Digitised International Cloud Atlas launched on World Meteorological Day


On 23rd March 2017 - World Meteorological Day - the World Meteorological Organization (WMO) released its new, online, digitised International Cloud Atlas, which is the global reference for observing and identifying clouds. It contains a number of new cloud classifications, including the eagerly-awaited asperitas, a dramatic undulated cloud which has captured public imagination. A summary of the new cloud descriptions can be downloaded below.

WMO Secretary-General Petteri Taalas said “The International Cloud Atlas is the single most authoritative and comprehensive reference for identifying clouds. Its reputation is legendary among cloud enthusiasts and it serves as an essential training tool for professionals working in meteorological services, and in sectors such as aviation and shipping,” 

The Society was involved in various aspects of the new Cloud Atlas, as outlined chronologically below.

RMetS Involvement


On December 2008, Gavin Pretor-Pinney, of the Cloud Appreciation Society (CAS), approached the Society to present his proposal for a possible new cloud feature, which he originally called asperatus. There were a number of photograph submissions from people around the world to the CAS website which showed a ‘roughened’ cloud base, which did not seem to fit any of the current classifications.

This presentation to the Society was part of a BBC TV documentary called Cloudspotting.  In the documentary, Gavin showed photographs of the proposed new cloud feature to a panel from the Society consisting of Liz Bentley (Head of Communications at the time), Paul Hardaker (Chief Executive at the time), Simon Keeling (meteorologist and Society member) and George Anderson (meteorologist and Society member). The panel recommended that the next step was for Gavin to take his proposal to the World Meteorological Organization.

Original news story >>

A time-lapse of the cloud can be viewed here >>    

Read about CAS invlovement here >>

Clouds caused by human activity

In November 2012, a research paper by Spanish researchers entitled 'Clouds caused by human activities' (Mazon et al. 2012) was published in the Society’s Weather journal. George Anderson was one of the reviewers. The paper concluded that man-made, or anthropogenic clouds should be classified, and the authors proposed classifications such as anthropoCumulus, anthropoStratus, anthropoCirrus. 

Production of new International Cloud Atlas & inclusion of new cloud classifications

In summer 2013, George Anderson was invited to join the World Meteorological Organization's Task Teak for the Revision of the International Cloud Atlas, representing both Society and the Met Office.  At that time George was on the Weather editorial Board as the Photo Editor. The full WMO ICA Task Team comprised of members from each of the following countries, assisted by staff from the WMO Secretariat: 

  • United Kingdom (two from the Met Office: George Anderson and Frank Le Blancq, both Society members)
  • Australia (Bureau of Meteorology)
  • South Africa (South African Weather Service)
  • USA (National Centre for Atmospheric Research)
  • Switzerland (Meteo Swiss)
  • Barbados, Caribbean Institute for Meteorology and Hydrology
  • Argentina (National Weather Service) 
  • China (Hong Kong Observatory)

In November 2013, George led the Task Team in considering opportunities presented by publishing the Altas digitally and the need for any new classifications. Specifically, whether asperatus and anthropogenic clouds should be classified. In addition George proposed that all 'special clouds' which were not currently officially classified - e.g. Kelvin-Helmholtz waves, Fallstreak Holes, man-made clouds (pyrocumulus, contrails), the wall cloud and certain other features associated with severe convective storms - should be formally classified with Latin names, to follow cloud-naming convention. 

In summary, it was agreed to:

  • include upper atmospheric clouds in more detail than in the existing Cloud Atlas including the full classification scheme (George’s proposal)
  • add a Glossary of terms that are not necessarily part of the official classifications. 
  • accept Asperatus as a new Supplementary Feature (although the name later changed to Asperitas on the advice of a Latin expert).
  • classify anthropogenic (man-made) clouds. But not using the Greek 'anthropo' as suggested by the original authors of the research paper, instead using George’s proposal to adapt the existing 'mother-cloud' part of the existing classification scheme to include new Latin terms 'homogenitus' and ' homomutatus'.
  • classify certain well-defined features associated with severe convective storms, for example, the 'wall cloud' as a Supplementary Feature using the Latin name murus (George’s proposal)    
  • classify fallstreak holes as a supplementary feature using the Latin name cavum  (George’s proposal)
  • classify clouds associated with fires and industry. But not using the Greek 'pyro-'  Instead George proposed to modify the existing 'mother-cloud' part of the classification scheme to include flammagenitus for  clouds initiated by the thermals from wildfires, and homogenitus for clouds generated by thermals from industry. 
  • classify Kelvin-Helmholtz waves as a supplementary feature using the Latin name fluctus (George’s proposal).
  • introduce a new species classification, volutus, for Roll clouds. These were previously classified as an arcus (proposed by the Australian task team member)
  • expand the section on 'other meteors'  (George’s proposal) 
  • classify remaining 'special clouds' - e.g. those formed from large waterfalls (cataractagenitus) and those formed above forest canopy by the additional moisture from evapotranspiration (silvagenitus).
  • extend the use of the existing species floccus (normally used for Altocumulus) to also include Stratocumulus. 

An image submission website was also set up for people around the world to upload photographs of clouds and other weather phenomena (such as rainbows, halos, snow devils and hailstones), and associated metadata. As a result, the new Atlas contains hundreds of images submitted by meteorologists, photographers and cloud lovers from around the globe. 

The full press release can be found here >>

World Meteorological Day webpage >>

The new, online version of the International Cloud Atlas can be found at >>

BBC news item >>

The Times article >>

The Met Office press release can be found here >>

A summary of the new cloud descriptions can be downloaded below.


(Image: Asperitas by Brett Bumpus)



News Date: 
Thursday, March 23, 2017