华东地区强对流降水过程湿斜压涡度的诊断分析

湿斜压涡度(Moist Baroclinic Vorticity,MBV)、湿热力斜压涡度(Moist Thermodynamic Baroclinic Vorticity,MTBV)及湿位涡(Moist Potential Vorticity,MPV)是能够完整表征涡度三维信息的物理量,其中MBV代表切变风对湿比容的平流输送作用,MTBV反映了垂直气压梯度、对流稳定度、风垂直切变与湿比容水平梯度之间的耦合效应。本文利用这些物理量对2009年8月17日发生在华东地区的一次强对流降水过程进行了诊断分析。该过程是在高空急流、中层浅槽和低空切变线的密切配合下产生的,共经历了"团状结构—带状结构—团状结构"三个发展阶段。诊断结果表明,MPV、MBV和MTBV的异常值区与降水落区有较好的对应关系;随着强对流降水的发展演变,MPV、MBV和MTBV都产生了相应的变化,MPV、MBV和MTBV对降水和对流系统有追踪指示意义。相对而言,在反映降水强度变化方面,MBV和MTBV比MPV更具优势。

Diagnostic Analysis of Precipitating Convective Process in East China with Moist Baroclinic Vorticity Parameters

The moist baroclinic vorticity (MBV) and moist thermodynamic baroclinic vorticity (MTBV) contain the vorticity information perpendicular to the potential temperature gradient which is excluded by moist potential vorticity (MPV). The MBV represents horizontal advection of the moist specific volume by shear wind. The MTBV indicates the coupling of the vertical pressure gradient, convective instability, vertical wind shear, and horizontal gradient of moist specific volume. A strong precipitating convective process in East China on August 17, 2009, is studied with these physical variables in this paper. The results show that a close configuration of a high-level jet stream, mid-level shallow trough, and low-level shear line induces this event. The convective system in this process undergoes three development stages: the nonsquall cluster stage, squall line and nonsquall cluster coexistence stage, and the nonsquall cluster redevelopment stage. It is shown that the MPV, MBV, and MTBV can indicate the location and evolution of the precipitation inside the convective system effectively. However, the MBV and MTBV are more sensitive to the change of the precipitation intensity and thus more capable of indicating precipitation in this case.