Formation and evolution mechanisms of a destructive-wind-producing thunderstorm in Shanghai

Abstract

The formation and evolution mechanisms of a destructive-wind-producing thunderstorm that occurred in Shanghai were studied using a Weather Research and Forecasting model simulation. To understand the formation mechanisms of the severe winds, we separately analyzed the downdrafts and accelerations of horizontal winds by zonal and vertical momentum tendencies. Also, the effects of temperature and humidity on the thermodynamics and cloud microphysics were diagnosed. It was found that wind gusts with large horizontal extent and strong wind speed mainly occurred during the maturation stage, and then widespread severe winds still maintained when the storm entered the decaying stage. Analysis also showed that the meridional advection of the zonal wind gradient and rainwater evaporation, which was significantly enhanced by the melting of graupel aloft, were the main factors causing the severe winds during the maturation stage. In the decaying stage, meanwhile, the accelerations of horizontal winds associated with cold pools accompanied by the large horizontal perturbation pressure gradient force and widely distributed drag force of rainwater were the main factors that maintained the large extent of severe winds near the surface.