Abstract:To study the mesoscale characteristics and causes of extreme short-time severe precipitation at night in Tianjin，by using automatic weather station data, minutely precipitation data, Doppler weather radar data, wind profile data and ERA5 reanalysis data, this paper analyzes the extreme short-time severe precipitation that occurred in Tianjin in the early morning of 3 July 2022. The results show that there was no significant low-value weather system at 500 hPa and no synoptic-scale low-level jet background at the lower level when this severe precipitation occurred. It was a rainstorm process mainly caused by small-scale and meso scale systems forcing under a typical circulation situation, having obvious local, sudden and extreme characteristics. The meso-β scale convective system that caused the precipitation was present in the form of a well-organized multi-cell storm, which was formed by the merger of scattered echoes. Its radar echo had a high centroid, showing the characteristics of continental severe convective echoes. With high temperature and humidity, the enhancement of the 975 hPa warm shear line in the boundary layer cooperated with the mesoscale convergence line on the surface, and the mid-level dry cold air intrusion enhanced instability triggering the initial convection. The cold pool formed by the initial convection made up of a clear and irregular outflow boundary with the ambient wind, and the forcing action of the bottom cold pool led to the formation and development of meso-γ scale vortex in front of the outflow boundary. The ageostrophic wind rotation caused by the inertial oscillation of the boundary layer at night and the gradually developed inversion stratification made the warm and moist air from the southeast sea continuously strengthen into the boundary layer jet, causing the vertical wind shear of 0.1-2.5 km to increase correspondingly. The interaction between the low-level wind shear and the gradually enhancing cold pool reached a temporary equilibrium. Thus, the vortex in front of the outflow boundary continued to strengthen and developed from the bottom to top. The strong dynamic convergence accompanying the vortex directly led to the rapid growth of minute-level rain intensity lasting for several minutes, which finally resulted in the emergence of extreme short-time severe precipitation. The results could provide a reference basis for predicting local short-time severe precipitation at night and exploring its occurrence and development mechanisms in North China.