ANALYSIS ON THE ENVIRONMENTAL CONDITIONS AND DYNAMIC TRIGGER MECHANISM OF A SEVERE CONVECTIVE RAINSTORM IN BEIJING

Through the analysis of a severe convective rainstorm occurring in a synoptic-scale ridge on June 29, 1998 in Beijing, it is found that the interaction of the middle-level ridge, low-level convergence system and surface cold air produced a meridional circulation in the lower and middle atmosphere which stored up instability energy and maintained the ascending motion in the storm area. Dynamic frontogenesis was formed in the ground layer and intensified the latent instability at the lower and middle levels. Moreover, the positive vorticity advection of short wave disturbance in the upper troposphere initiated the ascending motion at the upper level and the releasing of the latent instability by ageostrophic balance processes. The short wave disturbance did not match the undulation of the wind field, and the characteristics of its phase propagation were similar to those of gravity waves.