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The Learning Kingdom's Cool Fact of the Day for July 26, 1999
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Why are cities usually warmer than the country?
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A large city can create its own local weather patterns, including a
bubble of warm air called an "urban heat island." The heat island is
created by rooftops, streets, and parking lots, which absorb the sun's
energy during the day, and radiate it at night.
In moderately moist climates, these warm city "bubbles" can cause
clouds and even thunderstorms to form. The warm air rises up from
the city, creating an area of low pressure that pulls in moist air
from the surrounding countryside. The rising air cools, and clouds
can condense.
If there's enough water in the air, thunderstorms can occur. As a
result, cities like Atlanta, St. Louis, and Paris experience more
thunderstorms than the rural areas that surround them.
Atlanta's heat island contributes to pollution:
http://svs.gsfc.nasa.gov/imagewall/LandSat/
atlanta_heat_background.html
The Heat Island Group looks for ways to solve the problem:
http://EETD.LBL.gov/HeatIsland/LEARN/
NASA studies the role of trees in keeping urban temperatures down:
http://wwwghcc.msfc.nasa.gov/land/heatisl/heatisl.htm
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