Unusual clouds spotted over southern England

There were a number of sightings of unusual and striking cloud formations over the weekend as the UK experienced a mix of weather. Photos were taken in Dorset, particularly the Poole and Bournemouth areas.

Asperitas cloud

Image courtesy of Steven Poulton

This particular photograph looks as if it is an example of a new cloud formation which is in the process of being named. Asperitas (ass-pair-it-ass) is the proposed name for this cloud formation that doesn’t fit easily into the current classifications of the World Meteorological Organization (WMO) International Cloud Atlas. It is a relatively rare formation that has only recently started to gain recognition. This is thought to be due to the increased availability of digital cameras and the internet to share information, as opposed to this being an entirely new formation.

These cloud formations first started gaining wider attention around a decade ago, with the formation of the lighthearted Cloud Appreciation Society by Gavin Pretor-Pinney. He asked for members of the society to submit photos of clouds, and soon started seeing a number of images of clouds with a roughened appearance that didn’t seem to fit into traditional cloud classifications. He went on to propose that a new cloud classification would be required, and suggested the name “asperatus”, approximately translating to “roughened” in Latin. The name ‘asperitas’ is now used rather than ‘aperatus’, on the advice of a Latin expert, in order conform with the form of existing cloud names.

Gavin went on to collect more information and examples of the cloud. In 2010, as part of a Masters degree, Graeme Anderson, observations research and development scientist at the Met Office, showed that the reported cloud formations formed most frequently in connection with large-scale thunderstorms in the United States. However, these have been observed all over the world, and are not always associated with thunderstorms. Their rarity and lack of direct observation makes it difficult to determine what causes them, although one theory is that the waves form when mammatus clouds descend into air where the wind direction changes with height.

The WMO is currently reviewing the International Cloud Atlas, to decide on whether it needs updating and whether any new cloud classifications are required. A decision on whether asperitas is to gain its own classification is expected in the coming months. If this happens, then it would be the first new definition in over 50 years.

There are a number of different types of cloud which will continue to be classified and named as new research and understanding of their properties comes to light. If you would like to know more about the different types of cloud and how to identify them you can use our cloud spotting guide or download our latest mostly weather podcast on clouds.

Here at the Met Office we always welcome weather information and photos from the general public, if this is something you would be interested in check out our Weather Observation Website (WOW) or you can share your photos with us on Twitter or Instagram using #loveukweather.

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One Response to Unusual clouds spotted over southern England

  1. Ann says:

    They’re pretty clouds xxx

    Sent from Ann”s iPad xx

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