August 17, 2025
You were not dropped into the cosmos as a stranger. You came from it entirely: borrowed from stars, carried by Earth, warmed by the Sun, and...
Asperitas Clouds Over New Zealand
Birthday · August 17, 2025
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APOD published August 17, 2025. Credit: Witta Priester. A publication-date match, not a photo taken on your date. Independent of NASA.
What kind of clouds are these? Although their cause is presently unknown, such unusual atmospheric structures, as menacing as they might seem, do not appear to be harbingers of meteorological doom. Formally recognized as a distinct cloud type only last year, asperitas clouds can be stunning in appearance, unusual in occurrence, and are relatively unstudied. Whereas most low cloud decks are flat bottomed, asperitas clouds appear to have significant vertical structure underneath. Speculation therefore holds that asperitas clouds might be related to lenticular clouds that form near mountains, or mammatus clouds associated with thunderstorms, or perhaps a foehn -- a type of dry downward wind that flows off mountains. Clouds from such a wind called the Canterbury arch stream 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.
Image credit: Witta Priester