“2009.11”山西大暴雪天气过程诊断分析

利用山西省109个测站的降雪资料、FY-2C卫星云图和华北雷达拼图,分析了2009年11月9～13日山西大暴雪天气过程的环流背景、中低空系统配置、物理量场中相对湿度、散度及垂直速度沿112.5°E的空间垂直剖面。结果表明,此次暴雪天气以500hPa南支槽与西风槽的相继影响为背景,有利的中低层(700hPa切变与急流、850hPa东风急流)系统配置为持续降雪提供了有利条件。在强降雪时段,物理量场的空间垂直剖面呈现出相对湿度在200hPa以下形成≥80%深厚的湿空气柱,整个对流层为高层辐散、低层辐合的不稳定结构,山西处于上升运动区,最大负值中心(-36×10-3 hPa.s-1)位于400～500hPa,这种配置构成了强降雪产生的有利条件。FY-2C云图的云团发展与华北雷达拼图的组合反射率因子的演变类似,强降雪主要由3次大范围的中低云系和强回波东移影响所致。

Diagnostic Analysis of Snowstorm in Shanxi Province in November 2009

Using the snowfall data at 109 observation stations in Shanxi Province,the FY-2C satellite cloud image and radar image in North China,the circulation background,the middle and lower altitude system dispositions,the relative humidity of physical quantity field,the divergence and the spatial-vertical cross-sections of vertical velocity field,the snowstorm occurred on 9~13 November 2009 were analyzed.The results showed that the storm weather took 500 hPa southern branch trough and the westerly trough one before and after influence as background;the favourable system disposition in the middle and lower levels provided the conditon for continuous heavy snowfall;In the severe snowfall time interval,the spatial-vertical cross-sections of physical field showed that the relative humidity center more than 80% uplifted over 200 hPa at 36°N,the unstable structure of upper divergence and lower convergence were formed in the ranges of 900~200 hPa,34°~40°N,Shanxi Province was in ascending motion zone,the maximum negative center(-36 × 10-3 hPa·s-1) was on 400~500 hPa,this configuration formed the favourable condition of heavy snowfall.The evolution of FY-2C cloud image was similarly to the radar reflectivity factor over North China,the severe snowfall were mainly produced by three times wide ranges of middle and lower cloud systems and strong echo moved to the east.