Glaciating Cirrus Clouds

April 13, 2012


: Donald Collins; Don’s Physics Photo of the Week site 
Summary Authors: Donald Collins; Jim Foster

Glaciation in clouds is the rapid growth of ice crystals, most often in cirrus clouds, usually leading to precipitation of the crystals. The wispy cirrus clouds featured above floated over Warren Wilson College near Asheville, North Carolina. The comma-like appearance is caused by the falling of the larger, glaciated, ice crystals into a region of a different wind direction. In this case, the lower altitude wind is from the south -- from the right in the photograph. The upper parts of the cirrus clouds (the top “roots” of the clouds) are receding from the observer -- moving from the west. The movement and formation of the comma-like tails can be seen in the time-lapse animation (click here). Photo taken December 3, 2011.
Photo details: Make: Canon; Model: Canon EOS DIGITAL REBEL XSi; Exposure Time: 0.008; Exposure Program: Normal program; Aperture Value: 5.625; F Number: 7.1; ISO Speed Ratings: 100; Metering Mode: Spot; Focal Length: 18; White Balance: Manual white balance. Animation was made by means of an interval timer (Aputure) triggering the camera (Canon TSi) every 10 seconds using programmed auto exposure; ISO 100; focal length 18 mm. The clouds were receding, so each frame had to be aligned using two cloud roots and Maxim DL astronomy software.  Animated GIF image assembled using Easy GIF Animator.