Riming-splintering mechanism

Sutherland Heights storm total now 0.71 inches as of 7 AM; soil turning green as moss look alike growth reminding one of Seattle spurts from bare ground!

First, in blogging for dollars, this:

3:55 PM. Rainbow fragment and solar home. Yesterday's visual highlight. Yours for $1995.95. If you call now, we'll throw in a exact same photo FREE! — 3:55 PM. Rainbow fragment and solar home, an extraordinary combination.. It was yesterday’s visual highlight. Yours for $1995.95. And, if you order now, we’ll throw in a second, exact copy of this extraordinary, magical scene FREE!

Here’s a nice one from the day before as the clouds rolled in, starting with Cirrus and Altocumulus, lowering to Stratocumulus later in the afternoon.

5:04 PM, 30 Dec. Sun break amid Stratocumulus. Stratus fractus topping mountains.

Yesterday’s clouds; an extraordinary day with a little drizzle amid light showers

Hope you noticed the true drizzle that occurred yesterday, namely, fine (larger than 200 microns, smaller than 500 microns in diameter), close TOGETHER (critical to the definition of “drizzle”) drops that nearly float in the air. They may make the least impression, or none, when landing in a puddle.

When you see drizzle, you have the opportunity of chatting up your neighbor by educating them informally to what drizzle really is (many, maybe most, TEEVEE weatherfolk do NOT know what “drizzle” is, btw), and 2) by telling your neighbor, if he/she is still listening to you, that the droplets in the clouds overhead must be larger than 30 microns in diameter, or better yet, “larger than the Hocking-Jonas diameter of 38 microns, at which point collisions with coalescence begins to occur” and “drizzle is not produced by ice crystals in the clouds overhead; they’re not enough of them to produce ‘fine, close together drops.'” Your neighbor has likely left the building at this point, but, oh, well, you tried.

Here, in Arizona, shallow clouds, such as we had yesterday, hardly ever can produce the broad droplet spectrum in which clouds have droplets larger than 30 microns in diameter. Its because this far inland from the ocean, where the air is very clean, the air has picked up natural and anthro aerosol particles that can function as “cloud condensation nuclei” (CCN). As a result of ingesting dirt and stuff, clouds have too many droplets here as a rule for the droplets in them to grow to larger sizes. They’re all mostly less than 20-25 microns, sizes in which even if they collide, they can’t coalesce.

In “pristine” areas, if you go to one, such as on a cruise out in the oceans, droplet concentrations in clouds are much lower, and even a little water that might be condensed in a shallow cloud can produce a broad spectrum, one that extends to droplet larger than 30 microns.

So even little or shallow layer clouds can precip over the oceans, produce drizzle or light rain showers (in which the larger drops are bigger than 500 microns in diameter). Of course, here we recall that the (whom some consider “villainous”) geoengineers want to stop drizzle out over the oceans so that clouds have longer lifetimes, are darker on the bottom, and reflect more sunlight back into space.

Those guys can be lumped into the same ilk as those who want to change the color of the sky from blue to whitish or yellowish by adding gigantic amounts of tiny particles in the stratosphere, again for the purpose of cooling the planet! Unbelievable. Please ask before doing this!!!

A Pinatubo sampler for what “geoengineering” would do to our skies, say, sunsets in particular. I took this photo from the University of Washington’s research aircraft in 1992 off the Washington coast in onshore flow. But we saw these same sunsets, sunrises, yellowed by the Pinatubo eruption of June 1991 everywhere we went, including in the Azores in June 1992.

OK, pretty boring, whiney, really, so inserting picture of a nice horse here to make people feel better if you’ve been depressed about what our scientists have been pondering to do about global warming other than controlling emissions:

8:57 AM. Zeus. Led cloistered life for 13 years; likes to bolt now that he's getting out. — 8:57 AM. Zeus. Led cloistered life for 13 years; likes to bolt, now that he’s getting out on the trails.

7:40 AM, yesterday, Dec. 31st. The low hanging Stratocumulus clouds, about 1500 feet above Catalina, and the mountains had a bit of an orange tinge. It was probably due to sunrise color on a separate much higher layer.

Later….drizzling Stratocumulus, same view:

10:30 AM. Stratocumulus praecipitatio, if you want to go "deep" into cloud naming. "Stratiformis", too, covers a lot of the sky. — 10:30 AM. Stratocumulus praecipitatio, if you want to go “deep” into cloud naming. “Stratiformis”, too, covers a lot of the sky. Note misty-like view, lack of shafting.

12:48 PM. More Stratocu P., an example of those clouds in the distance that kept dropping little and light rain showers on Catalina.

1:01 PM. Highlighting amid the RW-- , (weather text for "very light rain showers"). — 1:01 PM. Highlighting amid the RW– , (weather text for “very light rain showers”). Stratcu P., with maybe Stratus fractus or Cumulus fractus below. The shadowed, dark shred clouds in the mddle would be Stratus fractus IMO.

3:55 PM. Zooming in on that pretty rainbow. You know, this is a cloud heaven here. I hope you all appreciate it! Maybe that’s why I get upset over “geoengineering” and changing the sky anywhere.

3:57 PM. Between showers, but new ones erupted upwind. This one have a shaft, implying a higher cloud top than the prior, non-shafting clouds that brought us semi-steady RW--. — 3:57 PM. Between showers, but new ones erupted upwind. This one have a shaft, implying a higher cloud top than the prior, non-shafting clouds that brought us semi-steady RW–.

The second extraordinary thing about yesterday was that the top temperatures of these clouds was around -10° C (14° F), temperatures that ice does not form act as a rule in Arizona. To get ice at temperatures that high, you also need larger cloud droplets, and they have to occur in the -2.5° C to -8° C range. In this range, it was discovered that falling ice crystals, mostly faster falling ones like “graupel” (aka, soft hail) when colliding with larger drops, ice splinters are produced. The cloud droplets must be larger than 23 microns in diameter in THAT particular temperature zone, something that would occur more often in our warm, summer clouds, but would rarely be expected in our winter ones.

Why?

Again, it goes back to clouds in inland regions ingesting lots of natural and anthro aerosols that cut down on droplet sizes in clouds (by raising droplet concentrations in them). Our recent rains have helped cut down on that process on ingesting dirt, for sure, and was a likely player yesterday. Furthermore, our winter clouds are moisture challenged relative to the summer ones with their tropical origins and high cloud base temperatures, a second reason not to expect larger droplets in our winter clouds.

Here is the TUS sounding with some writing on it for yesterday afternoon from IPS MeteoStar. (Satellite imagery was also indicating warmer than usual tops for precipitating clouds yesterday.):

The TUS balloon sounding ("rawinsonde" in techno speak) launched at about 3:30 PM yesterday afternoon. Balloon rises at about 1,000 feet a minute, FYI. Typically they pop up around 100,000-120,000 feet! Instruments are parachuted down. Sometimes they are found and returned to the NWS and re-used! How great is that? — The TUS balloon sounding (“rawinsonde” in techno speak) launched at about 3:30 PM yesterday afternoon. Balloon rises at about 1,000 feet a minute, FYI. Typically they pop up around 100,000-120,000 feet! Instrument package is parachuted down so it doesn’t conk somebody on the head. Sometimes they are found and returned to the NWS and re-used! How great is that?

Here’s the punchline: If clouds are drizzling, then they are ripe, if the tops get to lower temperatures than about -4° C for what we’ve termed “ice multiplication” or “ice enhancement”. A very few natural ice nuclei at temperatures between -4° and -10° C, say, starts the process, those forming “soft hail” which then leads to ice splinters. This is the leading theory of this anomaly of ice in clouds at temperatures only a little below freezing, if you think 23° to 14° F fits that definition.

There are exceptions where this process did not explain the ice that formed at such high temperatures, so standby for further elucidation about how in the HECK ice forms in clouds at some point in the future.

As usual, no time to proof, so good luck in comprehending what’s been written.

The weather just ahead:

The second main rainband is just about here at 9:25 AM. Cloud tops will be deeper and colder than in the prior rains, raising the possibility of some thunder today, and maybe another third of an inch of rain. Watch for an windshift line cloud (“arcus” cloud) might well be seen today. That’s always dramatic and exciting here in Catalina cloud heaven.

The End at last!

And a happy, weatherful year to all!

Weather “stagecoach” full of storm presents set to arrive on Friday

Don’t really need me anymore. Everyone’s on top of this ” incoming” now, set to begin in the area overnight on Thursday, the one you’ve been reading about here since maybe last October I think. So, feeling sad today, also because it looks like its going to be a bit too warm for snow, which I think I mentioned about a dozen times. Maybe I will take it out on you by boring you with a science story, one about ice in clouds…but one featuring such stalwarts as Sir Basil Mason, Stan Mossop, John Hallett, Pete Hobbs, Alexei Korolev, and others. Interested now?

But first, a few nice cloud shots from yesterday so you don’t get too mad at me for boring you first:

2:07 PM. CIrrostratus fibratus (has detail, not just an amorphous veil).

4:21 PM. Cirrus spissatus patches and dog, Zuma (named after the acclaimed dramatic series, Baywatch, which took place at Zuma Beach, also where the author, whilst not storm chasing spent a LOT of time. — 4:21 PM. Two dense patches of Cirrus spissatus patches and dog, Zuma (named after the acclaimed dramatic series, Baywatch, which took place at Zuma Beach; also where the author, whilst not storm chasing, spent a LOT of time.

5:22 PM. Cross section of a Cirrus uncinus (hooked at the top). This shows how the ice crystals forming at the top first get heavy enough to fall out, but if encountering drier air, start to evaporate, slow in fallspeed, and as in this case, form a flat layer of tiny crystals at the bottom of the head of Cirrus uncinus. Likely a little moist again at that bottom location so the tiny guys don't away very fast. — 5:22 PM. Cross section of a Cirrus uncinus (hooked at the top). This shows how the ice crystals forming at the top first get heavy enough to fall out, but if encountering drier air, start to evaporate, slow in fallspeed, and as in this case, form a flat layer of tiny crystals at the bottom of the head of Cirrus uncinus. Likely a little moist again at that bottom location so the tiny guys don’t away very fast.

5:29 PM. Sunset in Cirrus (spissatus and others).

Cloud ice science story

(drink some coffee, maybe take an extra swig of an “energy drink” if venturing forward)

Kind of takes the fun out of it when other people are saying what you want to say by yourself, lilke today’s forecast for Friday’s storm. Kind of like being second when you publish “new” results behind other researchers who “got in” a little a head of you (like Korolev et al.-with Hallett!) did in 2004 reporting the FIRST image of a shattered frozen drop they said.

Drop shattering during freezing; what about it?

It was thought not to happen in natural clouds after that embarrassing episode back in the 1960s when the Great Knighted, Sir B. J. Mason¹ and his student, Swinbank (1960), reported drops exploded with they froze. Liquid centers tried to get out of the ice shell as the drop froze from outside in, as you would expect, but then blew up when the freezing water expanded inside the shell. Looked pretty good.

There was only one thing wrong, their findings weren’t valid for real clouds.

They put too much CO2 in their cloud chamber (that’s right, the very SAME stuff that’s supposed to make the earth warmer and warmer year after year but has been sitting around lately, about 15 years actually, not doing anything) and that CO2 in the experiments turned out to make the outer ice shell real weak, and also the CO2 came out of solution in the water in the liquid center to make matters worse by expressing gas through the shell. I wonder how many people have done that?

This was found out by researchers in my very own group before I got there, Jim Dye and Peter Hobbs, a few years later. When real air was used, the drops didn’t explode. So, down that hypothesis went that exploding drops caused a lot of ice to form in natural clouds.

End of story? Nope.

Later, Hobbs with grad student, Abdul Alkezweeny, repeated the experiments with freezing drops, but this time instead them just sitting there, had them rotate as they froze and they DID shatter some, but not a lot! This was back in 1968.

But no one was reporting images of shattered drops.

In those days, there was a HUGE amount of unexplained ice in clouds. Cloud chambers on the ground and in aircraft, found that little ice formed until the air IN THE CHAMBER was at least as cold as -20 C (-4 F), but instrumented aircraft repeatedly found tremendous amounts of ice in clouds that had never been colder than -10 C (14 F). Hence, an enigma.

But the explanation that a few drops exploded, sending out thousands of ice shards never gained any ground because there was never any observational evidence that it happened. Instead, an Australian researcher, originally from South Africa, Stanly C. Mossop, with John Hallett, discovered in 1974 that a bar moving through a cloud chamber between -2.5 C and -8 C, caused ice splinters to eject from SOME of the little drops hitting the bar and freezing on it. But the drops had to be at least 24 microns in diameter, fairly large for cloud droplets, or nothing happened. Also, if they moved the bar too fast or too slow, nothing happened. So, there were a lot of criteria involved in this process, temperature range, drop sizes, speed.

So, the Hallett-Mossop riming-splintering hypothesis was born. They assumed the bar, moving at the fall speeds of soft hail, showed what soft hail did inside clouds: multiply ice content!

It was an exciting time to see that the mystery of all that ice in clouds at higher temperatures was finally explained, not needing, shattered drops or anything else.

But there were some problems. In the early days, it was thought that this process, to raise the ice concentrations in clouds much, would take as long as 1-2 hours because it was a “cascade” process. The few first splinters had to grow to sizes there they fell fast enough to bump into drops and cause ice splinters to eject. Well, that wasn’t right. Natural clouds formed ice MUCH faster than that, as you here in Arizona know so well.

The experiments continued and it was found that shattering helped this process (assuming it occured, but even more important was the freezing of drizzle and raindrops. When those froze, they became instant rimers, splintering objects, and so the time for a cloud, but one having drizzle and raindrops in it, and in the right temperature zone, just between -2.5 and -8 C, was cut down to minutes, something like 10-20, to get ice concentrations from about 1 per cubic meter, to tens of thousands per cubic meter, a real rain cloud.

Except for a single image of a drop half by a researcher using a cloud camera with a glider in the 1970s, no one had reported a shattered drop. Then along come Korolev et al. (with the great Hallett!) in 2004 reporting shattered drop images in a Canadian frontal band using an advanced cloud camera. They wrote that it was the FIRST images ever reported of shattered drops. Rangno and Hobbs (2005) also reported images of shattered drops in clouds around the Marshall Islands, thinking at the time that they were going to be first in line, and then discovered the Korolev et al. report. It was a sad day to find that reference, as a researcher that was thinking about the glorious days ahead, the keynote addresses to important conferences, that would result from being first in line with something and then other people would always have to reference you.

As Ecclesiastes wrote, their is hardly anything new under the sun if you’re slow going about it.

Published another paper on shattered drops back in ’08. But, found they didn’t SEEM to be making a big contribution to the ice content in clouds, less than 10%. You can go here to see that I didn’t make that part up. That was kind of sad finding, too. You want what you find to be HUGE, and it wasn’t so huge as I hoped.

So, riming and splintering remains our best, most accepted explanation for the great amounts of ice in clouds that aren’t so cold, though the author and Hobbs, have mostly found it wasn’t powerful enough to account for the speed of ice development. Only the author’s friends, Stith et al (2004), have reported a lot of ice that couldn’t be explained by the riming-splintering mechanism as have R&H over the years.

But it would be so great if others confirmed the Stith et al findings.

The End for now.

———————-

1Wiki doesn’t do a very good job, and doesn’t even list his outstanding updated, Physics of Clouds text published in 1972, the “bible” of cloud physics in those days! Unbelievable.

²Riming: Think of what happens to an airframe in a liquid drop cloud at below freezing temperatures. HELL, here’s a photo by the author from the author-occupied Lear Jet 35 flying in supercooled clouds over Saudi Arabia, 2006, The weapon-looking things under the wings image precipitation particles like raindrops and snowflakes using laser beams with light sensitive diodes at the other end, one that when shadowed, give you a two dimensional image of what went through the laser beam.

ann DSCN1223 rime icing — 8:01 AM, December 16, 2006.

11:02 AM, December 10th, 2006. Had to land at Hail, a small, pretty town north of Riyad to pick up some supplies, ones for the randomized cloud seeding experiment underway. It was interesting that we could carry these boxes labeled "Explosive" to the Lear Jet without any notice. Hmmmm. — 11:02 AM, December 10th, 2006. Had to land at Hail, a small, pretty town north of Riyadh to pick up some supplies, ones for the randomized cloud seeding experiment underway. It was interesting that we could carry these boxes labeled “Explosive” to the Lear Jet without any notice. Hmmmm. They were there because that’s where another NCAR radar was besides the one at Riyadh, and a plane might have to land to continue seeding if it ran out of the seeding flares like the ones inside these boxes.