INTERDECADAL VARIABILITY OF SUMMER CLIMATE OVER EAST ASIA AND ITS ASSOCIATION WITH 500 HPA HEIGHT AND GLOBAL SEA SURFACE TEMPERATURE

摘要

Interdecadal variability of summer climate (rainfall and temperature) in East Asia (China and Japan) and its association with the anomalies of geopotential heights at 500 hPa over the Northern Hemisphere (NH), global sea surface temperature (SSTA), and outgoing longwave radiation (OLR) were examined. An abrupt change was found in the middle and by the end of the 1970s in the Variations of time coefficients of the second mode of singular value decomposition (SVD2) for the summer rainfall and temperature in China. The rainfall anomaly around 1977-1979 changes from above normal to below normal, and the temperature changes from below normal to above normal in the southern and southwestern parts uf China. A similar interdecadal variability was also found in the summer climate variations in the Southwest Islands of Japan. The 500 hPa height anomalies related to the spatial pattern of SVD2 shows a clear dipole pattern: the negative center is located in Mongolia and northeastern China, and the positive center is located in middle and southern China. The abrupt change of summer climate in the middle and by the end of the 1970s over the subtropical regions of East Asia is characterized with the intensification and westward and southward extension of the western Pacific subtropical high (WPSH). It is also observed in geopotential height variations over Eurasia around 1977-1978. An abrupt change of SST over the tropical Indian Ocean and tropical western Pacific was also found around 1976-1977. It is indicated that interdecadal variability of summer rainfall and temperature over East Asia is largely influenced by the change of SSTA and convective activity in the tropical Indian Ocean and tropical western Pacific. The convective activity over the tropical Indian Ocean and tropical western Pacific is usually enhanced when the SST is warmer than normal, so the subtropical high anomalies over the subtropical regions of East Asia are intensified through the enhancement of a Hadley cell. As a result the subtropical regions of East Asia, including southern and southwestern China and the Southwest Islands of Japan, are covered by a positive height anomaly at 500 hPa, where the temperature is above normal and the rainfall is below normal. [References: 18]