East Asia and Western Pacific METEOROLOGY AND CLIMATE

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I . INTRODUCTION
The structure of the East Asian summer monsoon regime is of
primary importance to the rainfall during rainy season of China. Tao
and Chen(1987) considered,, as far as the low leyel is concerned, the
Australian high to be the key component system of the East Asian summer
monsoon regime and excluded the Mascarene high from it. In this paper
it is argued that the key components should be the Mascarene high and
the NW Pacific high. A new schematic model of the summer monsoon regime
is then proposed.
The periodic variation of the atmospheric circulation with time
scales larger than a week at middle latitudes, namely, the cyclic
change of the westerlies index, has been described as early as in
forties (Starr 1942, Namias 1947). But for low latitudes, it was not
until the seventies, the 40-50 day oscillations of sea level pressure
and wind over the equatorial region was firstly noticed (Madden and
Julian 1971,1972). Thenceforth, many investigations have been
undertaken (e.g. Krishnamurti et. al., 1976, 1982/ 1985; Yasumari,
1980, 1981^Murakami and Nakazawa, 1985, and Lorence 1984). All these
investigations were mainly based on spectral analsis. This paper is
involved in investigating the substantial variations in intensity
and/or position of the circulation systems in low latitudes, such as
the equatorial westerlies, cross-equatorial currents, the NW Pacific
subtropical high, the Mascarene high and the Australian high. The
teleconnection between the variations of circulation systems over the
South Indian Ocean and the Northwest Pacific Ocean and its physical
processes are elucidated.
In order to verify the above findings, a global speatral
general circulation model is used to demonstrate the influence of
intensity changes of the Mascarene high on the variations of the
atmospheric general circulation. It is found that the experiaent
results are quite consistent with the observations. Further, an
anomalous intensification of Mascarene high will also have a
substantial contribution to the development of global low frequency
fluctuations of atmosphere. Three wave trains can be found, one in the
Sounthern Hemisphere and two in the Northern Hemisphere.
II. OBSERVATIONAL STUDY
(1) Structure of the Summer Monsoon Regime
The monsoon study is generally focused on the seasonal
variation of the low layer winds. But its activity should be considered
in accordance with two factors, the prevailing air currents and the
thermal properties of the air. In other words, the source regions
should be considered.
The summer monsoon of China usually develops at its culmination
in July each year. The monsoon currents penetrating into China can be
either the tropical maritime air from the NW Pacific Ocean or the one
from the southern Indian Ocean, passing over the Bay of Bengal. So the
monsoon can be southeasterly winds or southwesterly winds as shown in
Fig.Cl), and Fig.(2) protrays several air trajectories at the 850 hpa