When clouds raise an eyebrow: the case for a new supplementary cloud feature ‘Supercilium'

In 2017, the World Meteorological Organization accepted 12 revisions to the International Cloud Atlas, including the introduction of a new supplementary cloud feature, asperitas. Here, we present compelling photographic evidence gathered over recent years, which argues the case for an additional new cloud feature, ‘supercilium’, to be also considered for inclusion in the Atlas, which at present lacks a precise category or description of these clouds. ‘Supercilium’ are short-lived cloud features, which appear in turbulent airflow over, and to the immediate lee of, steep mountain peaks during periods of strong mountain summit level winds.