一次强飑线的成因及维持和加强机制分析

CASE ANALYSIS OF THE FORMATION AND EVOLUTION OF 12 JULY 2004 SEVERE SQUALL LINE

利用常规观测资料、多普勒天气雷达、自动气象站等资料对2004年7月12日影响上海的一次较长生命史的强飑线过程进行了综合分析,对这次强对流天气发生、发展、强度以及移动和传播的分析结果表明:副热带高压从华南沿海稳定地加强西伸,西风槽缓慢东移,导致华东地区850～500 hPa形成深厚西南急流,急流的加强促使低层锋生,配合K指数高能锋区的不稳定层结,大大增强了强对流天气发生的可能性;地面锋生作用和低层辐合、高层辐散造成的强抬升作用是主要的触发机制;较强的环境风垂直切变和雷暴内部上升气流与下沉气流的正反馈作用是飑线系统维持较长时间的原因,中尺度对流系统(MCS)多个雷暴单体间的相互作用使得南侧的雷暴单体加强、移动方向发生偏转.

Using the data from conventional weather observations, the Shanghai WSR-88D Doppler weather radar, and observations from automated meteorological stations, a longlived severe squall line on July 12, 2004 is analyzed. The case analysis shows that the intensification of the jet between 850 hPa and 500 hPa that causes the low level frontogenesis and high potential severe weather. The squall line triggers in the case are the surface front, the low level convergence, and the upper level divergence. The strong vertical wind shear and the feedback between the strong updrafts and downdrafts in the storm sustains the squall line in a severe stage for 6 hours. The interaction between the squall line and the outflow boundaries of the other storms along the same Mesoscale Convective System （MCS） intensifies the storm and changes its path.