East Asia and Western Pacific METEOROLOGY AND CLIMATE

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cell extended northward to 30 N. And during 28-31, the Hadley cell as a
whole moved to north, its descending brench extended to north of 3G°N.
Following the establishment of Hadley circulation, the NW Pacific
subtropical high was bounded to abjust itself properly in position and
intensity. The ridge, line moved rapidly northward and new centers
formed while some old centers disappeared.
In addition,, it is also pointed out that*the seasonal variation
of the latitudinal position of the westerly jet of temperate latitudes
is closely associated with the subtropical high ridge, but with a phase
lag (Huang and Tang 1962). This phenomenon is extremely prominent in
1979 too. Therefore we may consider that the intensity change of the
Mascarene high can affect the variation of the mid-latitude atmospheric
circulation over the Asia-Pacific region. Recently Huang and Li(l987)
and Nitta (1987) find that the response to strong convective heating
over the Fhillipine Sea region can induce low frequency wave train as
two dimensional Rossby wave propagating to high latitudes, through the
northern part of Pacific Ocean to eastern United States. We consider
that the strong convective heating over the Phitlipine Sea is caused by
the intensification of horizontal velocity convergence which results
from the strengthening of the equatorial westerlies and its eastward
extention into the NW Pacific. Therefore, the formation of the low
frequency wave train should be finally attributed to the intensity
variation of the Mascarene high.
I. NUMERICAL EXPERIMENT
In order to verify the above findings, a global spectral
general circulation model, designed by Bourke (1977) and improved by
Simmonds (1985) and Lin (1987), is used to demonstrate the effect of
intensity changes of the Mascarene high on the variations of the
atmospheric general circulation. The model is truncated at wave number
15 and variables are represented at nine sigma levels in the vertical.
Two experiments, a control one (Exp.l) and an anomaly one (Exp,2) are
performed. The climatological normals for SST, water vapor, C0 2/ 0$ /
snow cover and polar ice of July are used, and the sun's altitude is
fixed at the mid July position. In the anomaly experiment, an anomaly
geopotential height, with maximum value of 100 gpm centered at 35 a S,
60° E, is superimposed on the Mascarene high at 850 hpa level. The
initial field is the one of a certain day extracted from the results of
integrating the model for hundreds of days. The 850 hpa initial field
and the geopotential height anomaly field are respectively shown in
Fig.(12) and Fig.(13). Since it is found that the global averaged
kinetic energy at 850 hpa becomes steady just only one day after
integration from the initial state for Exp.2, analysis of the
Integrated results can start with the first three-day average field.
Fig, 14 (a) and (b) show the 850 hpa wind anomaly fields of the
first and the second three-day period respectively. A strong
anticyclonic circulation exists over the region where the Macarene high
is located. It then results In a strengthening of the Somalian
cross-equatorial currents and formation of a cyclonic vortex over the
central South Indian Ocean and an anticyclonic vortex over the coastal