Geoscience Reference
In-Depth Information
Figure 2.26 displays annual mean precipitation across the globe from the
CMAP climatology. Note the following:
• There is pronounced east-west structure in the precipitation ields. Latitude
is not necessarily a good indicator of rainfall rates, even within the ITCZ.
• The eastern sides of the Paciic and Atlantic Ocean basins are signiicantly
drier than the western sides in both hemispheres. The opposite is true in the
Indian Ocean north of about 15°N.
• In middle and high latitudes, land surfaces generally receive less rainfall than
ocean surfaces.
• In both hemispheres, regions of high rainfall extend diagonally off the east
coasts of the continents, to the southeast in the Southern Hemisphere and
to the northeast in the Northern Hemisphere. These are the land- based
convergence zones . In the Southern Hemisphere, these regions are known as
the South Pacific Convergence Zone (SPCZ), the South Atlantic Convergence
Zone (SACZ), and the South Indian Convergence Zone (SICZ).
Seasonality in global rainfall distributions is displayed in Figure 2.27 .
• In midlatitudes, rainfall is concentrated over the oceans in winter and tends
to be more continental in summer.
• The subtropical precipitation minimum seen in the zonal mean ( Fig. 2.25 ) is
associated with low rainfall rates over the eastern Pacific and Atlantic Ocean
basins, and low precipitation rates over northern Africa (the Sahara Desert)
and the Middle East, as well as parts of Asia (the Gobi Desert) and Australia.
• Tropical precipitation rates are greater in the Northern Hemisphere than
in the Southern Hemisphere for two main reasons. One is that the intense
precipitation band across the tropical Pacific just north of the equator
(ITCZ) remains in place all year around. The other is the high precipitation
rates, and great extent, of the summer monsoon in southeast Asia.
• The SACZ and the SICZ are features of the summer season. The SPCZ is
present during both summer and winter, but it is better defined during the
summer.
60°N
2
2
2
2
4
30°N
4
2
4
2
2
6
4
4
6
4
8
6
4
8
2
8
6
6
6
Equator
2
2
4
8
4
4
6
4
2
2
4
30°S
4
2
2
2
2
60°S
30°E
60°E
90°E 120°E 150°E 180° 150°W 120°W 90°W 60°W 30°W 0°
Figure 2.26 Annual mean precipitation climatology. Contour interval is 2 mm/day.
 
 
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