Asperitas: A cloud formation “made up of well-defined, wavelike structures in the underside of the cloud, more chaotic and with less horizontal organization than undulatus. It is characterised by localized waves in the cloud base, either smooth or dappled with smaller features, sometimes descending into sharp points, as if viewing a roughened sea surface from below. Varying levels of illumination and thickness of cloud can lead to dramatic visual effects. (Source: World Meteorological Organization.) Asperitas is a Latin word meaning “roughness” or “harshness”; the root is the source of asperity (harshness) and exasperate (to irritate or provoke).
Asperitas formation over Mesa, Arizona. Photograph via Cloud Appreciation Society.