一次梅雨锋暴雨发生发展机制的诊断与模拟

Diagnosing analysis and numerical simulation of formation and development mechanism of a rainstorm associated with Meiyu front

摘要:

采用NCEP/NCAR再分析资料、FY2E卫星资料和加密自动站资料，结合中尺度WRF模式对2013年苏皖地区的一次梅雨锋暴雨过程进行诊断与模拟。观测资料分析表明：在有利的环流背景和热动力条件下，此次暴雨发生在梅雨锋前暖区，雨带呈现"先带状后串波状"的分布特征，并随锋面南移。前期降水由地面中尺度辐合线触发，受两个相继发展的中α尺度的线状对流系统直接影响；后期降水受地面暖式切变线触发，有多个中β尺度对流系统沿切变线串状排列，并不断东移发展。模拟结果分析表明：降水过程中，大尺度非地转强迫作用也是强对流的触发机制之一。地面辐合线产生条带状的低层辐合区，从而产生条带状连续分布的上升运动，形成线状对流系统及带状降水。此外地面辐合线能够在暴雨区形成南北两个中尺度垂直次级环流，这是降水的增强机制。暖式切变线上的局部扰动在低层局部地区产生强辐合，由此沿切变线形成强上升弱下沉间隔分布的现象，局部强上升区使得对流系统于该处得到发展，并形成分散的强降水区。

关键词:梅雨锋暴雨;中尺度对流系统;辐合线;暖式切变线;数值模拟

Abstract:

Using the NCEP/NCAR reanalysis data,FY2E satellite data and the automatic weather station data,combined with the WRF(Weather Research and Forecasting) model,a Meiyu rainstorm occurred in Jiangsu and Anhui provinces in 2013 was analyzed.Observational data analysis results show that under favorable circulation background and thermodynamic conditions,the heavy rain occurs in the south warm side of Meiyu front,with a common influence of Northeast cold vortex,Meiyu front and Changjiang-Huaihe shear line.The water vapor is mainly from the northwest of South China Sea.Convective instability and symmetric instability locate in the rainstorm zone,which is favorable for the common development of both vertical convection and ramp-up airflow.The rain belt transforms from the ribbon to string shape distributions and moves southward along with Meiyu front.Early precipitation is triggered by the surface mesoscale convergence line,directly affected by two successive meso-α-scale linear convective systems.Later rainfall is triggered by the ground warm shear line.There are a string of meso-β-scale convective systems developing eastward along the shear line.High-resolution model outputs analysis results reveal that the large scale non-geostrophic forcing also plays an important role in triggering strong convection during the rainstorm.The ground convergence line produces a banded lower layer convergence zone,resulting in strip continuous distribution of ascending motion,which gives rise to linear convection system and banded precipitation.Additionally,the ground convergence line can form two mesoscale vertical secondary circulations in the north and south of rainstorm area,which is the precipitation enhancement mechanism.The local disturbance of warm shear line produces local strong convergence at low altitude,thus making strong ascending and weak descending interval distribute along the shear line.And then those convective systems develop in the strong ascending regions,bringing local heavy precipitation.

Key words:Meiyu front rainstorm;mesoscale convective system;convergence line;warm shear line;numerical simulation