Saturday, July 27, 2013

Warming After Midnight

Occasionally when I look at my weather station I see something interesting. That happened this morning. Usually we expect to see temperatures to fall all night after the sun goes down. That didn't happen last night. At 2:00 this morning the temperature increased almost five degrees! What caused this?...It was the wind!
(c) bkb
Winds were blowing at 2 mph, but were gusting at 8 mph. If you were to stand outside you would feel warm gust of air. 

Wind mixes air from above down to the surface. This brings warmer air in two ways. First, air aloft is usually warmer at night. This is called an inversion. Air is cooled from the surface up at night, and winds can mix that warmer air aloft down. The other way descending air causes warming is because of thermodynamic effects. When air descends it is compressed. As a result, the temperature increases. The nighttime cooling finally took effect after 3:00.

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