Extremes of East Asian Weather during the Post ENSO Years of 1983/84

[摘要] Climate of East Asia marked significant fluctuations between winter 1983/84 and summer 1984: It was severely cold in winter and very warm and dry in summer. A diagnostic study on the features of atmospheric circulation and their association with the convective activity and SST (sea surface temperature) in the western tropical Pacific region is made in relation to these extremes of East Asian weather, with special emphasis on the midlatitudes-tropics interaction. The features are compared with those of climate 1982/83.In winter 1983/84 a deep trough persisted northeast of Japan, sustaining a significant meridional flow over East Asia. Zonal flow index was significantly low only second to winter 1967/68 in the last 40 years, and winter mean temperature in Central Japan was lowest since winter 1944/45, indicating a contrast to mild winter 1982/83. Meanwhile convective activities were significant around Indonesian maritime continent, and very weak around the date line. Thus winter 1983/84 showed a marked difference in distribution of convective cloud from the previous winter 1982/83. It is suggested that East Asian winter weather is closely associated with the interannual fluctuation of the convective activity in the western tropical Pacific Ocean.During summer 1984 the atmospheric circulation feature was quite different between early and later summer. During June and July a ridge northeast of Japan and a trough over China were almost stationary, and south-westerlies were prevalent over the eastern East Asia. In midsummer subtropical High (Sub High) developed north of the normal position and stayed for about a month near Japan, leading to hot and dry weather from south China to Japan. The formation of this Sub High followed the active convection around the Philippines from late July through August.In striking contrast to the continuation of lower SST during El Nino event of 1982/83 in the western tropical Pacific, it was above normal during winter 1983/84 through summer 1984. The convective activity in the region was also significant in phase with higher SST, suggesting that higher SST may have contributed to the active convection to a certain extent.

[学科分类] 大气科学