Ask A Scientist© Environmental Earth Science Archive

  >    name         Dana
 >    status       student
 >    age          11

 >    Question -   Why is it colder at the top of a mountain; when it is
 > closer to the
 >heat from the sun?

Dear Dana-

   Your question about why temperatures on mountains aren't warmer, is a good
one. But in reality, the air is not warmed directly by the sun's rays, but
by infrared, or long-wave radiation from the earth. The sun's rays strike
the earth, and are absorbed by the earth, which raises the temperature of
the earth. The earth reradiates the energy at a wavelength dependent on the
temperature of the earth. The air is able to absorb the earth radiation, and
becomes warmer. At high altitudes, as on mountain tops, strong winds keep
the air mixed, and prevent much rise in temperatures near the surface of the
mountain.

As you go up in altitude from the surface of the earth, the air cools at a
fixed rate. This is called the "lapse rate," and for unsaturated air, that
rate is about 5 deg. C. for each thousand feet of altitude. For saturated
air, the rate is about 3.5 deg.C. for each thousand feet of altitude.

Wendell Bechtold, meteorologist
Forecaster, National Weather Service
Weather Forecast Office, St. Louis, MO

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