Abstract:Using the climatological mean pentad precipitation data in eastern China,annual variations of monsoon precipitation within the four subareas,i.e. South China,the middle-lower reaches of Yangtze River,Huaihe Basin and North China,are studied.Especially the stages and regional features of summer monsoon precipitation are discussed in detail.By harmonic analysis method,climatological variation of precipitation within each subarea is decomposed into annual cycle mode,seasonal mode,intra-seasonal oscillation mode and intra-monthly oscillation mode.Results show that the impact of interactions among the four modes on the stages and regional features of precipitation are significant.The annual cycle mode is the main mode influencing rainy season,and the seasonal mode and CISO(climatological intraseasonal oscillation) mode are important to determine the flood season.Based on the four climate modes,a new division method of rainy season and flood season in eastern China is put forward.It may be more objective and reasonable as compared to former division methods,though the method is simple.