Abstract:Based on surface conventional meteorological data, hourly observation data from regional meteorological stations and ERA5 reanalysis data, the evolution characteristics and formation mechanism of mesoscale low-level jet and mesoscale vortex during the severe torrential rain process in Henan Province from 19 to 20 July 2021 are analyzed. The results show that the process of this extreme precipitation was directly related to the formation and development of the low-level jet and mesoscale vortex. The establishment and development of low-level jet was synchronized with the occurrence and enhancement of precipitation, while the mesoscale vortex appeared about 10 hours later than the establishment of low-level jet, and the low-level jet developed strongly with the enhancement of low-level vortex development. The strengthening and westward extension of the western Pacific subtropical high and eastward movement of the low pressure on the southeast of the Hetao Area increased the geostrophic wind, which was the main reason for the formation of the low-level jet. The existence of allobaric wind was the main reason for the easterly jet. The horizontal convergence and torsion in the lower troposphere caused by low-level jet were the main reasons for the development of mesoscale vortex in the middle and lower troposphere. The vertical vorticity advection caused by the vertical motion was the main reason for the enhancement of the voriticy in the middle troposphere. The condensation latent heat in the middle troposphere was another important reason for the vortex development.