Interdecadal variations of West Pacific Subtropical High area and changes in summer precipitation over China in boreal summer during the last 57 years.

Using the NCEP/NCAR reanalysis from 1951 through 2007,the precipitation data at 160 stations and the circulation index in the same period released by the National Climate Center of China,we have investigated in the present paper the abrupt changes in area of summertime mean West Pacific Subtropical High(WPSH) and interdacadal variations in summer precipitation over China during the last 57 years.The results suggest that under the background of the global warming,the area of WPSH also showed an apparent increasing trend especially in the mid-1960s and the late 1990s(i.e.an interdecadal change character of quasi-20 years).In the three quasi-20 year periods of the 1950s—1960s,the 1920s—1980s and the 1990s—2007,summer precipitation and atmospheric circulation over China were obviously changed:along with successive increase in the area of WPSH,the East Asian monsoon became anomalously weak;and the precipitation pattern over China changed from positive anomaties in Southern China-negative anomaties in Southern China in the 1950s—1960s to negative anomaties in Northern China-positive anomaties in Southern China in the 1990s—2007;and the area where the precipitation linearly increased also showed a northward migration trend.