A day with rare and regular clouds

Yesterday, whilst disappointingly dry, no rain fell here overnight was a day of rare cloud sightings, most of it involving the rarely seen, “Cumulo-cirrus¹“, a cloud fakery situation where extremely cold (less that -40°Ç, -40° F)and clouds at Cirrus levels appear to be ordinary little Cumulus fractus clouds. I hope you weren’t fooled by those impersonators. You’d be pretty embarrassed at the next meeting when we go over yesterday… Yesterday was, in essence, a test for you, and I hope you passed.

Along with the rare “Cumulo-cirrus” sightings, there were intricate patterns in Cirrocumulus clouds that may have caught you’re eye. However, with the wind aloft being so strong (around 90-100 mph at 18,000 feet) you didn’t have a lot of time to enjoy them.

Yesterday’s clouds

10:01 AM. These were the first “Cumulus” pretenders I saw yesterday, though I suppose the discerning eye might have called them “Altocumulus” as well. When they first formed they look hard and rounded like they might have had cloud droplets. But then within seconds, that brighter look caused by high concentrations of droplets or tiny ice crystals (sometimes called “germs” because they have no particular shape when just formed) fades as the concentrations decline rapidly due to evaporation and mixing with the dry environmental air around them. Eventually, they become transparent. Also notice that you don’t see trails come down out of them. This is likely because the concentrations are so high that competition for moisture keeps all of the ice crystals so small they can’t really fall out.

10:01 AM. Zooming in. The brighter ones have just formed. The faded ones are the older ones heading for extinction. Many more shots of “Cumulo-cirrus” to follow. Got kind of carried away, as usual.

10:18 AM. Another moist layer shot in, first showing up as Cirrocumulus, though this cloud was in the middle levels, not at Cirrus heights. The fine granulation makes it look higher than it really is. This was probably around 12, 000 feet above the ground, if that. One giveaway was the rapid movement of the cloud itself, and compared to the cirriform clouds above it. If they are near the same levels, they won’t move much at all relative to one another. Anyway, these patterns changed by the SECOND! It was amazing how quickly they devolved into something completely different.

10:27 AM. A wid angle view of another incoming group of “Cumulo-cirrus.” The thinnest clouds are the ghostly remains of those clouds. The more compact and brighter ones are the youngest ones.

10:27 AM. A closeup of a just formed globule. Everything around it was onece like that but now has the visual attributes of regular Cirrus.

10:42 AM. One of the strangest cloud sights ever seen by yours truly, CMP. Here a layer of Cirrocumulus (note fine patterns lower center) passes rapidly underneath those globules of fake Cumulus clouds full of ice.

Explanatory figure below:

11:22 AM. Another patch of fake Cumulus fractus at Cirrus levels comes by. Note the true Cirrus in the background, and was higher than the fake Cu fra.

11:36 AM. Was beside myself seeing this! Just incredible!

11:38 AM. Just two minutes later! Look what has happened to that puff ball of ice. The turbulence up there must have been tremendous.

11:57 AM. Some real fakery here. Ordinary people would have said, “Oh, those are just little Cumulus fractus over our Catalinas.” But not you. You would have chided them in friendly, gentle way, telling them they were WAY too high for Cumulus clouds and are mainly composed of ice, not possible for low Cumulus fractus clouds. You could have also pointed out that the cloud in the upper part of this photos were way below those Cumulus fakeries, and that they about to obscure them as this encroaching layer slid underneath them. Also, try not to be condescending, act superior like you know so much even though you do. You might lose your friend if you do that.

11:53 AM. Another zoomed view of one of those icy puff balls, not long after it formed.

4:01 PM. Altocumulus opacus underneath a Cirrostratus layer. A great sunset was in the works with that opening to the southwest. Also notice, no ice or virga evident. Guess that the temperature at the tops of this layer, likely only a couple of hundred meters thick, is warmer than -10° C.

5:31 PM. Altocumulus opacus at sunset. The height of this layer was about 8,000 feet above Catalina by the TUS sounding, top temperature about -5° C. “No virga, no cry,” as Bob Marley said.

The End

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¹Though it fits, I made this cloud name up. Probably would be Cirrus floccus, maybe Cirrus castellanus in the humped up cases.

By Art Rangno

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.

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