Abstract: Based on the NCEP/NCAR reanalysis data with resolution of 1°×1° and from four aspects of circulation situation, water vapor, dynamics and unstable stratification, a comparative analysis of the two rainstorms in Hunan province in November 2015 is maked. The results show that the two rainstorms are related to the abnormal large-scale circulation background. The province large area and strong intensity of subtropical high are beneficial for water vapor to converge into Hunan province along the southwest side of subtropical high. The intensity of polar vortex is stronger than the annual average, which makes the intensity of cold air stronger. The strong cold air in the south intersects with the warm and wet air in the north, causing the heavy precipitation weather process. Ground inverted trough and low-level eddy shear are the main influence systems of the two heavy precipitation processes. In process 2, the ground inverted trough has strong intensity, wide range and slow movement, and corresponds to the low-level eddy shear intensity. In process 1, the ground inverted trough and the low-level eddy shear intensity, range and duration are lower than those in process 2. The water vapor of 700 hPa is the main transport source of the two regional rainstorms. The water vapor of process 1 is mainly from the South China Sea and process 2 is from the Bay of Bengal, and the water vapor condition is stronger than that of process 1. In process 1, the vertical upward motion zone extends upward at a higher altitude, with deep convergence layer in the lower layer, strong frontal zone and unstable energy accumulation. In process 2, stable precipitation is dominant, vertical upward motion, convergence and divergence are shallow, mainly concentrated in the middle and low levels.

Key words: rainstorm in winter flood season, comparative analysis, weather process, Hunan province