19 April 2016


Known informally as Undulatus asperatus clouds, they can be stunning in appearance, unusual in occurrence, are relatively unstudied, and have even been suggested as a new type of cloud. Whereas most low cloud decks are flat bottomed, asperatus clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperatus clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn wind -- a type of dry downward wind that flows off mountains. Such a wind called the Canterbury arch streams toward the east coast of New Zealand's South Island. The featured image, taken above Hanmer Springs in Canterbury, New Zealand, in 2005, shows great detail partly because sunlight illuminates the undulating clouds from the side. 
This was NASA's Astronomy Picture of the Day.


  1. Don't ask me why, but the official name has recently been changed to asperitas; i.e., the noun "roughness" instead of the former adjective "roughened".

  2. The Cloud Appreciation Society also uses the term asperitas, so I've changed the title. Tx, Drabkikker.

  3. That photo looks like something out of a Lovecraft story.


  4. these are obviously clouds emitted by and to conceal UFOs.......


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