DECADAL CLIMATE VARIABILITY OF RAINFALL AROUND THE MIDDLE AND LOWER REACHES OF THE YANGTZE RIVER AND ATMOSPHERIC CIRCULATION

This study examined the rainfall around the middle and lower reaches of the Yangtze River and related atmospheric circulation by using NCEP reanalysis data. The purpose of this study is to analyze their decadal variation and the relationship among rainfall, atmospheric circulation around East Asia and the ENSO episodes. Current results are presented as follows: (1) Very clear increasing trend of the rainfall around the middle and low reaches of the Yangtze River during the Meiyu period and June to July is found in the recent 15 years. Meanwhile, the geopotential height at 500 hPa around the Okhotsk Sea also holds similar increasing trend. It is noticeable that ENSO episodes tend to occur more frequently in the recent 15 years. (2) An index describing East Asian summer monsoon is well correlated with the SST in the Nino-3 region in preceding autumn in the recent 20 years but is not prior to the period. This means that the El Nino phenomenon exerts more impacts on East Asian summer monsoon recently. (3) The warm phase of PDO in the recent 20 years basically coincides with the increasing trend of the atmospheric circulation in East Asia.