Physics Photo of the
December 2, 2011
Ominous Thunderhead - Photo by Gretchen Whipple
Dr. Gretchen Whipple photographed this developing
thunderstorm at dusk in late August from Bedford, VA a
couple of years ago.
Thunderstorms often appear in the early evening during the
summer months. They are fed by the rising warm moist air
on hot and humid days. The air cools as it ascends, and
clouds form due the the temperature falling below the dew
point. Paradoxically, the condensation of air into cloud
releases more thermal energy from the latent heat of
fusion. The extra heat gives the condensing cloud even
more buoyancy. This positive feedback causes the cloud
to rise and tower to very high altitudes. Usually the
thunderclouds reach the height of the "tropopause" - the
elevation where the ambient temperature suddenly increases
instead of decreasing with increasing altitude. As a
result of the high altitude inversion, the cloud no longer has
positive buoyancy above the inversion layer and the cloud
spreads out - giving the common anvil shaped top.
The time of day - close to sunset - accentuates the details of
this cloud - accenting the details through the shadows.
Thanks go to Dr. Gretchen Whipple of the Mathematics
Department for this interesting photo.
Physics Photo of the Week
is published weekly during the academic year on Fridays by
the Warren Wilson College Physics
Department. These photos feature interesting
phenomena in the world around us. Students, faculty,
and others are invited to submit digital (or film)
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Atmospheric phenomena are especially welcome. Please
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see the Physics Photo of the Week Archive.
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