Temperature, Elevation, and Fog
Name: Karalin H.
My house is high up on a mountain. Sometimes it is up to ten degrees warmer
at my house, and sometimes up to ten degrees cooler than at my school on the valley floor.
I know that as you go higher in altitude, the pressure goes down and the temperature
usually goes down. What is happening when the temperature goes up as I go up to my
house like today when this morning, our house sat up out of the fog and haze that
blanketed the valley below?
During clear nights (especially in the valley), long wave terrestrial radiation (heat
energy) escapes easily to space. As this happens, the air near the valley floor cools
more rapidly than the air at higher elevations (for instance at your house). This creates
what is called a temperature inversion. It is called an inversion because the usual
change in temperature with altitude (warmer at the surface and cooler with increasing
altitude, like you mention) is inverted (reversed). On clear nights, the temperature
near the valley floor therefore becomes cooler than at your house.
In the morning, fog occurs in the valley because the temperature there cooled enough
during the night that the air became saturated. However, at your house, the temperature
is higher than in the valley and the air is not saturated; therefore, your house is above
the fog layer.
Thank you for providing an excellent example of a nighttime temperature inversion!
David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory
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Update: June 2012