Mostly in absentia yesterday: contrails

Yesterday was as remarkable in its way as the day before in its generic beauty.  Delicate Strands and fibrous blobs of Cirrus in interesting shapes floated by overhead with nary a contrail to contaminate those scenes.  While our little part of the sky above Catalina, Arizona,  is a low contrail impacted zone of the sky, yesterday seemed exceptional.   It mgiht have been because, and since I am guessing here, will not check it out, those wonderful clouds and that moist layer they were embedded in was LOWER or HIGHER than usual, and the flight levels that the jets were flying in remained very dry so that they don’t persist.  Its the ambient humidity up there that makes them various lengths.  If its too dry, there is only that bit right behind the jet–recall Appleman (1951) and the Appleman diagram.

Also, the wind direction at flight levels helped; due west generally keeps those contrails packing airways just to the north of us and to the south streaming along beside us, not over us.  That always helps.

But, I didn’t really see much off to the north, where there are usually a half dozen or so on any “Cirrus-ee” day.

Was it because it was New Year’s Day and air traffic is unusually low because no one wants to travel because they wouldn’t be able to watch the Rose Parade and various football bowl games?  Don’t know, but maybe.

I have given you a LOT of things to think about, and while you’re doing that, I will post some evidence, contrail-less Cirrus skies.  You won’t find this kind of day we had yesterday along the Atlantic Seaboard on any day with Cirrus with all the jet activity.

7:53 AM. Here come those Cirrus clouds!
9:25 AM. Cirrus spissatus (dense Cirrus) approaches, the only kind of Cirrus in which gray shading is allowed.
11:16 AM. Quite oddly, whilst talking about a lack of contrails, I show a snippet of one here. It had quite the long virga trails. Those trails would have been composed of larger crystals that grew in the moist air in the exhaust of the jet.
They’re long because the air was moist below the jet, but just for that bit where it flew and hit a moist patch at flight level and below it.  Perhaps he was changing flight levels?
11:24, just eight minutes later, this same contrail segment. Estimating length of those trails, a kilometer, about 3,000 feet. What is also a bit odd, they’re hanging almost straight down below the original contrail for such a great distance before curving off. This tells you that over a fairly great depth, a few thousand feet, the wind did not change in velocity or direction, a bit unusual. You likely pointed that out to your friends yesterday anyway, but I thought I would mention it.
1:45 PM. Delicate Cirrus fibratus (more or less has straight fibers), and NO CONTRAILS. This was an amazing sight to me since you’re staring right out into one of the heaviest air corridors near us. Well, maybe on on the far, far horizon.
4:47 PM One of the most interesing/odd sights, this angular piece of Cirrus spissatus (popularly called, “Cis spis.”) I thought I would show off some camera razzle dazzle by pointing it at exactly the angle required to get an internal glint, a reflection, that points to that interesting Cirrus cloud I wanted to blab about.
5:04 PM. Same cloud almost overhead with a razzle dazzle glint-reflection pointing to the “tail”, that last bit of snow/ice crystals falling out of this Cirrus patch.
5:43 PM. Another one of the reasons we live here; our fine, fine sunsets, so many.
Here what you are seeing underlit are the tiny ice crystals that are in the last stages of being evaporated, once having falling out of their parent clouds higher up. Because they are now so tiny, and about to disappear, they have almost no fallspeed and kind of float at one level for awhile. You can see here how flat that is in the sunset. A new spec of parent cloud is also visible, one that has just formed and has no trails yet (slightly left of center).

The weather ahead?

There isn’t any.  Well, any worth mentioning right now.  Gotta get through this week or two dry spell somehow…

Will dredge up some January climo tomorrow or the next day.


The End.


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.