Asperatus Clouds over New Zealand, photographed by Witta Priester

Clouds of this type show up every several years over Hanmer Springs, South Island, New Zealand.


NASA’s Photograph of the Day [] on February 27, 2013.

Photograph © Witta Priester. All rights reserved. Reproduced here by kind permission of the photographer.

Recently, I was watching a show on the Weather Channel about the “discovery” of a previously unrecognized type of cloud. This intrigued me, as I’ve always wondered how the “official” classifications of various kinds of things come about, and just who has the authority somehow to establish the classifications and terminology. We all know at least some of the standard cloud types – cirrus, cumulus, cumulonimbus, etc. (If you want to know all the types and subtypes, check out Wikipedia’s “List of cloud types”.) Who decided on those names and types, and why?

My curiosity led me to the website of the Cloud Appreciation Society, where I was greeted by the exhortation “Cloud Lovers, Unite!”


It’s not all as fluffy as it might seem. There’s some serious cloudspotting involved. In fact, CAS cloudspotters from around the world use a mobile app to input cloud data that the National Aeronautics and Space Administration (NASA) accesses to fine-tune their state-of-the-art CERES) cloud-observing satellite equipment. This helps to improve the accuracy of NASA’s modeling of our future climate.

At the CAS website, I found this “Attention All Cloudspotters” posting dated July 20, 2011:

“Members and visitors might remember that a couple of years ago we proposed that a new classification of cloud should be added to the official classification system. Photographs of this cloud formation had been sent in by Society members over the years, and we’d never known quite how to classify them since we felt that they didn’t easily fit into the existing cloud terms.

“The cloud looks a little like the surface of the sea on a choppy day, which is why we proposed that it should be called asperatus from the Latin verb ‘aspero’, meaning to make rough. The term was used by Roman poets to describe the sea as it was roughened by the cold north wind. …

“Soon, the term was being adopted by cloudspotters around the world. But we always thought it a pretty unlikely to ever be accepted as an official term. This, we were told by our friends at The Royal Meteorological Society would only happen if it were acknowledged by the World Meteorological Organisation in Geneva, who publish the rather dry but thorough bible of cloud classification, The International Cloud Atlas.

“For asperatus to stand a chance of becoming official, we were told, we’d need some idea of the atmospheric conditions that cause it to appear. Finding this out sounded like a lot of work. So we were pleased to learn that Graeme Anderson, an MSc student at the Department of Meteorology, Reading University, had decided to write his dissertation on the cloud, and was happy to trawl through the meteorological records for the dates and locations of the asperatus sightings we’d been sent to try and work out what caused the formation.”

I looked up the dissertation, “Asperatus: the Application of Cloud Classification to a Suggested New Cloud Type.” For a taxonomist like me, it was gratifying to see the opening paragraph:

“In all areas of science, the ability to adequately categorise characteristics in the things we observe has played a vital role in developing our understanding of the world we live in. This is true of meteorology, where the classification of clouds has allowed us to successfully describe the features of the sky we see to others who cannot, in order to give them an understanding of the conditions at the time. For those who understand them, terms such as cumulus and cirrus bring to mind images of small, fluffy clouds or thin, wispy trails, respectively. To this end, the World Meteorological Organisation (WMO) has developed the International Cloud Atlas (ICA), to provide definitions of clouds that can be interpreted globally.”

With all due respect for the WMO and the valuable services it provides, some might say, “Official, schmicial!” And indeed, in this case the cart of public usage seems to have rolled ahead of the horse and driver who are supposed to be leading the way, perhaps pulling them along. Anderson concludes:

“Due to growing public interest in these cloud formations, the term ‘asperatus’ has already been used frequently by the media. With this terminology entering the public vocabulary before the cloud has received any scientific scrutiny presents an unprecedented situation in the history of cloud nomenclature. …

“If the WMO were to classify these formations as ‘asperatus’, using the information already collected, then by using the growing community of amateur cloud spotters as a resource to collect information on these formations could potentially make the process of defining a new cloud type significantly easier than it may have been in the past.

“With the analysis, experimentation and consideration presented in this report, it is hoped that a basis has been formed for officially classifying a new cloud type. It can be noted however that the term ‘asperatus’ has already spread widely via the ubiquity of the internet as a tool of the modern age, and so although these features have yet to gain official recognition, the spectacular forms that these features take has already led them to gain their own place in the nomenclature of the skies.”

Cloud lovers, unite and classify!

Barbara Gilles, Taxonomist
Access Innovations, Inc.