Geoscience Reference
In-Depth Information
January
February
March
April
0
4
4
200
4
8
8
4
8
-4
400
-4
12
12
600
-4
8
800
8
8
-4
4
-4
4
4
4
0
1000
0
May
June
July
August
0
0
0
-4
-
-8
-
-8
-12
200
-4
-8
-12
-8
-12
400
600
800
-8
-12
-8
-8
-8
-4
-4
0
-4
0
-4
0
1000
September
October
November
December
0
-
-8
4
200
-4
4
8
4
-12
-4
400
8
-12
600
800
4
8
-4
-8
4
4
-4
-4
0
0
1000
30°S
Equator
30°N
30°S
Equator
30°N
30°S
Equator
30°N
30°S
Equator
30°N
Figure 7.3. The Stokes stream function for each month. Positive (negative) contours indicate clockwise
(counterclockwise) circulation. Contour intervals are 2 × 10
10
kg/s and vertical axes are in hPa.
• Rising air in the up-branch of the Hadley circulation near the equator
supports the zonal mean precipitation maximum, the ITCZ (
Figs. 2.25
and
2.26)
, which is located in the summer hemisphere (in the zonal mean).
Air rises in concentrated areas of convection and sinks weakly between
convective towers.
• Precipitation minima (deserts) are found in the subtropics
(Figs. 2.25
and
2.26)
, where convection is suppressed in the broad subsiding down-branches
of the Hadley circulation.
• The location of the zonal mean evaporation maxima in the subtropics
(Figs.
the Hadley circulation, which consists of dry air moving equatorward in an
environment of large-scale subsidence and, therefore, suppressed convection.
This connection to the Hadley circulation explains why the zonal mean
precipitation and evaporation maxima are not located at the same longitude.
• The salinity maximum in the subtropics
(Figs. 2.19
and
2.20)
is also related
to the Hadley circulation; it is a consequence of excess evaporation over
precipitation.
