The International Cloud Atlas is exactly what it sounds like – a visual guide to the world’s many and varied cloud formations. The last time it received a major new addition that did not star Tom Hanks was in 1951, with the introduction of cirrus intortus, but after all that time a new challenger has appeared: undulatus asperatus (or just asperatus). The name literally means “agitated waves,” and as that phrase implies, this cloud formation is terrifying and visually spectacular.
Try to imagine standing under one of these great waves and looking up — the official description submitted for consideration in the Atlas describes it as like “viewing a roughened sea surface from below. Indeed, it might feel very much the same way too, as the ominous-looking movements actually tend to form after storms, rather than before them. Asperatus could be super-sized versions of the long-known undulatus clouds, which look more like mild ripples than full-on waves, or it could be an all-new type of formation caused by distinct weather patterns. While they may look unique, that doesn’t mean that these clouds are in fact an all-new type of cloud; figuring out just what causes these clouds to form will have a lot to do with deciding if it warrants inclusion in the cloud atlas.
Asperatus was first discovered thanks to the efforts of the Cloud Appreciation Society, and extensive library of cloud pictures it maintains. Gavin Pretor-Pinney, founder of the site, found that soon after opening the ways for picture submissions from the public he began to see formations that did not conform any known archetype. In particular, he saw a recurring formation that struck him as highly odd: enormous, rolling waves. They were hard to see at first, since their true oddness can only be seen in sped-up motion. Above, a time-lapse gif shows how asperatus clouds move over time.
The Cloud Appreciation Society has an amusing, but not altogether joking mandate to make clouds more popular — not as gloomy harbingers of rain, but incredible visualizations of pressure and moisture. Clouds let us see some of the swirling dance that’s going on around us all the time, invisible currents and sub-currents of air that form three-dimensional rivers and, occasionally, odd recurring patterns like asperatus clouds. The Society argues that clouds are unjustly maligned, and wants to put an end to phrases like “blue sky thinking.”
Asperatus will need the approval of the World Meteorological Society if it’s to have a place in the cloud atlas, and a 2010 paper describing the clouds will likely have a lot of weight in that regard. It’s worth noting that these groups, while inherently stodgy and resistant to change, need attention and public profile as much as anybody — whether you’re cataloging clouds, planets, or human psychological disorders, there’s always an incentive to make interesting changes, year over year. If you don’t do that, then what exactly are you accomplishing, anyway?