective cloud  in Israel would exceed a vertical extent of 2 to 3 km(Freud and Rosenfeld, 2012).

This process normally takes “tens of minutes”? It’s not is clear what the authors are referring to.  Is “tens” of minutes from the first visible evidence of a cloud?

If not, F2015 need to walk along the beaches of Israel when the skies are boiling with Cumulus to Cumulonimbus transitions as I did.  RH95 show incontrovertible evidence of the rapid glaciation of Israeli clouds, within a few minutes.

But let us assume a Cumulus cloud forms (becomes visible) at 800 m above the Med.  It contains a 5 m sˉ¹ updraft.  From an 800 m it would reach the freezing (typically about 2500 m above sea level on rainy days), in 340 s, and the 700 mb level (3000 m) in 440 s, where the temperature is typically about -5°C.  To reach 4000 m ASL, about 600 mb, would take 640 s since the cloud first appeared above the Med Sea.  The temperatures are now typically-10°C or lower on Israel rain days at 600 mb (4000 m).

      The 700 to 600 mb (4 km ASL) temperatures are typically in the zone where ice is initiated in Israeli clouds (-5°C to -10°C).   At still lower cloud top temperatures, the ice concentrations would increase (in non-chimney clouds).

Ice would be appearing rapidly in such a cloud in just over ten minutes from its initial appearance as a visible cloud, and certainly, if it reached the -12°C to -15°C, would contain hundreds per liter of ice particles from its first appearance, and in just a few minutes after surpassing the freezing level.   Go to your radars and look at the time to first echo.

   But why do we have to go through this simple example?

Please allow me to take your research plane up next winter (with a 2-DC probe that works).  How about if I bring DMT’s Darryl Baumgardner or Duncan Axisa along to insure accurate 2-DC concentrations from the DMT CAPS probe?  I bet that in the first two hours of flight I can find the highest concentration of ice particles that has ever been REPORTED by the HUJ-CSG in 40 years.  I may not find the highest that they have measured; only the highest that they have REPORTED.  (They seem not to want their funders, nor the rest of the science community, to know just how high ice particle concentrations can be in Israeli clouds.  Is there another reason why they don’t report them in airborne study after airborne study?)

The authors, or at least one of them, is well aware of this fast-glaciating behavior of Israeli clouds and has been for at least 30 years (e.g., Rosenfeld 1997; Rangno and Hobbs, 1997.)

Perhaps the phrase, “tens of minutes” was a careless entry in the original ms?

Fig. 11 shows the evolution of the DSD with increasing height in convective clouds over the Mediterranean Sea on 12Jan 2012. The mean DSD of every  cloud  pass is given  as a single  curve  in the plot. The clouds were repeatedlypenetrated close to their tops as they grew,  until  small  precipitation particles (diameter ~100 μm) were detected bythe  CIP at the altitude of 3000 m, on that day.

 How close to cloud top?  Too close to cloud top misses the formation of precip because they lag the smaller droplets at the tippy-top.

These cloud-top “precipitation embryos” become much larger (N 1 mm) as they fall through the cloud and collect othercloud droplets and precipitation particles. On other days, precipitation embryos were detected in the growingconvective  clouds at other altitudes depending on the  specific  conditions (Freud and  Rosenfeld, 2012). However,most of the time that happened when the volume-weighted mode of the DSD exceeded ~ 20 μm.

For comparing the vertical evolution of the DSD for clouds growing in different aerosol environments, it is easier to represent the entire DSD with a single  number,  such  as  the cloud  drop effective radius. This was  derived from  the binned

“EQUATION”

The values of re, the mode of the volume-weighted DSD and the  droplet mean volume radius (rv) are linearlycorrelated as most DSDs have  a generally similar shape (Freud et al., 2008). Freud  and  Rosenfeld (2012)  showed  that  these  relations  are independent of geographical location. They also showed both theoretically and  empiricallythat the  mode of the  DSD and  rv have  values that indicate the  initiation of rain.  This  is  why vertical profiles ofre, derived from satellite retrievals (Rosenfeld and  Lensky,  1998) can  be  used  in  real  time  to  estimate the droplet sizes at cloud  top, as well as their potential for forming precipitation even  before it is detectable by the  precipitation radars. This concept is already in use  in the  operational cloud seeding program in Israel.  An example of the retrieval of the  cloud  microstructure for 10 Dec 2012,  at 10:56 GMT (12:56 LT),  in the form  of re vs. cloud  top  temperature, is presented in Fig. 12.

This retrieval is based on NPP/VIIRS high-resolution data, which allows effective analysis of differences in the  microstructure of clouds developing in rather small user-selective areas (Rosenfeld et al., 2014).

What is the depth of cloud from which these retrievals were derived?  One meter? 10 m? 100 m? 1-km?  This should be stated here for the AR reader.  Ice will certainly fall out of super cooled liquid-topped layers in the Golan; Re will mislead in those instances.  Another reason for ground obs in the Golan.

 There are three T–re  profiles for different regions in this  figure; the  Mediterranean Sea (area 3), the Galilee (2) and  the Golan  Heights (1).  The median re  (the bright-green curve  in each sub-plot) in areas 3 and 2 reached 15 μm at a temperature of about -5 °C. In addition, the  T–re  profiles in these two areas indicate that  cloud   glaciation  has   occasionally occurred  at temperatures as  warm as  -10  °C.

Can F2015 supply numbers to quantify the “occasionally” statement?  Also, isn’t this old news, about 30 years old, about clouds glaciating/raining when their tops are >-10°C?  (See R88; not cited here, as one would expect by the HUJ-CSG).  Also, from the IMS, 1986:  “We get good rains from clouds with tops at -10°C.”  This quote demonstrates how the every day weather forecasters within the IMS could have prevented the early cloud misinformation published by the HUJ-CSG, that clouds had to be much colder–topped before they rained.

Glaciation is  indicated by spikes of high  re  and  by  a red  tone of the cloudy pixels.

In contrast, the median re  of the clouds over  the Golan  Heights (area 1) did  not reach the  precipitation thresholdof 14  μm (Rosenfeld and Gutman, 1994) and did not show any indication of glaciation. The cloud  tops thereappear to contain mostly super-cooled drops despite developing above  the -10  °C isotherm.

To emphasize, in more stratiform clouds, the top of ice-producing clouds is often supercooled droplet clouds, as reported on several occasions (e.g., Cunningham 1957, RH85, Rauber and Tokay 1991).  The Re reported here is likely to be misleading.  Ground confirmation is required for assertions of “non-precipitating clouds” as indicated by an Re value.

Perhaps, since F2015 do not discuss it, they are not aware of the problem in using Re when precipitating clouds have liquid tops from which ice emanates?   Can they supply hourly precipitation data, radar imagery or weather reports for these times in the Golan?

While there may be, indeed, supercooled LWC at cloud top, it is from that liquid top that ice crystals are spawned, grow, and breakup increasing ice particle concentrations below top (Hobbs and Rangno 1985).   In turn these consume water vapor via deposition/riming in ice supersaturated conditions.  Is F2015 sure they want to disrupt this system by seeding a liquid topped ice-producing layer?

While  Fig. 12  presents a  snapshot of a  single  case,  as  an example of how the different re profiles look in cloudsdeveloping in different areas,  it is useful  to use  a statistical approach and examine additional cases.  Fig. 13 showshow  the  cloud  droplet effective radius varies with the cloud top temperature. It is based on all high-resolution satelliteretrievals from the rainy season of 2012–2013 that were suitable for obtaining the  T–re  profiles for  clouds over theMediterranean Sea and over the Golan Heights. In total,  seven retrievals from  days  with seeding potential, according  to  the  criteria of  Israel-4,  contained  clouds with varying tops in  both areas.   The  cloudy pixels   were grouped according to  their 11.8  μm brightness temperature to  clusters with the same temperature ± 1 °C, and then differentpercentiles of re were calculated for each group. Fig. 13 displays the first and third quartiles for each  cluster and area  as dashed lines, and the median re in each  area  as a solid  line. Only clusters containing more than 100  data  points are  displayed for more robust statistics.

All the curves in Fig. 13 show an increasing re with colder cloud  tops,  but  the  change tends to be more substantialover the  sea. The median re over  the  sea (blue solid  curve) crosses the precipitation threshold of 15  μm alreadyat − 3 °C, even before the  silver   iodide can  have   any  effect,  compared to − 12 °C over  the Golan  Heights (redsolid  curve).

I applaud the authors for this information, highlighted above.  It gives one hope that we may not travel down the same path that the HUJ-CSG has traveled so many times before.  We rephrase the authors’ somewhat obtuse description more simply for the reader:

The clouds moving into Israel from the Mediterranean Sea are unsuitable for seeding with silver iodide. 

This is a new finding for the HUJ-CSG, and it should have been given more attention in F2015.  R88 should have been cited here, who concluded virtually the same thing 27 years before F2015 were able to discover it.

By not citing those who went before, it makes F2015 look like the work of small minds, not that of disinterested scientists only interested in truth.  Omitting relevant work is devious, harms conscientious workers, and degrades the HUJ.

Is this really how F2015 want to represent their home institutions?  It would seem so.

This means that on average, the clouds over the  Golan  Heights have  to acquire a greater vertical extent than theclouds over  Sea to  start precipitating. The probable cause for that is the greater aerosol and  CCN concentration(e.g.  Fig. 8) and  less  sea  salt particles further inland (Fig. 7). But the  different characteristic dynamics andthermodynamics of the clouds may contribute to the differences as well.

As  in  Fig.  12,  Fig.  13  also   shows  indications  of  early glaciation over the sea at rather warm temperatures ofaround − 10 °C,  where  the  75th  percentile of  re   is  close   to  the saturation value  of 40  μm. Furthermore,  thecurves indicate that the clouds over  the sea  tend to  have  a greater vertical extent and  reach colder temperatures.

The temperature bugaboo strikes again.

This is probably caused by the stronger convection over  the  sea  that encourages the formation of  deep clouds,  while the clouds over  the  Golan Heights normally have a more orographic nature and a layered structure, accordingto our subjective observations.

In November, and in later winter and spring, thunderstorms are as common at inland hill regions as over the Mediterranean (e.g., Altaratz et al. 2003), so the idea of perpetual stratiform clouds over the Golan as suggested by F2015 is flawed and needs to be revised to draw this out.  Too, clouds may not be ripe for seeding in these deeper convective situations that occur in November and later in the spring.  Further independent airborne work is needed.

This is also supported by the differences in the  patterns of rain  durations and  intensities between the coastal and hilly stations in Israel (Goldreich, 2003), where rainfall at the coastal plain  is much more intense and has a shorterduration.

It is important to keep in mind that the colored curves in the subplots of Fig. 12 can be considered as verticalprofiles in the convective clouds because the cloud  base  temperature do not tend to vary much within the sameconfined area. re also shows little variance in a given area and altitude (Freud et al., 2008) and the  cloud  top  re  at  agiven  temperature does  not  vary  much during the lifetime of a convective cloud (Lensky and Rosenfeld, 2006). Fig.13, however, is based on seven different profiles, not necessarily with the  same cloud  base temperature and probably with varying aerosol properties and atmospheric thermodynamics. This is why the curves in Fig. 13 cannot really bereferred to as vertical profiles that represent the  development of individual deep convective clouds.  They  should be treated as  a  general statistical view of the T–re  relations in the indicated areas.

These are excellent qualifiers, as scientific writing should contain when necessary.

        The  large number of flight  hours and  the penetration of clouds at  various heights and  in differentgeographical areas facilitate a similar statistical analysis to what is presented in Fig. 13 for satellite data,  with thein-situ data.

The flight hours are really not so large at <81.

What is far more important, to repeat, is the synoptic setting in which the flights actually took place.  As a reviewer, I would have mandated a supplemental appendix with synoptic maps and satellite imagery for each flight be supplied by the authors prior to publication.

I am sorry to say that the HUJ-CSG long ago forfeited the right to make general statements without comprehensive backup material that independent researchers can investigate for reliability.  Furthermore, and I repeat for emphasis, videos of flights should be made available on request or made

available online.  Most of us “senior researchers” who know well the trail of the prior reports from the HUJ-CSG, understand why more evidence is required from them in their cloud seeding reports than might be the case for another institution.  “Fool me once, shame on you; fool me twice, shame on me.”

The 1 Hz measurements inside the clouds represent a spatial averaging along a ~ 100  m  long  path.  Thesemeasurements from  15  research flights  that were conducted during the physical experiment were groupedaccording to the measured temperature at the flight  elevation. The percentiles of the CDP-derived  re  were calculated  for  each   group  of  measurements  and   no  other filtering or normalization was applied except thegeographical separation between the clouds over the Mediterranean Sea and the Golan Heights. Fig. 14 shows acomparison between the re values of the clouds sampled over  these areas.  Here  too the apparent trend ofincreasing re with colder temperatures is more pronounced over  the sea  than over  the Golan  Heights, as  in Fig.13.

The  two profiles appear to  separate around the temperature of − 5 °C, where the marine cloud seems to maintain its convective profile,  i.e. increasing re  with colder temperatures. Over the  Golan  Heights, however, the  effects  ofelevated cloud layers   with embedded  convection and/or  secondary droplet nucleation, may  explain the offset  ofthe peak  between re and LWC (see Fig. 17).  This  is  supported by  the statistics of the droplet numberconcentrations around those peaks (not shown here). The differential likelihood of freezing of larger cloud droplets,elevated cloud  layers,  cloud-top entrainment and precipitation, may  all contribute to maintaining a low  median re attemperatures below − 10 °C.

References supporting the freezing of larger drops could have included, for example,  Vali 1971, Pitter and Pruppacer (1973), among many others.  FYI:   HR85 used the large size end tail of the cloud droplet spectrum (the so-called, “threshold diameter”) as measured by a FSSP-100,  in newly risen, low ice containing Cumulus turrets as a predictor of later maximum ice particle concentrations.  It worked pretty well except in short-lived narrow “chimney Cu”.

The  percentile-profiles of  the   satellite-derived re   of  the convective clouds over  the sea  exhibit greatervariance than those of the orographic clouds over the Golan Heights (Figs. 12 and  13). This is partly caused by theso-called 3D effects  — the variable illumination of the cloud  tops by the sun  due  to their inhomogeneous physicalstructure (Marshak et al., 2006). The cloud   top   re  of  cloud   surfaces that  incline away   from   the satellite, i.e. ina direction that increases the sun–cloud–satellite angle,  would be  overestimated (even more in  shaded cloud surfaces). The cloud  surfaces that incline towards the  satellite would have  their re underestimated due to theopposite effect, resulting in a falsely wide  re distribution for clouds with a non- horizontal cloud  top surface. This, ofcourse, does  not apply  for in-situ derivation of re, as in Fig. 14.

Outstanding distinterested writing by the authors describing issues, both above and below!  Here the paper has the feel of real science!  I’m excited.

Furthermore,  the  absolute re  values that were calculated from  the  CDP measurements,  are  typically smaller inFig. 14 than the satellite-derived re shown in Fig. 13. Possible  sources for this apparent discrepancy include

1) Our  focus  was  on  documenting the  evolution of the  cloud DSD as it grew  and  on measuring the formation ofprecipitation embryos and  the  initiation of effective precipitation.

What is “effective precipitation”?

In addition, we tried to avoid  flying higher than ~ 5 km or in heavy precipitation from  mature clouds due  to flight safety  and  performance reasons.

F2015 stated that they had targeted growing, “hard-topped” Cumulus, filled with supercooled liquid water that would cause heavy icing on their twin-engine, turboprop Beechcraft King Air C-90 aircraft.

Icing is one of the great dangers of sampling Cumulus congestus clouds at below freezing temperatures.  When Cumulus congestus transition to those modest Cumulonimbus clouds of the Mediterranean loaded with ice crystals, the supercooled liquid water disappears and they are virtually harmless to aircraft as an icing threat.

F2015 seem to be indicating that they are unaware of the reduction of icing hazard when this transition to the modest Cumulonimbus clouds, the vast majority are not strong enought to produce lightning.  We’re not sure what hazard they could possibly be thinking about.

 High ice particle regions of clouds have, as a rule, little icing in them and less turbulence, and MANY in Israel in those low theta-e air masses will be found with tops less than 5 km ASL.  In this airborne researcher’s experience in similar clouds in the Washington State coastal waters, such clouds have never posed a hazard to our aircraft except via icing because of sampling too many new turrets too quickly.   (Icing buildups can be removed by descending to lower, warmer levels.)

The highlighted sentence is incomprehensible as a reason not to have sampled the maturing and dissipating portions Cumulonimbus clouds in the eastern Med.

This is why  our  sampling strategy did not cover the area uniformly but instead favored clouds in their early  growingstages — unlike the satellite retrieval.  The aging  of the  deep convective clouds allows more time for  the  collision and   coalescence process to produce large  droplets and  increases the  chances for  ice formation.Therefore  the underrepresentation of the  mature clouds in  the  in-situ measurements and  in  Fig. 14 reducesthe re values.

Qualifying one’s measurements doesn’t get any better than this!  Thank you, authors! Just for the record, this reviewer believes that GN74—written in 1972) represented one of the best examples of objective writing within the often murky domain of weather modification/cloud seeding, where “confirmation bias”, monetary considerations so abound that they deflect true science into something else.

But, this outstanding description begs the question, “How were L929496 able to sample mature, full of ice Israeli clouds, and F2015 were not?”  Isn’t the HUJ-CSG more experienced in airborne research? To the cynical, it could look like an excuse not to sample high ice concentrations in even modest Cumulonimbus clouds.  Authors:  please explain why L929496 was, and you weren’t able to do this.

 2)  The CDP measures only  droplets with a diameter smaller than 50 μm. If larger drops or even  small  iceparticles are present at the  cloud  top or slightly below it (or  even  as a thin cloud layer above  it) then thesatellite-derived re might be overestimated Point (1) above also helps explaining why the blue profile in Fig. 13  is  deeper than the   red  profile,   but in  Fig. 14  it  is shallower. We basically stopped climbing when cloud waterwas mostly converted to precipitation or glaciated. This happened on average at a  slightly warmer temperature  over  the sea,  and hence the shallower profile  in Fig. 14. The clouds over  the  sea often reached much higher altitudesthan over the Golan Heights (e.g. Fig. 12) due  to the  more unstable conditions.

To repeat, the situation highlighted  is often reversed early winter, and certainly during the spring in major troughs when thunderstorms are as common inland as over the Sea.  This needs to be revised to reflect this reality.

The satellite retrievals  reflect this,  but the   in-situ measurements  do  not because of the sampling strategy

4.3. Formation of hydrometeors

Supercooled cloud  water tends to be quite abundant in northern Israeli rain clouds.

F2015 do not provide specific data on this “tends to be abundant” claim anywhere in this paper, nor do they seem to realize that supercooled water is often short-lived in Israeli clouds due to the rapidity of ice formation.

Most of the rain that falls in northern Israel during the winter initiates as mixed phase hydrometeors in clouds withtops  that are  well  above  the  0 °C level.

Omit, “well”;   “above the 0°C level” is sufficient for the “initiation” of precip.  Furthermore, in low stratiform clouds that are thickening upward as an upper trough approaches, drizzle and mist-like rain from warm rain processes are initiated (as was observed on several occasions during the reviewer’s 1986 experiences in Jerusalem).  One suspects drizzle will also occur in hill locations in the far north of Israel as well.  It seems strange to tell people who live in Jerusalem about this!

This again speaks to the critical importance of having independent ground obs at Mt. Hermon;  maybe Har Kana’an, as well.

This has been documented with the help  of the  CIP that provided 2D images of the  hydrometeors in  its  sampledvolume of cloud/ air.  Although  the  CIP does  not  allow  distinguishing between spherical super-cooled liquid  dropsand slightly irregular frozen drops at diameters smaller than ~ 100  μm — due  to its 15 μm resolution, riming offrozen drops and  graupel particles can be easily   identified.  These  particles  provide  clear   indication  of ongoingmixed-phase processes in the clouds.  Quantifying the ice  content in  the  cloud  with a  2D imaging probe is  highly uncertain, however we were still able to see and  document the increasing concentrations and  sizes  of the iceparticles as the clouds matured and the  water content decreased.

Here’s what a Droplet Measurement Technologies rep has to say about the “highly uncertain” claim in F2015 concerning its CAPS probe:

I agree with you that the authors could have reported the ice particle concentrations from the CIP if they wanted to. I see CIP images in Fig 15 (of F2015), so the authors should be able to get particle concentrations. The CIP does report particle concentrations and processing software is capable of producing high quality particle concentrations.”

Doesn’t this make the “highly uncertain” claim in F2015 a falsehood?  Its does to this reviewer.  But where were the other reviewers, if any, of this article???

The American Meteorological Society (AMS) has recently issued a Monograph (Field et al 2017) focused on secondary ice particles and the efforts to explain them, authored by our leading scientists.  Most of the observations discussed in that Monograph are due to measurements with a 2-DC probe!

A possible cynical translation of the HUJ-CSJ “highly uncertain” claim about ice content:   “We measured really high ice particle concentrations similar to those of L929496  but we,  F2015, wish not to reveal in an article about cloud seeding potential having such high concentrations of ice as we found.  We therefore have invoked the excuse that the “mature” clouds of Israel were too dangerous for our aircraft to sample where all that ice was.  Its amazing to us that Zev Levin was able to do it!”

2-D artifact reduction:  Since the 1970s, there have been ways in software of reducing 2-DC artifacts caused by, say, shattering on probe tips.  Indeed, in F2015 they inform us that they used 2-DC probes with “pointy tips” to reduce shattering artifacts.  But then they reverse course, and tell us they can’t report what they found with that probe.  This is sad, because it appears to be another omission of important data by the HUJ-CSG.

Maybe we shouldn’t be surprised at such an omission, except that it appears in a peer-reviewed journal.   What ARreviewers, ad nauseum,  allowed an omission of such critical data in an evaluation of cloud seeding potential?

If this type of “editing” of findings in F2015 was what convinced the INWA to proceed with rudimentary operational seeding or “Israeli-4”, then the HUJ-CSG has misled them once again.   It is likely, in such an experiment with an unbiased draw, that no statistically-significant results from seeding will accrue (providing the evaluation is conducted by independent non-HUJ statisticians).

Fig. 15  shows some 2D images of the hydrometeors that were observed at  different altitudes over  the sea  on  12  Jan 2012,  as an example.

The images are quite nice; shows what we can do today.

However, a series of single strips of hydrometeors chosen by F2015 in Figure 15, does not suffice to prove much.  They have omitted (sound familiar?) those images and concentrations of sheaths and needles, those crystal habits that form at temperatures  > -10°C  which would document the prolific operation of a secondary or other ice particle production mechanism that operates in the clouds of Israel.    The aerosol environment of Israel, with its large CCN and often high concentrations of smaller droplets due to pollution in the Hallett-Mossop riming/splintering zone creates the “perfect storm” for ice multiplication in their clouds, as F2015  should know when they cite Mossop (1978).

 Figure 15 is not acceptable to this reviewer without extensive 2-D imagery with “best possible” concentrations available online.

The CIP particle size distributions for the same cloud/area were shown in Fig. 11. According to the combinedCDP/CIP particle size distributions, the mode of the cloud  DSD reached ~ 20  μm at  an  elevation of slightly below3000  m. This is also where the CIP water content of ~ 100  μm particles  became  more  significant. Fig. 15  showsthat these precipitation embryos are  spherical,  i.e. probably still  in  the liquid  phase, although the temperature isclose to − 8 °C.  The LWC at  that elevation reached 1.6  g m-3  and  there was  no indication for ice. Higher  up inthe  cloud  the particles became even  larger and  started having a more irregular shape.  The irregular particles seenat temperatures warmer than − 5 °C are not likely to have frozen at the  observed elevation, but rather have  fallen  from  above   while riming smaller particles. This leads  to another small  mode in  the far  right  of the  CIP size distribution (Fig. 11) rather than a more continuous decline in LWC with increasing particle diameter in the  CIP range.

            Documenting a similar process of cloud droplet growth, the formation of precipitation embryos and theirfreezing over the Golan Heights was much more challenging due to a number of reasons.  It  was  difficult to  follow   the   same cloud   element through

its lifetime due  to the more orographic nature and layered structure of the  clouds.

The authors recover from the omissions discussed previously and write an outstanding couple of qualifying sentences, the type that normally accompany a great science piece!  I’m excited again!

And even  if distinct convective cloud tops were identified, they often quickly drifted eastwards into  Syria, where itwas  not possible flying to. The impression was  that often the clouds there would consist only  of supercooled waterwith no  precipitation, unless having embedded convection or ice particles falling from above.

The above is good, and the use of the word, “impression” makes it even better.  Thank you authors!

Fig.  16  presents the   profile   of  the concentrations of hydrometeors with diameter greater than 100  μm in  clouds over the Sea and the Golan Heights — as measured by the CIP. It is based on the same 15 flights  used  forthe  analysis in Fig. 14 and  both figures have  some common features.  As with the cloud  droplet effective radius,the  concentrations of the large hydrometeors increase with decreasing temperatures  in  the developing convectiveclouds over  the  sea. This is because as the cloud grows and its top becomes colder,  the cloud droplets and  the hydrometeors that do not fall become larger,  and  also because the freezing of the largest droplets, which may  push them over the 100 μm cutoff size used  in Fig. 16, is more likely.

The  statistics of  the hydrometeor concentration over  the Golan  Heights, on the other hand, shows a maximumconcentration between − 5 and  − 10 °C, with median concentrations close  to 10 L-1. The inclusion of cloud  layers with colder bases, smaller droplets and  less  LWC might explain the decreasing hydrometeor concentrations atcolder temperatures over  the Golan Heights. This might not, however, explain the finding that the CIP concentrations inthe − 5 to − 10 °C temperature band are considerably higher over the Golan Heights than over the sea.

This doesn’t make sense.  The reality would be just the opposite if they had been more adventurous with their aircraft sampling in the Med.  The reason for the lower concentrations in the -5° to -10°C temperature range over the Mediterranean where ice multiplication is rampant, compared to those concentrations found in the Golan,  is the sampling by F2015 of young, newly risen,  “hard” turrets before the ice explosion occurs over the Med.

It is worth noting that the temperature of maximum hydrometeor concentration over  the  Golan  Heights coincideswith the activation temperature of the silver-iodide which was released upwind during most of the sampling.

WHY would one sample, at great operating cost, clouds when seeding was underway upwind???  Isn’t that a waste of precious INWA resources?  Was this unintentional?  Are there no data from your flights that were gathered in the Golan without seeding taking place?  Did you measure ice nucleus concentrations, ones that could have alerted you to this problem?  This, unfortunately, raises the issue of incompetence unless there were mitigating circumstances.

It is also close to the temperature of maximum Hallet–Mossop ice multiplication rates, which may be suppressed instrong convection (over the sea) due to relatively short residence time of the graupel in the optimal temperature band for ice splinter production (Hallett and Mossop 1974).

Suppressed H-M process?  This is non-sense.  Gimmee your plane!  These authors need to go outside and watch there incoming Cumulus congestus clouds as they convert to ice (and small Cumulonimbus clouds) within minutes after reaching very much above the -5°C level.  With proper aircraft sampling, the authors would have found a ton of H-M generated (and/or that by other processes) ice crystals (needles and sheaths) in the temperature zone (-3° to -10°C) where H-M-produced ice can reside (as at Mt. Hermon on many occasions).

One wonders why the analysis goes so badly here?  Who was directing the aircraft?  Who wrote this segment?

But this process may  be  enhanced by  the embedded convection that often occurs over  the Golan  Heights.  Thisis because the mixing of the convective cloud  element with the stratiform cloud  with a colder base,  can  result in abroad, or even  bi-modal, droplet size distribution, which is favorable for ice splintering (Mossop, 1978). It is notpossible, however, to quantify the relative contribution of each factor to the observed hydrometeor concentrationswithout a very  detailed case  by case  analysis, because the variation from  cloud  to cloud,  and even  within a cloud  is rather high.

Send me the videos from these flights, your ice and droplet concentrations and spectra, and I promise to help you understand what you did!  Better yet, give me your research aircraft for the month of January and we will find some ice, and some new findings commensurate with those of L929496.

4.4. Availability of supercooled cloud water

The supercooled liquid  water content of the clouds over the Mediterranean Sea and over the Golan Heights, atdifferent temperatures, is presented in Fig. 17. The water content was integrated over the binned CDP data and, ifnecessary, slightly adjusted to match the measured content of the Hot-wire probes. Fig. 17 is based on the samedataset as Figs. 14 and 16. Note that the abscissa in Fig. 17 is in the log-space due  to the large  possible variationin  LWC. At  the initial stages,  as  the clouds develop,  their tops   get cooler   and   the   LWC  values increase bothover  the Mediterranean Sea and  over  the Golan Heights. At − 4 °C, 25% of the  measurements that were taken over the Golan  Heights had  a LWC greater than 0.4  g m− 3, while over  the  Mediterranean Sea that number,  at  thesame temperature, was slightly smaller.

As the authors noted previously, they don’t know what happened to the LWC in the clouds at the upwind side of the Golan because it went over toward Syria.  That should be re-iterated here, lest the AR reader be misled by the F2015 claim that this is unambiguously potential water for seeding purposes.  That potential remains to be seen without more comprehensive measurements, such as ground measurements of ice crystal concentrations, habits, riming characteristics at the top of Mt. Hermon, which is often in the H-M temperature zone during precip events in Israel.

Mt. Hermon crystal data would make a stupendous paper of itself.  But could we trust the HUJ-CSG, with so much seeding baggage, to do it objectively?  I really don’t think so.  What a shame that a “senior” researcher, who is extremely familiar the output of the HUJ-CSG over several decades, feels this way.

Further up the LWC values over the Golan Heights started decreasing, while the LWC over the sea  continued toincrease as  the  cloud   tops developed further.

As mentioned in Sections 3.3 and 4.2, the sampling strategy over  the  Mediterranean Sea and  over  the Golan Heights was often  different because of the different typical cloud  structure/ dynamics as well as flight safetyrestrictions. While over the sea “hard” tops of deep convective clouds were more abundant and favored, over theGolan  Heights the maneuvering was more  restricted and  the  sampling covered the  area  more homogeneously.

Here and below, the authors divulge critical pieces of information about sampling that represents the highest form of objective, scientific writing for their readers!

Preferential sampling of developing cloud  tops  with relatively little history of mixing over  sea,  versus measuring mostly orographic layer  clouds over  the Golan  Heights,  can explain the  greater LWC values over  the sea  and the positive trend all the way up. More than half of the samples over the sea at  a  temperature around − 16  °C had  a  LWC greater than 1 g m− 3.

The quote above about 1 gm m-3 at -16°C concerns liquid water that would be very short-lived,  indeed, as I believe the authors know, or should know.    Would it last at that level even five minutes in a Langrangian sense?  Give me your research plane and we will see!

The  likely   explanation  for  the LWC “bump” only   over the Golan  Heights is the sampling of cloud  layers  withbases at  colder lower temperatures  and   hence reduced LWC. As Fig. 3 illustrates, the  clouds over  the Golan Heights tend to  have  a structure of layers (on the days that we chose to sample on) and  a more homogeneouscoverage of the area  would include sampling of those layer  clouds.  This explanation is supported by Fig. 14, asnew  high  cloud  layers that are separated from the clouds below, are expected not only to have  low values of LWC,but also small re (Fig. 14). The LWC in those elevated cloud  layers  would increase little with height due to the coldlow temperatures, but re might increase rapidly due to the low concentration of CCN and hence also cloud  droplets, even  in the undiluted parts of the clouds.

This doesn’t make any sense to this reader; “re might increase rapidly..”   Where?

Another possible contributor to the changing trend of LWC over   the   Golan   Heights  at  temperatures  below − 8  °C is the conversion of liquid  cloud  water into  ice  (which is not measured by the CDP or by the Hot-wires). Theconcentrations of the  hydrometeors (Fig. 16) are at maximum at that temperature and  that might not be justcoincidence — as discussed in Section 4.3. In order to determine the causes and the effects  of the observedrelations, as well  as the contributions of the  seeding operations versus the  natural processes, other methods arerequired.

Again, why spend so much on research targeting natural clouds when seeding is going on?  Its crazy.

So, within the scope of this study, it is practically impossible to quantify the relative impacts of the explanationsabove  to the observed different trend of LWC versus the temperature over the sea and over the Golan Heights without analyzing a larger dataset and  a more dedicated planning and  filtering.

Yes! Thank you, authors, for this candid assessment.  I would love to take part in those additional studies!  “Call me!”   Furthermore, having a senior researcher as a kind of “Resident Skeptic” would improve the credibility of future HUJ-CSG publications.

However, despite the reduction in LWC with altitude, and  regardless of its true explanation, there are still  non-negligible amounts of  super-cooled LWC over  the Golan   Heights.

The end result of the supercooled water they observed at the upwind side of the Golan is not known.  Caution is advised in what to make of this statement.

As far as  cloud seeding  is  concerned,  the relevant question is  the precipitation efficiency of  the orographiclayer  clouds.  Obviously, this type of cloud  is inexistent over sea.

Fig. 18  provides the probability distribution and  the cumulative distribution function of the  supercooled water content over  the  (upwind side of the) Golan  Heights at temperatures  colder lower than − 8 °C.

You can’t emphasize the sampling bias contained in Figure 18 enough; otherwise it will likely mislead the INWA or other organizations into funding cloud seeding with no real return, as we saw the HUJ-CSG caused the INWA to do in the past at great expense to the people of Israel.

While some of the water might have been converted to ice due  to the  seeding operations, the  remaining liquid  water might mark the  potential of additional precipitation enhancement.  It shows that 55% of the measurements in theclouds had less than 0.2 g m-3 of super-cooled water, but it means that 45% had more. 20% of the data had  morethan 0.5 and  ~ 4% even more than 1.0 g m-3 of liquid  water with a potential to freeze with silver-iodide.

This sentence is lacking the very nice qualifiers you incorporated in this piece at other points.  Were these questionable portions written by only one of the authors?  One wonders.  But, unless the writing is partitioned in a footnote, all of the writers are responsible for a paper’s content.

Since the flight pattern over the Golan Heights was  more or less fixed, this represents the  true areal  fractional coverage of these clouds during the flights there. Therefore, this represents significant amount of super-cooled cloud water and indicates that ice  nuclei may  still  be  a  limiting factor in  the conversion of LWC into ice and further toprecipitation. So there might be room for extending the seeding efforts that target the clouds over  the  Golan  Heights torealize more of their seeding potential.

  1. Summary and conclusions

A key  factor  that determines the seeding potential of the clouds is the quantity of super-cooled water in the clouds,  the time that the water droplets remain in the super-cooled region and  the temperatures at  which supercooled waterpersists.

Add this sentence after, “persists”:  “We were unable to do all the necessary maneuvers to establish these parameters.” ( It doesn’t mean you failed….)

More  super-cooled water, longer time and  colder lower temperatures,  all  lead   to  greater  seeding potential  as  there  is  a possibility to convert more of the super-cooled water into  ice and  precipitation.

After analyzing 27 research flights during four rainy seasons (2009–2013) we  see  that although the  naturalprocesses of converting  cloud   water  into   precipitation  is   often    quite efficient,

Yep.

there  are  still  occasions with good  potential for precipitation augmentation by glaciogenic cloud  seeding.

        Remains to be seen.  “Good” potential was not demonstrated in this paper.  There were too many unanswered questions.  This sentence appears to have been written for funders, not for those of us senior researchers who know the paper trail of the HUJ-CSG literature well.  One wonders how F2015, who wrote so eloquently about the drawbacks of this study, and the questions that remain, could have written this sentence?  Here the questioning and objectivity have disappeared.

One natural seeding process is  the  hygroscopic seeding by  the abundance of sea  salt aerosols in the boundarylayer  close  to the coast due  to the strong winds and  rough seas.  Another natural seeding process is called  the“seeder–feeder” mechanism,   where hydrometeors from   more mature  and   higher clouds fall through the clouds atlower levels and collect or rime their water content.

        In this scenario, there well might be an underlying, shallow orographic Stratocumulus layer that is present before the rainy/icy complex of Cbs arrive.  If precipitation is falling over mesoscale regions, downdrafts can be present that weaken of dissipate the lower Stratocu layer as the complex barges into the hill regions and the Golan.  This is a reviewer speculation; I just don’t think we have enough information to know what exactly happens, how much supercooled water there is when weakening Cb clusters/lines organized by upper troughs arrive in the northern mountains.   Observations at Mt. Hermon, to repeat, are critical in answering this question.

The results of this study have  been already applied for the design of the Israel-4 cloud seeding experiment.

        I find this statement sad, because this study/proposal was not reviewed properly, and those who assembled it have so much cloud seeding baggage, as is demonstrated in this review.  I feel sorry, too, for the Israeli people who paid millions based on prior faulty interpretations of cloud seeding results and seeding potential based on fictitious cloud descriptions.   The HUJ-CSG for too long has prospered on the backs of the Israeli people with their biased, self-serving presentations of clouds and seeding potential.

            Finally, why wasn’t I sent this manuscript in the first place?  One of the authors, DR, knows I am “above ground”, and I do not oppose seeding in proper circumstances.  I do know Israeli clouds pretty well….

This was done by  an  addition of  an  eastern seeding line  for  targeting the clouds developing over  the  Golan  Heights and  by positioning the ground generators accordingly. The main objective of the Israeli rain enhancementprogram is to increase the amount of water that reaches the Sea  of  Galilee,  therefore adding an eastern seedingline  contributes to  fulfilling  this objective in four ways: 1) The Golan Heights contribute most of the water to the Sea  of Galilee;  2)  The  clouds over  the Golan  Heights typically undergo less natural seeding by mature cloudsand sea spray;

There is quite a bit of conjecture in item 2.  This study didn’t quantify how much “less natural seeding by mature clouds” happens in the Golan.  Such a study would take several winters in this reviewer’s opinion, of combined satellite andsurface observations, and many more flights than in this study.   To repeat, such a study shouldn’t be done by the HUJ-CSG for the highest credibility.  They had their chances over so many years to get it right, and couldn’t do it.

Cloud tops are colder in extreme northern Israel and offshore region compared with those areas to the south (GN74; RH95) as noted.  Decreased cloud top temperatures lead to more ice and deeper clouds.  Presumably more Cbs, organized by troughs and by the Cypress low, would move onshore and into the Golan in most rainy day situations.  Whether the underlying orographic forcing would supply enough water for seeding purposes in the context of these mesoscale systems remains unknown.

 3) The clouds over  the Golan Heights occasionally have relatively high  concentrations of supercooled water attemperatures in which silver iodide can serve as efficient ice nuclei;

Add this qualifying sentence:  “Due to flight limitations, it is not known whether this liquid water persists long enough to be a viable seeding target.”

 4) There  is a greater seeding potential for the less convective clouds (King and  Ryan, 1997), such  as thoseclouds over  the Golan Heights.

Who knows?  Don’t count on it, Israel.  Be cautious.

A further indication of citation sloppiness, and a poor manuscript review of this article; “King and Ryan” should be Ryan and King (1997).

This whole article has degraded AR in my opinion.

            The Israel-4 randomized seeding experiment started in November 2013.  The expected duration of theexperiment is about 6 winters, during which the randomized seeding will be done in the  same consistent way, and  further accompanied by the cloud  physics measurements by aircraft and  satellites.

Acknowledgements

This study was funded by  the Israeli  water authority for supporting the rain enhancement project.

Very sad to read that this article, or some other version of it in a proposal, led to INWA to seed operationally or otherwise.     Doesn’t the INWA have any cloud expertise within it, or consultants to rely on?  It doesn’t seem like it.

Nevertheless, the INWA is to be admired and congratulated for having the wisdom to do a randomized experiment even if deemed premature, rather than just initiate another operational seeding project,  while asserting to its public, with little evidence, that rain is being increased.  It doesn’t happen in the US!

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Reviewer “baggage” module: bio, a priori convictions, and a little about the reviewer’s 1986 11-week cloud investigation in Israel

Background:  Chased storms, cloud photographer.

I have worked on both sides of the seeding fence, having participated in operational seeding projects in South Dakota twice, India, Washington State, and in the Sierras of California.  I was a forecaster for the Colorado River Basin Pilot Project (CRBPP), a large, multi-million dollar advanced randomized cloud seeding experiment in Colorado from 1970-1975.  Beginning in 1976,   I worked in airborne studies of clouds and the origin of ice in clouds in the University of Washington’s Cloud and Aerosol Research Group for the 28 years.  I was a “flight scientist” for NCAR during the 2006-07 winter during their Saudi Arabia cloud seeding potential study.

A priori convictions concerning cloud seeding:

Cloud seeding works in limited situations, principally via the seeding of non-precipitating, supercooled clouds (e.g. Hobbs et al 1981, an experiment suggested by the reviewer; “wonderful experimentation”).  Whether there is economically viable return from such seeding, I don’t know.  I begin every talk I give with, “Cloud seeding works!”, and show a couple of examples of effects of seeding (those resembling Schaefer’s dry ice seeding experiments in 1947)

Motivation for this review:

The review of F2015  was motivated by the absence of post-publication comments on F2015 over the past three years.   And it comes from the emotional reaction after I read it recently for the first time: “Someone has to do something about this!”, the very same feeling I had before I went to Israel in 1986 as a skeptic of ripe-for-seeding cloud claims emanating from the HUJ-CSG.  (That same emotional reaction first happened during the CRBPP which led to a “career” of own-time scrutiny of suspect cloud seeding publications (e.g., Rangno 1979).

The 1986 Israel cloud investigation

 At the end of 1985 I resigned my job with the Cloud and Aerosol Research Group over issues of credit, and went to Israel in early January 1986 to investigate their clouds[1].  I was skeptical that those many descriptions of them in the peer-reviewed literature and in conference presentations were correct.   I did not go to Israel without “baggage,” but had done a considerable amount of “homework.”

A note-sized paper asserting that the Israeli clouds were not as they were being described in journal articles and elsewhere, had been rejected in 1983 (B. Silverman, Ed., J. Appl. Meteor.,  personal communication).

That rejection was instrumental in my 1986 trip.

The several reviewers’ negative takes on my 1983 “Comment”, including that of the leader of the HUJ-CSG at that time who lectured me in person at the 1984 Park City weather mod conference about how wrong I was about his clouds,  had no effect whatsoever about what I thought about them.  He had also been a reviewer of that “Comment.”

To repeat, I had done my homework, plotted numerous soundings when rain was falling at launch time or within the hour at Beirut and Bet Dagan, and had scrutinized all of the HUJ-CSG cloud reports in great detail.  Even the daily rainfall in the Israel Meteorological Service (IMS) monthly weather reports indicated something was terribly wrong with clouds that were being described as highly inefficient rain producers.

While in Israel in 1986, that same leader of the HUJ-CSG prevented this writer from visiting the HUJ-CSG-controlled radars to evaluate cloud top heights during rain spells.  I wanted to see what top heights were, and indirectly via IMS rawinsonde soundings, obtain top temperatures.  (The HUJ-CSG leader, “AG,” did allow a brief “show and tell” visit to his Ben Gurion AP radar in February as a storm approached[2] as part of our third and last meeting in February 1986.)

To disallow a bona fide worker in the field of cloud microstructure and weather modification access to data/measurements to test claims about the Israeli clouds was demonstrable scientific misconduct IMO[3].   The clouds of Israel can only be studied in Israel, and as scientists we must be open to cross-checking of our results; having our findings tested.  It’s what we do in science (e.g., see Blyth and Latham’s 1998 criticisms of the glaciation papers of Hobbs and Rangno and our Reply (Hobbs and Rangno 1998) as a great example of open criticism).

But this was not what the leader of the Israeli experiments understood about science.  If he was deluded about his clouds, or was correct about them, I would have been welcomed, I thought.  If he had “contrary knowledge”, I would be blocked.  Q. E. D.

My findings (R88), in lieu of radar data, were based on Israel Meteorological Service’s (IMS) four-times-a-day rawinsondes, and were published in 1988.  They strongly suggested that there was a serious problem with the HUJ-CSG’s ultra “ripe-for-seeding” cloud descriptions.  Rosenfeld and Farbstein (1992) within the HUJ-CSG, belatedly discovered that “dust-haze” when present, apparently produced efficiently raining clouds in Israel, findings that supported R88.   Dust-haze has been around for quite awhile in Israel.

Later independent aircraft reports by Tel Aviv University (Levin 1992, 1994, Levin et al. 1996, hereafter L929496) also supported R88 and further exposed the faults in the HUJ-CSG cloud descriptions.

Today, and at last in F2015, the HUJ-CSG finally acknowledges, implicitly, why the leader of the Israeli experiments refused this visitor access to radars in 1986:   the high precipitating efficiency of Israeli clouds was going to be obvious in radar cloud top imagery.[4]  F2015 offers additional confirmation of those long ago findings in R88.  Lahav and Rosenfeld (2000), and Rosenfeld et al. 2001 had also found unsuitable clouds for seeding, but did not state that as explicitly as did F2015, or only alluded to “some clouds.”

Too, the high precipitation efficiency of Israeli clouds, too, is not limited to “dust-haze”; it never was.  The belief that the Rosenfeld and Farbstein (1992) attribution of “divergent seeding effects” to dust-haze was unreliable was the “acorn” of conviction that led to the “oak” of RH95.[5]

Rather than “dust-haze, that high efficiency is due relatively low droplet concentrations in Mediterranean clouds moving into Israel.    Larger droplets in clouds accelerate the formation of precipitation via several processes.

End of “baggage” module.

[1] Done on “own time, own dime”; not on grant monies.  I went to Israel in 1986 after I became convinced that the cloud reports by the HUJ-CSG were in substantial error and that the people of Israel were likely paying for the seeding of unsuitable clouds: “Someone has to do something about this!”  It was a “do-gooder” thought, and felt I COULD do something about it due to my background in airborne studies in the Cloud and Aerosol Research Group at the U of Washington, as a weather forecaster, as a storm chaser, and as a cloud photographer.  I spent 11 weeks in Israel watching the clouds and storms and working within the IMS.  I lived off my savings ($$$$) the rest of 1986 after I left Israel while preparing the manuscript that became R88.  It was submitted to the QJ in January 1987.  “Quasi-altruistic”?  Yep. I wanted to also demonstrate that I was the BEST at “outing” bogus cloud seeding work that none of my gullible peers suspected, to be completely candid.  Yes, it was a little megalomaniacal…

[2]Marked by a mid-level overcast of Altostratus and some lower Altocumulus with dust.

[3] After being asked to leave the offices of the HUJ-CSJ and not come back at the end of my 2nd meeting with AG in Janaury, I wrote to several scientists around the world about that event. Those I wrote to were: P. V. Hobbs and Lawrence F.  Radke, University of Washington; Gabor Vali, University of Wyoming; Roscoe Braham, Jr., North Carolina State University; and S. C. Mossop, CSIRO, Australia.

[4] Those within the HUJ-SU had about ten years of viewing and recording storms on their Enterprise 5-cm radar by the time of my  1986 visit.  Was no one “minding the store”?

[5] Also done on “own time, own dime”; not on grant monies.  Crackpot alert?

[1] As experienced in this writer’s 11-week stay in 1986, events in which embedded, much taller clouds sprang forth as the upper trough approached.

[1]Not cited by the HUJ-CSU in this paper. We expect studies that offer counter views to F2015 findings not to be cited by them at this point.  Perhaps they are taught that at the HUJ?  HUJ, are you listening?

[2] The reviewer believes that it is critical that the INWA or other organization certify that the list of random decisions provided prior to each season for Israeli 2 by statistician Ehud Shimbursky are, in fact, the ones that were used in Israeli 2.  This reviewer is doubtful, to add yet another layer of darkness to this analysis.  It’s just too tempting for those in the cloud seeding realm to say that, “Yes, we seeded that heavy rainstorm.”

[3]The authors omit the indication of the remarkable biased random draw of Israeli 2 experiment in which the rain in the south target was “statistically significant” in terms of standard error from average amounts on rain days (Gabriel and Rosenfeld 1990).

[4] Also from Gabriel and Rosenfeld (1990):  “The easiest explanation is to ascribe everything to chance, and accept H00 (the null hypothesis) . But the majority of the analyses run counter to this simplistic summary. Most of the evidence favors a positive effect of seeding in the north, and there is more evidence for a negative effect in the south than for a zero effect.”  This interpretation no longer holds water.

[5] The random draw for Israeli 2 was much different than for Israeli 1.  In Israeli 1 (1961-1965 daily randomization period), there were few consecutive draws of the same sign (13%) of the total of draws (Gabriel 1967, Table II).  In Israeli 2, consecutive draws of the SAME sign predominated (58%).  The list of random days for Israeli 2 was provided to Peter Hobbs in 1983 by A. Gagin.  Further investigation will likely find that this is the root cause of the lopsided draw in Israeli 2.

[6] From the Weather Modification Association’s Code of Ethics:  “Falsification: changing or not reporting appropriate data or results (i.e. the purposeful omission of conflicting data or information with the intent to falsify results; deceptive selective reporting). Isn’t that the purpose of “one-sided” citing as well?   Of note:  The American Meteorological Society does not have a Code of Ethics, but rather “suggestions” or “guidelines” for professional conduct.

[7] See the discussion of operational seeding below for details.

[8] Sound familiar? We repeat the WMA Code point for your consideration:  falsification: changing or not reporting appropriate data or results(i.e. the purposeful omission of conflicting data or information with the intent to falsify results; deceptive selective reporting).

[9] We can only imagine how these results would have been spun around if this had been a suggestion of an 8% increase in rain.  How many statistical tests would be tried?  Would the authors really just say, “inconclusive”?

[10] Sharon et al (2008), and the reports that it was distilled from (Kessler et al. 2002, 2006), are nowhere to be seen in the HUJ-SU authors’ paper.  Should we be surprised at this point?  I don’t think so.  This is not science as we know it.  HUJ, are you listening?

[11] While the original INWA program was terminated, some additional experimental-operational seeding did carry on, beginning with the 2007-08 rain season; it was terminated again in 2013 (according to F2015).  The reviewer does not yet know the details to the “supplemental” seeding following the termination in 2007.

[12] Alpert et al 2008 and Halfon et al 2009, and the exchange between Givati and Rosenfeld, also go uncited, strengthening a pattern of deception by the HUJ-SU; such actions by the authors that can no longer be attributed to oversights, but are meant to keep the ARreaders in the dark about the quality of the HUJ-CSG research.

[13] “Cast of thousands!” (except me..)

[1] Retiree, Cloud and Aerosol Research Group, Atmos. Sci. Dept., University of Washington, Seattle, 1976-2006.

[2] I dedicate this review to Jerzy Neyman, whom I greatly admired for his careful and voluminous criticisms of papers in the cloud seeding arena; to K. Ruben Gabriel, who was able to “stay above the fray” as a careful and objective statistician for the Israeli experiments, and lastly to Karl Rosner, Mekoroth’s Chief Meteorologist for Israeli 1 and 2, for his ability to remain objective within the “halls of seeding.”

[3] The great Nobel Laureate, Irving Langmuir, comes to mind, who once bitten by AgI, believed that any rainfall event could be explained by cloud seeding had there been any, no matter how large or far away from the release the event was.

[4] The above provocative conclusion comes from someone who has followed the HUJ-CSG reports over the past 35 years or so; is it me or them?

 

[5] The reviewer is not and has never been a faculty member at a university and therefore can raise such an issue with impunity unlike those with faculty status due to the “live and let live” de facto rules of the “faculty club.”

[6] This was the last mention of a numerical result of seeding in the south target of Israeli 2.

[7] The several IMS forecasters I spoke with when I worked within the Israel Meteorological Service (IMS) in 1986 were well aware of the “efficiency” that Israeli clouds exhibited.  One stated, “We get good rains out of clouds with tops at -10°C.”

 

[8] It had to be done by an outsider.

[9] Width (and implicitly, cloud top lifetime) has a direct bearing on the production of precipitation (e.g., Schemenaur and Isaac 1984; Rangno and Hobbs 1991.

[10]Whom also goes uncited (strangely) since one of the authors of F2015 (DR) commented on his BAMS cloud seeding review.  Small-mindedness here as well?  Or is it the desire by the authors to hide alternative views from their funders and journal readers?

Cloud Seeding and the Journal Barriers to Faulty Claims: Closing the Gaps

This manuscript had a close call in being accepted into the American Meteorological Society’s  Bull. Amer. Meteor. Soc. in 1998-1999.  The key reviewer that I had to satisfy (according to journal Editor  I. Abrams)  insisted that I make it clear that the cloud seeding experimenters in Colorado  and Israel did the “best they could with the tools available at that time”, paraphrasing here.

I couldn’t do it.

I had personal experience with the leaders of both those benchmark experiments; one was intransigent regarding new facts that upset a key claim he repeatedly made about the height of cloud tops in the Rockies during storms, and the other leader denied me access  to his radar to observe cloud top heights (and thus obtain temperatures).  I went to Israel suspecting that his many papers on the clouds of Israel were in major error.  (They were later proved to be in major error  on several occasions over the following 20 years.)

So, how could I agree with the key, “Reviewer B” stating that those experimenters did the best they could?  I might have “got in” by doing that.  Both cloud seeding leaders caused their respective country’s millions of dollars in wasted cloud seeding efforts.

An updated  “Gaps” manuscript was rejected a second time (!) in 2017 or so by the editor of the weather modification/cloud seeding issue of “Advances in Meteorology”, L. Xue, as “not the kind of paper we were looking for.”  Perhaps, though, it’s the kind of article YOU were looking for:

2017 Gaps-revised following comment

Review and Enhancement of “Literature Review and Scientific Synthesis on the Efficacy of Orographic Cloud Seeding”

PROLOGUE

Dr. Reynolds, the sole author of this monumental review I critique  has done a masterful job of surveying an enormous amount of cloud seeding literature in his “draft” report to his former employer, the Bureau of Reclamation.  The BOR was  the primary sponsor of cloud seeding programs throughout the West in the 1960s to the 1980s.  However, as was also seen in a recent review of the 2009 Springer book,  “Impacts of Aerosols on Precipitation,” such a task appears to be too much despite Reynold’s valiant efforts to “get it right.”   Reynold’s discussions of the benchmark randomized experiments in Colorado that led to the nation’s largest, most costly randomized orographic cloud seeding experiments, the Colorado River Basin Pilot Project, is an example of the problem of having too much to review and not enough time to scrutinize the details of so much literature.

Reynold’s review is well-written, most of the necessary citations are in it that help the reader to understand the topic.    That is,  except for those elements in his review that I am perhaps, a little too familiar with and I feel must be addressed in this VERY belated review of his 2015 draft report.

“Too familiar?”

That’s what happens to someone who has spent thousands of volunteer hours (crackpot alert!) rectifying faulty cloud seeding and cloud claims in peer-reviewed journal articles because he felt, “Someone has to do something about this!” (Second crackpot alert, with possible megalomaniacal implications).   I was employed as a weather forecaster for the Colorado River Basin Pilot Project for all of its five winter operating seasons, 1970/71 through 1974/75.  No one can know about that project and the faulty literature it was based on more than me.  I came in naive and idealistic about the scientific literature on cloud seeding;  I didn’t leave that way

I was not asked to review Reynold’s 2015  review before he posted his report to the BOR  online as a “draft,” the status it retains as of today.   I contacted Dr. Reynolds recently and informed him that I had a few comments on and corrections to his review.  He replied that he was not interested in correcting his review or making changes at this time.  This seemed odd to me, so here we are.

Also, in the spirit of “author disclosure,” I should mention that Dr. Reynolds was also an informal reviewer of my manuscript co-authored with Prof. Dave Schultz, Manchester U., on the history of the BOR-funded Colorado River Basin Project.  It was recently rejected by the J. Appl. Meteor.  due to length.  We are in the process of seeing where that manuscript can be trimmed down without losing  important parts of the story.

The comments pn Reynold’s review would have likely been unnecessary had I reviewed it beforehand, or if Dr. Reynolds  wished to consider my comments and corrections today.    I was well known to Dr. Reynolds as an expert on clouds, cloud seeding, and the weather  in Colorado and Israel ;  he had previously cited my work his 1988 article in the Bull. Amer. Meteor. Soc.   With Professor Peter V.  Hobbs in tow, I dissected those landmark experiments in Colorado and Israel and showed they were, as Foster and Huber (1997) described faulty science,  “scientific mirages.”  They were “low-hanging fruit” that poor peer reviews of manuscripts had let in, mostly, appearing Amer. Meteor. Soc. journals.  It didn’t take a genius to unravel them.

Dr. Reynold’s comprehensive  review can be found here.  It is too long to be a blog post here that includes my embedded comments.  Since I am only commenting on certain sections,  I have extracted only those portions of Reynold’s review where I have made comments.  It may be that only those familiar with this topic, orographic cloud seeding, will be interested, but, oh, well….  It has to be done even if for only ONE person!

My goal is to be objective and not short change Reynolds’ work on what is really an astounding effort.  It would take me two lifetimes to do what Dr. Reynolds has done.

I also believe Dr. Reynold’s made a great effort to be objective in discussing a topic that almost always brings controversy.  The literature in this field is filled with pro-seeding partisans that have often edited results so that cloud seeding has been presented with a happier face than it should have been.  After all, no one got a job saying cloud seeding doesn’t work (is not viable for producing worthwhile amounts of water.)

Considering his background in the cloud seeding arena, Reynolds final conclusion, copied below, must be considered an example of high integrity and his conclusion is one that this author fully agrees as of this date:

“5.3.2 Final Conclusion 

Based on both the historical evidence and the last decade of research, it is reasonable to conclude that artificial enhancement of winter snowpack over mountain barriers is possible. It is very difficult to quantify the seasonal increases to be expected both in snowpack and subsequent spring runoff. This is because each target area has to be investigated as to the meteorology of the winter clouds and their seedability, and the engineering aspects of effectively seeding the clouds to maximize increases. Winter orographic cloud seeding should thus continue to be supported both from the scientific and operational community working together to further the science and operational outcomes. It must be stated however, that as of yet, no rigorous scientific study conducted as a randomized confirmatory seeding experiment with pre-defined primary response variables and requiring an established threshold of statistical significance has demonstrated that seeding winter orographic clouds increases snowfall. As such, the “proof” the scientific community has been seeking for many decades is still not in hand. “

================THE REVIEW=================

My comments, corrections and question on Dr. Reynolds review begins below and are in a red font.   Highly relevant citations are missing  and there are citations in the Reynold’s references that do not appear in the text.  The missing ones, annotated with a “u” ,  have been added at the end of this review.

The portions of Reynold’s review that I examined begins here:

———————————————————————-

1.0 Introduction 

1.1. Introduction to Winter Orographic Cloud Seeding In its most basic form, artificial seeding of clouds for precipitation enhancement can be divided into two broad categories: 1 – cloud seeding to enhance rainfall i.e. summer convection, 2 – winter orographic cloud seeding to enhance snowfall. The scope of this paper is only concerned with the latter. Winter orographic cloud seeding occurs when very small particles, typically silver iodide, are introduced into a cloud which is below freezing. The cloud moisture collects onto the small particles, freezing the moisture into tiny ice crystals which continue to grow until they become too heavy to remain in the cloud and then fall out as precipitation (typically snow). This process can happen rapidly on the windward slopes of mountains allowing the snow to fall near the crest of the mountain which causes a local enhancement to the amount of precipitation that would have fallen naturally (Figure 1.1).

The situation is complicated if the natural crystals are becoming rimed and due to riming, fall more quickly.  Adding more ice crystals via cloud seeding may result in raising their trajectories by reducing riming and the snow may not be increased snow where it is wanted, or will evaporate in the descending, drying  air on the lee side.  The schematic below would be valid for naturally non-precipitating clouds.  

The properties of clouds that don’t naturally precipitate vary with location.  Maritime clouds along the west coasts of continents generally can precipitate without ice.  Farther inland, where the clouds become impacted by natural and anthropogenic aerosols, ice is generally required for precipitation and may not develop until cloud tops are cooler than about -12°C.  These latter non-precipitating clouds make viable seeding targets.

Figure 1.1 – Simple model of winter orographic cloud seeding. 1 – Introduction of seeding material, 2 forced ascent due to topography, 3 – enhanced precipitation falling out of cloud. 

1.3 Relevance and Need for a Reassessment of the Role of Winter Orographic Cloud Seeding to Enhance Water Supplies in the West 

Weather modification is most commonly conducted through “cloud seeding,” the introduction of chemical agents with the intent of affecting precipitation processes. A number of academic and private entities exist that offer services to states and local governments with the aim of increasing water supplies through inducing precipitation volumes above which would occur naturally. From the 1960s through the 1980s, Reclamation was involved in a variety of weather modification initiatives in the west under Project Skywater. This project included the Colorado River Basin Pilot Project, the High Plains Experiment (summer only), and the Sierra Cooperative Pilot Project. Project Skywater was terminated in 1988, but Reclamation continued to be involved with weather modification efforts. Reclamation participated in the development of the California Department of Water Resource’s design and conduct of the Oroville Reservoir Runoff Enhancement Project from 1988 until 1994. Reclamation also supported other efforts through the mid-2000s, including the Weather Damage Modification Program. 

Based upon scientific literature through 2006 and discussions with experts in the field, the efficacy of weather modification appears to be unsettled. In 2003, the National Research Council (NRC) report “Critical Issues in Weather Modification Research” (NRC 2003), concluded that “there is still no convincing scientific proof of the efficacy of intentional weather modification efforts”. The NRC goes on to state that new technology allows for potential new research to help understand the process of precipitation and if weather modification is a viable means to increase water supplies. 

The NRC 2003 review of cloud seeding cited above  did not measure up to the one the NRC published in 1973.  I reviewed NRC 2003.  If anyone cares, can be found here:         

 A Critical Review of NRC 2003 Critical issues in weather modification NATIONAL ACADEMIES PRESS

As seems to be typical of reviews, there was just too much literature to review for the scientists involved, and also likely, not a top priority for those assigned to this task having other research on their plates.   Prof. Hobbs, with my acquiescence, helped compromise this review by declining an offer by Prof. Garstang, chair of the review committee, to review before it was published, a huge mistake.  Garstang admonished  Peter to not to comment on it AFTER it came out.  But that’s exactly what Peter told me we would do if needed.  I nodded and went back to my desk.  He said we would have “more impact” by doing that.  I hope you appreciate getting stories from behind the scenes.

In 2002-2003, Reclamation funded, through earmarks, weather modification studies in the states of Nevada, Utah, California, North Dakota, and Texas. The studies did not provide convincing scientific evidence that weather modification reliably generates additional water. However, there are a number of studies, including from within Reclamation (Hunter 2004 – cited within LBAO (Lahontan Basin Area Office) EA discussed later), that indicate that cloud seeding can significantly increase precipitation amounts for targeted locations. 

Statement on the Application of Winter Orographic Cloud Seeding For Water Supply and Energy Production 

In 2005, Reclamation primarily stopped involvement in weather modification efforts at the program level. As identified within Q&As developed by the Research and Development Office explaining Reclamations abandonment of the practice: 

•Weather modification is not an operational function of Reclamation.

•In a letter dated December 13, 2005, sent to then-Texas Senator Kay Bailey Hutchison(R), the White House Office of Science and Technology Policy (OSTP) said there aresignificant concerns about liability and legal ramifications of weather modification,including whether weather modification can be demonstrated to actually be effective.

Since 2006, continuing drought conditions, and a strong interest amongst some Reclamation stakeholders, Reclamation engaged in two research projects related to weather modification in support of cold-season snowfall enhancement. 

•In 2010 the Mid-Pacific Region’s LBAO finalized an Environmental Assessment (LBAOEA) proposing to provide $1.35 million from Reclamation’s Desert Terminal LakesProgram to the Desert Research Institute (DRI) for a cloud seeding project in the WalkerRiver Basin.

•At a March 12, 2014 meeting of the Upper Colorado River Commission, weather modification was specifically identified as one of three activities that the Upper Basin states propose to include within their drought contingency plans. The Upper Basin states asked that Reclamation provide partial support for Wyoming’s eighth year (2014) of an ongoing weather modification study / program being conducted with the National Center for Atmospheric Research (NCAR). This request resulted in Reclamation’s Upper Colorado Region obligating $200,000 to the State of Wyoming for weather modification research and development efforts conducted by NCAR, with these monies obligated through an amendment to an existing cooperative agreement between Reclamation R&D and Universities Corporation for Atmospheric Research.

The Upper Basin states have noted that state and private entities in Colorado and Utah spend over $1M and $500,000 respectively on weather modification, and estimate efficacy between 6% and 20%. At the low end, the Upper Basin states identify that a benefit of 6% is inexpensive water within the Colorado River Basin. The Upper Basin states have argued that Reclamation’s documents from the 1960s – 1980s identified positive results of weather modification.

This above section needs supporting references for the assertions made about seeding results, the benefit claim, and who are those “Upper Basin States”?  Otherwise these statements should be taken with extra caution.

1.5 Brief History of Federal and State Authorizations for Weather Modification 

The following is taken from Chisolm and Grimes (1979): 

In 1968, the Colorado River Basin Project Act of 1968 (Public Law 90-537) was passed by Congress to provide for the further comprehensive development of water resources of the Colorado River Basin and for the provision of additional and adequate water supplies for use in the upper as well as lower Colorado River Basin. Under Title II of this Act, the Secretary of the Interior was authorized to prepare and implement an augmentation plan to meet the water requirements of the new projects created by the Act (Central Arizona Project and Colorado River Storage Project), existing projects and water allotments, and the 1944 water treaty with Mexico. 

Augmentation was one of the main issues in the deliberation on the Act. The Act defines augmentation as, “ ‘augment’ or ‘augmentation’ when used herein with reference to water means to increase supply of the Colorado River system or its tributaries by introduction of water into the Colorado River system, which is in addition to the natural supply of the system.” The Statement of the Managers on the part of the House with regard to augmentation stated “all possible sources of water must be considered, including water conservation and salvage, weather modification, desalinization and importation from areas of surplus.”

The Colorado River Basin Pilot Project (CRBPP) was the Bureau’s first major effort on weather modification in Colorado under the auspices of Project Skywater and P. L. 90-537. The purpose of the Colorado River Basin Pilot Project was to provide for scientific and economic evaluation of precipitation augmentation technology and to increase precipitation. The specific objectives to be achieved were (l) to establish and operate a ground-based meteorological network in and near the San Juan Mountains of Colorado to provide data input in the selection of suitable storms for seeding, and (2) to establish and operate a ground-based silver iodide seeding system to increase snowfall in the project target area. The field phase of CRBPP began with the winter of 1969-1970 (installation of gauges and seeding generator siting) while the random seeding phase began with the 1970-71 season and ran through the 1974-75 season (not the 1973-74 season as the author stated).

Date corrections are needed from the original text, not a good sign of the author’s knowledge concerning the CRBPP.  What is incomprehensible is that the goal of replicating the large percentage increases in snowfall reported in three randomized experiments by the author’s former home institution, Colorado State University, is left out of this rationale for the CRBPP.  Surely, the author knew, also as a long term BOR cloud seeding division employee, that those experiments were the primary motivation for the BOR to spend $40-50 million (in 2023 dollars) on the CRBPP.

At about the time of completion of CRBPP in Colorado, the Bureau began funding Project Snowman in Utah. Project Snowman was conducted for the Bureau by Utah State University’s Water Research Laboratory. The objective of this four-year project was to develop cold-cloud seeding technology using airborne generators and ground-based generators located in the northern portion of the Wasatch Mountains.

References are also needed here.

The Bureau’s early work on precipitation augmentation in Colorado was based on a fairly extensive background of research activities. Three major research efforts in winter seeding contributed directly to the Bureau’s CRBPP project in the Upper Colorado River Basin. These were: 

  1. The National Science Foundation sponsored research experiments by Colorado State University at Climax, Colorado, during the 1960’s.

“1” above is not a sufficient description of the motivation for the CRBPP.  The Climax experiments were reported on numerous occasions in the peer-reviewed literature as cloud seeding successes when air mass temperatures were high (i. e., high 500 hPa and 700 hPa equivalent temperatures as by Grant and Mielke 1967u, Kahan et al. 1969u, Grant et al. 1969u, Mielke et al. 1970u, 1971u, among others).  The BOR had a LOT of peer-reviewed evidence on which to base the CRBPP and in particular, in the Grant et al. 1969u Interim Report to the BOR that described the results of the Climax I results, and the preliminary results of Climax II and the Wolf Creek Pass experiments.  The findings in these three experiments, as described by Grant et al. 1969u,  were remarkably supportive of one another.  Climax II was a confirmatory experiment; nothing was changed from Climax I.

2. The operational research funded by the State of Colorado during the 1960′ s at several mountain passes, particularly Wolf Creek Pass in the San Juan Mountains, and,

The Wolf Creek Pass experiment mentioned above was a six winter season,  fully RANDOMIZED  experiment where entire winter seasons were randomized.  This experiment was critical to where the CRBPP was located since it appeared to have produced more water than seeding had in northern Colorado where the Climax experiments took place.

3. The Bureau sponsored experiments in the Park Range near Steamboat Springs, Coloradoduring the late 1960’s.

Rhea et al.’s 1969u “Final Report” to the  BOR concerning the Park Range Project  is eventually cited by Reynold’s, but is not in Reynold’s references.  This report was a “heads up” on all the problems that would be “rediscovered” during the CRBPP (e.g, as reported in Willis and Rangno 1971u).

The results of the Colorado River Pilot Project indicated the need for further verification and improvement in technology before a large augmentation program could be undertaken again.

This is a vague description of the CRBPP results, perhaps intentionally so. Why not just say what happened for the reader right here in plain language?   “The results of the earlier CSU experiments could not be replicated in the CRBPP (Elliott et al. 1978u followed by a citation to the “Comments” on Elliott et al’s findings by Rangno and Hobbs 1980-the latter reference is contained in Reynold’s references but is not discussed in his review.   Later, it was discovered that those early optimistic CSU results and the microphysical foundation on which they rested on were all ersatz leaving no real basis for the CRBPP  (e.g., Mielke 1979u, Rangno 1979u, Hobbs and Rangno 1979u, Rhea 1983, Rangno and Hobbs 1987u, 1993, 1995a, u)”

The Wolf Creek Pass seeding effort was designed to test whether a viable signal in runoff from Wolf Creek Pass could be produced by seeding all winter.  The Wolf Creek Pass experiment, conducted from the winters of 1964/65 through 1969/70 produced stunning results when the three randomly chosen seeded seasons were compared with the long historical runoff record (Grant et al. 1969u, Morel-Seytoux and Saheli 1973u).  Furthermore, the results of seeding on  individual days during the seeded winters appeared to replicate the results of Climax I.  It doesn’t get any better than this for a trifecta of apparent cloud seeding successes!  

But, it was all a mirage (e.g., Rangno 1979u), which makes this story so interesting from a scientific viewpoint.

Thus, the Bureau’s research program continued.

Winter experiments were conducted outside of the Colorado River Basin at: Elk Mountain, Wyoming (University of Wyoming) Bridger Range, Montana (Montana State University) Jemez Mountains, New Mexico (New Mexico State University) Pyramid Lake Pilot Project (University of Nevada) In addition, the Bureau continued to provide supplemental funds to Colorado State University’s NSF research and to Utah State University’s state -sponsored research project. Through the Emergency Drought Act of 1977 the Bureau granted over $2 million to six states for supplemental support of their cloud seeding projects including over $1 million to the States of Colorado and Utah for cloud seeding in the Colorado River Basin. 

1.6 Current Policy Statements from American Meteorological Society and World Meteorological Organization on Efficacy of Winter Orographic Cloud Seeding 

The two leading organizations representing the atmospheric science scientific establishment, the World Meteorological Organization and the American Meteorological Society, have both issued policy statements on the efficacy of winter orographic cloud seeding. These are relevant to review given the NRC 2003 conclusions. 

The current statement from the World Meteorological Organization (WMO 2010) on weather modification in general and relating specifically to winter orographic cloud seeding efficacy is stated below. 

“The scientific status of weather modification, while steadily improving, still reflects limitations in the detailed understanding of cloud microphysics and precipitation formation, as well as inadequacies in accurate precipitation measurement. Governments and scientific institutions are urged to substantially increase their efforts in basic physics and chemistry research related to weather modification and related programmes in weather modification. Further testing and evaluation of physical concepts and seeding strategies are critically important. The acceptance of weather modification can only be improved by increasing the numbers of well executed experiments and building the base of positive scientific results.” 

“Cloud seeding has been used on both cold clouds, in which glaciogenic seeding aims to induce ice-phase precipitation, and warm clouds, where hygroscopic seeding aims to promote coalescence of water droplets. There is statistical evidence, supported by some observations, of precipitation enhancement from glaciogenic seeding of orographic supercooled liquid and mixed-phase clouds and of some clouds associated with frontal systems that contain supercooled liquid water. “ 

The current AMS policy statement (AMS 2010) does not address specifically the efficacy of winter orographic cloud seeding but much like the NRC 2003 report identifies uncertainty and risk with much the same conclusions. These are listed below. 

UNCERTAINTY – Planned weather modification programs benefit from a comprehensive understanding of the physical processes responsible for desired modification effects. Recent improvements in the composition and techniques for dispersion of seeding agents, observational technology, numerical cloud models, and in physical understanding of cloud processes permit evermore detailed design and targeting of planned weather modification effects, and more accurate specification of the range of anticipated responses. While effects are often immediately evident in simple situations, such as when cloud seeding is used to clear supercooled fog and low stratus cloud decks, in more complex cloud systems it is often difficult to determine a seeding effect on a cloud-by-cloud basis. In these more complex situations, large numbers of events must be analyzed to separate the response to cloud seeding from natural variability in cloud behavior. Rigorous attention to evaluation of both operational and research programs is needed to help develop more effective procedures and to improve understanding of the effects of cloud seeding. Research and operational programs should be designed in a way that will allow their physical and statistical evaluation. Any statistical assessment must be accompanied by physical evaluation to confirm that the statistical results can be attributed to the seeding through a well-understood chain of physical events. It should be noted, though, that in practice large potential benefits can warrant relatively small investments to conduct operational cloud seeding despite some uncertainty in the outcome. 

The text in blue font seems like PR, Dave, and should be updated due to the lack of proof of seeding induced increases in snow we now have. Neiburger (1969u, WMO Tech Note) warned that such thinking usually excludes the idea that seeding might result in decreases in precipitation in addition to mistargeting, faulty operations.  

1969 CLOUD SEEDING REVIEWS MORRIS NEIBURGER ocr

RISK MANAGEMENT – Unintended consequences of cloud seeding, such as changes in precipitation or other environmental impacts downwind of a target area, have not been clearly demonstrated, but neither can they be ruled out. In addition, cloud seeding materials may not always be successfully targeted and may cause their intended effects in an area different than the desired target area. This brings us to the ethical concern that activities conducted for the benefit of some may have an undesirable impact on others; weather modification programs should be designed to minimize negative impacts.. At times unintended effects may cross political boundaries, so international cooperation may be needed in some regions. Precipitation augmentation through cloud seeding should be viewed cautiously as a drought-relief measure because opportunities to increase precipitation are reduced during droughts. A program of precipitation augmentation is more effective in cushioning the impact of drought if it is used as part of a water management strategy on a long-term basis, with continuity from year to year, whenever opportunities exist to build soil moisture, to improve cropland, and to increase water in storage. From time to time methods have been proposed for modifying extreme weather phenomena, such as seeding severe thunderstorms with aerosols to diminish tornado intensity, or seeding tropical cyclones to cause changes in their dynamics and steer them away from land and/or diminish their intensity. Some experimentation has taken place in these areas, but current knowledge of these complex weather systems is limited, and the physical basis by which seeding might influence their evolution is not well understood. Weather modification techniques other than cloud seeding have been used in various areas of the world for short periods of time to achieve goals similar to those of cloud seeding. Much less is known about the effects of these other techniques, and their scientific basis is even further from being demonstrated, either statistically or physically, than it is for cloud seeding. Application of weather modification methods that are not supported by statistically positive results combined with a well-understood physical chain of processes leading to these results, and that can also be replicated by numerical cloud modeling, should be discouraged.

Other organizations such as the North American Interstate Weather Modification Council, The Weather Modification Association, the American Society of Civil Engineers, and the Western States Water Council have also adopted policy statements or adopted resolutions relating to the use of weather modification for increasing snowpack and water supply. These are referenced in Ryan (2005) and will not be repeated here. Most if not all of these statements are much more positive in their support of the application of weather modification for enhancing snowpack and runoff despite the lack of evidence as reported in NRC 2003.

To the uninitiated reader to the field of weather modification/cloud seeding, it will seem odd that there are government entities that will pay huge sums of tax payer monies for cloud seeding with no viable evidence that it does anything, evidence being in the form of randomized experiments, the “gold standard” of scientific proof.  

Why would those entities take such chances?  

If you haven’t guessed by now, it’s because those government entities are telling their constituents directly or implicitly that they are doing SOMETHING about a drought.  It’s a great ploy, and usually works except in the minds of those who know the science.  

What science?  

Two modern randomized experiments testing to see if cloud seeding can increase precipitation in mountainous regions (Wyoming and in northern Israel) ended with  no indications that cloud seeding increased precipitation.  These null findings have been published by Rasmussen et al. 2018u for Wyoming, and by Benjamini et al. 2023u for Israel.  Now you know.  

Did the “null” finding reported by Rasmussen et al. 2018 terminate cloud seeding in Wyoming?  Of course  not.  It just looks too good to the public that you’re doing something about water needs.  

1.7 Generalized Concepts of Winter Orographic Cloud Seeding 

It is useful to review the general principles of winter orographic snowfall and whether this process could be modified or enhanced by artificial means. The basic physical concepts associated with seeding winter orographic clouds are not debated even though there is considerable debate over weather modification and its efficacy. These basic physical concepts are reviewed in the following section. There are several text books and encyclopedia articles available for a more in-depth discussion or broader overview of the physical basis of cloud seeding (Hess 1974; Dennis 1980; Dennis 1987; and Heymsfield 1992). 

Dennis in his (1980) Academy Press book, “Weather Modification by Cloud Seeding,” relied heavily on the 1977 BOR Monograph Number 1 (yes, it was deemed that important by the BOR to name it as NUMBER ONE),  became outdated almost immediately when external critics (guess who?) found serious flaws in that “meta-analysis.”     The BOR study, published in 1978u (Vardiman and Moore) was retracted in 1980  by Rottner et al. 1980 as critical “Comments” on their paper by, yep, Rangno and Hobbs (1980) were being published.  Thus, Dennis (1980) might be reconsidered as a reference here.  The BOR was too willing to believe in cloud seeding success mirages that led to this major embarrassment.

Too, much of the cloud seeding literature in Hess (1974) has been overturned in reanalyses or has not been replicated, as in the recent Wyoming and Israel experiments.  But, “hey,” you can read about global cooling in Hess (1974), thought to be underway at that time.

Figure 1.2 from Ludlam (1955), reproduced below, describes the process that remains to this day the fundamental conceptual model associated with winter orographic cloud seeding. Figure 1.2 shows a shallow orographic cloud, where the liquid condensate produced by forced assent over a mountain barrier is unable to be converted to snowfall before the air descends and evaporates in the lee of the mountain. During wintertime the freezing level (height of the 0oC isotherm) varies dependent on the origin of the air mass impinging on the mountain barrier.  This varies from north to south with the freezing level being lower in altitude at the northern latitudes of the western US and the inter-mountain west where the air masses that impact this area are usually modified maritime polar or continental polar.

and height allowing the crystals to grow at the expense of the cloud water that in (a) was lost to the lee, bringing this moisture down on the windward side of the mountain.

1.2a is the non-precipitating cloud that forms the low, demonstrable end of seeding potential.

The text in blue in the body of the paragraph may be true, but….. warm air masses during times of upper level ridges along the West Coast shunt warm air mass storms into the central and northern Rockies, so this “paradigm” often does not hold.  Surface temperatures may be well below freezing, but much higher temperatures usually exist aloft in those warm aloft regions of winter storms.  The Climax I experiment, for example, had numerous warm aloft storms overrunning colder air with west-northwest flow due to this synoptic scenario.   Quantification of this claim would have been very informative and would have pinned it down for the reader…and me!

Freezing levels are usually below ground level in mountainous regions except in the warmest storms. In the Ludlum model, it is assumed the orographic cloud has a significant depth of cloud below 0 oC and thus the cloud moisture is said to be supercooled. The critical uncertainty with regard to successful conversion of the unused cloud condensate to snowfall prior to passing over the crest is the location, duration, temperature and concentration of the supercooled liquid water (SLW).

As Ludlum describes it may take as much as 1500 seconds once artificial ice crystals are initiated to grow and fall out before passing to the lee of the mountain crest.  This can vary by several tens of minutes based on SLW concentration, temperature vertical profile and winds.

The process of crystal growth is almost always much fast than “as much as” 25 minutes to fallout cited by Ludlum  (e.g., Auer et al. 1969, Cooper and Vali 1981).

So the critical factors for achieving success are getting the seeding agent into the cloud at the right location where it will generate enough ice embryos such that they will utilize the available SLW prior to passing over the crest. There are many complex interactions that have made it very difficult to demonstrate the efficacy of winter orographic cloud seeding to the satisfaction of the scientific community. These factors are described in the following paragraphs. 

So true.

 1.7.1 The Initiation, Growth and Fallout of Snow in Winter Orographic Clouds 1.7.1.1 Converting Supercooled Liquid Water (SLW) to Snow

Supercooled liquid water (SLW) in the atmosphere is made up of tiny cloud droplets that are colder than 0 oC. There are two processes in nature by which SLW in the atmosphere can freeze to initiate snowfall: 1. Heterogeneous nucleation or 2. Homogeneous nucleation. Heterogeneous nucleation occurs when the supercooled liquid drop comes in contact with what is called an ice nucleus (IN) that emulates the crystalline structure of ice and causes the droplet to freeze. These can be dust particles, biological particles or a combination of the two. These aerosols can come from as far away as Asia and Africa initiating cloud ice in orographic clouds in the western US (Cremean et al. 2013). They are made of very small particles of tenths of microns in size. They are most active at cloud top and tend to activate the growth of snowflakes from the top of the cloud down. The warmer the cloud top the less percentage of ice makes up the cloud (Cremean et al. 2013).

Sidebar:  An interesting feature, first observed in the 1950s (e.g., Cunningham 1957u) and afterward was the “upside down” storm structure where few ice crystals were found at low cloud top temperatures consisting mostly of supercooled liquid water with increasing ice crystal concentrations below the top. The increasing concentrations of ice crystals were mostly due to the fragmentation of delicate ice crystals. The most recent description of this scenario was by Rauber and Tokay (1991u) and Hobbs and Rangno (1985).

Lower down, within a km of the surface, ground observations have shown that riming and and aggregation occur that increase snowfall rates. This lower region near mountains cannot be sampled by aircraft if precipitation is falling and as a result, has mainly been documented  in ground observations (e.g, Hobbs 1975). Thus, aircraft observations can often be seen as under measuring ice particle concentrations in mountainous regions.  For example, we at the University of Washington often overflew shallow orographic clouds with liquid tops at >-10C with snow falling out underneath, but we couldn’t sample them because the tops were too close to the tops of the Cascade Mountains.

When clouds are dominated by warm rain processes, the aerosol makeup of the cloud is more sea salt and biological particles which act as condensation nuclei producing larger cloud droplets which grow to raindrops via collision coalescence. Homogeneous nucleation occurs when the air temperature drops below -40 oC and the water droplet spontaneously freezes without the aid of a nucleating agent. The most basic hypothesis in winter orographic cloud seeding is that in the presence of SLW droplets, ice crystals will grow at the expense of the drops. This means the drops will convert back to vapor allowing the crystals to grow by vapor deposition unless too many ice crystals have resulted from seeding in which case they might not grow at all. The driver for crystal growth is related to the concentration of SLW and the temperature regime of the SLW (Ryan et al. 1976; Heymsfield 1992; Pruppacher and Klett 1978).

In the presence of moderately high concentrations of SLW and with somewhat preferred growth temperatures (Ryan et al. 1976, Figure 1.3) enough of the initial ice crystals can grow and then begin to aggregate into larger flakes leading to higher fall speeds and earlier fall-out. If these artificial crystals encounter additional SLW as they fall back toward the mountain crest, the individual crystals or aggregates may collect these SLW drops (called riming) which will also increase the crystals fall-speed. If the naturally created ice crystals are unable to utilize all the available SLW, and some SLW evaporates to the lee of the mountain, the cloud is said to be less than 100% efficient. This provides the opportunity for the artificial injection of a nucleating agent to create the additional ice crystals necessary to bring the residual cloud water to the ground before it is lost to the lee of the mountain. This is the basic principles described in Ludlam’s model. 

Aerial Seeding window 

Ground based seeding temperatures 

General seeding window based on Figure 1.5 and observed SLW 

As Super and Heimbach (2005) noted, the frequency of occurrence of SLW is temperature dependent with higher frequencies and amounts at (higher) supercooled temperatures. This is true for all mountain ranges where SLW has been observed. There are two main reasons for this. First, the amount of water vapor in the atmosphere can be higher at warmer (higher) temperatures. Second, as the atmosphere cools and clouds form and reach temperatures lower than -10 oC, and especially at -20 oC, an abundance of natural ice can occur that depletes the supercooled cloud water. Thus, there is less SLW available for cloud seeding to enhance the natural precipitation process as the air approaches these temperatures. It should be noted that studies (Reinking et al. 2000; Super 2005) have found significantly higher amounts of SLW (.5 to 1 mm integrated SLW) in wave clouds during winter storms and noted that others had observed such amounts during brief periods in other western mountain locations. However, the overwhelming amount of observations utilizing microwave radiometers (Heggli and Rauber 1988; Huggins 2009; Super and Heimbach 2005), in-situ aircraft observations, and mountain top icing rate meters indicate that SLW is concentrated in the lowest 1000m along the windward slopes of mountain ranges during passing winter storms. The primary SLW zone rapidly dissipates downwind of the crest because of warming produced by subsidence and by depletion from conversion to snowfall (Boe and Super 1986; Rauber et al. 1986; Rangno 1986 (the rapid dissipation of SLW, one of my main points), Huggins 1995; Super 2005; Huggins 2009).  There are observations that confirm the simple conceptual model espoused by Ludlam when natural ice does not form. The location of many of the research studies referenced in this report along with other locations that will be referenced later in this report are shown in Figure 1.4b. One can compare these locations to Figure 1.4a which shows the location where operational winter orographic cloud seeding is conducted circa 2006 per Griffith et al. 2006. Coastally influenced areas would be west of the Sierra Nevada and Cascades while the intermountain region refers to areas east of these two ranges. 

The actual temperature relationship to SLW occurrence varies geographically. For the intermountain west, where the cloud drop size distributions are more numerous at the smaller drop sizes (10 to 15 microns; what is referred to as a continental drop size distribution), lower temperatures are reached before a sufficient number of natural ice crystals develop to utilize the available SLW. Thus, SLW can exist, at least briefly, at temperatures as low as -15 to -20 oC. Super and Heimbach (2005) provide a comprehensive review of SLW climatology in the intermountain west. 

In more coastal regions, such as the Sierra Nevada and Cascades, the drop size distribution can be broad (what is referred to as a maritime drop size distribution). The drops can begin to collide and coalesce because of the varying fall speeds of the drops with a broader distribution of cloud droplets (extending into and above 30 microns diameter). This leads to larger cloud drops (approaching drizzle size) that can be carried upslope into coastal mountains like the Cascades and Sierra Nevada ranges where just a few of these droplets can freeze leading to rime splintering or secondary ice-crystal production (Hallett and Mossop 1974; Dong and Hallett 1989; Mossop 1985). This can, and has been observed to lead to high concentrations of ice crystals with cloud temperatures warmer than -10 oC (Reinking 1978; Cooper 1986; Marwitz 1986; Hobbs and Rangno 1985; Rauber 1992).

Nieman et al 2005u reported  occurrences of the “warm rain” process in Northern California and Oregon were common.  Will cloud seeding increase precipitation if nature is providing rain via collisions with coalescence?

Other factors (Rango  (sic) 1986) can lead to high ice crystal concentrations with relatively high cloud top temperatures. Mixing of very dry air into cloud tops can initiate cloud droplet freezing (e.g., Koenig 1968; Hobbs and Rangno 1985). This has been observed in the Cascades, Sierra Nevada and southern Utah. In the post-frontal airmass, where most of the shallow orographic clouds exist, very dry air can exist above cloud top. This is caused by sinking air parcels in the region behind the upper-level jet-stream that usually passes just ahead of the surface cold front  (Heggli and Reynolds 1985). Thus the coastal mountain clouds will have a lesser degree of supercooling, meaning that the clouds will be only marginally supercooled as natural ice production will utilize the available SLW within moderately supercooled clouds. Reynolds (1995) documented that over an 8 year period in the northern Sierra Nevada, 80% of the hours reporting SLW from mountain-top icing rate meters were at temperatures warmer than -4 oC. Reynolds (1996) also reported that 70% of the hours with precipitation had icing (riming?) reported. Approximately 300 hours of icing were reported per season. However, some seasons had average temperatures during icing warmer than -2 oC which may be too warm for any known seeding agent to work effectively unless seeded aloft using aerial seeding. Studies examining mountain top temperatures in Colorado and Utah revealed that SLW in clouds is mildly supercooled in a large portion of all storm passages, which means clouds are too warm for effective AgI seeding (Super 2005). Refer to Figure 1.5 for activation levels of the various cloud seeding agents currently used or proposed.

Why aren’t supercooled non-precipitating clouds’ occurrences documented for whole seasons as in Ludlams’s simple case? Seems this information would form a great starting point that could determine how much seeding can unequivocally increase snow.  The reader would like to know.

There are many studies (Heggli et al. 1983; Boe and Super 1986; Rauber and Grant 1986; Heggli and Rauber 1988; Super and Huggins 1993; Super 2005; Huggins 2009) that state SLW within a cloud varies rather rapidly with time over any given point. Due to this variability in SLW, identifying seeding potential within winter orographic storms will require identification of the proper seeding agent and delivery technique and applied at the correct time and location (Hunter 2007; Huggins 2009). Huggins (2009) suggests that any cloud seeding program will necessarily be treating clouds that at any given time may not have sufficient SLW (when the seeding agent arrives) given its variability. This begs the question as to whether seeding in these situations may have negative impacts on snowfall production. This will be further discussed in Section 1.7.4. Even though the location of SLW concentrations is known, the exact lower threshold for SLW concentrations to be sufficient for enhancing snowfall has not been quantified. It is believed to be greater than .05 mm integrated in the vertical derived from microwave radiometers (threshold used by Super and Heimbach 2005 and Manton et al 2011). However, Murakami (2013) used .2 mm as the lower threshold for determining cloud seeding feasibility and theorized that .3mm was probably the minimum threshold for viable increases in orographic precipitation enhancement.

For what durations of this SLW threshold? Did those these researchers report how long it lasted?  Did they make any seasonal estimates of these occurrences?  The reader would want to know.

This is a critical question as frequency distributions of SLW concentrations from radiometer data (Reynolds 1988) indicate that 85% of the SLW reported were at concentrations below .2 mm (Figure 1.5).What constitutes a necessary and sufficient concentration of SLW for effective cloud seeding is still in debate. 

Several studies (Rosenfeld 2000; Givati and Rosenfeld 2004; Rosenfeld and Givati, 2006; Griffith et al. 2005; Hunter 2007) have described decreases in orographic precipitation due to pollution.

The above requires some exhaustive comments:

Reynolds was unaware that when the claims of Givati and Rosenfeld concerning air pollution were examined by external skeptics they have not been substantiated.   I think this same view should be taken with Givati and Rosenfeld (2006) for pollution effects on West Coast precipitation.  We need this latter study to be validated by an external skeptic!  Yes, I am excited here.

I suspect, as in the Givati and Rosenfeld’s (2005) Israel study, where more than 500 standard gauges and 82 or so recording gauges were available to cherry-pick whatever result one wants, this may well have been  done in the 2006 study.   Kessler et al. (2006u), in an evaluation of the Israeli operational seeding program wrote: “No supporting evidence was found for the thesis of Givati and Rosenfeld (2005) regarding the decline in the Orographic (sic) precipitations due to the increase of air pollution.”

The air pollution claims, while superficially credible except for their sudden hypothesized appearance in Israel after 1990 when operational seeding produced a slight indication of decreased rainfall (Kessler et al. 2006u), were also evaluated by several independent groups and scientists: Alpert et al. (2008u, 2009u); Halfon et al. (2009u); Levin 2009u.   The Givati and Rosenfeld (2005) claims were also addressed in a review by Ayers and Levin (2009u). All these independent re-analyses and reviews of the hypothesized effect of air pollution on rainfall found the argument that air pollution had canceled seeding-induced increases in rain in Israel unconvincing.   In the few cases that Dr. Rosenfeld’s papers have been reviewed by external skeptics, they don’t hold up.  Ask Prof. Levin, Tel Aviv University, Professor Sandra Yuter, North Carolina State University, Nathan Halfon, Tel Aviv University, or me.   Hence, Caveat Emptor!

This specifically impacts the collision coalescence process and what is called warm rain, i.e. no ice processes involved. These studies discuss that pollution can slow down the collision coalescence process by narrowing the drop-size distribution. This, in turn, slows down the warm rain process and would have the largest impacts in the low-elevation coastal ranges along the west coast where the freezing level is well above the elevations of the coastal mountains, i.e. around Los Angeles where it has been proposed to reduce precipitation. Typically the decrease in orographically enhanced precipitation is greatest downwind of a major metropolitan area that is producing pollution. Givati and Rosenfeld (2004) showed precipitation losses near orographic features downwind of coastal urban centers corresponding to 15-25% of the annual precipitation.

Caveat emptor re Givati and Rosenfeld’s findings!

This loss of precipitation can be greater than the gain claimed by precipitation enhancement techniques in portions of California (Hunter 2007). Hindman et al (2006) noted that the trend over the past 20 years, from cloud droplet measurements at Storm Peak in the northern Rockies, has shown a decrease in CCN and an increase in cloud drop size. The conclusion was a decrease in upwind CCN concentrations (less pollution) but no relationship was found with precipitation rate. Thus, the change in cloud droplet spectra was not impacting riming growth efficiency (Borys et al 2003). It was noted by Creamean (2013) that pollutants, such as from human activity, were found mostly in the boundary layer and with frequently higher concentrations preceding surface cold fronts. The pollutants become trapped in the stable air as the air warms aloft and surface flows tend to be from the southeast to east tapping polluted sources from the central valley of CA. Once the front passed, the air-mass off the ocean did not contain these pollutants. It is the post–frontal cloud systems that have been identified as the most seedable in the northern and central Sierra (Heggli and Reynolds, 1985). It is not anticipated that pollutants play a significant role in these post-frontal shallow orographic clouds.

It should be noted that a more recent survey article by Tanre’ et al (2009), reviewed the impact of aerosols on precipitation and concluded: “Even though we clearly see in measurements and in simulations the strong effect that aerosol particles have in cloud microphysics and development, we are not sure what is the magnitude or direction of the aerosol impact on precipitation and how it varies with meteorological conditions. Even the most informative measurements so far on the effect of aerosols on precipitation do not include simultaneous quantitative measurements of aerosols, cloud properties, precipitation and the full set of meteorological parameters.”

Thanks to Tanre’ et al. (2009)!

The current CALWATER II experiment running this winter in California is an attempt to provide such information.

(Did it?)

The main limitation is very similar to the problems inherent in quantifying the impacts of artificial seeding of winter orographic clouds. That is the observing systems that we apply to quantifying the impacts have large measurement uncertainties and are of a magnitude similar to the expected aerosol influence on precipitation. Tanre’ notes that satellite and radar measurements have 20-30% errors in the measurement of aerosol optical depth, while aircraft sampling in-cloud can introduce changes in the cloud that can compromise the utility of the aircraft observations. In-deed measurements of surface precipitation, especially snowfall water equivalent can have 10-15% measurement uncertainty given gauge location and thus exposure to wind, minimum threshold/resolution, and such problems as capping. These types of measurement uncertainties require longer term on-going statistical analyses to reduce the random noise in the observations much like is required for cloud seeding experiments, thus reducing the influence of measurement uncertainty so as to extract the small signal that might exist. 

1.7.1.3 Artificial Stimulation of Snowfall by Seeding Agents

Artificial stimulation of snowfall is conducted through the application of aerosols that mimic natural ice nuclei to enhance the heterogeneous freezing of available SLW or by chilling the air below -40 oC to initiate homogenous nucleation. It is well known that the effectiveness of the heterogeneous seeding agent is highly temperature dependent. Artificial cloud nucleating substances (AgI, CO2, Liquid propane, SNOWMAX) are dependent on the presence of SLW at temperatures slightly below 0 oC for CO2, propane, and SNOWMAX (Ward and Demott 1989) or below -5 C to -8 oC for AgI mixtures (Figure 1.6). 

Figure 1.6 – Seeding activation versus temperature for seeding agents that have been used or proposed

These seeding agents act in different ways. Solid or liquid CO2 and liquid propane work by homogenous nucleation. These seeding agents need to be directly released in the presence of SLW for them to be effective. AgI and SNOWMAX work by heterogeneous nucleation, meaning they mimic the structure of natural ice nuclei. They do not have to be released directly into cloud or SLW. The aerosol can be carried aloft into clouds and when it encounters SLW at the right temperatures will begin generating ice crystals by contact nucleation. As shown in Figure 1.6, SNOWMAX works at the warmer (higher) end of the SLW temperature spectrum and its effectiveness does not vary greatly with temperature. To the author’s knowledge, SNOWMAX is not used in any operational seeding program but is used almost exclusively for snowmaking at ski resorts. The effectiveness of AgI to nucleate ice crystals increases by orders of magnitude from -5 oC to -12 oC (Super 2005). It should be noted that under transient water supersaturations, AgI can activate more rapidly and at temperatures near -5 oC through the condensation freezing mechanism (Pitter and Finnegan 1987). Chai (1993) explained the only way AgI could have been an effective seeding agent in the Lake Almanor seeding experiment (Moony and Lunn 1969) was through the fast activating condensation freezing process.

Mooney and Lunn (1969)… The westerly case where it was reported there had been large increases in snow reported due to seeding, was not reported for Phase II of the Lake Almanor experiment (Bartlett et al. 1975u). This omission should be unsettling to any objective scientist.

If the AgI is burned below cloud base or at temperatures warmer than -5 o C, the aerosol will not produce sufficient ice embryos until temperatures colder than -8 oC are reached (Super and Heimbach 2005). Huggins (2009) found the best temperatures for SLW in the Bridger Range Experiment occurred at < -9 oC using AgI, which suggests the AgI acted through contact or deposition nucleation. The central reason to explore propane seeding is its characteristic to be effective in mildly supercooled clouds that would be too warm for AgI. Propane dispensers tend to be more reliable, less complicated and less expensive than AgI generators. SLW temperatures in CO frequently range from -4 to -13 oC depending upon location and elevation (Boe and Super 1986; Rauber and Grant 1986; Huggins 1995; Super 2005; Huggins 2009). Due to the mildly supercooled nature of some CO locations, propane could be a useful alternative to AgI generators (Boe and Super 1986; Hindman 1986). The cloud base in California is often warmer than 0 oC while the top of the SLW near the mountain crest is usually > -12 oC (Heggli et al. 1983; Heggli and Rauber 1988; Huggins 2009). This is why propane was adopted by Reynolds (1995) as the seeding agent of choice in the Lake Oroville Runoff Enhancement Program (LOREP) in northern California (see Figure 1.4b). 

Cloud base altitude is an important consideration when siting propane dispensers which must be in-cloud or just below cloud base (at ice saturation) to be effective (Super 2005). Super and Heimbach (2005) indicate that even in the intermountain region, a significant number of hours with SLW are at temperatures where the release of AgI at elevations below -5 oC and out of cloud would not reach elevations cold enough to activate a sufficient quantity of the AgI to effectively “seed” the cloud and produce meaningful increases in snowfall. Thus, the 300 to 600 hours of reported SLW over the intermountain region during the 5 month snowfall season would require a mixture of seeding delivery methods including a mixture of high elevation ground released AgI and liquid propane or seeding from multiple aircraft. 

All weather helicopters with ceilings above 20,000 feet ASL  might be useful for targeting small watersheds when shallower clouds are present.

1.7.2 Transport and Dispersion of Seeding Material

1.7.2.1 Ground Releases 

Flow over complex terrain is not a simple and straightforward problem therefore making targeting a challenge. Trying to disperse AgI from ground based generators has proven to be very difficult (Super and Heimbach 2005). There are two critical issues here. One is whether a parcel of air starting out near the foothills or a valley location will be carried over the mountain in the prevailing wind direction or whether it will flow around the mountain. This is determined by the static stability of the air mass and the strength of the flow perpendicular to the mountain, often noted by the Froude number. When the velocity of the flow is strong enough to overcome the air parcels static stability, a Froude number greater than 1 is produced, meaning the parcel of air will pass over the mountain and not flow around the mountain. The depth of the boundary layer is also very important as ground based cloud seeding efforts are located within this layer. If AgI is released below cloud or at temperatures warmer than -5 oC, the aerosol will have to be carried up into the cloud to a level where the temperature is colder than -8 oC. If the boundary layer is shallow and does not allow the aerosol to reach the appropriate temperature level or that level is reached very near the crest of the mountain, there will be no impact on the windward slopes of the mountain. The depth of the boundary layer is a function of low level wind shear (Xue 2014), which is the change in direction or velocity of wind with height. The stronger the wind shear, the greater the depth of the boundary layer. Strong low level flow perpendicular to the mountain, along with strong wind shear and at times weak embedded convection, will provide the mechanism for lifting the aerosol up the mountain. This allows dispersal of the aerosol to seed more cloud volume. If the temperatures are cold enough and SLW is continuous, an increase in snowfall will occur on the windward slopes and increase the precipitation efficiency of the orographic cloud. The targeting issue has been described by many weather modification researchers (Super and Heimbach 2005; Reynolds 1988; Warburton et al. 1995a and b) as the single most critical issue that has compromised the success of both operational as well as research field projects. Again, reason to emphasize that effective cloud seeding is an engineering problem. 

It has been shown that ample seeded crystals with sufficient concentration need to be dispersed so that a substantial volume of cloud over the target is treated for more than trace snowfall rates to occur (Super 2005; Huggins 2009). The seeding material must be injected into the SLW in sufficient quantities to generate 50 to 100/L or more initial ice embryos. This will then utilize the available SLW and fall out of the cloud prior to the snowflakes passing over the summit of the mountain and sublimating in the lee of the mountain. An example of the use of a rather simple targeting model (GUIDE, Rauber et al , 1988) used in the Lake Oroville Runoff Enhancement Project (LOREP ) to target ground-based liquid propane seeding effects is shown in Figure 1.7. This project used the tracer SF6 co-released with the propane from two sites to validate the GUIDE and assure accurate targeting. The GUIDE plumes as shown both horizontally and vertically along with the vertical motion field from a locally released rawinsonde. 1.7.2.2 Seeding from Valley Locations Many operational cloud seeding projects have placed AgI generators in valley locations as they are easily accessible and can be manually ignited when needed. However, a considerable body of evidence indicates valley released AgI plumes are often trapped by stable air (high static stability), especially when valley-based inversions are present (Langer et al. 1967; Rhea 1969-cited but does not appear in Reynolds references; Super 2005). Often times in past projects AgI plumes from valley located generators were not tracked sufficiently to determine exactly where the aerosol plumes drifted (Smith and Heffernan 1967; Super 2005). As noted earlier, this is a recurring issue that has been raised in many winter orographic cloud seeding articles ( Elliott et al. 1978u, Rangno 1979u; Reynolds 1988; Super 2005; Hunter 2007; Huggins 2009). The aerosols may pool in the valley or may move in a direction around the mountain, only to be carried aloft when the static stability of the airmass decreases and low level winds increase. This usually occurs near and behind the surface cold fronts associated with winter storms. Thus, the AgI aerosol may travel far distances from the target but is unlikely to have appreciable effects far from a target due to the low concentrations that eventuate after many hours or days of travel. 

1.7.2.4 Seeding from Airplanes or Helicopters

Seeding by aircraft can be an alternative mechanism in locations where there is insufficient time to activate the seeding agent and grow the crystals to sufficient size for fallout to occur on the windward slopes of the barrier. These situations mainly occur within coastal mountains where the SLW near the crest of the mountain is only slightly sub-cooled. Typically the clouds extend up to a kilometer above and well upwind of the crest such that cloud top temperatures are -6 oC to -8 oC or lower. In these situations, the aircraft or helicopter can fly (hover above) in the tops of the clouds and either drop crushed dry ice, AgI droppable flares, or ignite AgI wing-tip generators or stationary flares that will directly inject the seeding material into the cloud. The dispersion would be especially enhanced in the downwash below a helicopter. Using crushed dry ice or droppable flares will create a curtain of ice crystals some 1000 m below the aircraft. This will spread at a rate of 1-2 m/s dependent upon the amount of vertical wind shear (Borovikov et al. 1961u, Hill 1980; Reynolds 1988). For these seeding curtains to merge together over the intended target area, the length of the seed line cannot be more than 30 to 40 km long (Deshler et al. 1990). However, the watershed of a large river basin can be several hundred kilometers wide. One aircraft will treat only a small portion of the watershed (see Figure 1.8). In addition, the duration of the seeding aircraft is usually about 2 to 4 hours, with the possibility of the aircraft having to descend to deice several times during the seeding mission. Aircraft operations are also expensive. For these reasons, many operational seeding programs use ground based seeding platforms, even if they are only viable a small percentage of the time. 

1.7.4 Extended Area Effects fromWinter Orographic Cloud Seeding (ones that have not been sufficiently investigated for lucky draws/synoptic biases)

The reason why I added this to the title is that I deem this part of the survey the weakest part.  No one talks about how low the concentrations of AgI would be in far away, so-called downwind affected regions, and god save anyone who looks at synoptics for a bias! Meltesen et al.(1978) did look at synoptic bias for the claimed downwind seeding increases from Climax and look what they found;  a synoptic bias that produced the illusion of downwind increases in snow!

Hunter (2009) prepared an extensive literature review of the current state of knowledge on extra or extended area effects from winter orographic cloud seeding. The main impetus for this report was to present any documented evidence that determined that seeding on one mountain barrier resulted in a possible reduction of the amount of precipitation downwind. This has been coined “Robbing Peter to pay Paul”. Hunter provided the following table which is reproduced here (not all references are included in Section 6). In every case, the seeding agent was silver iodide. These results indicate that once the AgI nuclei are released into the atmosphere, they can remain active for many hours, if not several days. If pooled in high concentrations, the AgI nuclei can seed areas well away from the intended target areas. However, the impacts of these extra-area effects are just as uncertain as the increase documented in the primary target areas. That is, without strong physical observations to compare with rigorous statistical analyses, there is still a significant level of uncertainty as to the efficacy of seeding with AgI to increase precipitation within large areas outside the intended target area. 

Table 1.2 here

The little bit of seeding (hour long pulses) or in six h blocks during the last season of the Park Range Project, made this claim ludicrous.  By 1979 it was recognized that a Type I statistical error (Mielke 1979u) affected both Climax experiments.  One of the interesting facets of Climax I that  prevented the seeding researchers from recognizing a Type I error was attributing heavier snow on seeded days upwind of Climax to seeding at Climax (Kahan et al. 1969u) 

1.7.5 Statistical Analyses

Statistical analyses have been a key part of assessing past cloud seeding experiments. Credence has usually only been given to those experiments that have been randomized and run as a confirmatory experiment. Key historical projects such as Climax and the series of Israeli cloud seeding experiments run as confirmatory, and meeting or exceeding the level of statistical significance set out in the experimental design, have come under further scrutiny and found to suffer from what is called Type 1 errors (Mielke 1979u; Rhea 1983; Rangno and Hobbs 1987u, 1993; Rangno and Hobbs 1995a,u,  b; Rosenfeld 1997, Rangno and Hobbs 1997a,u, b u).

Rosenfeld’s (1997) “Comments” cited by Reynolds were replied to by Rangno and Hobbs (1997a,u) in short form, and “Comprehensively” at the Cloud and Aerosol Research Group’s website. This dual approach was favored by Professor Peter V. Hobbs.

http://carg.atmos.washington.edu/sys/research/archive/1997_comments_seeding.pdf

Its surprising that Dr. Reynolds did not know of our responses to Dr. Rosenfeld’s many specious comments

============================

Some background on the Israeli work I did: these many exchanges led the Israel National Water Authority to form an independent panel to evaluate its operational seeding program targeting Lake Kinneret (aka, Sea of Galilee), Israel’s primary water source (Y. Goldreich, 2018, personal communication). The expert panel  that was constituted could find no evidence of increased rain the in the catchment of Lake Kinneret between 1975 and 2002  (Kessler et al. 2006).  The independent panel’s findings reversed the optimistic findings of Nirel and Rosenfeld (1995) of a statistically significant 6% increases in rain through 1990. The panel could also not replicate the 6% increase reported by Nirel and Rosenfeld using the same control stations.  Here is what Kessler et al. (2006) reported in graphical form. 

Why is this Israeli discussion important in Reynolds’ review?

The preliminary findings shown in this figure caused Rosenfield to immediately look for an “out,” and with more than 500 standard gauges and 82 recording gauges in Israel (!)  he found it by cherry-picking and claiming what Reynolds suggests in his review: air pollution was decreasing rain as much as cloud seeding was increasing it.  Givati and Rosenfeld’s conclusions did not stand up to independent investigators as was documented earlier, nor by the subsequent investigations for California cited by Reynolds.

This is typical in scientific statistical testing. It is considered less incorrect to not detect a relationship when one exists rather than detect a relationship when one does not exist. Other statistical methods, such as the use of covariates, can be useful in determining the statistical success of seeding operations (Dennis 1980; Mielke et al. 1981; Gabriel 1999; Gabriel 2002; Huggins 2009). A problem common to the statistical method of historical regression is the assumption that climate has been stable over many decades (Hunter 2007) which is called stationarity, and not declaring covariates in advance of experimentation.

1.8 Summary 

From the information summarized above it is worth reviewing the key questions as outlined for winter orographic clouds as listed in Table 1.1. 

What is the location, duration, and degree of supercooling of cloud liquid water in winter orographic clouds? 

•Concentrated in the lowest km on the windward slopes of mountain (Super andHeimbach, 2005)

•Highly variable in space and time given fluctuations in wind speed/direction and naturalprecipitation processes.

•Higher concentrations and higher frequency of SLW at warmer (sic) (higher) temperatures for all mountain ranges•SLW >.05 mm vertical integrated has been used as lower threshold for cloudseeding initiation.

Are their man-made pollutants or natural aerosols/particulates impacting the target clouds that could modify the cloud droplet spectra/IN concentrations to impede seeding effectiveness? 

•Pollutants acting as CCN can narrow the droplet spectrum and slow down the collision coalescenceprocess (warm rain) reducing rainfall downwind of major pollution sources.(Rosenfeld 2000; Givati and Rosenfeld 2004; Givati and Rosenfeld 2005.  See earlier discussion of the latter report.)

•It was found in SCPP that SIP (secondary ice production) produced high ice concentrations at relatively high cloud top temperatures (-5 to -10 oC)

•If pollutants narrow the droplet spectrum, then pollutants in theory should reduce SIP.

Mossop (1978u) found that increases in small (<14 um diameter) droplets combined with those >23 um diameter increased the efficiency of the riming-splintering process.  So it is possible, with the presence of larger droplets say, due to seaborne or other large aerosols combined with pollution sources, that the Hallett-Mossop riming-splintering process is enhanced.

•If high concentrations of pollution produce high concentration of cloud droplets in a narrow size range, this could reduce riming and reduce snowfall on the windward slopes of narrow mountain ranges where growth times are critical.

•A more recent survey article on the role of pollution on clouds and precipitation (Tanre’, 2009) concluded it was still uncertain as to the magnitude of the impact of pollution or whether pollution increases or decreases precipitation based on the meteorological setting.

•Dust (Saharan and Gobi desert) and aerosols (bacteria) acting as IN can enhance natural s

Are their significant enough differences in maritime influenced winter orographic clouds versus continental orographic clouds that strongly influence the natural precipitation process? 

•Yes. Maritime clouds with broader drop size distributions are subject to SIP and thus clouds are more efficient at higher temperatures.

•Continental clouds have relatively more SLW at lower temperatures given the lack of SIP.

•Evidence of this is well-documented when one compares SCPP and Washington studies with interior mountain studies.

====================End of Comments and Corrections  by ALR==========================

References that were uncited in the Reynolds review but were mentioned in this “review and enhancement.”

Alpert, P., N. Halfon, and Z. Levin, 2008: Does air pollution really suppress precipitation in Israel?  J. Appl. Meteor. Climatology, 47, 943-948.

Alpert, P., N. Halfon, and Z. Levin, 2009:  Reply to Givati and Rosenfeld.  J. Appl. Meteor. Climatology, 48, 1751-1754.

Auer, A. H., D. L. Veal, and J. D. Marwitz, 1969: Observations of ice crystals and ice nuclei observations in stable cap clouds.  J. Atmos. Sci., 26, 1342-1343.

Ayers, G., and Levin, 2009:  Air pollution and precipitation.  In Clouds in the Perturbed Climate System.  Their Relationship to Energy Balance, Atmospheric Dynamics, and Precipitation. J. Heintzenberg and R. J. Charlson, Eds.  MIT Press, 369-399.

Bartlett, J. P.,  M. L. Mooney, and W. L. Scott, 1975:  Lake Almanor cloud seeding program.  Preprint, San Francisco Conference on weather modification, Amer. Meteor. Soc., 106-111.

Benjamini, Y, A. Givati, P. Khain, Y. Levi, D. Rosenfeld, U. Shamir, A. Siegel, A. Zipori, B. Ziv, and D. M. Steinberg, 2023:  The Israel 4 Cloud Seeding Experiment: Primary Results.   J. Appl. Meteor. Climate, 62, 317-327.  https://doi.org/10.1175/JAMC-D-22-0077.1

Borovikov, A. M., I. I. Gaivoronsky, E. G. Zak, V. V. Kostarev, I. P. Mazin, V. E. Minervin, A. Kh. Khrgian and S. M. Shmeter, 1961:  Cloud Physics. Gidrometeor. Izdatel. Leningrad. (Available from Office of Tech. Serv., U. S. Dept. of Commerce.)

Cooper, W. A., and G. Vali, 1981:  The origin of ice in mountain cap clouds.  J. Atmos. Sci., 38, 1244-1259.

Cunningham, R. M., 1957:  A discussion of generating cell observations with respect to the existence of freezing or sublimation nuclei.  In Artificial Stimulation of Rain, H. Weickmann, Ed.  Pergamon Press, NY.,  267-270.

Elliott, R. D., R. W. Shaffer, A. Court, and J. F. Hannaford, 1978:  Randomized cloud seeding in the San Juan Mountains, Colorado.  J. Appl. Meteor., 17, 1298–1318.

Foster, K. R., and P. W. Huber, 1997: Judging  Science–Scientific Knowledge and the Federal Courts.  The MIT Press, Cambridge, MA, 333pp.

Grant, L. O., and P. W. Mielke, Jr., 1967: A randomized cloud seeding experiment at Climax, Colorado 1960-1965.  Proc. Fifth Berkeley Symposium on Mathematical Statistics and Probability, Vol. 5, University of California Press, 115-131.

Grant, L. O., Chappell, C. F., Crow, L. W., Mielke, P. W., Jr., Rasmussen, J. L., Shobe, W. E., Stockwell, H., and R. A. Wykstra, 1969:  An operational adaptation program of weather modification for the Colorado River basin.  Interim report to the Bureau of Reclamation, Department of Atmospheric Sciences, Colorado State University, Fort Collins, 98pp.

Halfon, N., Z. Levin, P. Alpert, 2009:  Temporal rainfall fluctuations in Israel and their possible link to urban and air pollution effects.  Environ, Res. Lett., 4, 12pp. doi:10.1088/1748-9326/4/2/025001

Hobbs, P. V., and A. L. Rangno, 1979: Comments on the Climax randomized cloud seeding experiments.   J. Appl. Meteor., 18, 1233-1237.

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Kessler, A., A. Cohen, D. Sharon, 2003:  Analysis of the cloud seeding in Northern Israel.  Interim report submitted to the Israel Hydrology Institute and the Israel Water Management of the Ministry of Infrastructure.

Kessler, A., A. Cohen, D. Sharon, 2006:  Analysis of the cloud seeding in Northern Israel. Final report submitted to the Israel Hydrology Institute and the Israel Water Management of the Ministry of Infrastructure, In Hebrew with an English abstract. 117pp.

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Mielke, P. W., Jr., L. O. Grant, and C. F. Chappell, 1970: Elevation and spatial variation effects of wintertime orographic cloud seeding. J. Appl. Meteor., 9, 476–488; Corrigendum, 10, 842; Corrigendum, 15, 801.

Mielke, P. W., Jr., Grant, L. O., and C. F. Chappell, 1971:  An independent replication of the Climax wintertime orographic cloud seeding experiment.  J. Appl. Meteor., 10, 1198-1212.

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Rangno, A. L., 1979:  A reanalysis of the Wolf Creek Pass cloud seeding experiment.   J. Appl. Meteor., 18, 579–605.

Rangno, A. L. and P. V. Hobbs, 1980: Comments on “Randomized cloud seeding in the San Juan Mountains, Colorado,” J. Applied Meteorology, 19, 346-350. 

Rangno, A. L., and P. V. Hobbs, 1987: A re-evaluation of the Climax cloud seeding experiments using NOAA published data.  J. Climate Appl. Meteor., 26,  757-762.

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https://doi.org/10.1175/1520-0450(1997)036%3C0272:R%3E2.0.CO;2

Rangno, A. L. and P. V. Hobbs, 1997b: Comprehensive Reply to Rosenfeld, Cloud and Aerosol Research Group, Department of Atmospheric Sciences, University of Washington, 25pp.  http://carg.atmos.washington.edu/sys/research/archive/1997_comments_seeding.pdf

Rasmussen, R. M., S. A. Tessendorf, L. Xue, C. Weeks, K. Ikeda, S. Landolt, D. Breed, T. Deshler, and B. Lawrence, 2018: Evaluation of the Wyoming Weather Modification Pilot Project (WWMPP) using two approaches: Traditional statistics and ensemble modeling. J. Appl. Meteoro. Climatol., 57, 2639–2660, https://doi.org/10.1175/JAMC- D-17-0335.1.

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Vardiman, L, and J. A. Moore, 1978: Generalized criteria for seeding winter orographic clouds. J. Appl. Meteor., 17, 1769-1777.

A Review and Enhancement of Chapter 8 in the book, “Aerosol Pollution Impacts on Precipitation:  A Scientific Review” 

PROLOGUE

Below is the impressive list of “Scientific Reviewers” of this volume before this belated review by yours truly happened, ones listed in the 2009 Springer book,  “Aerosol Pollution Impacts on Precipitation:  A Scientific Review.”  The authors of this book, including Chapter 8, had to review an enormous amount of literature which the reviewers also had to know in great detail.

From a reading of this book in those areas of my expertise, such a task is too much despite the authors’ valiant efforts to “get it right.”  Chapter 8  is an example of the problem of having too much to review and not enough time to scrutinize the details of so much literature in one topic.  Chapter 8 is well-written, most of the necessary citations are in it that help the reader to understand the topic.    It does an outstanding job of making a case about the, “Parallels and Contrasts” in deliberate seeding and aerosol pollution.  That is,  except for those elements in Chapter 8 that I am perhaps, a little too familiar with and feel must be addressed in this VERY belated review.

“Too familiar?”

That’s what happens to someone who has spent thousands of volunteer hours (crackpot alert!) rectifying faulty cloud seeding and cloud claims in peer-reviewed journal articles because he felt, “Someone has to do something about this!” (Second crackpot alert, possibly with megalomaniacal implications.)

It goes without saying that I was not asked to review Chapter 8 before it was published.  This would have made these comments unnecessary.  I was well known by the authors of this review as an expert on clouds, cloud seeding, and the weather in the two regions where landmark experiments are reviewed in Chapter 8; those in Colorado and Israel .   With Professor Peter V.  Hobbs in tow, I dissected those landmark experiments in Colorado and Israel and showed they were, as Foster and Huber (1997) described faulty science,  “scientific mirages.”  In fact, they were “low-hanging fruit” that poor peer reviews of manuscripts had let in the journals.  It didn’t take a genius to unravel them.

I read this chapter only recently after I was given the book by one of its authors.  I wondered if Chapter 8 had been reviewed at all by any of the illustrious reviewers listed by Springer since some oversights are so egregious.  However, I was pleased to see that almost all of my work with Prof. Hobbs on those benchmark experiments was cited, except the one I deemed most important.  Odd.

Some background 

Chapter 8 was originally assigned to Prof. Peter V. Hobbs, the director of my group at the University of Washington.  He was going to use portions of a rejected manuscript of mine on cloud seeding  and peer-review entitled, “Cloud Seeding and the Journal Barriers to Faulty Claims: Closing the Gaps.”  He described the segments he was going to use, the rise and fall of the Colorado and Israeli cloud seeding experiments, as, “pretty good.”   Peter was not easy to please.  That was the highest compliment I had ever received from him for my writing.   The manuscript, submitted in 1997,  was ultimately rejected in 1999 by the Bull. Amer. Meteor. Soc., I. Abrams, Editor,  and again in an updated version by  Advances in Meteorology in 2017 as “not the kind of paper we were looking for” in their issue on weather modification (L. Xue, Editor, personal communication).    But maybe its the kind you were looking for!  So, in a sense that manuscript has been rejected twice, sometimes the sign of something especially good.   (Off topic! Get Back, “Jojo,” as the Beatles sang.

Due to pancreatic cancer, Prof. Hobbs was unable to do this piece chapter and Prof. William R. Cotton, Colorado State University, who later has become a close friend,  took over with the additional “contributors” according to Springer,  Dean Terblanche, Zev Levin, Roelof Bruintjes, and Peter Hobbs, as listed by Springer, and all of whom I greatly admire, making these comments “difficult;” “Why am I doing this?”  Etc.

For review purposes, I have copied under the rubric of “fair use,” only those portions of Chapter 8 relevant to my expertise.   To repeat, overall, its a good review.  However, I have added commentaries in a red font following the original statements of the authors (black font) that need clarification, correction, or additions.  References to relevant articles that went uncited in Chapter 8 have been added at the end of this review and are appended with a “u” for uncited.  I have added after those all the references that WERE cited in this review and appear in the original text.  Mielke (1976) cited by the authors, does not appear in the list of their references.

========================================

List of illustrious reviewers of the Springer volume:

Chairperson: Dr.George IsaacEnvironment Canada.                       (Name, affiliation, country).

Ayers, Greg,  CSIRO Marine and Atmospheric Research, Australia

Barth, Mary, National Center of Atmospheric Research, USA

Bormann, Stephan,  Johannes-Gutenberg-University, Germany

Choularton, Thomas, University of Manchester, UK.

DeMott, Paul, Colorado State University, USA.

Flossmann, Andrea, Laboratoirede Mitiorologie Physique/OPGC Universiti: Blaise Pascal/C RS, France

Kahn, Ralph, Jet Propulsion Laboratory, USA

Khain, Alexander, The Hebrew University ofJerusalem, Israel

Leaitch, Richard, Environment Canada, Canada

Pandis, Spyros, University of Patras, Greece

Rosenfeld, Daniel, The Hebrew University ofJerusalem, Israel.

Ryan, Brian, CSIRO Marine and Atmospheric Research, Australia

Twohy, Cynthia, Oregon State University, USA.

Vali, Gabor, University of Wyoming, USA.

Yau,  Peter, McGill University, Canada

Zipser, Ed, University of Utah, USA

=============================================

….and now, very belatedly reviewing Chapter 8, yours truly, the less illustrious,  Arthur L. Rangno,  retiree,                                                                                                                                                                                                Research Scientist IV, Cloud and Aerosol Research Group, Atmospheric Sciences Department, University of Washington, USA:

================

Chapter 8 in Aerosol Impacts on Precipitation:“Parallels and Contrasts Between Deliberate Cloud Seeding and Aerosol Pollution Effects”

8.1    Deliberate cloud seeding, with the goal of increasing precipitation by the injection of specific types of particles into clouds, has been pursued for over 50 years. Efforts to understand theprocesses involved have led to a significant body of knowledge about clouds and about the effects ofthe seeding aerosol. A number of projects focused on the statistical evaluation of whether a seeding effect can be distinguished in the presence of considerable natural variability. Both the knowledge gained from these experiments, and the awareness of the limitations in that understanding, are relevant to the general question of aerosol effects on precipitation. Definite proof from the seeding projects for an induced increase in precipitation as a result of the addition of seeding material to the clouds would represent a powerful demonstration of at least one type of dominant aerosol­ precipitation link in the clouds involved. Therefore, in this chapter we review the fundamental conceptsof cloud seeding and overview the parallels and contrasts between evaluations of deliberate and inadvertent modification of precipitation by aerosols. It is not our intent to provide a comprehensive assessment of the current status of cloud seeding research. We direct the reader to more compre­hensive weather modification assessments in NRC (2003), Cotton and Pielke (2007), Silverman (2001, 2003),and Garstang et al. (2005).

Deliberate cloud seeding experiments can be divided into two broad categories: glaciogenic seeding and hygroscopic seeding. Glaciogenic seeding occurs when ice-producing materials (e.g. dry ice (solid CO2), silver iodide, liquid propane etc.) are injected into a supercooled cloud for the purpose of stimulating precipitation by the ice particle mechanism (see Sect. 2.2). The underlying hypothesis for glaciogenic seeding is that there is commonly a deficiency of natural ice nuclei and therefore insufficient ice particles for the cloud to produce precipitation as efficiently as it would in the absence of seeding.

The second category of artificial seeding experiments is referred to as hygroscopic seeding. In the past this type of seeding was usually used for rain enhancement from warm clouds (see Cotton 1982 for a review of early hygroscopic seeding research).

However, more recently this type of seeding has been applied to mixed phase clouds as well. The goal of this type of seeding is to increase the concentration of collector drops that can grow efficiently into raindrops by collecting smaller droplets and by enhancing the formation of frozen raindrops and graupel particles. This is done by injecting into a cloud (generally at cloud base) large or giant hygroscopic particles (e.g., salt powders) that can grow rapidly by the condensation of water vapour to produce collector drops (see Sect. 2.3).

Static Glaciogenic Cloud Seeding

Static cloud seeding refers to the use of glaciogenic materials to modify the microstructures ofsupercooled clouds and precipitation. Many hundreds of such experiments have been carried over the past 50 years or so. Some are operational cloud seeding experiments (many of which are still being carried out around the world) which rarely provide sufficient information to decide whether or not they modified either clouds or precipitation. Others are well designed scientific experiments that provide extensive measurements and modeling studies that permit an assessment of whether artificial seeding modified cloud structures and, if the seeding was randomized, the effects of the seeding on precipitation. While there still is some debate of what constitutes firm “proof”(see NRC 2003; Garstang et al. 2005) that seeding affects precipitation, generally it is required that both strong physical evidence of appropriate modifications to cloud structures and highly significant statistical evidence be obtained.

My comprehensive, “critical” review and enhancement of NRC 2003 is here.  Compared to the 1973 NRC review, the NRC 2003 one was merely a superstructure, a Hollywood movie set, not the real deal.  

The reason?  

Too much literature to review in depth even for the illustrious authors of the NRC 2003 report.   Professor Garstang did ask my boss, Prof. Peter V. Hobbs to participate in the 2003 review, but he declined the offer telling me that it would be better if we “commented” on the 2003 review after it was published if necessary.  I nodded and went back to my desk.  Peter usually knew best.  Fate intervened.  Peter came down with pancreatic cancer and our review  of the 2003 report never happened until I got to it years later.

  • Glaciogenic Seeding of Cumulus Clouds

The static seeding concept has been applied to supercooled cumulus clouds and tested in a variety of regions. Two landmark experiments (Israeli I and Israeli II), carried out in Israel, were described in the peer-reviewed literature. The experiments were carried out by researchers at the Hebrew University of Jerusalem (HUJ), hereafter the experimenters. These two experiments were the foundation for the general view that under appropriate conditions, cloud seeding increases precipitation (e.g. N.R.C. 1973; Sax et al. 1975; Tukey et al. 1978a, b; Simpson 1979; Dennis 1980; Mason 1980,1982; Kerr 1982; Silverman 1986; Braham 1986; Cotton 1986a, b; Cotton and Pielke 1992, 1997; Young1993).

Nonetheless, reanalysis of those experiments by Rangno and Hobbs (1993-sic) suggested that the appearance of seeding-caused increases in rainfall in the Israel I experiment was due to “lucky draws” or a Type I statistical error.

The correct year for Rangno and Hobbs is 1995, not 1993 .   Having the wrong year in a reference is a not a good sign right off the bat.  

The first evidence for a lucky draw in Israeli I was presented by Wurtele (1971u) when she reported that the little seeded Buffer Zone between the two targets exhibited the greatest statistical significance in rainfall in either target on Center seeded days.  Wurtele (1971u) quoted the Israeli I chief meteorologist that the Buffer Zone could only have been inadvertently seeded but 5-10% of the time, and “probably less.”  Wurtele should have been cited.  The wind analysis when rain was falling at the launch site near the BZ in Rangno and Hobbs (1995) supports the chief meteorologist’s view.  It would have taken a very bad pilot to have seeded the BZ if he had been instructed not to.

Furthermore, Rangno and Hobbs (1993 sic) argued that during Israel II naturally heavy rainfall over a wide region encompassing the north target area gave the appearance that seeding caused increases in rainfall over the north target area.

The first evidence for naturally heavy rain over a wide region in Israel II, including both targets on north target seeded days, was presented by Gabriel and Rosenfeld (1990u), a critical article  that somehow that went uncited by the authors of Chapter 8.   Gabriel and Rosenfeld stated that the degree of heavy rain on north target seeded days in the south target, from a historical study, was “clearly statistically significant.” 

Rangno and Hobbs (1995) added to that evidence by analyzing rainfall over wide region that included Lebanon and Jordan on north target seeded days.  The Rangno and Hobbs (1995) analysis corroborated the statement by Gabriel and Rosenfeld (1990) concerning a lopsided draw on north target seeded days of Israeli II that affected most of Israel.  In fact, the greatest apparent effect of cloud seeding on north target seeded days was in the south target at Jerusalem (Rangno and Hobbs 1995)!

Deeply troubling, too,  is why the “full results” of the Israeli II experiment by Gabriel and Rosenfeld (1990u) was not cited in a supposed review of those experiments.  The null result of the “full analysis” of Israel II which incorporated random seeding in the South target,  had been omitted in previous reporting by Gagin and Neumann (1976u, 1981).  The “full” results reported by Gabriel and Rosenfeld (1990u) was an extremely important development:  Israeli II had not replicated Israeli I when evaluated in the same way.  Furthermore, the a priori design of Israeli II specified by the Israel Rain Committee mandated that a crossover evaluation be carried out (Silverman 2001).

However, the null result of Israeli II left some questions in the minds of Gabriel and Rosenfeld (1990u).  Were actual rain increases in the north canceled out by decreases in rain on seeded days in the south target resulting in a null overall result?

This idea was later posited by Rosenfeld and Farbstein (1992) as a valid explanation and the disparate results was attributed to dust/haze.  This hypothesis ignored the fact that unusually heavy rain fell on the south target when the north was being seeded.   This left little chance for the south target’s seeded days to overcome this lopsided disadvantage, thus  leaving the impression that seeding had decreased rainfall when rainfall on the control and seeded days in the south target were compared.  Why this was not clear remains a puzzle.

At the same time, lower natural rainfall in the region encompassing the south target area gave the appearance that seeding decreased rainfall over that target area. But this speculation could not explain the positive effect when the north target area was evaluated against the north upwind control area.

Levin et al. 2010u (and unavailable to these authors) also reanalyzed Israeli II and found that a synoptic bias had produced the misperception of seeding effects downwind from the coastal control region mentioned above.    Levin et al’s 2010u conclusions corroborated the Rangno and Hobbs (1995) evaluation of Israeli II described inappropriately as “speculation” by the authors of Chapter 8.  

Details of this controversy can be found in the March 1997 issue of the Journal of Applied Meteorology (Rosenfeld 1997; Rangno and Hobbs 1997a; Dennis and Orville 1997; Rangno and Hobbs1997b; Woodley 1997; Rangno and Hobbs 1997c;  Ben-Zvi 1997; Rangno and Hobbs 1997d; Rangno and Hobbs 1997e). Some of these responses clarified issues; others have left a number of questions unanswered.

The authors should have indicated for the reader what questions were left unanswered.  

However, the exchanges between pro-seeding partisans and Rangno and Hobbs (1997) were extremely important because they led the Israel National Water Authority to form an independent panel of experts to ascertain what the result of operational seeding of the watersheds around Lake Kinneret (aka, Sea of Galilee) was over the decades.  Operational seeding began during the 1975/76 rain season.

The reports of the independent panel (Kessler et al. 2002u, 2006u) were apparently unknown to the authors of this review.  Key elements of the final 2006 report were reprised by Sharon et al. (2008u):  Twenty-seven winter seasons  (75/76 through 01/02)  of operational seeding had not led to an indication that rain had been increased, due to cloud seeding,  an astounding result considering the cost of seeding for so long a period.

Below is a graphical presentation of the independent panel’s findings in their 2006 final report:

Figure 1. The results of operational seeding on the watersheds of Lake Kinneret (aka, Sea of Galilee) as reported by Kessler et al. 2006.  (a) is that result of seeding on rainfall reported by Nirel and Rosenfeld (1995), b-d are the results found for various periods, including the very same era evaluated by Nirel and Rosenfeld (1995).[1]

————-footnote———-

[1] The findings of Kessler were challenged by seeding partisans at the HUJ and who claimed that “air pollution” was decreasing rain as much as cloud seeding was increasing it.  While this was a convenient explanation, it was not found credible by many subsequent independent investigators, including by Kessler et al. (2006).

—————————continuing with Chapter 8————–

8 Deliberate Cloud Seeding and Aerosol Pollution Effects

It is interesting to note that in the Israeli experiments the effects of artificial seeding with silver iodide appeared to be an increase in the duration of precipi­ tation, with little if any effect on the intensity of precipitation (Gagin 1986; Gagin and Gabriel 1987), a finding compatible with the “static” seeding hypothesis.

The ersatz Colorado State University cloud seeding experiment results had exactly the same outcome as those described above in Israel.  In retrospect, the duration findings from both the Colorado and Israeli scientists were huge red flags that a natural bias on seeded days had occurred in these experiments as was shown in later reanalyses by external skeptics (e.g., Rhea 1983u, Rangno and Hobbs 1987).

Givati and Rosenfeld (2005) wrote, “that cloud seeding with silver iodide enhances precipitation especially where the orographic enhancement factor (see Chapter 6) was the largest. Likewise, the pollution effects reduced precipitation by the greatest amount at the same regions”. They suggestedthat this is because the shallow and short-living orographic clouds are particularly susceptible to such impacts. This suggests that attempts to alter winter precipitation should be concentrated on orographic clouds. Or interpreted in terms of inadvertent modification of clouds; winter orographic clouds may be the most susceptible to precipitation modification by pollution.

The Israeli “experimenters,” who cost their government so much in wasted cloud seeding effort, could not walk away and apologize for their misguided findings and withheld results.  So Givati and Rosenfeld (2005) generated the argument that pollution was exactly canceling out cloud seeding effects!  Of course, the air pollution argument was nonsense, the result of cherry picking amid the 500 or so Israeli rain gauges in Israel.   Here’s what the uncited Kessler et al. (2006u) report had to say about the Givati and Rosenfeld (2005) claims about air pollution:

No supporting evidence was found for the thesis of Givati and Rosenfeld (2005) regarding the decline in the Orographic precipitations (sic) due to the increase of air pollution.”

The air pollution claims by Givati and Rosenfeld (2005), while superficially credible,  except for their sudden hypothesized appearance that canceled out cloud seeding effects, were also evaluated by several independent groups and scientists in later publications not available to the authors of this review:  Alpert et al. (2008u); Halfon et al. (2009u);  Levin (2009u), Ayers and Levin (2009u).  All these independent re-analyses and reviews of the hypothesized effect of air pollution on rainfall found the argument that air pollution had canceled seeding-induced increases in rain unconvincing.

This also suggests that the conceptual model on which the Israeli cloud seeding experiments was based is not exactly as postulated. The seeding was originally aimed at the convective clouds that formed over the narrow coastal plain, with the intent of nucleating ice crystals and forming graupel earlier in the cloud life cycle (Gagin and Neumann 1974), thus leading to increased rainfall in the catchment basin of the Sea of Galilee to the east of the Galilee Mountains. However, the report of Givati and Rosenfeld (2005) concluded that “cloud seeding did not enhance the convective precipitation, but rather increased the orographic precipitation on the upwind side of the Mountains, probably by the Bergeron-Findeisen process.”

The above is not what Kessler et al. (2006u) concluded.   It was a shame that the authors did not know about Kessler et al.’s report.

To update this review, the idea posited by Rosenfeld and Givati (2005) about seeding orographic clouds, promoted by these authors, was tested in Israel-4, a seven season randomized experiment (Benjamini et al. 2023u).  Seeding in the orographic north of Israel resulted in no viable effect on rainfall.  This should not be surprising.

The lack of enhancement of the convective clouds in Israel might be explained by their tendency to mature and dissipate inland during the winter storms. Seeding of mature convective clouds cannot affect them much. The lack of enhancement is also consistent with the microphysically maritime nature of the convective clouds.

The authors seem to be unaware that for decades the cloud seeding experimenters had reported in their many publications that the clouds of Israel were “continental” in nature (e.g., Gagin and Neumann 1974, 1976u, Gagin 1975u), that is, they contained high droplet concentrations that made them extremely “un-maritime.”  This in turn helped generate scientific consensus that seeding such clouds had produced viable results on rainfall  in Israeli I and Israeli II because it was hard for them to rain and needed cloud seeding  (e.g., Kerr 1982, Silverman 1986, Dennis 1989).

This appears to be caused mainly due to the natural hygroscopic seeding by sea spray or mineral dust particles coated with soluble material (Levin et al.1996, 2005) in the winter storms that enhance the warm precipitation (Rosenfeld et al. 2001) as well as promoting the formation of ice hydrometeors that is followed by ice multiplication (Hallett and Mossop 1974).

In a surprising oversight in a supposed “scientific review,” the authors do not cite Rangno (1988) who described so long ago the clouds of Israel as we know them today; ones that rain via warm rain processes and precipitate regularly via the ice process when top temperatures are >-10°C, all contrary to the many reports of the cloud seeding experimenters (e.g., Gagin 1986).

Moreover, it has not been satisfactorily determined why the Israeli cloud seeding experimenters could not discern the natural precipitating characteristics of their clouds with all the tools available to them for so many decades.  Did the wind not blow over the Mediterranean during Israeli I and II, thus did not “maritimize” clouds when Prof. Gagin was observing them with his radars and sampling them with his research aircraft?

I spent 11 weeks in Israel from early January through mid-March 1986 studying the precipitating nature of Israeli clouds. I spoke with Israel Meteorological Service forecasters, and the chief forecaster of the Israeli randomized experiments.   Not surprisingly, they were all aware of the natural character of their rain clouds that so eluded the cloud seeding researchers at the HUJ; faulty descriptions of clouds were published by HUJ seeding researchers repeatedly in peer-reviewed journals.  How did this happen?

These suggestions are supported by the results of glaciogenic cloud seeding in Tasmania, which targeted a hilly area by seeding along an upwind coastline. The seeding in Tasmania was shown to enhance precipitation from the stratiform orographic clouds, but not from the convective clouds (Ryan and King 1997). This is consistent with the microphysical conclusions of Rangno and Hobbs (1993 sic), who asserted that, cloud seeding as done in Israel could not have possibly caused the statistically documented rain enhancement from the convective clouds there.

Again, the correct year for Rangno and Hobbs is 1995.  

The minimal amount of cloud seeding in Israeli I should have been discussed. The experimenters realized this post facto of Israel-1 and added a second seeding aircraft and no less than 42 ground generators (NRC 1973) when conducting Israel II.  The difference in released seeding material in Israeli II from the ~1000 grams released in all of Israeli I (Gabriel and Neumann (1967) has to be stupefying and raises questions.

Do the authors of this chapter really think that only 70 h of line seeding by a single aircraft upwind of each target per whole Israeli rain season could have produced a statistically significant result in rainfall in Israeli I?  Do they know that the coverage of convective clouds with rising air below cloud base is spotty,  that the rain that comes into Israel from the Mediterranean are “tangled masses” in various life cycle stages  (as described by Neumann et al. 1967)? 

Recently, Givati and Rosenfeld (2005) carried out a study in which the effects of pollution on rainfall suppression in orographic clouds were separated from the effects of cloud seeding in Israel. They concluded that the two effects have the opposite influence on rainfall, demonstrating the sensitivity of clouds to anthropogenic aerosols of different kinds. By analyzing the rainfall amounts in northern Israel during the last 53 years during days in which no seeding was carried out, they observed a decreasing trend of the orographic factor R0 (discussed in Chapter 6) with time from the beginning of the study. They associated this decrease with the increase in aerosol pollution. The same trend, but shifted upward by 12-14%, was observed for days in which seeding was carried out. Thus, it appears that the opposing effects of air pollution and seeding appear to have nearly canceled each other.

The air pollution canceling cloud seeding claims by Rosenfeld and colleagues have not been deemed credible to those who have investigated them, listed previously.  

Another noteworthy experiment was carried out in the high plains of the U.S. (High Plains Experiment (HIPLEX-1) Smith et al.(1984).Analysis of this experiment revealed the important result that after just 5 min, there was no statistically significant difference in the precipitation between seeded and non-seeded clouds, (Mielke et al. 1984). Cooper and Lawson( 1984) found that while high ice crystal concentrations were produced in the clouds by seeding, the cloud droplet region where the crystals formed evaporated too quickly for the incipient artificially produced ice crystals to grow to appreciable sizes. Instead, they formed low density, unrimed aggregates having the water equivalent of only drizzle drops, which were too small to reach the ground before evaporating. Schemenauer and Tsonis( 1985) affirmed the findings of Cooper and Lawson in a reanalysisof the HIPLEX data emphasizing their own earlier findings (Isaac et al. 1982) that cloud lifetimes were too short in the HIPLEX domain for seeding to have been effective in the clouds targeted for seeding (i.e. Those with tops warmer than -12°C). Although the experiment failed to demonstrate statistically all the hypothesized steps, the problems could be traced to the physical short lifetimes of the clouds (Cooper and Lawson 1984; Schemenauer and Tsonis 1985). This in itself is a significant result that shows the ability of physical measurements and studies to provide an understanding of the underlying processes in each experiment. The results suggested that a more limited window of opportunity exists for precipitation enhancement than was thought previously.  Cotton and Pielke (1995) summarized this window of opportunity as being limited to: Clouds that are relatively cold-based and continental; Clouds with top temperatures in the range -1O° to-25°C, and a timescale confined to the availability of significant supercooled water before depletion by entrainment and natural precipitation processes.

Today, this window would even be viewed as too large, since many cold based continental clouds with tops>-25°C have copious ice particle concentrations(e.g., Auer et al. 1969u, Cooper and Saunders 1980u, Cooper and Vali 1981u, Grant et al. 1982u.  These references were added to make them more appropriate for inland mountain locations). The HIPLEX results also indicated that small clouds make little contribution to rainfall.

This begs the question, should we expect a similar window of effectiveness for inadvertent IN pollution?

 8.1.1. Seeding Winter Orographic Clouds

The static mode of cloud seeding has also been applied to orographic clouds. Precipitation enhancement of orographic clouds by cloud seeding has several advantages over cumulus clouds. The clouds are persistent features that produce precipitation even in the absence of large-scale meteorological disturbances. Much of the precipitation is spatially confined to high mountainous regions thus making it easier to set up dense ground based seeding and observational networks. Moreover, orographic clouds are less susceptible to a “time window” as they are steady clouds that offer a greater opportunity for successful precipitation enhancement than cumulus clouds. A time window of a different type does exist for orographic clouds, which are related to the time it takes a parcel of air to condense to form supercooled liquid water and ice crystals while ascending to the mountain crest.

Missing in this discussion is the time that ice forms in orographic clouds after the leading edge forms as a droplet cloud. Ice particles have been shown to form a short distance downwind at surprisingly high temperatures as reported by Auer et al (1969u), Cooper and Vali (1981u).  

What then is the effect of introducing ice by AgI at an upwind edge where ice is already going to form immediately downwind in those situations?  Does this case represent a productive seeding possibility?  This scenario should have been discussed by the Chapter 8 authors.

The special case described here of non-precipitating clouds, where cloud seeding will be effective without question is not quantified.  How often do they occur, and how thick are they?  What is their cloud top temperature?  Are bases low enough so that the light, seeding-induced snowfall will reach the ground?  Will it be enough to justify the cost of seeding, by ground or aircraft?

The Chapter 8 authors were not aware of Rangno (1986u) who displayed the rapid changes in cloud characteristics that made seeding even orographic clouds problematic due to those changes in cloud top temperatures and in wind directions over periods of just 3-4 hours.

So many questions, so few answers by the authors, elements that point to the extreme difficulty of proper reviews in any field in meteorology!

If winds are weak, then there may be sufficient time for natural precipitation processes to occur efficiently. Stronger winds may not allow efficient natural precipitation processes but seeding may speed up precipitation formation. Stronger winds may not provide enough time for seeded icecrystals to grow to precipitation before being blown over the mountain crest and evaporating in the sinking sub saturated air to the lee of the mountain. A time window related to the ambient winds, however, is much easier to assess in a field setting than the time window in cumulus clouds.

The landmark randomized cloud seeding experiments at Climax, near Fremont Pass, Colorado (referred to as Climax I and Climax II), Colorado, reported by Grant and Mielke(1967) and Mielke et al.( 1970,1971) suggested increases in precipitation of 50% and more on favorable days (e.g. Grant and Mielke 1967; Mielke et al. 1970,1971), and the results were widely viewed as demonstrating the efficacy of cloud seeding (e.g. NRC 1973; Sax et al. 1975; Tukey et al. l978a, b; American Meteorological Society 1984),even by those most skeptical of cloud seeding claims(e.g. Mason 1980,1982). Nonetheless, Hobbs and Rangno (1979), Rangno and Hobbs (1987, 1993) question both the randomization techniques and the quality of data collected during those experiments and conclude that the Climax II experiment failed to confirm that precipitation can be increased by cloud seeding in the Colorado Rockies.

It appears that these cited critical papers by the present writer were not read by the authors of this review.  Hobbs and Rangno (1979), a study originated and carried out by the second author, demonstrated that the claims about a physical foundation for the Climax experiments were bogus.  These important findings was left out of the discussion above.   The experimenters had claimed out of thin air (Grant and Mielke 1967) that the stratifications by 500 mb temperatures were reliably connected to cloud top ones.

Moreover, the precipitation per day (PPD) does not decrease at Climax (or elsewhere in the Rockies) after a 500 mb temperature of -20°C is exceeded as the experimenters claimed (e.g., Grant et al. 1969u, 1974u, Chappell 1970u).  Rather, the PPD continues to increase at temperatures above -20°C as shown in Rangno 1979, Hobbs and Rangno (1979).   The decrease in PPD that occurred during Climax I when the 500 mb temperature was >-20° C was indicative of a bias in the draw on the Climax I control days rather than representative of PPD climatology. 

Hobbs and Rangno (1979) further demonstrated that the master’s thesis repeatedly invoked by the experimenters in support of the 500 mb/cloud top temperature correspondence claim (e.g., Grant and Elliott 1974) did no such thing,  but rather proved just the opposite.  This was due to the way that meteorological data were assigned to experimental days by the experimenters (i. e., as described by Fritsch in Grant et al. 1974u).   Critical papers were not read by the authors.  Q. E. D.

Quoting the authors from their paragraph above:  “the quality of the data collected during those experiments”.

This is a euphemism for what Rangno and Hobbs (1987) found.

The experimenters repeatedly described the NOAA-maintained recording gauge in the center of the Climax target as “independently” collected data (e.g., Mielke et al. 1970).  Rangno and Hobbs simply went to the NOAA hourly precipitation data publication for Colorado and used those data to evaluate the Climax experiments. Those published data were not the same as those used by the experimenters. 

The experimenters had, in fact, reduced the recording charts at that key gauge in Climax II themselves as revealed by Mielke 1995, and in doing so, helped the seeded day cases (Rangno and Hobbs 1987).  Climax II, not so lucky in its storm draw on seeded days as Climax I, was plagued by “helpful” errors.  Thirty-two of 43 differences in precipitation between that used by the experimenters and that in the NOAA publication helped the seeded cases.  The chance that such results came from an unbiased source can be rejected at a P value of 0.0001.

Climax I, however, benefitting from a storm draw on seeded days that favored the appearance of a cloud seeding effect in its first half of conduct,  had virtually no errors in data.

What do we make of this?  Circle the wagons? 

Or come to a logical conclusion that someone helped the Climax experiment replicate Climax II?  At this time, mid-way through Climax II, the Bureau of Reclamation’s cloud seeding division had begun spending hundreds of thousands of dollars on the planning of the Colorado River Basin Pilot Project.  There was, therefore, enormous pressure on the experimenters to have Climax II replicate Climax I.  

We let the reader decide what may have happened.

———-

Inexplicably, the authors of this chapter omit the reanalysis of Mielke et al. (1981) by Rhea (1983u).  Indeed, this author’s own independent reanalysis of the Climax experiments (rejected in 1983) was partially because reviewers’ thought Rhea’s reanalysis, simultaneously under review and that came to the same result, was more robust.  Rhea showed that the mismatch between the time the control gauges were read and when the Climax target gauges were read resulted in the false impression that Climax II had replicated Climax I.  When the gauges were synchronized by Rhea (1983u), the Climax II seeding increases disappeared (as they also did using the published NOAA data in Rangno and Hobbs (1987).

A background note:  Grant et al. 1983u, however, strongly criticized the Rhea reanalysis before it was published.  Rhea altered his reanalysis along the lines suggested by Grant et al. prior to publication.  Nevertheless, Grant et al. did not revise their published comment to account for Rhea’s revisions.  Grant, in a personal note to Rhea at that time, did not know why he and his group had not altered their criticism of Rhea’s revised manuscript.

The published record concerning Rhea’s reanalysis is, therefore confusing; the experimenters appeared to critique Rhea’s paper while not actually doing so.

Even so, in their reanalysis, Rangno and Hobbs(1993) did show that precipitation increased by about 10% in the combined Climax I and II experiments.

First, the so-called “10% increase in precipitation for all of the Climax I and II experiments was “built in” by the choice of control stations mid-way through Climax I by the experimenters  as demonstrated in Rangno and Hobbs (1993).   We are sure the authors did not read that 1993 paper.  Control stations should have been selected prior to the Climax I experiment as good design demands.  Otherwise, the temptation to cherry-pick control stations that prove what the experimenters already believe becomes too big a temptation and that is surely what happened in Climax I at the half-way point.

If the seeding effect is real, it will continue following a cherry-picked group of control stations.  If there is no further sign of seeding, as shown in “Climax 1B,” the second half of Climax I by Rangno and Hobbs (1993) then we know that the gauges were picked because it showed what the experimenters believed before the experiment even began.  The lack of any sign of an effect of cloud seeding on precipitation continued through all of Climax II as well (Rangno and Hobbs 1993).

Finally, 1000 re-randomizations of the Climax data performed by the University Washington Academic Computer Center by Irina Gorodnoskya (unpublished data) showed that the 10% claimed increase in precipitation by the authors above was in the noise of these experiments.  It should not be quoted as an increase in snow due to seeding as the authors do here.

This should be compared, however, to the original analyses by Grant and Mielke (1967), Grant and Kahan (1974), Grant and Elliott (1974), Mielke et al. (1971), Mielke et al. (1976) and Mielke et al. (1981) that indicated greater than 100% increase in precipitation on seeded days for Climax I and 24% for Climax II.

Two other randomized orographic cloud seeing experiments, the Lake Almanor Experiment (Mooney and Lunn 1969) and the Bridger Range Experiment (BRE) as reported by Super and Heimbach (1983) and Super (1986) suggested positive results.

Of concern is that the “cold westerly” case in Phase I of the Lake Almanor experiment, where large seeding effects were reported was not reported in Phase II (Bartlett et al. 1975).   Also, the large increases (40%) in snow  reported in Phase I for cold westerly cases, is suspect since such clouds are likely to develop high natural ice particle concentrations naturally.  The Lake Almanor Phase I  is badly in need of a reanalysis by external skeptics;  its results should not be taken at face value.

 However, these particular experiments used high elevation AgJ generators, which increase the chance that the Agl plumes get into the supercooled clouds. Moreover, both experiments providedphysical measurements that support the statistical results (Super and Heimbach 1983, 1988).

There have been a few attempts to use mesoscale models to evaluate cloud seeding programs. Cottonet al. (2006) applied the Colorado State University Regional Atmospheric Modeling System(RAMS)to thesimulation of operational cloud seeding in the central Colorado Mountains in the 2003-2004 winterseason. The model included explicit representation of surface generator production of Agl at thelocations, burn rates, and times supplied by the seeding operator. Moreover, the model explicitlyrepresented the transport and diffusion of the seeding material, its activation, growth of icecrystals and snow,and precipitation to the surface. Detailed evaluation of model forecast orographicprecipitation was performed for 30 selected operational seeding days. It was shown that the model could be a useful forecasting aid in support of the seeding operations. But the model over-predictednatural precipitation, particularly on moist southwest flow days. The model also exhibited virtually no enhancement in precipitation due to glaciogenic seeding. There are a number of possiblecauses for the lack of response to seeding, such as over prediction of natural precipitation, which prevented the effects of seeding from being seen. In addition, the background CCN and INconcentrations are unknown, therefore lower CCN concentrations than occurred would make the cloudsmore efficient in precipitation production, thus reducing seeding effectiveness.

Finally, Ryan and King(1997) reviewed over 14 cloud seeding experiments covering much of southeastern, western,and central Australia, as well as the island of Tasmania. They concluded that static seeding over the plains of Australia is not effective. They argue that for orographic stratiform clouds, there is strong statistical evidence that cloud seeding increased rainfall, perhaps by as much as 30% over Tasmania when cloud top temperatures are between -10 and -l2°C in southwesterly airflow. The evidence that cloud seeding had similar effects in orographic clouds overthe mainland of southeastern Australia is much weaker. Note that the Tasmanian experiment had bothstrong statistical and physical measurement components and thus meets, or at least comes close to meeting, the NRC (2003) criteria for scientific “proof.” Cost/benefit analysis ofthe Tasmanian experiments suggests that seeding has a gain of about 13:1. This is viewed as a real gain to hydrologic energy production.

A complication revealed in the analysis of some of the Australian seeding experiments is thatprecipitation increases were inferred one to three weeks following seeding in several seedingprojects(e.g. Bigg and Turton 1988). Bigg and Turton ( I988) and Bigg ( 1988, 1990, 1995) suggestedthat silver iodide seeding can trigger biogenic production of additional ice nuclei. The latter research suggests that fields sprayed with silver iodide release secondary ice nuclei particles at intervals of up to ten days.

In summary, the “static” mode of cloud seeding has been shown to cause the expected alterations incloud microstructure including increased concentra­ tions of ice crystals, reductions of supercooled liquid water content, and more rapid production of precipitation elements in both cumuli (Isaac et al.1982; Cooper and Lawson 1984)and orographic clouds(Reynolds and Dennis 1986; Reynolds 1988;Super andBoe 1988; Super et al. 1988; Super and Heimbach 1988). The documentation of increases in precipitation on the ground due to static seeding of cumuli, however, has been far more elusive, with the Israeli experiment (Gagin and Neumann 1981) providing the strongest evidence that static seeding of cold-based, continental cumuli can cause significant increases of precipitation on the ground.  

Tukey et al. (1978b, Appendendix C, pC.1) wrote:   “The strongest evidence for rainfall enhancement involving the seven latest substantial experiments this task force has studied seems today to be that from the two Israeli experiments….”  The statement in blue (highlighted by this writer) which is almost the exact wording as that found in Turkey et al. (1978b) 30 years before the Springer book was published) is troubling indeed.    The assessment by Turkey et al. in 1978 was valid; it was not valid 30 years later when so much water has gone under the bridge concerning the Israeli cloud seeding experiments (or,  “too little water” due to cloud seeding).

Moreover,  citing Gagin and Neumann (1981) in 2009 as the strongest evidence in support of cloud seeding as they do,  demonstrated that the authors of this review were not aware of,  nor understood the literature in the topic they are supposedly reviewing.  The omission of critical literature by the authors as was proof of this assertion.

Why wasn’t I asked to review this manuscript in advance of publication since I am well-known as an expert on both the Colorado and Israel clouds, weather, and cloud seeding experiments?  Moreover, the authors of this review knew this.

The evidence that orographic clouds can cause significant increases in snowpack is far more compelling, particularly in the more continental and cold-based orographic clouds (Mielke et al. 1981; Super and Heimbach 1988).

The authors omit Rhea’s 1983u reanalysis of Mielke et al. 1981 and that of Rangno and Hobbs (1987) in remarking that “significant increases in snowpack” have been compellingly shown by Mielke et al. 1981.

Update to the orographic seeding claim above by the authors:  The NCAR Wyoming experiment, completed in 2013 (Rasmussen et al. 2018u), could find no viable evidence that seeding from ground generators had increased precipitation after six seasons of randomized seeding.

Perhaps, however, the most challenging obstacle to evaluating cloud seeding experiments to enhance precipitation, is the inherent natural variability of precipitation in space and time, and the inability to increase precipitation amounts to better than ~10%. This last obstacle puts great demands on the measuring accuracy and the duration of the experiments. Shouldn’t we expect similar obstacles in evaluating inadvertent effects of IN pollution on precipitation?

A well-stated description of the problem.

===================================================

 List of references mentioned in the critical review that were uncited by the authors, or are relevant papers for an enhancement of Chapter 8 that were unavailable to these authors because they were published after Chapter 8 appeared.

Alpert, P., N. Halfon, and Z. Levin, 2008: Does air pollution really suppress precipitation in Israel?  J. Appl. Meteor. Climatology, 47, 943-948.

Alpert, P., N. Halfon, and Z. Levin, 2009:  Reply to Givati and Rosenfeld.  J. Appl. Meteor. Climatology, 48, 1751-1754.

Auer, A. H., D. L. Veal, and J. D. Marwitz, 1969: Observations of ice crystals and ice nuclei observations in stable cap clouds.  J. Atmos. Sci., 26, 1342-1343.

Ayers, G., and Levin, 2009:  Air pollution and precipitation.  In Clouds in the Perturbed Climate System.  Their Relationship to Energy Balance, Atmospheric Dynamics, and Precipitation. J. Heintzenberg and R. J. Charlson, Eds.  MIT Press, 369-399.

Bartlett, J. P., M. L. Mooney, and W. L. Scott, 1975:  Lake Almanor Cloud Seeding Program.  Preprint, Weather Modification Conference, San Francisco, 106-110.

Benjamini, Y, A. Givati, P. Khain, Y. Levi, D. Rosenfeld, U. Shamir, A. Siegel, A. Zipori, B. Ziv, and D. M. Steinberg, 2023:  The Israel 4 Cloud Seeding Experiment: Primary Results.   J. Appl. Meteor. Climate, 62, 317-327.  https://doi.org/10.1175/JAMC-D-22-0077.1

Chappell, C. F.,  1970:  Modification of cold orographic clouds.  Atmos. Sci. Paper No. 173, Dept. of Atmos. Sci., Colorado State University, Fort Collins, 196pp.

Cooper, W. A., and C. P. R. Saunders, 1980:  Winter storms over the San Juan mountains.  Part II:  Microphysical processes.  J. Appl. Meteor., 19, 927-941.

Cooper, W. A., and G. Vali, 1981:  The origin of ice in mountain cap clouds.  J. Atmos. Sci., 38, 1244-1259.

Dennis, A. S., 1989: Editorial to the A. Gagin Memorial Issue of the J. Appl. Meteor., 28, 1013.  No doi.

Gabriel, K. R., and Y. Neumann, 1978:  A note of explanation on the 1961–67 Israeli rainfall stimulation experiment.  J. Appl. Meteor., 17, 552–556.

Gabriel, K. R., and Rosenfeld, D., 1990: The second Israeli rainfall stimulation experiment: analysis of precipitation on both targets. J. Appl. Meteor., 29, 1055-1067.  https://doi.org/10.1175/1520-0450(1990)029%3C1055:TSIRSE%3E2.0.CO;2

Grant, L. O., DeMott, P. J., and R. M. Rauber, 1982:  An inventory of ice crystal concentrations in a series of stable orographic storms.  Preprints, Conf. Cloud Phys., Chicago, Amer. Meteor. Soc. Boston, MA. 584-587. No doi.

Grant, L. O., J. G. Medina, and P. W. Mielke, Jr., 1983:  Reply to Rhea. J. Climate Appl. Meteor., 22, 1482–1484.

Grant, L. O., C. F. Chappell, L. W. Crow, J. M. Fritsch, and P. W. Mielke, Jr., 1974:  Weather modification: A pilot project.  Final Report to the Bureau of Reclamation, Contract 14-06-D-6467, Colorado State University, 98 pp. plus appendices.

Grant, L. O., Chappell, C. F., Crow, L. W., Mielke, P. W., Jr., Rasmussen, J. L., Shobe, W. E., Stockwell, H., and R. A. Wykstra, 1969:  An operational adaptation program of weather modification for the Colorado River basin.  Interim report to the Bureau of Reclamation, Department of Atmospheric Sciences, Colorado State University, Fort Collins, 98pp.  (Available from the Bureau of Reclamation, Library,   Federal Building, Denver, Colorado 80302.

Halfon, N., Z. Levin, P. Alpert, 2009:  Temporal rainfall fluctuations in Israel and their possible link to urban and air pollution effects.  Environ, Res. Lett., 4, 12pp. doi:10.1088/1748-9326/4/2/025001

Kessler, A., A. Cohen, D. Sharon, 2003:  Analysis of the cloud seeding in Northern Israel.  Interim report submitted to the Israel Hydrology Institute and the Israel Water Management of the Ministry of Infrastructure.

Levin, Z., N. Halfon, and P. Alpert, 2010: Reassessment of rain enhancement experiments and operations in Israel including synoptic considerations.  Atmos. Res., 97, 513-525.

                        http://dx.doi.org/10.1016/j.atmosres.2010.06.011

Levin, Z., N. Halfon, and P. Alpert: 2011:  Reply to the Comment by Ben-Zvi on the paper “Reassessment of rain experiments and operations in Israel including synoptic considerations” Atmos. Res., 99, 593-596.

Mielke, P. W., Jr., 1995:  Comments on the Climax I and II experiments including replies to Rangno and Hobbs.  J. Appl. Meteor., 34, 1228–1232.

National Research Council, 1973: Weather & Climate Modification: Progress and Problems. National Academy of Sciences, 258 pp., https://doi.org/10.17226/20418.

Neumann, J., K. R. Gabriel, and A. Gagin, 1967: Cloud seeding and cloud physics in Israel:  results and problems.  Proc. Intern. Conf. on Water for Peace.  Water for Peace, Vol. 2, 375-388.  No doi.

Rangno, A. L., 1979:  A reanalysis of the Wolf Creek Pass cloud seeding experiment.   J. Appl. Meteor., 18, 579–605.

Rangno, A. L., 1986:  How good are our conceptual models of orographic clouds?  In Precipitation Enhancement–A Scientific Challenge, R. R. Braham, Jr., Ed., Meteor. Monographs, 43, Amer. Meteor. Soc., 115-124. Invited paper, title assigned by A. S. Dennis.

 https://doi.org/10.1175/0065-9401-21.43.115

Rangno, A. L., 1988: Rain from clouds with tops warmer than -10 C in Israel.  Quart J. Roy. Meteor. Soc., 114, 495-513.

   https://doi-org/10.1002/qj.49711448011

Rasmussen, R. M., S. A. Tessendorf, L. Xue, C. Weeks, K. Ikeda, S. Landolt, D. Breed, T. Deshler, and B. Lawrence, 2018:  Evaluation of the Wyoming Weather Modification Pilot Project (WWMPP) using two approaches:  Traditional statistics and ensemble modeling.  J. Appl. Meteor. and Climate, 57, 2639-2660.

Rhea, J. O., 1983:  “Comments on ‘A statistical reanalysis of the replicated Climax I and II wintertime orographic cloud seeding experiments.'”  J. Climate Appl. Meteor., 22, 1475-1481.

Rosenfeld, D., 1998: The third Israeli randomized cloud seeding experiment in the south: evaluation of the results and review of all three experiments. Preprints, 14th Conf. on Planned and Inadvertent Wea. Modif., Everett, Amer. Meteor. Soc. 565-568. No doi.

Sharon, D., A. Kessler, A. Cohen, and E. Doveh, 2008:  The history and recent revision of Israel’s cloud seeding program.  Isr. J. Earth Sci., 57, 65-69.     https://DOI.org/10.1560/IJES.57.1.65.

Wurtele, Z. S., 1971: Analysis of the Israeli cloud seeding experiment by means of concomitant meteorological variables. J. Appl. Meteor., 10, 1185-1192.    https://doi.org/10.1175/1520-0450(1971)010%3C1185:AOTICS%3E2.0.CO;2

Totality of References  in Chapter 8.1, “Introduction” through 8.2.2 “Seeding Winter Orographic Clouds” 

=================================

American Meteorological Society, 1984: Statement on planned and inadvertent weather modification.  Bull. Amer. Meteor. Soc., 66, 447–448.

Ben-Zvi, A., 1997:  Comments on “A new look at the Israeli randomized cloud seeding experiments.” J. Appl. Meteor., 36, 255-256.

Bigg, E. K., 1988: Secondary ice nucleus generation by silver iodide applied to the ground. J. Appl. Meteor., 27, 453-488.

Bigg, E. K., 1990:  Aerosol over the southern ocean. Atmos. Res., 25, 583-600.

Bigg , E. K., 1995:  Tests for persistent effects of cloud seeding in a recent Australian experiment.  J. Appl. Meteor., 34, 2406-2411.

Bigg, E. K., and E. Turton, 1988: Persistent effects of cloud seeding with silver iodide.  J. Appl. Meteor., 27, 505-514

Braham, Roscoe R., Jr., 1986:  Rainfall enhancement–a scientific challenge.  Rainfall Enhancement–A Scientific Challenge, Meteor. Monogr., 21, No. 43,  1–5.

Cooper, W. A., and R. P. Lawson, 1984:  Physical interpretation of results from the HIPLEX-1 experiment.  J. Climate Appl. Meteor., 23, 523-540.

Cotton, W. R., 1982: Modification of precipitation from warm clouds. A review.  Bull. Meteor. Soc., 63, 146-160.

Cotton, W. R., 1986a: Testing, implementation, and evolution of seeding concepts–a review.  In Precipitation Enhancement–A Scientific Challenge, R. R. Braham, Jr., Ed., Meteor. Monographs, 43, Amer. Meteor. Soc., 63-70.

Cotton, W. R., 1986b: Testing, implementation, and evolution of seeding concepts–a review.  In Precipitation Enhancement–A Scientific Challenge, R. R. Braham, Jr., Ed., Meteor. Monographs, 43, Amer. Meteor. Soc., 139-149.

Cotton, W. R., and R. A. Pielke, 1992:  Human Impacts on Weather and Climate. ASteR Press, 271pp.

Cotton, W. R., and R. A. Pielke, 1995:  Human Impacts on Weather and Climate, 1st edition, Cambridge University Press, 288pp.

Cotton, W. R., and R. A. Pielke, 2007:  Human Impacts on Weather and Climate, 2nd edition, Cambridge University Press, 308pp.

Cotton, W. R., R. R. McAnelly, G. Carrio, P. Mielke, and C. Hartzell, 2006:  Simulations of snowpack augmentation in the Colorado Rocky Mountains.  J. Weather Modification, 38, 58-65.

Dennis, A. S., 1980:  Weather Modification by Cloud Seeding.  Academic Press, 267pp.

Dennis A. S., and H. D. Orville, 1997: Comments on “A new look at tbe Israeli cloud seeding experiments.” J. Appl. Meteor., 36, 277-278

Gagin, A., 1986:  Evaluation of “static” and “dynamic” seeding concepts through analyses of Israeli II experiment and FACE-2 experiments.  In Rainfall Enhancement–A  Scientific Challenge, Meteor. Monogr., 43, Amer. Meteor. Soc., 63–70.

Gagin, A., and K. R. Gabriel, 1987:   Analysis of recording rain gauge data for the Israeli II experiment. Part I:  Effects of cloud seeding on the components of daily rainfall.  J. Climate Appl. Meteor.,  26,   913–926.

Gagin, A., and J. Neumann, 1974: Rain stimulation and cloud physics in Israel. Weather and Climate Modification, W. N. Hess, Ed., John Wiley and Sons,  454–494.

Gagin, A., and J. Neumann, 1981:  The second Israeli randomized cloud seeding experiment: evaluation of results.  J. Appl. Meteor., 20, 1301–1311.

Garstang, M., R. Bruintjes, R. Serafin, H. Oroville, B. Boe, W. R. Cotton, J, Warburton, 2005:  Weather Modification; Finding common ground. Bull. Amer. Meteor. Soc. 86, 647-655.

Givati, A., and Rosenfeld, D., 2005: Separation between cloud-seeding and air pollution effects. J. Appl. Meteor. Climate, 44, 1298-1314.    https://doi.org/10.1175/JAM2276.1

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