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Deserts Are...
Mon Sep 19, 2005
Listen in RealAudio 
Did you ever wonder why the earth’s deserts are where they are? Maybe not, but the
answer is pretty interesting anyway! Hi, I’m Bryan Yeaton, and this is The Weather
Notebook.
If you look at deserts around the globe, , you may notice that they fall within a fairly
narrow band at around 30 degrees North and South latitude. Most of the reason for that
is due to the global circulation incited by the sun’s heat, and our magical 23 _- degree
tilt.
The sun’s heat causes air to rise at the equator, causing wet and stormy weather. But
it diverges at the stratosphere, circulating in north and south loops, and pulling air in to
fill the void. If our planet were not tilted, this might just form one big loop of air in each
hemisphere. But no! The air drops back to earth at about 30 degrees of latitude,
although, this can vary by 10 degrees or more. This air warms and dries as it
descends, and there you go: Sahara, Mojave, Gobi; and in the southern hemisphere,
Kalahari, Atacama, and the Great Victoria Desert.
The air rises again at about 60 degrees, causing more storminess, and falls back
again around 90 degrees, which puts us right at the poles. Now, we consider the poles
very snowy and cold places. But: Antarctica is actually one of the driest deserts on
earth. It may only get a couple of inches of snow in a year (the water equivalent of which
is just a few millimeters). But what does fall tends to stay, as it is too cold to melt. In
fact, ice cores in Antarctica and Greenland have been drilled two miles deep, and have
provided climate history back for more than 110-thousand years.
The Weather Notebook is funded by Subaru of America. Find us online at
www.weathernotebook.org.
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