new type of cloud found
An unusual type of storm cloud could become the first new variety of cloud to be officially identified in more than half a century.

Meteorologists believe they have discovered a new classification of cloud after the unique formation has been spotted in skies around the world.

Experts at the Royal Meteorological Society are now attempting to have the new cloud type, which has been named "Asperatus" after the Latin word for rough, officially added to the international nomenclature scheme used by forecasters to identify clouds.

If successful, it will be the first variety of cloud to be classified since 1953.

The new type of cloud forms a dark, lumpy blanket across the sky and has been sighted in locations all over the world, including above the hills of the Scottish Highlands and above Snowdonia, Wales.

"It is a bit like looking at the surface of a choppy sea from below," said Gavin Pretor-Pinney, founder of the Cloud Appreciation Society, who first identified the asperatus cloud from photographs that were being sent in by members of the society.

"We try to identify and classify all of the images of clouds we get in, but there were some that just didn't seem to fit in any of the other categories, so I began to think it might be a unique type of cloud.

"The underside of the clouds are quite rough and choppy. It looks very stormy, but some of the reports we have been getting suggest that they tend to break up without actually turning into a storm."

The Royal Meteorological Society is now gathering detailed weather data for the days and locations where the asperatus clouds have been seen in an attempt to understand exactly what is causing them.

Among the worldwide locations where asperatus clouds have been spotted are above the flat plains of Iowa and Australia and also over the arctic sea just off the coast of Greenland.

The undulating and lumpy underside, however, is thought to be caused by warm and cold air meeting a the boundary between the lower and middle atmosphere creating a transition effect similar to those seen when oil and vinegar mix.

Officials will then apply to the UN's World Meteorological Organisation in Geneva to have the new cloud type considered for addition into the International Cloud Atlas, which is used as the worldwide standard for meteorologists.

Professor Paul Hardaker, the Chief Executive of the Royal Meteorological Society, said: "The process is a long and convoluted one to get through, but we believe there is a good case for this cloud to be added.

"There would probably need to be quite a lot of heat around to produce the energy needed to generate such dramatic cloud formations. They are quite dark structures so there must be a lot of water vapour condensing in the cloud."

Clouds are classified in an internationally recognised way that identifies where in the atmosphere they form, the amount of moisture they hold, their shape and appearance.

Luke Howard, a British pharmacist, first proposed a nomenclature system for clouds at the start of the 19th century, which was adopted as the standardised way of categorising cloud types.

The system, which is governed by the WMO, uses three layers of classification and was developed to help forecasters predict oncoming weather conditions from the cloud cover in the sky.

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.

Mr Pretor-Pinney is to publish a new book, The Cloudspotter's Guide, next week which provides detailed descriptions and photographs of all the different cloud types. It comes at a time when clouds are taking on a new importance in meteorological work after falling out of fashion as forecasters used satellite images and radar to help their predications rather than using cloud formations.

Professor Hardaker said: "Clouds are very important in the Earth's climate as depending where they are in the atmosphere they will either reflect heat or absorb and trap heat. We are only just starting to understand that role."

The Met Office is also to release another book later in the month, called Extraordinary Clouds, which features dramatic photographs of clouds.

Richard Hamblyn, from the environmental institute at University College London and author of the Met Office book, added: "Clouds are beautiful things that have volume, form and shadow, yet they float in the sky.

"There can't be many people who have not wondered at some point how they stay up there, as nothing else in our world behaves in that way."

To see more examples of unusual types of clouds see here