Geoscience Reference
In-Depth Information
(a
)
40°N
1020
1040
1020
1000
30°N
1020
20°N
1020
1020
1020
1000
10°N
1000
1000
Equator
10°S
20°W 10°W
0°
10°E
20°E
30°E
40°E
50°E
60°E
70°E
80°E
90°E 100°E
10
(b
)
40°N
960
920
940
980
1020
900
920
960
30°N
1000
940
900
20°N
940
920
960
980
980
10°N
1000
1000
Equator
10°S
20°W 10°W
0°
10°E
20°E
30°E
40°E
50°E
60°E
70°E
80°E
90°E
100°E
20
Figure 7.4. Wind vectors and geopotential height contours for (a) January and (b) July
at 900 hPa in the vicinity of the African and Indian monsoon systems. Values are
extrapolated where the 900 hPa surface is below the physical surface.
and it is centered at about 600 hPa (see
Fig. 7.5b
). Easterly flow south of the
Saharan high is known as the
African easterly jet
.
WALKER CIRCULATIONS
A third example of thermally direct circulations in the atmosphere is the
Walker
circulation
. This is a series of east-west overturning cells close to the equator
where Coriolis forces are small. Rising branches are located over relatively
warm areas (the western warm pool in the Pacific, equatorial South America,
and equatorial Africa) and sinking branches are over cooler areas (e.g., the
eastern Pacific and Atlantic cold tongues; see
Fig. 2.6
).
