Asperitas: Our new cloud became official in March 2017

In 2008, Gavin Pretor-Pinney, Member 001 of the Cloud Appreciation Society, argued that we need a new classification of cloud to describe a chaotic, turbulent formation photographed by members of the Cloud Appreciation Society. The formation, known as Asperitas, has likely always existed, but smartphone technology combined and the interconnectivity of the Internet enabled our network of sky observers to reveal this distinctive feature not previously identified. Over the years, many more examples of the cloud have been sent in and added to the Society photo gallery.

Now, the World Meteorological Organisation has launched a new edition of their authoritative reference work on the classification of clouds, The International Cloud Atlas. First published in 1896, this is the definitive work on the official naming system for clouds, and it has been updated every few decades. The team responsible for this update to Atlas made several changes and additions to the list of cloud classifications. One was to include the Asperitas formation as a new cloud ‘supplementary feature’. Its name comes from the Latin word for ‘roughness’. (This term is closely related to the name ‘Asperatus’, or ‘roughened’, that we originally proposed back in 2008. The reason for the slight change is that the names for the supplementary feature type of classifications are always Latin nouns.) The Atlas includes Asperitas as a supplementary feature associated with the main cloud types Altocumulus and Stratocumulus (see the listing for Altocumulus supplementary features and Stratocumulus supplementary features).

In response to the cloud’s acceptance, Gavin Pretor-Pinney said, “Asperitas was identified with the help of citizen science enabled by modern technology. When Cloud Appreciation Society members send us photographs of dramatic skies from around the world, we are able to spot patterns, which is how our proposal for a new classification came about. We are delighted the WMO has chosen to include Asperitas in their definitive reference work for cloud classification.”

Interview requests with Gavin Pretor-Pinney should be made to

Asperitas Cloud Images for publication

The members of the Cloud Appreciation Society who took these photographs of Asperitas clouds have agreed that they can be published in media stories about the new cloud classification. Permission for publication is dependent on full photo credits, as listed with each image.