山西省北中部初冬一次暴雪天气诊断分析

Diagnostic Analysis of a Snow Storm Process in North-central Shanxi in Early Winter

为了探讨暴雪天气的成因和机理,为暴雪预报提炼技术指标,利用常规气象观测资料和MICAPS资料,对2015年11月5—7日出现在山西北中部的暴雪天气过程进行了诊断分析。结果表明:(1)暴雪产生在高低纬冷暖气流相互作用的有利背景下,地面倒槽与回流共同作用的形势中,冷空气从高压中分裂南下在东北平原堆积是回流形成的机制;(2)低空、超低空急流的维持和叠置,为暴雪的出现提供了充沛的水汽。水汽通量大值区与低空急流的位置很吻合,水汽通量散度辐合区与暴雪区很吻合,对暴雪落区预报有明显指示意义;(3)回流降雪的开始与辐合上升关系密切,当回流干冷东北风到达山西北部,与低空偏南暖湿急流汇合形成切变线和干线时,降雪开始,此后随着切变线和干线的南下,降雪也逐渐向南扩展。切变线和干线是此次暴雪的抬升触发系统,切变线和干线北侧的东北气流起着冷垫作用,使暖湿气流沿冷垫爬升,促使上升运动加强,促使暴雪产生。

The paper aims to explore the causes and mechanism of snow storm and extract the technical indicators of snow storm forecast.The conventional meteorological observational data and MICAPS data were used to carry out a diagnostic analysis of a snow storm process occurred on November 5-7,2015 in northcentral Shanxi.The results showed that：（1）the snow storm occurred under a favorable background caused by the interactions of airflows separately from high and low latitude,and by the combined effect of the surface inverted trough and the backflow,the formation of the backflow was caused by the cold air which was divided from the high pressure and blew southward and stored in the northeast China plain;（2）the maintenance and superposition of low-level jet and super low-level jet were benefited to the abundant provision of water vapor for the snow storm area;the big vapor flux area was consistent with the position of the low-level jet,and the convergence area of moisture flux divergence had a very close relationship with snow storm area,which had a significant instruction for snow storm forecast;（3）the start time of snow was closely related to the convergence and ascending motion;when the dry and cold northeaster flew back to the northern Shanxi and converged with the warm and wet south low-level jet,the shear line and the dry line were formed and the snow was began;after that,the snow gradually expanded to the south with the move of shear line and the dry line southward.The shear line and the dry line was the trigger system of the snow storm process;the northeast cold air on the northern side of the shear line and the dry line played a role as a cold pad,which forced the warm moist air flow to climb along the cold pad,then ascending motion was strengthened and the snow storm was prompted.