In this study,the characteristics of intraseasonal evolution of precipitation in the rainy season of Jiangnan(24-30°N,110-120°E) and its interannual and interdecadal variations are researched,using daily precipitation data for the period of 1961-2008,based on the analysis of climatic characteristics of precipitation over southeastern China.The results are as follows:
1)A significant twin-peak feature in the intraseasonal evolution of precipitation in Jiangnan is demonstrated,with mid-April and mid-June as the twin-peak periods.The peak precipitation first appears in Jiangnan in mid-to late April,then extends southward.Southern China reaches its peak precipitation period in early to mid-June,after which the heavy precipitation center moves northward,and Jiangnan experiences the second precipitation peak in mid-to late June.Meanwhile,the precipitation in the Jianghuai area(32-35°N) shows a single peak type.The first peak of the Jiangnan rainy season appears very early,and this is the first sign of the rainy season in eastern China.The second peak is the performance of the main rain belt moving northward.
2)The correlation coefficient between the regional averaged twin-peak precipitation in Jiangnan and actual precipitation is 0.69,which indicates that the twin-peak precipitation shows the intraseasonal evolution features of the Jiangnan rainy season.The precipitation intensity of the Jiangnan rainy season mainly depends on the precipitation intensity of the bimodal peak in the rainy season(April-June),and this also shows that the twin-peak precipitation characteristics in the Jiangnan area can reflect the change characteristics of the actual precipitation.
3)The twin-peak precipitation of the Jiangnan rainy season displays significant interannual and interdecadal variations.The interannual periods are found every 2-3 years,and strong signals are mainly centered in the late 1960s to 1970s and mid-1980s to the beginning of the 21st century,while the interdecadal periods are shown every 8-10 years on the whole time domain,and their strong signals are centered in the early 1980s to late 1990s.
4)On the interdecadal scale,although the intraseasonal features of precipitation display a significant twin-peak precipitation pattern in the Jiangnan rainy season,the characteristics of the intraseasonal evolution also show skipped-significant features.A twin-peak precipitation pattern is notable in the 1960s,1980s and the beginning of the 21st century,while in the 1970s and 1990s the twin-peak pattern is insignificant.