Asperitas (cloud)

Asperitas (formerly known as Undulatus asperatus) is a cloud formation first popularized and proposed as a type of cloud in 2009 by Gavin Pretor-Pinney of the Cloud Appreciation Society. Added to the International Cloud Atlas as a supplementary feature in March 2017, it is the first cloud formation added since cirrus intortus in 1951.[2] The name translates approximately as "roughness".[3]

Asperitas cloud
Asperitas over Tallinn, Estonia.
GenusAltocumulus or Stratocumulus depending on height, as Asperitas is thought to be a cumuliform structure [1]
AltitudeBelow 2,000 (or higher with altocumulus) m
(Below 6,000 -or higher with altocumulus- ft)
AppearanceWavy undersurface
Precipitation cloud?No, but may form near storm clouds.

The clouds are closely related to undulatus clouds.[3] Although they appear dark and storm-like, they almost always dissipate without a storm forming.[4] The ominous-looking clouds have been particularly common in the Plains states of the United States, often during the morning or midday hours following convective thunderstorm activity.[5][3][4]

History of observations

Margaret LeMone, a cloud expert with the National Center for Atmospheric Research has taken photos of asperatus clouds for 30 years, and considers it in her own words, a new cloud type.[2]

On June 20, 2006 Jane Wiggins took a picture of asperatus clouds from the window of a downtown office building in Cedar Rapids, Iowa.[6] In March 2009, Chad Hedstroom took a picture of asperatus clouds from his car near Greenville Ave in Dallas, Texas. Soon after taking it, Wiggins sent her Cedar Rapids image to the Cloud Appreciation Society, which displayed it on its image gallery.[7] Wiggins' photograph was posted on the National Geographic website on June 4, 2009.[6] On July 23, 2013, Janet Salsman photographed them along the South Shore of Nova Scotia, Canada. On October 28, 2013, an Asperitas cloud layer formed over Tuscaloosa, Alabama.[8] On July 7, 2014 asperatus clouds in Lincoln, Nebraska, have been caught on tape by Alex Schueth.[9] One of the most dramatic formations was captured by Witta Priester in New Zealand in 2005. The photo was posted by NASA as the Astronomy Picture of the Day and shows great detail, partly because sunlight illuminates the undulating clouds from the side.[10]

Since 2006, many similar cloud formations have been contributed to the gallery, and in 2009 Gavin Pretor-Pinney, founder of The Cloud Appreciation Society, began working with the Royal Meteorological Society to promote the cloud type as an entirely new type in and of itself.[3]

The 2017 edition of the World Meteorological Organisation (WMO) 's International Cloud Atlas included asperitas as a supplementary feature. Pretor-Pinney gave an invited presentation at the WMO in Geneva for the launch of the revised Cloud Atlas, on World Meteorological Day 2017. He has worked with scientists at the Department of Meteorology, University of Reading on possible mechanisms for the formation of asperitas, co-authoring a paper[11] published in the Royal Meteorological Society's journal Weather. This described a series of sightings of the cloud, which were interpreted as being associated with the propagation of gravity waves through a pre-existing cloud layer.

See also


  1. "June 2009". The Cloud Appreciation Society. Retrieved 2012-12-20.
  2. "PICTURES: New Cloud Type Discovered?". National Geographic News. 2009-06-03.
  3. "Asperatus: gathering storm to force new cloud name". London: The Guardian. 2009-06-02. Retrieved 2010-03-28.
  4. Luke Salkeld (2009-06-02). "The cloud with no name: Meteorologists campaign to classify unique 'Asperitas' clouds seen across the world". Daily Mail.
  5. "New Cloud Type Discovered: 'Undulus Asperatus'". Meteorology News. 2006-04-28. Retrieved 2012-12-20.
  6. MICHAEL J. CRUMB (2009-06-11). "Iowa Woman's Photo Sparks Push for New Cloud Type". Associated Press.
  7. "Cloud Photos". The Cloud Appreciation Society. Retrieved 2012-12-20.
  8. James Spann
  9. Alex Schueth
  10. "APOD: 2013 February 27 - Asperatus Clouds Over New Zealand".
  11. Harrison, R. Giles; Pretor‐Pinney, Gavin; Marlton, Graeme J.; Anderson, Graeme D.; Kirshbaum, Daniel J.; Hogan, Robin J. (2017). "Asperitas – a newly identified cloud supplementary feature" (PDF). Weather. 72 (5): 132–141. doi:10.1002/wea.2996. ISSN 1477-8696.
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