Cloud of the Week # 4: Cirrus uncinus

  Some of you may remember this cloud from an earlier "Accidental Naturalist" blog posting. This solitary cloud is an unusual form of a type of cirrus cloud called cirrus uncinus. 'Uncinus' (pronounced un-sun-us) means that the streaks falling behind the main clump of ice crystals are in the shape of hooks or commas. A common type of cirrus uncinus, one familiar to many people, are the 'mare's tails,' which, as you might expect, look like a horse's tail (mare or stallion, or even pony if you ask me).
   Unfortunately, I don't have any photographs of mare's tails and because I am trying to behave on the Internet, have chosen not to cut and paste someone else's photo in here. But here is a link.
  Not describing someone else's photo turned out to be a good thing for many reasons. It took me almost an hour (!) to select the three photographs posted here. Why? Because I am in the habit of turning my camera sideways to capture a scene vertically and I often forget to include a piece of landscape in the photograph. This is a problem when I want to post a sequence of photos to show the progression of a cloud over several minutes. I had posted some very wonderful cirrus uncinus, but had to delete them when I couldn't be sure I had the orientation and chronology correct. After I checked the time stamp on the images, I fixed the chronology problem, but then couldn't be sure up was up and down was down. One of my cirrus uncinus seemed to be doing cartwheels.
      The photo above and the two below are correctly sequenced and oriented thanks to some trees, bushes, what would otherwise be called an eyesore--a lampost.
   Because I was standing in the same place, I know that the cloud was moving west to east (right to left in the photos) and that the clumps were moving at a slower pace than the tails. Note that the tails get longer with each photo, indicating that they were trailing behind in slower, lower wind. This photo was hard to decipher because "behind" should be to the right, right? Yes, if the winds were blowing in a single direction throughout the troposphere. But they are not--and clouds are what show us they are not. I love this about clouds. They allow us to see the winds.
If you spend some time watching cirrus uncinus, you can watch the cloud age before your eyes. The ice-crystal tails will grow longer and longer with time and then dissipate altogether as the ice crystals evaporate. 

Lessons: When photographing clouds, don't zoom in so close that you can't figure out the relationship of the cloud to the earth. Always include a piece of landscape or even an unsightly structure you can crop out later. When photographing a single cloud, take several pictures a few minutes apart so you can see the subtle changes in the cloud's form.