Rules Of Summer Rainfall Abnormity In Sanxia Region And Its Cause Analisis

With the analysis methods of EOF, REOF, wavelet, correlation, running mean, and synthesis, Sanxia summer precipitation (SXSP) anomaly rules and its reasons is studied.The results show that:(1) SXSP anomalies exhibit remarkable variation cycle of 15 years, 6-7 years and 2~3 years. The distribution of SXSP is in phase with the middle-low reaches of the Yangtze river, While it is out of phase with that of middle and west of Sichuan Basin. (2) SXSP anomaly is closely related to the abnormity of 500hPa geopotential height field over the East of Ural and Yakutsk area, western ridge point and area of subtropical high, the cold air abnormity from north of China and the position of upper level westerly jet over East Asia. (3) Obviously differences exist in the location of East-Asia block high , the area of subtropical high and its position between extreme flood year and flood year in SXSP. (4) SXSP bears close positive correlation with lower-level northward moisture flux over Bengal Bay, and negative correlation over Okhotsk and Japan. (5) There is close relation between SXSP and the East of Pacific in prior autumru the same winter and spring, among which, the correlation coefficient in the same winter over the area of 11.5-6. 5 S, 93. 5-87. 5 W is the most significant.