Asperatus - A New Cloud Variety?

asperatus new cloud

Everybody’s talking about a new cloud type called ‘asperatus’. The Society
has been inundated with international media requests and the story even made
it onto ‘Have I Got News for You?’. So just what is this cloud and is it really
a new cloud type?

The story starts with Gavin Pretor-Pinney, the founder of the Cloud Appreciation
Society, who over recent years has received a number of cloud images that
he was unable to identify. At the time, he gave the clouds the nickname ‘Jacques
Cousteau’ since the cloud base resembled a choppy sea when viewed from below.

As more and more images arrived with similar characteristics, Gavin decided
to look for a more official-sounding name and choose ‘asperatus’ which is
the Latin for ‘roughed up’. Asperatus was used by Classical poets to describe
the sea when it has been agitated by strong winds. Gavin is proposing that
asperatus should be adopted as a new ‘variety’ of cloud.

There are 10 basic cloud forms, or genera, that describe where in the sky
they form and their approximate appearance, including stratus, cumulus and
cirrus clouds. The genres are subdivided into cloud species, which describe
shape and internal structure, and cloud variety, which describes the transparency
and arrangement of clouds.
Below: Gavin Pretor-Pinney at the Royal Meteorological
gavin pretor pinney at the royal meteorological society

In December 2008, Gavin visited the Royal Meteorological Society headquarters in Reading to review some images and to discuss the proposal for a new cloud variety. The Society had arranged for a panel of meteorologists and cloud experts to view the images in the Society’s meeting room, where a large portrait of Luke Howard hangs on the wall. Luke Howard was the man who in his 1802 paper to the Askesian Society invented the basis of the cloud classification system that meteorologists use today. The Society had also retrieved some of Luke Howard's original cloud sketches which are on loan to Science Museum.

Gavin presented to a panel comprising Liz Bentley (Head of Communications), Paul Hardaker (Chief Executive), Simon Keeling (weather consultant) and George Anderson (Photo Editor for Weather). He had also brought with him a television production company, calledSkyworks, to film the meeting. This footage would be used in a BBC4 documentary called Cloudspotting, a 90 minute programme bringing to life Gavin's international bestseller, The Cloudspotter's Guide, which draws on science, meteorology and mythology for a magical journey through the world of clouds. The documentary also followed Gavin’s quest to have ‘asperatus’ recognised as a new cloud variety.


Gavin noted that the last time a new cloud term was added to the internationally agreed system that identifies where in the atmosphere they form, the amount of moisture they hold, their shape and appearance, was in 1953. The system, which is governed by the World Meteorological Organization (WMO), uses three layers of classification to assist meteorologists in predicting oncoming weather conditions from the cloud cover in the sky.

The Society has agreed to gather detailed weather data on the day and in the location where the asperatus clouds have been seen. Analysis of the meteorological situation will uncover exactly what is causing them. It is likely that the undulating and lumpy underside is caused by warm and cold air meeting at the boundary between the lower and middle atmosphere. It shares some similarities with existing formations such as the more regular waves of undulatus clouds and the hanging pouches of mamma clouds.

If there is evidence to support a new cloud variety then the Society will assist Gavin in applying to the WMO in Geneva to have the new cloud type considered for addition into the International Cloud Atlas.

Whether ‘asperatus’ is recognised as a new cloud variety or not, these spectacular cloud images have sparked the imagination of many and encouraged us all to look to the skies.

News Date: 
Friday, June 12, 2009