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Name: Karalin H.
Status: student
Age: 11
Location: N/A
Country: N/A
Date: 1/14/2004

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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