一次暴雨与特大暴雪并存的华北强降水过程分析

Analysis on Severe Heavy Precipitation Event with Rainstorm and Large Blizzard in North China

应用常规观测资料、NCEP 1°×1°再分析资料,对2012年11月3—4日华北地区产生大范围雨雪天气的成因和降水相态进行分析。结果表明:深厚的低涡和地面气旋是本次过程的直接影响系统,东南风低空急流带来东部海上的充沛水汽,使得暴雨雪区整层大气可降水量远高于当月平均值;低涡和气旋等低层辐合系统与高空辐散叠置,为强雨雪天气提供了持久强烈的上升运动,暴雨区、暴雪区分别为对流不稳定、条件性对称不稳定大气层结,而锋生作用更有利于暴雪产生;雪花形成和增长的环境条件与雪花下降过程是否融化在判断降水相态方面同等重要,二者兼具才能保证地面降雪的出现。

Based on conventional observations and NCEP 1° × 1° reanalysis data,causes and precipitation type of the rain and snow weather process in North China during 3—4 November 2012 are analyzed.The results show that the deep low vortex and surface cyclone are the systems that directly impact the process.The southeast low-level jet transporting the abundant moisture from the eastern sea leads to the atmospheric precipitable water over the entire rain and snow storm area,exceeding the average of the month.The high-level divergence systems superimposed on the low-level convergence systems of the vortex and the cyclone provide a strong and lasting upward movement for the severe rain and snow storm.The heavy rain area and the blizzard region respectively stand for the convection instability stratification and the conditional symmetric instability stratification,and the frontogenesis favours the heavy snow storm.The environmental conditions of the snowflake formation and growth,and the melting of the snowflakes falling are equally important in determining the precipitation type.The combinations of the two reasons mentioned above ensure the emergence of snow on the ground surface.