Asperatus cloud formations are very rare worldwide – so rare they were not proposed as a separate cloud classification until 2009. The name translates as roughened or agitated waves. It is thought that asperatus clouds’ choppy undersides may be due to strong winds disturbing previously stable layers of warm and cold air.
Undulatus asperatus, says Britain's Cloud Appreciation Society is a cloud variant that, until recently, had gone unnoticed.
Graeme Anderson, an MSc student at the Department of Meteorology, Reading University, studied weather records and used a computer model to simulate the cloud formation. In doing so, Graeme found that asperatus clouds form in the sort of conditions that produce mamma clouds (also known as mammatus); asperatus clouds form when the winds up at the cloud level cause the cloud to shear into wave-like forms known as undulatus.If accepted as a new classification, asperatus will be the first new classification in the World Meteorological Organization's International Cloud Atlas since cirrus intortus in 1951.
This image, captured by Merrick Davies, is of a rather turbulent sky over Hanmer Springs, South Island, New Zealand. Such cloud formations have been seen all over Britain, as well as in the plains of the USA.
Undulatus Asperatus clouds, also called river of the sky clouds, are very rare. They created an eerie landscape in the sky over Atlanta on February 25 2014
Undulatus asperatus is a cloud formation, proposed in 2009 as a separate cloud classification. If successful it will be the first cloud formation added since cirrus intortus in 1951 to the International Cloud Atlas of the World Meteorological Organization. The name translates approximately as roughened or agitated waves. These formations were photographed in Northern Wisconsin.
11Alive Meteorologist Chesley McNeil said the clouds are very rare in the southeast, but more common in the midwest. He also says there's debate over what causes the phenomenon. Scientists agree it's a meeting of two fronts, but are split on whether it's caused by a cold/warm front or a dry/moist front. The Royal Meteorological Society is documenting their appearance to see if they deserve a separate cloud classification. If that happens, it would be the first cloud named since 1951.
"They're very ominous looking," McNeil said. "They're rolling, and that's where the name 'river of the sky' comes from." The name is roughly translated "roughened or agitated waves".