Little low goes by at 30,000 feet

While working on a climate issues rant due to an article in the latest issue of Scientific American (May 25th), we had an interesting cloud day yesterday.  I needed a cooling off period anyway, so I thought I would point out some interesting things from yesterday, June 3rd.

Here is yesterday’s cloud movie pointed at the Catalinas, and courtesy of the University of Arizona‘s Atmos Sci Dept.  This is interesting because you will see the Cirrus moving out of the west in the morning, with some Altocumulus, Cirrocumulus underneath, then by afternoon, you will see the Cirrus moving from the east!   Hardly ever see that much change in wind direction at 30-40 kft in such a short time.

Also in the movie you will see a couple of great examples of Cirrus uncinus, tufted Cirrus with trails of snow coming out, actually more like single, tiny ice crystals maybe only a few human hairs in diameter (say 300 microns or so).  What type of crystal?  Of course, toward the bottom of the trails, you always want to guess, “bullet rosettes.”  Toward the top of those clouds they are likely simpler crystals, like short hexagonal columns or tiny hexagonal plates, not that you would care THAT much.

24 h satellite loop of water vapor channel showing itty bitty low that went just to the south of us yesterday.  Look hard in SW Arizona in the beginning and you’ll be able to just make out a little swirl in the wind.

Height of clouds above us?  About 25,000 to 30,000 feet.

Along with that low going overhead, is this strange event:  almost no wind between 25,000 and 30,000 feet, indicating that the exact center passed almost overhead.  It would be like having calm winds on Mt. Everest; just doesn’t happen very often.  Here is the TUS sounding for 5 PM AST yesterday.  And, if, like me, you thought you were looking at the same blob of Cirrus for hours, you just about were!  That due to the winds coming to a virtual halt.  Where the lines (temperature and dewpoint) pinch in together in the sounding below is where the clouds were located, and in the first column to the right of the box are the winds.  Notice what they were at the “400” and ” 200″ levels (millibars, between 23,000 and 40,000 feet above sea level):  “light and variable.”

It was about this time, 1 PM AST, that I began to notice that something was “wrong.”  When I came out of the gym an hour later, this patch of Cirrus, the one I had taken a picture of going in, was still there in pretty much the same spot.  By 4 PM AST, it had drifted ever so slightly to the north, but there it was, still hanging around, as was the case at 5:40 PM and 6:51 PM, shown in the the next two shots.  Even at sunset, those Cirrus clouds were still around.

BTW, these would not be the same cloud particles up there, since the crystals are always falling out and have to be replaced by newly formed cloud.  Those tufts and compact specs at the top of these clouds (well, that’s where they are if you can’t tell) in these photos represent that process.   In those tufts the concentrations are tremendous, but once formed they gradually spread out, much like a plume of smoke.