Cold mountain
![Mountains stick up like islands in the cold atmosphere [Sean Linehan, NOAA]](http://www.wonderquest.com/images/2004-02-27-rocky-mountains.jpg) Why is it colder in the mountains than in the valley? The mountains are closer
to the sun. Marissa, Mountain Home, Idaho
The Sun’s rays pass right through the atmosphere.
Earth’s surface absorbs them and re-radiates the energy in the form of heat that
air can absorb. Thus, the Sun warms the air by warming the ground. Air closest
to the Earth’s surface is, in general, warmest. Air as high as a mountain is
poorly warmed and, therefore, cold.
Mountains stick up like islands in the cold
atmosphere. Photo courtesy of Sean Linehan, NOAA.
Air temperature normally drops 1.8 to 3.6 degrees Fahrenheit
(1 to 2 degrees Celsius) for each 1000 feet (300 m) of altitude.
Mountains poke up through the atmosphere like islands above a
sea. The temperature of the enveloping atmosphere cools mountain ground even
though — you’re right — the Sun warms the high ground. The influence of
atmosphere temperature on a mountain is similar to that of the sea’s temperature
on an island. The higher and the more isolated the mountain, the closer its
temperature is to the cold air around.
Mountain weather, however, is fickle — changing like a
shifting kaleidoscope with every passing cloud or gust of wind. The soil surface
on a mountain can get hotter than the valley soil surface because of the Sun’s
greater intensity up high where the air is thin and clean.
Mountain soil can be as hot as desert dirt. In the Alps at
6800 feet (2070 m), the soil temperature one day shot up to 180 degrees F (80
degrees C) on a dark humus slope near the timberline. The slope faced southwest
at a gradient of 35 degrees. Dark humus soil absorbs the Sun’s energy better
than light sandy soil. A southwest-facing slope of 35 degrees in the Alps
receives the Sun’s rays more directly than does flat ground.
A mere five feet above the warm surface, however, was frigid,
cooled by the surrounding atmosphere. Alpine plants grow low to the ground — to
stay warm.
Further Surfing:
University of Colorado: Mountain climate by A. Bach
(Answered Feb. 27, 2004; updated Nov.1, 2007)
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