Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.
Mr. Cloudmaven person foretold certain cloud types would occur yesterday in conjunction with “storm” 3 yesterday (which was really only the passage of an upper level trough over us–see map for 5PM yesterday). Let’s see how he did, that is, whether he is an actual “cloudmaven”:
(0=not observed, 1 observed, -1, cloud observed, not predicted:
Cirrocumulus, 0
Altocumulus floccus virgae, 0
Cirrus, 1
Cumulus fractus, -1
Cumulus humilis, -1
Cumulus mediocris, -1
Stratocumulus, -1
Stratocumulus virgae, -1
Cloud score: -4 =s bad cloudmaven; credentials suspect.
Here are some of the cloud sights from yesterday in case you miseed them and want to fill in some entries in your cloud diary: 1) 4:42 PM, 2) 5:26 PM, 3) 5:53 PM, has band of cirrus with trough passage, and 4) 6:12 PM, with some virga/ice fallout showing (darkish veils below clouds).
However, I did opine that there might be a sprinkle with this trough (see map again for example of yesterday’s “trough.” (Sounds like the stockmarket in ’09.) Having been specially trained to recognize virga and precipitation when a forecast of precipitation is on the line, I found it easy to recognize just how close I came to getting that sprinkle as evidenced by some virga trailing down from some of the patches of Stratocumulus clouds. See above hills in photo at left.
You now know, if you have been reading this blog and thinking about it all day, that ice formed in these clouds because they had crossed a temperature threshold, had gotten cold enough to form ice. That “virga” was, if you flew through it, snow flurries. Where it melted into raindrops closer to the ground is not visible. However, it is unlikely that virga of this magnitude reached the ground.
You might now even guess the temperature which the tops of the clouds reached. My guesstimate from the TUS sounding at 5 PM yesterday is somewhere between -15 to -20 C, a threshold for ice (precip) formation in shallow clouds such as these. Estimated depth of the thicker clouds seen here? About 2000 feet or so is all.
BTW, if you noticed these very subtle virga/ice in these Stratocumulus clouds that began to show up late in the afternoon, you are a cloud observer supreme!
But first, “storm” 3 of six as foretold many days ago by our wonderful numerical models having “billions and billions and billions” of calculations (to use a numeric phrase made popular by the late Carl Sagan) is going to pass over today. Hoping for a sprinkle late in the day, but virga seems likely in the Altocumulus clouds that will develop/move in today.
The jet stream is powerful over us from the southwest, and when you have these weaker disturbances with marginal moisture, you can get some glorious, fine granulations in the clouds (Cirrocumulus to be exact) as we saw two days ago. See photo below. So, I am expecting to see the following types of clouds today: Altocumulus with virga, some clusters large enough to produce a sprinkle even at the ground (see second photo from two days ago with “mammatus”-see footnote below and virga), Cirrocumulus, and some cirrus. Could be a fabulous sunset with these kinds of clouds around.
OK, so “storm” 3 today may be just a few clouds without any precip. Oh, well.
Cold and unusual snow occurrences ahead for the West and for Cat Land, too
The low pressure center and accompanying Arctic blast now developing in the Pacific Northwest will be historic. What I mean is the that climate record books will be altered for things like late snow occurrences, one of the lastest snow occurrences (as in Seattle), latest lowest temperatures, all time February low temperatures, and unusual flurries and brief snow accumulations at anytime in places in California. This is a whopper of an atmospheric ice berg from the ground all the way up through the troposphere in the West as it progresses down the West Coast. Snowfall at SEA LEVEL is likely all the way down to….Los Angeles suburbs.
Then after shuttling down the coast, this “ice berg” takes a sharp right turn (as seen from the weather maps), that is, toward the east and to Arizona! Egad. Not only will it be unusually cold again, though nowwhere near the “historic” cold wave early this February when all kinds of low temperature records and pipes were busted, though another hard freeze does seem in the cards after the rain/snow/wind pass by. Monday and Tuesday mornings look awful darn cold right now.
Did I mention wind? Along with this situation will be an unusually strong low pressure center that will give us the kind of blustery day this Saturday as we had last Saturday with gust to 50 mph here on the Catalina Rise just west of the Cat Mountains. So, if you’ve got dried out, stiff palm fronds you’ll probably lose a few more in this one.
Did I mention snow? Its now looking like a greater chance for a small accumulation of snow as low as 3,000 feet here on the west side of the Catalinas on Sunday morning. I’m not buying skis just yet, but this is a real interesting situation.
And, finally, it looks like an appreciable rain, too, with this, maybe more than half an inch between later Saturday and Sunday night. Man, will this be welcomed around here!
Since I am overly excited about this interesting weather pattern that is on our doorstep, it should be noted that objectivity is in decline… At the Unviersity of Washington we had a forecaster who loved snowstorms. And so, when he saw a snowstorm coming and forecast an amount, say 10 inches, you had to divide that forecast by 100 to get the most snow that could possibly fall from that storm.
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Footnote: On the fifth floor of the Atmospherics Science Building at the University of Washington, there was a line of large cloud photos on the wall, one of which was a “Cumulonimbus mammatus” that strongly resembled the “mammatus” in the second photo below. The photo caption to that effect was vandalized, and we suspect by a female meteorologist/grad student who might have taken exception to this traditional, formal descriptor established decades ago. The word “mammatus” was crossed out and replaced by “testicularis.” It was horrible thing to see.
You’re probably smiling now remember singing this little ditty as a kid, maybe singing it with your friends on the bus, whenever you saw “Altocumulus floccus virgae” clouds such as are pictured in the first photo. Wasn’t it great when you saw these kinds of clouds while on a vacation trip and mom and dad had to stop somewhere to get you some pie after you sang that song? Well, I nostalgiate here.
To the right of the dead yucca stalk, Altocumulus tufts are shedding snow. The opacity of the virga is a give away that its snow, and not rain. In some of these little tufts, the water droplet cloud that preceeded the formation of ice has disappeared, and all that is left is falling snow. How much snow is it? Just a flurry, if you were up there, even though it looks pretty thick. Once in awhile in our research on ice in clouds at the University of Washington, we got to sample these from top to bottom. Because the ice crystal concentrations are usually pretty low in clouds like the ones shown, a few per liter and often less than 1 per liter, those delicate ice crystals don’t bump into each other much and break up, and you find gorgeous images of star-like crystals in these fall out streaks, the kind you see on Christmas cards (examples here). How do I know what from ten miles away and 16,000 feet or so below them. Its a funny thing, but ice crystals are differently shaped depending mostly on temperature. To get the temperature of these clouds you can get a pilot report (unlikely) or examine the humidity profile of the Tucson sounding for “00 Z” (5 PM LST yesterday afternoon and make an educated guess. The highest relative humidity on that sounding was at 525 mb ) about 15-16, 000 feet above the ground) with a temperature of -16 C (about 3 F), namely, darn cold. Continuing, we in this field have a well known chart by Magono and Lee (1966) that shows the temperature at which certain forms of crystals grow. At the temperature I am guessing those clouds were at, those crystals would have grown as stellars and dendrites, which grow between about -12 C and -18 C. Sometime I will show you some of these crystals, but for brevity will quit here on this topic.
The second and third photos show what one of these tufts looks like before the crystals have grown and fallen out. Top center, the largest raggedy tuft (Altocumulus floccus) show no fallout of ice. In the last photo, twenty-nine minutes later, there is a fine veil of ice crystals below it (upper right hand corner). Only now, with virga, are they “Altocumulus floccus virgae”! I’m singing right now! And, if you look really carefully you’ll see that most of those little guys have a little ice fall underneath them. Certainly, in those clouds you would find PERFECT crystal specimens!
I’ll end here on an exciting note. The Enviro Can model CONTINUES to show a very strong system moving into our area on Saturday afternoon, likely accompanied by winds as strong or stronger than we saw last Saturday, before the rain and cold air hits on Sunday. Snow levels are going to be really low and we might see some ice in the rain on Sunday here in Cat (alina) Land. Amounts are looking substantial at this point. Man, do we need it!
In the meantime, an upper trough off Baja passes over tomorrow. It has enough moisture with it to provide more “clouds for pies” (Altocumulus floccus virga, and, of course, Altocumulus castellanus virgae, which also qualifies as well for a pie). And, some cirrus will be around, too. However, I am going to stick my neck out and say there will be sprinkles tomorrow. Mods really don’t have a thing, so you’ll have to keep that in mind.
Be sure to keep you’re camera ready for sunsets like last night (see below)!
It was beginning to seem like measurable rain could not fall again here! But then those Stratocumulus clouds because closing in in the afternoon, then soon after that some snow virga began to trail down from them here and there, and the next thing, large regions of the sky were suddenly shedding virga and rain at the ground. Also, as with the day before anmd at the same time, a windshift line moved across the Tortolita mountains and into Oro Valley helping to augment those Stratocu. Here’s the pictorial record:
Your thoughts at this time: "Look, the clouds are quite thin, and the sun is going to be out soon! It will be a nice day after all." Background: the morning overcast of low clouds has dissipated and you are responding to new conditions.The lower clouds gradually fatten up on solar calories, and because there is a disturbance aloft approaching that you can't see, the clouds begin grouping into darker regions that cover ever larger portions of the sky. The upper air disturbance is the "conductor" of the cloud "orchestra" and its getting closer to passing overhead at the time of the 2nd photo. However, you may still not be too concerned, but after all, there is no precip drooping down from all these clouds that you now see. BTW, I went into the Tortolitas to get this 2nd panaramic shot looking downwind toward Oracle and the Oro Valley for you (hahaha-just kidding).
Quickfire quiz: Why isn’t there virga trailing down from those clouds in the 2nd photo, except in the very far away clouds where you can see just a tad????
(Answer, printed upside down if I could): “They are not cold enough yet to have ice form in them, and ice in clouds is necessary for rain at the ground, as a rule in AZ.”
So those Stratocumulus and some of them are starting to look more like Cumulus clouds at about this time (2nd photo), have to get colder by deepening upward some, and/or colder air must move in aloft to chill them down.
Weird factoid about ice in clouds: A cloud will form MORE ice for the same top temperature as its bottom gets warmer! That could be a whole 100 page discussion. Now, if you’re really pedantic, you can go here to read about all the mysteries that we (those who make a living studying clouds) are going to try to solve in a project in the Virgin Islands this summer, called “ICE-T” here.
In the 3rd and last photo, the nose of the windshift coming across Oro Valley is marked by that highlighted shred cloud in the center of the photo. It was moving from R to L, undercutting the higher based clouds that were still moving from the SW. As you can see by the obscured bases all around, there is widespread areas of rain at this time, augmented by taller clouds with thicker, darker shafts of rain, probably leaning toward a “weak” Cumulonimbus classification if you could see the whole thing. Note how the distant hills and mountains are obscured in rain. Yay!
It was after this shot that Catalina got its little amount.
Next “storm” this being 2 of the model foretold six days of rain some time ago? Wednesday. However, the mods are unimpressed with the moisture in this and none that I have seen have a drop as this upper air disturbance goes over us. At the LEAST, we should have some nice Cirrus, and probably Altocumulus clouds. And you know what that means now…. The possiblity of a trick sunset due to a parhelia (aka, sun dog, mock sun).
Also, I really like the the Canadian model run today that calculated where the highs and lows are going to be for the next several days based on last evening’s weather measurements around the globe. I really, really like it because it shows a huge storm here and in the SW six days out. My preference has nothing to do with objective science. The models have been fluctuating on how this next storm is going to be, minimal or gigantic, sometimes that’s just the way the models are when there is a lot of uncertainty about things upwind of us. Its one of those that is accompanied by an Arctic blast down the West Coast. Can’t wait!
Though HUGELY disappointing because only a trace of rain fell here as of 7 AM this morning, and only a little in the Canada del Oro wash watershed (amounts here), nevertheless, what a nice, classic passage of a cold front. A cold front, as it sounds, marks the advancing boundary of colder air that is displacing warmer air, and that went went by late yesterday afternoon. When it goes by, the wind direction changes almost instantaneously, the temperature begins to drop, often sharply at it did at 5 PM yesterday (see below), and the barometric pressure begins to rise.
But without measurements or satellite or other data, you yourself could have seen that invisible boundary approaching Catalina by the low, scruffy clouds that began to appear on the horizon to the northwest. Soon they were topping the Tortolita mountains, then the Catalinas. And you would have noticed that, unlike the clouds overhead, those lower clouds were advancing from the north. That evolving scene looked like this, finally ending up as a low overcast of Stratus clouds. The first shot below was at 4:40 PM, 20 minutes before the windshift and temperature plummet hit. The second shot is as the windshift was passing Golder Ranch Drive and shows the lower cloud bases associated with the cooler air racing south along the west side of the Catalinas. You can see that they are also connecting to the higher Stratocumulus layer. The third shot shows the Catalinas fully enveloped in the cooler air and lower clouds, and the last shot is of those much lower clouds (I would call them “Stratus”) over Catalina and Oro Valley, looking to the west.
You can also relive yesterday’s clouds and windshift from the vantage point of the University of Arizona’s timelapse film. You will see the windshift hitting there marked by puffs of dust from the NW and then those low scruffy clouds right behing beginning about 5:20 PM here.
So why didn’t it rain with all these clouds? What was missing? For almost every drop of rain that falls in Arizona, ice crystals are required to start the precipitation process going.
The formation of ice in clouds is a continuing scientific enigma, believe it or not. However, we know that they didn’t form, with brief exceptions yesterday afternoon when a few sprinkles (NOT “DRIZZLE”, dammitall! Sorry, lost control there for a second)…..formed in the higher deck of Stratocumulus clouds, and again last evening when it rained again for a few minutes.
The first thing you would guess then, since we are talking about the formation of ice in clouds, is that the tops of the clouds did not get cold enough, that is, were not high enough above us and upwind of us, for ice to form. That would be my best explanation for those periods where it was not raining, we had low clouds and they looked rather threatening for much of the time between 5 PM and dark. (After dark, some rain did briefly fall.)
However, the Tucson sounding launched yesterday afternoon around 4 PM shows that the tops were plenty cold enough; the top of the moist layer was about -20 C! (Note: soundings do not measure “clouds”, but rather humidity, from which we INFER clouds). Normally a considerable amount of ice would be expected in clouds having a top temperature that low. Tiny echoes did occur over and downwind of the Catalinas all around the time of that sounding which means that ice was forming precip here and there in the clouds we saw, and measurable precip was recorded in the CDO watershed.
Sure wish I could have been up there in our former research aircraft to check this out more! But, will have to leave this in a bit of an unsatisfactory way.
My apologies if this got a bit deeper than you really wanted to get into.
Late yesterday afternoon, the sun appeared to be setting in the wrong location, about 20-25 degrees south of where it is supposed to be at this time of year. Perhaps something horrible had happened, I thought. Retirement with a happy ending here in Arizona was too good to be true, I thought, and now it was all going to come to an end. First, some perspective on where the sun was going down BEFORE yesterday. This first shot was taken just a few days ago (Feb 13th). Note where the sun is relative to the Tortolita mountains on the right, and Twin Peaks, the two itty bitty humps to the left. For further perspective, at the winter’s solstice, December 21st, and from this same location, the sun sets next to Twin Peaks. So, in this first shot you can also see how much the sun has moved in two months.
But then yesterday, something awful seemed to be happening. The next photo was one to send chills down your back, and in fact, if the sun was setting over there in the winter as a matter of routine, the northern hemisphere would likely glaciate down to about Blythe in the winter, due to the NH sunlight being so weak (that is, with so much tilt of the earth’s axis about which it spins). The days here would, in that case, be about the length of those in Seattle with daylight only from about 8-4 PM in the wintertime because the sun would be taking such a low trajectory in the sky; would rise late and sink early.
So, while I was concerned with the earth-sun system and some kind of apocalypse yesterday evening, I have feeling that most people were thinking, “Well, I guess we’re not going to have such a great sunset. Seems to be too many clouds over there where the sun is setting.”
Or maybe you were thinking about that important Washington Husky Arizona Cats basketball game today and how it might go.
But “No!”, a little later the sun underlit all those clouds, appearing to have sunk in its proper position for this time of year (3rd photo)!
I felt relieved and started thinking about that important Washington Husky -Arizona Cats basketball game today and how it might go. Then I also started thinking about how I might have been the ONLY person to notice something was terribly WRONG with that sunset. I feel pretty good about that part.
So, what happened? This “trick” sunset, followed by a treat of a sunset was caused by a parhelia (explanation by my friend, Bob, here) whose accessible name is “sun dog” or “mock sun”, which we CERTAINLY had in this case!
Parhelia appear, if you don’t go to the site above for a more complete explanation, when the ice crystals in the cirrus clouds up there are hexagonal plates, and fall with their faces down. The sun’s light is refracted (bent) as it passes through jillions of these plates and at about 22 degrees from the sun’s position, an observer on the ground will see a bright spot, sometimes with a little coloration. Sometimes there is also a “22 degree” halo along with the sundog.
I should add that the “trick” parhelia was being produced by ice crystals in the cirrus clouds above and behind the altocumulus cloud deck yesterday. Of course, as you know, altocumulus clouds are comprised completely or mostly of droplets and cannot, therefore, produce parhelia.
Finally, to end, the last shot is almost at the winter solstice, taken on December 26th, and has a parhelia, aka, sun dog, mock sun, at left so you can see what they usually look like and how far away from the sun they are near sunset. Yesterday’s, though, I thought was astoundingly bright and really made it look like the sun was going down in the WRONG place.
While taking the dogs out for their daily jaunt over the equestrian trails hereabouts yesterday morning, I was fortunate enough to experience several tiny drops of rain at 7:10 AM. Rubbed a couple off the dusty car windows to be sure it was happening, it was THAT slight! It lasted for maybe 15 minutes. How tiny were the drops? Oh, maybe 500 microns in diameter, practically “drizzle-sized.” Recall this is ONLY THE BEGINNING of “stormy weather” in SE AZ, to quote a song title by Harold Arlen and Ted somebody.
What is “drizzle-sized” you ask? Well maybe you didn’t ask, but I am going to tell you anyway as part of a harangue about folks mis-indentifying drizzle occurrences. It happens a LOT even with your local TEEVEE weather presenter (can’t refer to anyone who doesn’t know what drizzle is as a “meteorologist”!)
Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter. A typical human hair is 100 microns in diameter. So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses. The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt. This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.
A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle” as “drizzle.” A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air. In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”! But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.” These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.
Since repetition is important for learning things, I have copied the two paragraphs above and have pasted them below:
Drizzle drops are defined by official weather folk who know what they are talking about as those drops between 200 and 500 microns in diameter. A typical human hair is 100 microns in diameter. So, they are darn small and have so slow a fallspeed that they appear to float in the air. If you ride a bike, you will know that no baseball cap will keep drizzle drops off your glasses. The World Meteorological Organization’s description, is “fine, close together drops.” Furthermore, unlike yesterday when those drops were incredibly sparse, drizzle occurrences are often noted by lots of tiny drops in the air, 1os per liter of air if you want a number, which I doubt. This often causes the visibility to be reduced, but it is also close to saturation in most drizzle, sometimes the visibility is reduced further also by fog.
A common misconception today by those ignorant of what drizzle is, is to refer to a “sprinkle” as “drizzle.” A sprinkle is a smattering of much larger drops that fall rapidly; never appear to practically float in the air. In the parlance of the old teletype weather reports, they used to be described in “hourly” station reports, such as at Tucson, as “RW–“, that is, “very light rainshower”, and NEVER as “drizzle”! But for some reason, not sure why, there has been a corruption of the word “drizzle” to more often indicate “sprinkles.” These have even crept into the official reporting records, particularly at military stations such as Davis-Monthan for some unknown reason.
Finally, I would like to insult you by quoting from the Bill Nye the Science Guy program, one sponsored by the National Science Foundation, BTW, and his science ditty, The Water Cycle Jump: “Your brain is on vacation, if you don’t know about precipitation.”
So there.
Finally, here are the clouds that produced the drizzle as it was happening. You are looking at the west side of the Cat Mountains and you can see that those “Stratocumulus” clouds are quite low based, necessary for drizzle drops to reach the ground. However, I have to say that they were still a surprisingly great height above the ground for a drizzle drop to have reached me. That drop HAD to be much larger coming out of the base to have fallen, say 3,000 feet and reach me as drizzle sized. An alternative explanation that would go with the very sparse nature of the drops was that the clouds reached below the freezing level and a few ice crystals formed, which then grew into raindrops (bigger than 500 microns in diameter). TUS sounding doesn’t support this, but, BUT, the bank of clouds over Catalina was NOT over TUS at the time of the sounding release, so I think this is still a viable explanation.
This is one of the best days in my life! The NOAA NCEP computer model has looked at the new data that came in overnight from around the world and now, in calculating the new maps from that data, it thinks we are going to have quite the series of storms here in SE AZ! Our spring grasses and wildflowers might yet get help in time to save the blooms!
Take a look at these images from last night’s NCEP model run reproduced by IPS Meteostar here (0ne of the best weather providers on the web in my opinion). Below are highlights from IPS Meteostar model reproductions, namely those half dozen “future maps” having rain in them for around here. BTW, a weather convention is that precip is colored green.
There are no less than six storms predicted to occur over the next two weeks! It doesn’t get any better than this in you live in a desert!
Of course, if you’re a real weather forecaster, you know that it is likely that none of the below will be accurate. But the excitement is in that it MIGHT happen just as the computers are predicting. It’s something like a Fantasy Baseball team you have assembled prior to the season and in your players you see all their potential maximized. In essence, it is just like this with last night’s model run, every rainstorm you see here, together as a unit of six, is like a fantasy team combining to win the pennant. It probably won’t happen quite. But, the excitement is in the air, until those models break your heart by taking all the rain away in the next few runs, as they sometimes do.
Here are some maps from last night’s wonderful run with brief notes:
1) Valid this Thursday, most likely just a close call. Note tiny green area just north of Tucson.
2) Below, valid Saturday, the 19th. Rain moves up northward from a band in northern Mexico and on this map, has already passed over Tucson.
3) Below, valid Sunday the 20th. Major southern California storm eases into southern Arizona!
4) Below, valid Wednesday the 23rd, another rain!
5) Below, valid Friday, the 25th of Feb, a real dump Mr. Model thinks.
6) Finally, valid on February 28th, still more! And man do we need it!
Now here’s something I have NOT seen before, which is pretty hard to have happen after decades of photographing the sky. Here’s what I saw around 1:30 PM yesterday over Catalina. I took three photos starting at 1:27 PM, 1:31 PM and 1:37 PM. Here they are:
So, how to explain this odd “stitched” contrail? Well, we can start with a few “facts” and hypotheses concerned with the aircraft and its crew.
1) Of course, with today’s modern instrumentation, pilots no longer have to actually fly commercial jets anymore. They simply set their destination with their Tom-Tom GPSes; flight levels and so forth, and then go to sleep until near landing time when they have to wake up again to be sure the automated process is still working. Perhaps when I took these photos, the flight crew was napping and the plane was kind of zig-zagging around that bit, I’m sure to the amusement of the passengers, who probably needed some excitement anyway to distract them from their cramped quarters.
2) The pilots WERE flying the plane, but weren’t focusing on the task at hand, but were distracted while talking about stuff, maybe sports; perhaps recounting the great classic Superbowl game matching up two historic Rust Belt sports franchises, the Packers and the Steelers.
3) Since alcoholic beverages are available on flights, perhaps the pilots had some beer and while not necessarily really drunk, weren’t able to fly in a straight line.
Personally, I reject all of the above. They appear to be “strawmen”, the result of superficial thinking strictly for entertainment purposes rather than having any intellectual depth.
Now for the “WHAT” part.
4) There are rarely seen regular undulations in the higher cirrus clouds in these photos, amazing ones really. These reveal waves pretty much perpendicular to the wind direction. The flight track is along the wind (tail wind). These waves in the atmosphere are like gigantic ocean swells, usually occurring where there is an noticeable increase in the wind with height.
Could these waves have produced this stitched pattern? I am thinking “yes.” That aircraft was likely close to the bottom of those cirrus (undulatus) clouds, and was SURELY experiencing those atmospheric waves, and likely exciting the passengers who probably needed some excitement to distract them from their cramped quarters-worth repeating.
We can’t tell here whether the contrail is rising and falling as would be happening in the cirrus lines and between them, respectively, or whether there is a perturbation to the horizontal winds associated with those waves. A time lapse would be great here, and here’s one though it had some problems yesterday, from the University of Arizona’s Atmospheric Science Department. A part of the contrail moves into the time lapse frames at 1:30 PM over Tucson, and from this angle, looking toward the Catalina Mountains to the N-NE, it does give an impression that the contrail was rising and falling. Confidence is low here, though, in that description.
Here’s the last shot as this phenomenon and cirrus waves raced over the east horizon. This last one makes it appear that the horizontal winds fluctuated more than the vertical winds under these waves producing a zig-zag in the horizontal.
With all the wonderful cirrus clouds around yesterday after a long absence, we had another one of those memorable Arizona sunsets, see last photo.
There have been a coupla comments on that aircraft effect in clouds blog of a coupla weeks ago and so I thought I would follow up with this sequence from the Atmos Sci Building rooftop at the University of Washington where I spent most of my time instead of at my desk.1
Here is a rarely photographed sequence of the effect of an aircraft on a supercooled cloud. The first photo, right after a contrail-like feature was seen in these Altocumulus clouds.
Look at what seems to be a dark contrail-like line in the middel of the photo. The Altocumulus (perlucidus) cloud layer, mostly comprised of supercooled liquid drops, is probably around -20 C, though I did not get a PIREP on this day for some reason.
In the minutes after this first photo, the aircraft trail seems to disappear as it widens and the shadow lessens. This stage is not shown because I didn’t realize what was going to happen until minutes later. This second stage is almost impossible to pick up visually because there are no ice trails yet, nor is the cloud opening up at this time. This “invisible” stage might last 5 minutes before you see the hair-like signs of a fallout of ice crystals.
This second photo is about ten minutes after the line in the first photo. Now it is clear that ice has formed, the crystals are growing and falling out as "virga", and a clearing is starting to open up.
Ice grows rapidly in the presence of the supercooled drops. Ice represents something of a low pressure center in the middle of all those droplets and that attracts the vapor from them, causing them to evaporate. That vapor deposits as ice on the newly present ice “germs”/crystals created by the aircraft. Since the drops are disappearing, before long, you get a hole or ice canal in the cloud where the droplet cloud used to be.
In this third photo, there is no longer any doubt about what's is going on. The hole is there, and its only a question of how much larger it will get.
The ice crystals shown above are clearly falling out (ever-so gradually because they are so small still, perhaps a few hundred microns in width). Becasue they are so small, they usually evaporate well before any precip reaches the ground. However, recently it has been shown that in deeper clouds and more moist conditions, that an aircraft can actually produce a bit of rain/snow at the ground due to this effect.
Here is last photo I took that day.
The ice crystal induced hole in the Altocumulus layer has gotten closer to exiting the liquid cloud (has moved to the edge of it) as well as expanding some. This suggests that the ice cloud was moving faster than the droplet cloud, something that happens when waves in the atmosphere are producing the droplet cloud. It was also getting closer to the observer, however.
Sometimes, if the cloud layer is lifting enough, the original Altocumulus clouds will gradually fill back in because all of the ice has settled below the liquid cloud layer.
For history buffs, holes in clouds with ice in the center, or ice canals were seen in the 1930 and 1940s, but as you can see, unless the observer saw the original trail (which they usually didn’t) no one knew what caused them. Eventually an ice canal was was photographed in 1946 that was so convoluted it was realized that ONLY an aircraft could have done it.
Furthermore, that report in 1946 preceded the discovery of modern cloud seeding with dry ice by Vincent Schaefer in 1947 who performed his most convincing, and could be seen as ironic, demonstration of seeding with a similar convoluted ice canal as was seen in 1946 in a supercooled Altocumulus cloud layer Its interesting in retrospect, as so many things are, that Schaefer did not have to drop dry ice on his clouds that day in 1947 in which he made history, but rather only had to fly his prop aircraft through them and likely would have gotten the same effect!
BTW, there is a lot of new interest in this topic, a new article recently appearing in Science mag.
I mention this cloud seeding benchmark since these aircraft events represent inadvertent cloud seeding, and in a sense they demonstrate that you CAN get something in the way of precip to fall out of a previously non-precipitating or barely precipitating cloud by seeding. When clouds are already naturally precipitating, what happens when you do cloud seeding is subject to question; the science domain in this murky world is highly polarized.
The “Story of APIPs”–Aircraft-produced Ice Particles) is told (in the usual “style” you will often find here) in the gigantic powerpoint “show” on this website under Sci Talks toward the middle of the show, around slide #472 (hahaha).
This ppt “show”, BTW, is WAY overdone, but, what the HECK! Why tell only “the whole 9 yards” when you can tell 12 or 14?
1Hahaha, sort of. Sometimes, looking at those several thousand film shots from the rooftop of the Atmos Sci Building, I do wonder about that. But then again, since I used 1/100 of a second exposures with my film cameras, these photos would only PROVE that I had been on the roof, maybe 30 seconds in 30 years there at the UW.
Feeling better now.
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