一次西南涡暴雨的湿位涡诊断分析

利用NCEP1°×1°再分析资料对2013年5月25~26日发生在我国中东部大范围的暴雨过程进行了湿位涡诊断分析,结果表明:(1)暴雨发生时低层湿位涡明显增加,湿位涡正压项自底层至高层呈现出“负-正”的分布特征,湿斜压项负值中心的演变反应出斜压性在强降水发生时所起的重要作用;(2)本次暴雨过程分两个阶段,第一阶段主要是因为强垂直风切变作用,使得降水具有强对流特征;第二阶段则是由于斜压性作用,降水分布广、持续时间长;(3)干冷空气沿着等熵面向下入侵到低层负位涡之上会导致对流不稳定度进一步加大,垂直运动发展使得低层水汽抬升,凝结潜热释放有利于中低层低涡的维持和发展。 

Diagnostic Analysis of Moist Potential Vorticity for Southwest Vortex Heavy Rain

With the NCEP/NCAR 1°×1° data the moist potential vorticity (MPV) anomaly of a highly intensive precipitation event in the central and eastern part of China from 25~26 May 2013 is diagnosed.The results showed that:(1) When heavy rain occurred,the distribution of MPV barotropic part was‘-+’ from low to high level.The evolution of low value centrer of MPV baroclinic showed the baroclinicity played an important role when a heavy rain occurred.(2) The process of the rainstorm divided into two stages,in the first stage,the rainfall was high convectiom feature because of the strong vertical wind shear;in the second stage,the rainfall was widely distributed and had long duration feature because of the atmospheric baroclinicity.(3) The dry cold air spread downward from the upper troposphere along the isentropic onto the negative MPV in low level,thus increased the convective instability,the development of the vertical motion maked the lower layer vapor lifting,latent heat release was beneficial to the maintenance and development of the low vortex.