Artifact skies

I use that expression not only to draw attention to myself since my name is Art, or, “Artie boy” to mom, but also because I had a role in bringing this phenomenon to the attention of the scientific community; that is, that an aircraft could glaciate portions of clouds at temperatures as high as -8°C.  This in a peer-reviewed article  so controversial it was rejected twice by journal reviewers  before “getting in “(pdf here)!  Some background on why this happened is found in a footer way down below….

Its common knowledge today that an aircraft can produce in essence a contrail in clouds at temperatures down to about -10°C and must be avoided when researchers are sampling the same cloud over and over at below freezing temperatures.

Back to the beginning:

The day began well enough with a nice sunrise over the Catalinas:

7:28 AM. Really cold Altocumulus perlucidus lurks over the Catalinas.   The sounding suggests that this layer was at -26̂°C, and yet no ice or virga is present.  This is not unusual.  Ice tends to form more readily when the droplets in clouds are larger–these were likely tiny, 10-15 microns in diameter, and, being a layer high in the atmosphere, not connected to the ground, meant there would be a dearth of ice-forming substances like dirt, well, kaolin mineral particles.
8:01 AM. Well, OK, for the really sharp-eyed cloud maven juniors, yes there was a trace of ice here and there in those clouds.

Here’s the early morning National Weather Service  balloon sounding from the U of AZ:

This sounding was launched about 3:30 AM AST yesterday morning. During the day, the bottom of the Altocumulus clouds lowered and got a little warmer, but still plenty cold for aircraft ice production.

Then, as the Altocumulus layer filled in from the west, the aircraft effects roared to life.  An example from yesterday, one that passed right overhead of little Catalina!

10:01 AM. A parch of aircraft-induced ice in this Altocumulus perlucidus translucidus composed of supercooled droplets otherwise, is about to pass overhead of Catalina.


10:08 AM. High temperature contrails rip through a Altocumulus perlucidud translucidus layer up around -25°C.
10:10 AM. Looking for some optical fireworks here, such as a tangential arc (halo curving the wrong way), but only a hint of one showed up. Can you see it?
11:23 AM. Another clearing with ice below it is seen just SW of Catalina from the parking lot of Basha’s where I went to get some cottage cheese.
11:33 AM. Sun dog (parhelia) lights up in the ice patch above after I came out of Basha’s with some cottage cheese.  Note to writers;  little, seemingly irrelevant details like what you bought in a supermarket makes your writing come alive for the reader.
1:21 PM. There’s another couple! They were just everywhere yesterday!
3:52 PM. Later as the moist layer deepened and lowered further, there was ice aplenty, but it was impossible IMO to tell whether it was au natural or aircraft-induced. Surely, some was due to aircraft penetrations of supercooled clouds. However, when the air is rising enough, a hole or ice canal may not appear since droplets can reform rapidly.
3:52 PM. Looking more to the west where the long trails of ice are more visible.
4:14 PM. I feel asserting here. I assert that this one is from an aircraft, but with droplet backfill that prevented a hole from forming.  Looks like “phony” virga to me, and, of course, to you, too, as a certified member of the cloud maven society.
5:21 PM. Interestingly nearly all virga disappeared about this time, certainly nothing extraordinary that led to the suspicion of aircraft induced ice. The sounding suggests that the higher temperatures that the Altocumulus layer was at may have been the reason. See below…
The U of AZ balloon sounding launched at 3:30 PM suggests the bases of the Altocu have dropped down to about 18,000 feet above sea level, 15,000 feet or so above Catalina, and are much warmer, and thicker than when the day started as we could see.



The weather ahead

More interesting middle and high clouds, probably a great sunset/sunrise or three, but no rain, just virga.  The present mass of middle clouds passing over has some virga and sprinkles, but that’s about it  from this episode.  No real support yet for a change in our dry, warmer than normal weather regime in spaghetti plots though one trough a week or so out is forecast to bring a little rain.

The End

Some background on “APIPs”

This phenomenon had been shot by photographers for decades, yep, DECADES,  BUT, it was believed (apparently) by those doing cloud research, that it only happened at very low temperatures such as those when the normal contrails we see occur (at temperatures lower than -35°C), viz.,  it was ignored.

Another factor was that all of the rare photos of this phenomenon, dubbed “Aircraft Produced Ice Particles” (APIPs, by yours truly, though not the greatest name)  appeared in lay or quasi-lay publications and were likely missed by those with big Ph. Ds. who only read technical journals.  An example of this was on the cover of  the Bulletin of the American Meteorological Society in 1968, a cover shot which drew the greatest amount of reader comments that the journal had ever seen!  They went on for a couple of months, some suggesting that the ice and hole in cloud was due to a meteorite!

Also, it was a rare case indeed when the photographer could report the temperature at which it occurred. 

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.