Temperature Changes and Altitude
Why does temperature decrease as one goes higher in the
...your question about how the atmosphere is heated is a good one, because
the correct answer is not quickly apparent...
You would surmise, that since the sun is the source of the heat for the
earth and atmosphere, that the atmosphere should be warmer at points closer
to the sun, like at the TOP of the atmosphere, instead of the reverse.
But the atmosphere is not warmed directly by the sun...it is warmed by the
EARTH...! Most of the energy from the sun arrives at the earth in the form
of light energy, or short-wave energy. The atmosphere is transparent to
short-wave energy, and most of the solar energy reaches the surface of the
earth, where it is absorbed. This energy warms the surface of the earth,
which, in turn, warms the atmosphere with long-wave energy. The type of
energy radiated by a star primarily depends on the temperature. So the
energy from the sun arrives at the earth as short-wave (in the visible part
of the spectrum) energy, and leaves the earth as long-wave (in the infra-red
part of the spectrum) energy.
The atmosphere is not transparent to long-wave radiation, and absorbs the
heat energy from the earth. That part of the atmosphere closest to the earth
gets the most energy and is the warmest.
Because the sun is nearly overhead in the latitudes nearest the equator,
those locations receive more solar energy per unit area, and become warmer
than those locations near the poles. This difference in the amount of energy
received and subsequent heating of the atmosphere and evaporation of water
from the lakes and oceans, is what drives the "weather machine" on the
I hope this has answered your question, Julie. If not, please let me know,
and I'll provide you additional information.
Wendell Bechtold, Meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO
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Update: June 2012