Interannual Variation of East Asian Summer Monsoon and the Relationship with Atmospheric Circulation and Rainfall
东亚夏季风的年际变化及其与环流和降水的关系

Using NCEP/NCAR reanalysis geopotential height and winds at 500 hPa and 850 hPa,precipitation rate,sea level pressure(SLP),as well as the observed precipitation from more than 600 stations in China in June-August from 1951 to 2006 and focusing on the East Asia-West Pacific region(10o-80oN,70o-180oE),interannual variation of East Asian summer monsoon(EASM) and the relationship with atmospheric circulation and rainfall are studied by means of statistical diagnose methods,such as 9 points high-pass filter,empirical orthogonal function(EOF) analysis,composite analysis etc.Some conclusions can be drawn as below:(1) From the EOF analysis result of SLP in the East Asia-West Pacific region,a zonal dipole oscillation mode between Mongolia cyclone and West Pacific anticyclone(APD) can be found and the APD index can act as an intensity index of EASM.(2) The EOF-1 of anomalies of geopotential height at 500 hPa show an obvious meridional East Asia remote correlation mode(EAP) and EAP index also can be seen as an intensity index of EASM.(3) The result of composite analysis to the years with high/low APD index reveals that APD index is closely correlated with EAP at 500 hPa/850 hPa.The correlation coefficient between APD index and EAP index is-0.23,which can pass the significant test at confidence level 0.1.(4) Both APD index and EAP index are closely correlated with rainfall in the flood season in China and precipitation rate in the East Asia-West Pacific region.The significant correlation areas at confidence level 0.05 are mainly located in the scope from the land south of the Yangtze River valley to the sea south to Japan,and the former/latter is positive/negative,respectively.