华东地区一次飑线过程的数值模拟与诊断分析

本文利用ARPS(Advanced Regional Prediction System)同化多部多普勒雷达观测资料和常规地面探空观测资料,对2009年8月17日发生在我国华东地区的一次飑线过程进行高分辨率数值模拟；利用模拟输出资料,分析该飑线过程的动力和热力特征和对流线单体后向新生的环境条件。研究结果表明:(1)在飑线系统初生阶段,从飑线后部(北方)的团状对流系统的低层MCV(mesoscale convective vortex)中南下的冷空气与西南暖湿气流相遇激发强对流,促进飑线发展；随着飑线系统的发展和南移,团状强对流系统的低层MCV的气旋性环流对飑线的影响逐渐减弱,而飑线本身产生的低层冷池向外辐散的冷空气与环境场西南暖湿气流辐合成为飑线持续发展的主要动力。(2)本次飑线系统属于典型的后向新生型飑线,由4条处于不同发展阶段的对流线合并而成,对流线上对流单体的后向新生是动力和热力过程共同作用的结果,既需要一定的对流抑制能量促进对流有效位能的累积,也需要一定的环境风场垂直切变、低层风场的辐合和水平涡管向垂直涡度的转化。

Numerical Simulation and Diagnosis Study of a Squall Line in Eastern China

A squall line that occurred in eastern China on August 17, 2009, was successfully simulated with the Advanced Regional Prediction System (ARPS) by assimilating high-resolution Doppler Radar data and conventional observations. Using the simulation output, we analyzed both the dynamical and thermodynamical characteristics of the squall line and diagnosed the environmental conditions of a back-building convective line that was a part of the squall line. Our major conclusions are as follows: (1) during the formative stage of the squall line, the southward-moving cold air from the low-level mesoscale convective vortex (MCV) in a clustered convective system, which was located to the north of the squall line, encountered southeastern warm moist air. This triggered strong convections and initiated the squall line. As the squall line propagated south, the role of the cyclonic circulation associated with the MCV in the maintenance of the squall line convection was reduced. Instead, cold surface outflow associated with the cold pool, which is an inherent part of the squall line, played a critical role by converging with the ambient air flow from the south. (2) The evolution of the squall line was enhanced by four convective lines that were formed by back-building convective cells. Several dynamical and thermal processes resulted in environmental conditions that favored the formation of the back-building convective cells. These conditions included: a small quantity of convective inhibition, a large amount of convective available potential energy, moderate vertical wind shear, strong low-level convergence, and large helicity.