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Circulation of the Wind Upon Earth
The Basics
The following paragraphs deal with the general (surface) circulation with
prevailing winds and nearby permanent pressure systems of belts. (See
fig. 10-1). In the Northern Hemisphere, the circulation is clockwise
about high-pressure areas (called anticyclones) and counterclockwise
about low-pressure areas (called cyclones). The reverse is true in the
Southern Hemisphere. At times, confusion arises from the meaning of
wind direction. Wind is always named by the direction from which it is
blowing.
The Doldrums
The equatorial belt of light and variable winds between the northeast
tradewinds of the Northern Hemisphere and the southeast trade winds of
the Southern Hemisphere is called the doldrums, or the intertropical
convergence zone.
The doldrums may vary in position. They tend to move north and south
of the Equator with the Sun, though more of the area is generally
located slightly north of the Equator. In the doldrums, the temperatures
are high and the wind convergent (a net inflow of air into the area),
which causes greater rainfall.
Figure 10-1. General circulation of air.
10-4
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