1次华北回流冷空气引发的罕见暴雪分析

Analysis of A Rare Snowstorm Weather Process in North China Aroused by Reverse-flow Cold

采用常规观测资料和NCEP再分析资料,对2009年11月华北出现的罕见暴雪进行分析。结果表明,暴雪发生在条件性对称不稳定大气层结中;500 hPa低槽、锋区和700 hPa横切变是影响这次暴雪的直接影响系统;700 hPa低涡前的西南急流是主要的水汽输送系统,900 hPa以下东北风急流携带的强冷空气是暴雪形成的重要动力条件和温度条件,这次暴雪具有典型的回流冷锋特征;极锋急流激发的次级环流的下沉支在暴雪发生前将高层高动量强冷空气携带到低层,加大低层的大气不稳定。

Based on routine sounding,surface observation data,and NCEP reanalysis data（1°×1°）,the snowstorm in North China in November 2009 was analyzed.The results showed that the snowstorm occurs in the sym-metric instability atmosphere,and 500 hPa cold trough,frontal zone and 700 hPa transverse shear are direct influence systems.The southwest jet in the front of the cyclonic vortex on 700 hPa is transportation system of water vapor.The strong cold air carried by the northeast jet below 900 hPa provides dynamic and temperature condition,which has typical characteristic of reverse-flow cold front.The subsidence branch of secondary circulation aroused by the polar jet transports momentum from high level to low level which increases instability of atmosphere.