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convection
CONVECTION
Smoke rising from a chimney,
a pot of boiling water or a thunderstorm - what do these have in common? Well,
they are all examples of convection or vertical movements of matter. Convection
is a process of heat transfer, or the movement of energy from a hot substance
to a cold one.
Convection is the most
important method of heat transfer in weather. It is also essential in the production
of thunderstorms. As the sun heats the ground, a pocket of air near the surface
heat up quicker and becomes lighter than the surrounding air. This pocket of
air will rise until it encounters a layer of air warmer than itself. This is
called an unstable environment. These vertical air motions, or convection, lead
to the turbulent motions in forming a thunderstorm.
Across the Inland Northwest,
the typical summertime thunderstorm develops over the mountains. The reason
for this is twofold. The first has to do with the mountains acting as permanent
barriers. When winds blow toward a mountain, the pockets of air have no where
to go but over the top. This vertical forcing is further enhanced by solar heating
and the resultant convection. With sufficient moisture in the atmosphere, this
lift may result in thunderstorms. These thunderstorms will follow a cycle of
growth and decay along the same ridge line for many hours, explaining why one
valley will receive heavy downpours while an adjacent valley will stay dry.
Thunderstorms which forms in the mountains are called orographic storms.
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