Geoscience Reference
In-Depth Information
(a)
40°N
12180
12080
12240
12200
12120
12280
12320
30°N
12320
12280
20°N
12240
12200
12200
10°N
12160
Equator
12160
12160
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
30
(b)
40°N
4320
4360
4280
30°N
4400
20°N
4280
4360
10°N
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
Figure 7.5.
Climatology of (a) 200 hPa and (b) 600 hPa geopotential heights
and winds in July. Contour intervals are 20 m.
The Walker circulation is particularly well developed in the equatorial Pa-
cific, with rising air in the west and subsidence in the east.
Figure 7.6a
shows
the Pacific vertical
p
-velocity climatology at 500 hPa, the level at which vertical
velocities are typically largest. The down-branch of the Pacific Walker circula-
tion, with positive values indicating sinking motion, is located the eastern
Pacific and the rising branch is in the west.
The SOI, that is, the strong correlation between surface pressures at Darwin,
Australia, and Tahiti (
chapter 3
), comes about as the Pacific Walker circulation
shifts with ENSO. The vertical velocity distribution typical of warm events (El
Niño) is displayed in
Figure 7.6b.
Sinking in the eastern Pacific is weakened
and confined south of the equator, and the border between positive and nega-
tive values is located farther east compared with the climatology. The region
