Analysis on the Interdecadal Change of Submonthly Time Scales Oscillation of Precipitation over North China during Rainy Seasons and Its Cause

Based on the daily precipitation data from 740 stations in China and NCEP/NCAR reanalysis daily datasets, the interdecadal change of submonthly time scales oscillation of precipitation over North China during rainy seasons and its cause are analyzed by means of the wavelet analysis method. Some results are discovered as follows: There exists significantly different submonthly timescales oscillation for the rainfall over North China during rainy seasons in the two different interdecadal periods due to interdecadal change of the western Pacific subtropical high and submonthly timescale oscillation of North China summer monsoon. There exists a significant high frequency rainfall with the 3－8-day synoptic timescale periodic oscillation in the flood period from the beginning to ending of the rainy season over North China. The daily rainfall over North China has a typical single-peak structure, which reaches the maximum in the last ten days of July and decreases gradually. The daily rainfall over North China obeys the rule which daily rainfall over North China frequently occurs in the last ten days of July and the first ten days of August. However, the distinct synoptic timescale high frequency rainfall does not take place until mid-July, which appears little later, and there is superimposition of 3－8-day synoptic timescale and 10－20-day timescale periodic oscillation for the daily rainfall over North China after 22 July. The daily rainfall over North China reaches the sub-maximum in the early ten days of July and decreases a little, then it reaches the maximum in the early ten days of August and decreases again, which shows a characteristic of low frequency oscillation. Furthermore, the low frequency precipitation begins with a negative phase and ends with a positive phase from 26 July to 6 August, which displays the different characteristics from the laws during the flood period that the peak rainfall over North China during the rainy season takes place in the last ten days of July and the first ten days of August.