East Asia and Western Pacific METEOROLOGY AND CLIMATE

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But, as discussed in the next section, the displacement of the
NW Pacific high ridge is closely teleconnected with the activity of
the Mascarence high. Therefore, the activity of Mascarene high seems
to play a leading role in the function of East Asian summer monsoon
regime. Any idea of the summer monsoon regime in which the Mascarene
high is excluded is certainly questionable. Accordingly, a schematic
modle to consolidate the structure characteristic's of the East Asian
summer monsoon regime can be constructed as shown in Fig.4(a). The
principal components of the monsoon regime in the low levels of the
troposphere are the NW Pacific High, Mascarene high, Australian high
and the Indian monsoon depression. The first two subtropical highs are
of primary importance. If we consider the three dimensional integrated
structure of the summer monsoon regime, we can construct a block
diagram illustrating the interconnection and interaction properties
among all the components of the monsoon regime, see Fig.4(b).
When one is interested in the Mei-Yu problem, one must take
into consideration the activity of the cold air from the north.
However, it is shown by Fig.5 that the characteristics of the variation
of the pented mean latitude position of the subtropical high ridge over
NW Pacific in the years of flood summer (e.g. 1954 and 1980) are
entirely different from those in the years of drought summer (e.g. 198
and 1981). In addition, we find froia Table 1 that during the flood year
(e.g. 1980 and 1983) the summer average moisture flux across the
equator between 40 P E and 70°E and the flux across the 20°N circle
between 3Q*E and 110°E are all much larger than the corresponding flux
during the rather drought years (e.g. 1981 and 1982). Therefore, the
summer precipitation in the middle-lower reaches of Yangtze River seems
still to be determined, to a great extent, by the influence of the
activity of the NVf Pacific subtropical high and the Mascarene high.
(2) Fluctuation of the Circulation Systems
It has been shown that a large number of circulation systems in
low latitudes, such as the subtropical highs, equatorial westerlies,
cross-equatorial currents and etc. exhibit an oscillatory character in
the variation of intensity and position during the months May through
September. The oscillation period may range from 10 to 50 days. Certain
20-40 day oscillations occur almost in the same period of time in both
hemispheres, but it occurs first over the southern Indian Ocean and
then the one over the north-western Pacific Ocean follows (Huang and
Tang 1982, 1987).
From Fig.(6), in which the curves a, b, c and d represent
respectively the pentad-by.-pentad variations of the intensity of the
Mascarene high, the intensity of the Australian high, the speed of
cross-equatorial current at (0*N, 105*E) and the westerly speed at (10*
N, 115*E), we find that the Australian high oscillates with a phase lag
of about 1-2 pentads relative to Mascarene high, but with a lead of
about 1-2 pentads over the V and U oscillations. As strong westerlies
prevail on the South of the Mascarene high and the Australian high,
so the intensification of the Mascarene high may, through the energy
dispersion, cause intensification of Australian high which is just