Geoscience Reference
In-Depth Information
Midnight
Convective
Cells
Upper level
Southeast
flow
12
10
Northeast
Monsoon
5
Land breeze
0
South China Sea
Borneo
08:00 Hours
Mature cloud system
12
10
0°C
5
0
Noon
Dissipating cloud system
12
10
Subsiding
Dry Air
5
Se
a
breeze
0
NW
SE
0
100
200
300
400
500
600
700
800
900 km
Figure 11.11
Schematic development of a non-squall cloud cluster off the north coast of Borneo: large
arrows indicate the major circulation; small arrows, the local circulation; vertical shading, the zones of rain;
stars, ice crystals; and circles, melted raindrops.
Source: After Houze et al. (1981). Courtesy of the American Meteorological Society.
there is divergence in the upper troposphere north
of the Tropical Easterly Jet (see also
Figure 11.40
).
They are several hundred kilometers long and
travel westward at about 50km hr
-1
giving squalls
and thunder showers before dissipating over cold-
water areas of the North Atlantic. Spring and
autumn rainfall in West Africa is derived in
large part from these disturbances. In wet years,
when the AEJ is further north, the wave season
is prolonged and the waves are stronger.
Figure
11.13
for Kortright (Freetown), Sierra Leone
illustrates the daily rainfall amounts in 1960-1961
associated with disturbance lines at 8°N. Here the
summer monsoon rains make up the greater part
of the total, but their contribution diminishes
northward.
C THE SOUTH ASIAN
MONSOON
The name monsoon is derived from the Arabic
word
mausim
, which means season, referring to
large-scale seasonal reversals of the wind regime.
The Asiatic seasonal wind reversal is notable for its
