Most of the non-polar
deserts lie within the two trade winds belt. From USGS
| As air
rushing into the low pressure regions rises, cools and then drops, these regions get most
of the rainfall and vice versa in the high pressure regions, where deserts can be
found. |
| Sea
temperature influence the water extraction rate and global pattern of currents. Far from
the desert belts, established in the polar regions, cold currents move to the equator and
may come up against the edges of continents. |
| Upwelling
from the very cold ocean depths adds masses of cold water to them. Wind blowing to the
land over the cold water is cold and can only carry little moisture, bringing fog and mist
but not rain. |
| Winds that
travelled a long distance lost their moisture (for example, the winds reaching Gobi and
the interior part of Sahara). Mountain barriers also extract water. (for example, the
comparatively low eastern highlands of Australian behind the Queensland coast) The
dehydration process from the wet mountain side to the dry desert side often occurs over a
horizontal distance of less than 161km (100 miles). That' s why some wettest and driest
area can be quite close to each other, separating by mountain barriers. © Copyright 1999,
ThinkQuest team 26634
All rights reserved. |
|
The earth rotates
around its axis at about 1676 km per hour at the equator but at nearly zero speed at the
poles. Hot air at the equator rises and spreads north and south before cooling and it
condenses and releases its moisture over the tropical zones. An equatorial zone of low
atmospheric pressure is created. The two tropical zones are at high pressure. Nearer to
the poles are 2 low-pressure belts of cold. The polar regions have descending air and high
pressure. As the denser air sinks towards the ground to the 2 subtropical high-pressure
belts, wind is created (easterly trades), which is hot and completely lacking of moisture,
blowing across the Sahara, the Middle East and the North America.
