A Case Study of the Mesoscale Disturbance Vortex in the Boundary Layer on the Meiyu Front

The heavy rainfall event along the Meiyu front on June 24, 2009 was analyzed using data from auto weather stations, high resolution radars, and simulations. The results show that several surface disturbance vortexes formed after the weak rainfall in the southern warm section of the Meiyu front. With the stabilizing and upward development of the disturbance vortex, a short duration rainstorm accompanied by gale occurred. After the strengthening and lifting of the westerly wind, a westerly jet formed with the jet axis between the planetary boundary layer and the low troposphere. Convergence and shear occurred after the southerly flow encountered the northerly wind. The southerly flow could have turned into convection through lifting by northerly wind. The vorticity of the planetary boundary layer increased gradually followed by synchronous enhancement of frontogenesis and convergence under the influence of surface shear and convergence. Then, the disturbance vortex could form and develop in the planetary boundary layer below the troposphere. The intensification of wind speed, shear, and convergence near the surface were the dynamic factors responsible for the formation of the mesoscale disturbance vortex.