THE INFLUENCE OF INTENSITY CHANCE OF MASCARENE HIGH ON THE GENERAL CIRCULATION OF ATMOSPHERE-A NUMERICAL EXPERIMENT
Yang Xiuqun, Huang Shisong(Department of Atmospheric Sciences Nanjing University)
Observation study of Huang and TangC3, 43 has shown that a largs number of circulation systems in low latitudes, such as the subtropical highs, equatorial westerlies, cross-equatorial currents etc. exhibit certain medium-range oscillation in-variation of intensity and position during the summer months. It occurs first over the southern Indian Ocean and then follows the one over the northwestern Pacific Ocean. The physical processes of teleconnection are elucidated. Besides, it is also pointed out that the key components of the Asian summer monsoon regime should be the NW Pacific High and the Mascarene High. A new schematic model of the summer regime is proposed. This paper mainly aims to verify the above findings. In order to do this, a global spectral general circulation model is used in simulation experiment to demonstrate the influence of intensity change of the Mascarene High on the variation of atmospheric general circulation. The model is truncated at wave number 15 and variables are presented by nine sigma levls in vertical. Three experiments, a control run and two anomaly runs, are performed. In the anomaly run, either a geopotential height anomaly or a vorticity anomaly is superposed on the Mascarene High at 850 hPa level. It is found that anomalous intensification of the Mascarene High will result in strengthening of the Australian High, the cross-equatorial currents, the tropical convergence zone, the Hadley circulation and the NW Pacific High. It is quite consistent with observation. Basides, anomalous intensification of Mascarene High will also make a substantial contribution to the development of global low frequency fluctuations of atmosphere. Three wave trains can be found. The first one is a zonal wave train of K=3 in the Southern Hemisphere. The second is the one with a low center to south of Japan, a high center over Okhotsk Sea, a low center over N. Pacific, a high center over Alaska and a low center over southern part of North America. The third is the one with a high center over Europe and a low center over Asia. So we may conclude that, during the northern Summer, the Mascarene High of South Indian Ocean acts as a key system in the interaction between the Northern and Southern Hemispheres. It is an indispensable constituent of the summer monsoon regime of East Asia. It influences, the variation of general circulation of atmosphere far into high latitudes.