An Observational Study on the Onset of the Summer Monsoon Over Eastern Asia in 1979.
NATIONAL AIR INTELLIGENCE CENTER WRIGHT-PATTERSON AFB OH
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This article analyzes the process of seasonal transition from spring to summer during the monsoon test period of May-July 1979. In the area of southern Asia and the northwestern Pacific, ten days before the outbreak of large scale summer monsoons, there was a strengthening process in upper atmosphere jet stream westerlies for the area of the southern hemisphere between 40 deg - 160 deg E in the middle latitudes. As far as the development of longitudinal circulation associated with the middle troposhere of the southern hemisphere as well as strengthening of cross-equatorial southerly air flows associated with lower layers of the troposphere are concerned, at this time, there was an increase in wind speed in southwesterly winds of the lower atmosphere in the tropical zones of southern Asia and the northwest Pacific. In conjunction with this, there was an expansion of ranges toward the north and an increase in tropical easterlies in the upper troposhere of the southern Asia area. Monsoon circulation patterns were strengthened, and the rainbelts of eastern China showed the appearance of seasonal northward shifts. It seems that changes in atmospheric circulation in the southern hemisphere have a triggering effect on the establishment of summer monsoons in the east Asian area as well as on the initiation of the pushing of them toward the north. AN