Multi temporal scale variations of summer precipitation in wet seasons over China and their association with 500 mb geopotential height

Abstract

Multi scale characteristics of summer precipitation variation were studied using rotated principle component analysis and wavelet analysis on 76 stations for the period 1968-1997. We found 2 significant precipitation periods in northern and southern China corresponding to the movement of the East Asian summer monsoon. The 2 precipitation periods are characterized by a continuous 3 d mean precipitation higher than 10 mm in northern China during early July to late August and higher than 20 mm in southern China during early May to late June. The precipitation amounts in the first half of August over northern China and second half of June over southern China are the major con- tributors to the total precipitation during the 2 rainy periods, respectively. In addition, a weekly time scale precipitation variation of about 7.2 d during the first half of August over northern China and an intraseasonal time scale of 25 d during the second half of June over southern China are evident dur- ing wet seasons. Case studies for 2 extreme wet seasons over northern China in 1994 and 1996 show that weekly time scale precipitation is associated with a 500 mb anomaly over the Sea of Japan dur- ing July to August. The 2 wet seasons over southern China in 1968 and 1994 show that intraseasonal time scale precipitation is closely associated with 500 mb geopotential height over the tropical west- ern Pacific during May to June.