The common name for
these clouds which resemble waves of the ocean breaking on the
shore is "Billow Clouds". They result from a shearing
instability formally called dynamic instability (or Kelvin-Helmholtz
instability, after Lord Kelvin and H. von Helmholtz). Such
shearing instability also causes the flapping of a flag.
In the case of
this picture, entitled "Waves of Ascension", there is a vertical wind shear
because winds near the summit of Mt. Shasta are ostensibly blowing
at slower speeds than the winds several hundred to a couple of
thousand feet higher up. Waves generated in a vertically sheared
layer of air, also form perpendicular to the wind shear, thus
waves, or ripples can still form in a stable layer of air if
vertical wind shear is sufficiently strong.
This example in the
afore said photograph is extremely rare to be so perfectly formed
and is one of the best examples ever seen, one that the majority
of people will never see in their lifetimes...This particular
picture has been viewed on the Pennsylvania public broadcasting
television station and was featured in an issue of "Weatherwise
Magazine."
This is an excerpt from
an article written by Lee Grenci, a meteorologist, describing in
full the dynamics of this system. This photograph has gone all
over the world, and is becoming well known and collectible.
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