The Unusual Case of Undulatus Asperatus

Classifying clouds isn't exactly the most exciting thing that comes to mind when weather is discussed with friends, or in the elevator. And cloud classification is not the most modern of sciences, especially with National Weather Service offices in the United States no longer required to report cloud type in their hourly observations. In fact, the last time the World Meteorological Organization (WMO) officially recognized a new cloud formation, Harry Truman was president. In 1951, they added Cirrus intortus to the official list of cloud formations. Now the WMO is thinking about reopening the dusty pages of the International Cloud Atlas (yes, there is an atlas of clouds) for the first time in 60 years.

After receiving a multitude of pictures of an unknown cloud formation from locations spanning the globe, they are investigating the conditions that give birth to these wavy clouds. If the WMO is successful in determining a unique set of circumstances and conditions for this class of cloud, they will be certified as a new cloud formation, and entered into the International Cloud Atlas.

Their current proposed name is based off of the Latin for "rough waves", which is what they look like in the sky. Whereas "traditional" clouds are flat on the bottom, these clouds exist at a height where the bottom is at a turbulent layer of the atmosphere. Thus the normally invisible dynamics of the boundary layer become visible through the motions of the cloud. All sorts of wave formations and instabilities appear, giving the cloud its distinguishing "choppy wave" appearance. Because they are wave-based, Undulatus asperatus do bear a relation to Altostratus undulatus clouds. However, the whole wave is not visible in  Altostratus undulatus, only the ridges of the wave. This distinction leads the asperatus variety to look much different than their Altostratus cousins.


Either way, it should be an interesting and historical process, as more people recognize, catalog, and photograph occurrences of Undualtus asperatus. Perhaps it will be time to dust off the atlas!

--Greg