北京地区一次强对流大暴雨的环境条件及动力触发机制分析

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

通过对 1 998年 6月 2 9日北京地区发生在天气尺度脊中的强对流大暴雨过程分析 ,得出该过程是由中层的高压脊和低层的辐合系统、近地面的冷空气之间的相互作用形成了具有聚能机制的中低空经向环流圈 ,维持了暴雨区中低空的上升运动 ,形成了近地面的动力锋生 ,使中低层的潜在不稳定加剧 .而对流层高层短波扰动的正涡度平流通过非地转平衡过程 ,引发中高层产生的上升运动 ,触发了潜在不稳定的释放 .该短波扰动与风场的波动不相匹配 ,其位相传播特征与重力波相似 .

WT5BZ]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.[WT5BZ] [WT5HZ]