What You Need to Know:
Name(s): Asperitas, Undulatus Asperatus, Wave Cloud
Common Altitudes of Formation: Below 2,000 m (6,000 ft) but higher with altocumulus Genus
Signals: Asperitas may form at the trailing end of convective thunderstorm activity.
Meaning of the Name: From Latin: the verb ‘aspero’ meaning to make rough
Elaborated, more comprehensive information:
It began in 2006, the naming of a previously unclassified cloud type. It was the first case since 1951, cloud enthusiasts and cooperating scientists had identified a cloud that didn’t quite fit any existing types. So in 2009, Gavin Pretor-Pinney, founder of the Cloud Appreciation Society (CAS); Latin scholar, Dr. Rick LaFleur, Franklin Professor of Classics Emeritus at the University of Georgia, one of the most respected Latinists in the United States; and Graeme Anderson, a meteorology student at Reading University in the U.K., proposed the name ‘undulatus asperatus’ (recognised by the World Meteorological Organisation as ‘asperitas’).
Undulatus asperatus, deriving from Latin, means ‘wave-like (and) rough’. It is interesting to note that Vergil in his first century B.C. epic poem, the Aeneid, used the phrase asperat undas describing a wintry storm or meaning ‘makes the waves rough’. In English, undulatus means to move with a sinuous or wavelike motion. As said in the Apalach Times article, Cloudy with a Chance of Crab Cakes, the und in undulatus is found in the word redundant, signifying the repetitive breaking of waves against the shore, which is similar to the wave-like motion of the undulatus. Asperatus also comes from Latin, the verb ‘aspero’ meaning to make rough. The asper in asperatus is found in the word asperity, meaning rough in touch, climate, or behaviour. It is also found in exasper meaning to roughen, irritate, annoy or anger.
The clouds require a large amount of heat/energy in the atmosphere as well as synergy between extremely moist and dry air. The water vapour in the clouds is supposedly the reason for the clouds’ dark shade.
Meteorology student, Graeme Anderson, completed his thesis on the cause of formation of undulatus asperatus. He studied weather records and used a computer model to simulate the cloud. He found similarities between asperatus and mammatus clouds though the differences between the two were that in an asperatus, the winds at cloud level cause it to form into wavelike forms (undulatus).
In 2010, the US National weather service acknowledged the asperatus. They described it as a rare, newly recognized cloud formation, common in the Plains states of the United States, during the morning or midday hours following convective thunderstorm activity. They also stated that although they appear dark and storm-like, they tend to dissipate without a storm forming.