Stationary rainbow sets duration record, maybe

Had another rainbow from those cloud “warriors” we call Cumulonimbus on the Catalinas. But, “If traces are your thing, Catalina is king!” as we recorded but a trace of rain again while soaking rains poured down just a couple of miles away on the Catalinas, to form a sentence with too much punctuation and a sentence within a sentence¹.

More interesting perhaps to some, this modest rainbow formed just after 5 PM yesterday toward the Charouleau Gap, as seen from Catalina, and was still in almost the same spot after 30 minutes. Have never seen that before since both the sun and the showers are drifting along and so the rainbow should change position.

First, in today’s cloud story, the strangely believe it rainbow part:

5:12 PM. Rainbow first spotted toward the Gap. Cumulonimbus cloud not sporting ice at top; ice is below flat top due to weak updrafts that allow the ice crystals to subside. — 5:12 PM. Rainbow first spotted toward the Gap. Cumulonimbus cloud not sporting ice at top; ice is below flat top due to weak updrafts that allow the ice crystals to subside while the top remains mostly liquid appearing. The smoothness on the side of the cloud above the rainbow is due to ice particles

5:42 PM. While the observer has moved some few hundred yards, the rainbow has stayed pretty much where it was after 30 min. A course in optics would be required to explain this and that’s not gonna happen (accounting for the sun’s movement, the rain, and the observer’s movement).

The whole day represented several phases, the early, spectacular eruption of clouds on the Catalinas as it started to warm up under clear skies, those low bases topping the mountains again indicating stupendous amounts of water are going to be in them when they grow up, the rapid appearance of “first ice” just after 10 AM, the heavy showers and cooling on the mountains and here (little thunder heard), the clearing due to the cooling, the warming, the rebuilding of the Cu on the mountains, and new showers–the rainbow was part of the second growth phase, and then the gradual die out of the Cu as sunset occurred.

Huh. I just realized that what happened to our temperatures yesterday was like a mini-sequence of the earth’s climate over the past 200,000 years or so, the prior Ice Age in the morning temps, the warm Eemian Interglacial as it warmed up, the last ice age when the cooling wind from the mountain showers hit, then the warm Holocene when the clearing and warming started up again in the afternoon! Cool, warm, cool, warm. Below, the Catalina temperature record that emulates earth’s climate over the past 200,000 years, beginning with next to last “ice age.” I can’t believe how much information I am passing along today! What a day you had yesterday!

Mock climate change for the earth's past, oh, 200, 000 years or so as indicated in yesterday's Catalina/Sutherland Heights temperature scale. — Mock climate change for the earth’s past, oh, 200, 000 years or so as indicated in yesterday’s Catalina/Sutherland Heights temperature scale. But, we have a LOT of days like yesterday’s in the summertime, but only now after 7 summers has it hit me how it mimics our earth’s “recent” past climate.

Cloud Alert: Yesterday might have been the last day for summer rain here. U of AZ mod from last night has plenty of storms, but we’re on the edge of the moist plume, and those storms take place just a hair east of us it says. So, while they may be on the Catalinas today, unless we get lucky, they’ll stay over there. Drier air creeps in tomorrow, too.

Here is the rest of our day in clouds, from the beginning, even if its not that interesting. In the interest of efficiency, you’d do a lot better by going to the U of AZ time lapse site to see all the wonderful things that happened yesterday, instead of plunking along one by one as you have to do here. (PS: Some functions in WordPress not working, would not allow some captions to be entered as usual.)

9:21 AM. This tall thin Cumulus cloud was a reliable portent for yesterday's early storms on the mountains. It just shot up! — 9:21 AM. This tall, thin Cumulus cloud was a reliable portent for yesterday’s early storms on the mountains. It just shot up!

11:57 AM. Thunder and downpours are widespread on the Catalinas.

2:46 PM. After the long clearing, Cumulus begin to arise on the Catalinas again.

DSC_0005-1 — 5:46 PM. A pretty, and isolated Cumulus congestus with a long mostly water plume ejecting toward the NW. Some ice can be seen falling out of that ejecting shelf. Now here’s a situation where an aircraft measuring the ice output from such a cloud can miss it because its formed as the turret subsides downstream, and most of the ice is substantially below its top, and under the shelf. If you cruised along the top of the shelf, you would miss most of the ice and measure ice particle concentrations that are much lower than what the cloud put out.

DSC_0017-1 — 6:17 PM. This same quasi-stationary cloud with its long shelf, still shedding ice just downwind of the cloud stem, is about to disappear. Note, too, that the ice fall quits after awhile going downstream even though cloud top temperature is the same for quite a distance. The ice was actually formed at lower temperatures in the protruding turret, not at the temperature of the shelf, which apparently were too high for ice to form. Also, cloud droplet sizes shrink from those in the protruding turret as evaporation takes a stronger hold. Larger droplet sizes are associated with greater ice formation at a given temperature.

6:12 PM. Like aspen leaves in the fall, but every day, our clouds change color as the sunsets. Here’s another memorable site, not only due to the color, but how tall and thin these Cumulus clouds are, showing that the atmosphere was still extremely unstable over the depth of these clouds, probable 2-3 km deep.

The End.

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¹Hahah-these are just a couple of the grammatical gaffes I actually know I’ve done!

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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