Abstract:Based on rainfall observation and EAR5 reanalysis data, 19 cases of extreme rainstorms induced by southwest vortex and seen in Sichuan Basin from 1981 to 〖JP2〗2020 are statistically analyzed, and the dynamic〖JP〗 synthesis analysis on the circulation background and the structural characteristics of the southwest vortex are carried out. The results show that the life time of the southwest vortex lasts for 48-132 h, and the extreme rainstorm generally breaks out within 18 hours 〖JP2〗after the southwest vortex is formed. The circulation〖JP〗 background of southwest vortex can be divided into two types: the east high west low type and the low trough type. The South Asian high and the subtropical high are strong in the east high west low type. The southern end of the 500 hPa Lake Baikal low trough is superimposed with the plateau low trough to form a deep low trough. Sichuan Basin is located in front of the trough and on the west side of the subtropical high. The low trough type is located in the east of 140°E of the subtropical high, and the South Asian high is more westward and southward than the east high west low type. Sichuan Basin is affected by the eastward shift of the low trough of the Qinghai-Tibetan Plateau. The both types have the water vapor transport channel from the Bay of Bengal to South China Sea to Sichuan Basin, and the water vapor transport of the east high west low type is much stronger. Under the background of east high west low type, the southwest vortex is stronger in intensity and larger in scope, having a deep warm core structure in the vertical direction, and a deep asymmetric distribution of the wind field. Under the background of the low trough type, the southwest vortex has a temperature anomalous distribution of “cold in the upper part-warm in the middle-cooler in the lower part”, and the asymmetry of the wind field is only maintained at the lower level. The common features of the two types are the high energy and high humidity in the lower layer, and the positive vorticity column has a “convergence in the lower layer and divergence in the upper layer” dynamic structure.