East Asia and Western Pacific METEOROLOGY AND CLIMATE

105
INFLUENCE OF VARIATIONS OF THE CIRCULATION SYSTEM OVER THE
SOUTH INDIAN OCEAN ON THE EAST ASIAN SUMMER MONSOON AND
THE NORTHERN HEMISPHERIC GENERAL CIRCULATION
OF THE ATMOSPHERE
Huang Shi-Song, Tang Ming-Min, Yang Xiu-Qun
(Department of Atmospheric Sciences; Nanjing University)
ABSTRACT
This paper aims mainly to investigate the influence of
variations of the South Indian subtropical high on the East Asian
summer monsoon and the Northern Hemispheric atmospheric circulation.
Observational studies show 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 their intensities and positions during May through
September. The oscillation occurs first over the southern Indian Ocean
and then the one over the northwestern Pacific Ocean follows. The
teleconnection is evident and clear. The physical processes of
teleconnection are elucidated.
Based on the daily, pentad and monthly low and high levels
average stream fields, the 850 hpa air trajectories entering China
during the Mei-Yu period and the above results relating to the
teleconnection processes, the principal components of the summer
monsoon regime of East Asia are reviewed. It is pointed that, as far as
the low level concerned, the key components should be the NW Pacific
High and the Mascarene High. A new schematic model of the summer
monsoon regime is then proposed.
In order to verify the above findings, a global spectral
general circulation model is used to demonstrate the influence 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.
It is found that the simulational results are quite consistent with the
observations. Further, an anomalous intensification of the 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 Southern Hemisphere and two in the Northern
Hemisphere.
So we may conclude that, during the northern summer, the
Mascarene High over the South Indian Ocean acts as a key system in the
interaction between the Northern and Southern Hemispheres, ft is an
indispensable constituent of the summer monsoon regime of East Asia. It
influences the variation of general circulation of the atmosphere far
into the high latitudes.