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
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
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
streams toward the east coast of New Zealand's
The above image,
Hanmer Springs in
New Zealand, in 2005,
shows great detail partly because sunlight illuminates the undulating clouds from the side.
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