Punch Hole Clouds may appear as a circular or oval holes in a layer of supercooled clouds; sometimes they assume a form of a perfect circle and persist for quite a long time, drifting together with the cloud layer. One explanation seems to blame the air traffic (the jet contrail intersections) combined with a thermal inversion (a circular motion of a rising warm air). Here is one, observed over the Gunnison Valley in Colorado:
Another strange hole in the cloud, reported from Mobile, Alabama USA, Dec. 2003 (and covered by BBC News):
It seems both rising and sinking air currents can create the same effect. Sometimes a very stable, uniform layer of high-altitude clouds can get "punched though" by a pocket of cold air, which sinks toward the ground - creating the circular hole formation.
These "cloud holes" can look like the footprints of some celestial being (UFO enthusiasts rejoice!) or can be amazingly round, like this pair observed in Gallatin, Tennessee by Wayne Carter:
NASA takes satellite images of this phenomenon
NASA Terra satellite equipped with the Moderate Resolution Imaging Spectroradiometer (MODIS) has captured these images over Acadiana area in southern Louisiana - a splattering of round holes actually stretched over several states: Oklahoma, Arkansas, Louisiana, and Texas. Some were elongated, some appeared to have smaller clouds inside them.
"This strange phenomenon resulted from a combination of cold temperatures, air traffic, and perhaps unusual atmospheric stability. The cloud blanket on January 29 consisted of supercooled clouds. Supercooled clouds contain water droplets that remain liquid even though the temperature is well below freezing, and such clouds are not unusual. As aircraft from the Dallas-Fort Worth airport passed through these clouds, tiny particles in the exhaust came into contact with the supercooled water droplets, which froze instantly. The larger ice crystals fell out of the cloud deck, leaving behind the “holes,” while the tiniest ice particles in the center remained aloft." (source)
Cloud Vortices: another "holey" sky phenomena
Theodore von Karman's "Cloud Vortices" are something else, again: they form when the wind encounters a barrier - such as the Aleutian islands, in this case - and the flowing eddies of cloud create a weird pattern. The image you see below was photographed from the International Space Station, and the animation shows the double row of vortices, which rotate opposite from each other.
More Incredible and Fascinating Clouds
...that make our sky worthy to look at from time to time (those who only look at the computer monitor, take note).
Spectacular lenticulars in the morning light... and a whole "pancake" stack of them, over at Mount Rainier in Washington:
http://amazing-events.blogspot.com/2009/01/rarely-seen-cloud-formations-amazing.html
