Relationship between the South Indian Ocean Dipole and the September Precipitation in Southwest China

Using Hadley sea surface temperature data from January 1979 to December 2018,monthly grid precipitation data of CRU TS v4.03,and NCEP/NCAR re-analysis of monthly average data. The relationship between the dipolar sea temperature of the South Indian Ocean and the early autumn precipitation in southwestern my country was studied. The results show that the second mode of the average Indian Ocean sea surface temperature EOF from July to August shows a significant northeast-southwest dipole mode,and the sea surface temperature on both sides of the northeast and southwest shows an inverse phase change feature,which is typical. The distribution of the South Indian Ocean Dipole(SIOD),whose time coefficient is a periodic change of more than 30 years,is defined as a new SIOD index; Corresponding to the positive SIOD anomaly from July to August,the convective activity in Southwest China increased significantly in September,while the negative anomaly was significantly suppressed and the SIOD index was strongly positively correlated with the September precipitation in Southwest China. The main ways that SIOD affects China's September precipitation are: The cross-equatorial air current formed in the northeastern Indian Ocean splits into two branches over the south of the Bay of Bengal. One of them enters southwestern China through the Bay of Bengal and the Indochina Peninsula. Precipitation occurs in southwest China. The results of this study are not only useful for understanding the possible impact of the South Indian Ocean air-sea system on precipitation in my country,but also for the development of early autumn precipitation prediction models in Southwest China.