Abstract/Summary

Cloud images obtained through a crowd-sourced international observing network suggest a cloud variety that has hitherto not been explicitly classified. This cloud feature shows a roughened base, which, under some solar illumination conditions, provides a particularly dramatic appearance. The growing body of photographic observations have led the World Meteorological Organisation to consider adding ‘asperitas’ to the 2017 edition of the International Cloud Atlas as a new form of supplementary cloud feature. We compare reported sightings with available meteorological data to investigate the conditions that give rise to this newly recognised cloud description.