Geoscience Reference
In-Depth Information
110°
120°
130°
140°
150°E
OCT-DEC
JULY-SEPT
MAY-JUNE
JAN-APR
40°N
40°N
LATITUDE OF
WEST PACIFIC
STHP RIDGE
AT 500mb
35°
0
miles
500
35°
0
km
500
30°
MID-AUG (30°)
30°
27°
MID-SEPT (27°)
MID-JULY (25°)
27°
25°
25°
MID-JUNE
(20°)
MID-OCT
20°
20°
17.5°
MID-MAY (17.5°)
17.5°
15°
MID-APRIL (15°)
15°
10°
10°
110°
120°
130°
140°
Figure 11.37
Typhoon paths over East Asia during January to April, May to June, July to September and
October to December related to the mean latitude of the central ridge axis line of the subtropical high
pressure cell at 500mb over the western Pacific.
Sources: Compiled from various sources, including Lin (1982) and Tao (1984). Reproduced by permission of the Chinese
Geographical Society.
Monsoon Trough to migrate regularly with the
seasons. In general, the West African Monsoon
Trough oscillates between annual extreme
locations of about 2
E CENTRAL AND SOUTHERN
AFRICA
N (
Figure 11.39
).
In 1956, for example, these extreme positions were
5
°
N and 25
°
1 The African monsoon
The annual climatic regime over West Africa has
many similarities to that over South Asia, the
surface airflow being determined by the position
of the leading edge of a Monsoon Trough (see
Figure 11.2
). This airflow is southwesterly to the
south of the trough and easterly to northeasterly
to its north (
Figure 11.38
). The major difference
between the circulations of the two regions is due
largely to the differing geography of the land-sea
distribution and to the lack of a large mountain
range to the north of West Africa. This allows the
N in August. The leading
edge of the Monsoon Trough is complex in
structure (see
Figure 11.40B
) and its position may
oscillate greatly from day to day through several
degrees of latitude. The classical model of a steady
northward advance of the monsoon has recently
been called into question. The rainy season onset
in February at the coast does propagate northward
to 13°N in May, but then in mid-June there is a
sudden synchronous onset of rains between about
9
°
N on 1 January and 23
°
°
N and 13
°
N. The mechanism is not yet firmly
