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Just Desert
10/02/2002
Listen in RealAudio 
Hi, I'm Bryan Yeaton and this is The Weather Notebook. Today we deal with the driest climate
zones on earth, the deserts. Sand dunes and camels are what we think about when we hear the
word desert. But deserts came be home to flowers and birds as well as ice and snow.
Most of the major deserts of the world are located about 3200 kilometers, or 2000 miles either
north or south of the equator, and run along lines mostly parallel to it. These lines are 23
degrees from the equator and are called the tropic of Cancer in the north and the tropic of
Capricorn in the south.
The major desert areas around the world are in the southwestern United States, northern
Africa, south central China, western Australia, and the west coast of South America. These
deserts all have one atmospheric quality in common; the air over them is generally sinking.
Rising air also called "unstable air" makes clouds and precipitation, and sinking air makes it
sunny and dry. In the big picture warm air rises over the equator, goes up 5 or 10 miles,
spreads out north and south, cools down because it's up so high and sinks back down in the
deserts, that's why they're there.
In Polar regions, the air is so cold and heavy it is almost always sinking, and this is where
you find the world's driest deserts. The South Pole is actually in the driest desert on earth,
in spite of the lack of sand dunes and camels. Hmmm. Lawrence of Antarctica, riding a polar
bear; I just can't picture it.
The Weather Notebook is made possible by a grant from The National Science Foundation, with
additional support from Subaru of America.
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