Mesoscale Characteristics Analysis of Rainstorm on the Edge of Subtropical High

Based on conventional and automatic weather station observation data,satellite,lightning location,radar data and NCEP reanalysis data,this paper analyzed the mesoscale convection condition and evolution characteristics of convective system in the disastrous rainstorm that happened in the west of Jiangxi from 24 to 25 May 2014.The conclusions are as follows.(1) Synoptic background of this rainstorm consists of eastward the movement of upper trough,strengthening of warm wet air in the edge of subtropical high,and the effect of cold air.(2) Surface mesoscale convergence line contributes to development and strengthening of MβCS.The long-time lasting of many dense MβCSs with smooth boundary in western Jiangxi leads to continuous heavy rainfall in the corresponding region.The cold cloud's position and intensity of TBB≤-62℃ are good indicators for surface precipitation,especially the center of TBB≤-72℃coincides with the rainfall center best.(3) In this rainstorm,distribution of 5 min rainfall is almost in accord with distribution of CG lightning number,which happends 10 min earlier than jump of surface precipitation.(4) Mesoscale vortex in radar velocity graph is one of the most important factors for this rainstorm.Western Jiangxi presents notable wind convergence and wind speed divergence.Low-level strong southwest jet's overlying deep radial wind convergence zone helps the strengthening and maintaining of the rain.In addition,with the help of dynamic convergence and mountainous topography,strong southerly jet with abundant water vapor meets in the west of Jiangxi,causing continuous heavy rainfall.(5) The change of biggest radar echo intensity assists estimating the change of 5 min rainfall intensity,but it is not a good indicator.Radar wind profile products are good indicators of heavy rainfall on the surface,which forecasted this heavy rainfall seen in western Jiangxi 2 h in advance.