山西一次低空偏东风暴雪天气结构特征分析

Structure Analysis of a Snowstorm with Low-level Eastern Wind in Shanxi Province

应用常规地面、探空观测资料和NCEP 1°×1°再分析资料,对2011年11月28-29日山西低空偏东风暴雪天气结构特征进行了探讨。结果表明:(1)这次低空偏东风暴雪是由高空西风槽、低空切变线、地面回流和倒槽共同影响造成。降雪前约18 h,山西925~850 hPa上空出现东北风;降雪前约12 h,山西中南部地面出现较强东北风,强降雪期间地面东北风强劲;降水开始前,低空东北风是干冷性质,降水开始后低空东北风是湿冷垫。(2)暴雪的水汽来源主要是源于西太平洋的偏东风水汽输送在北部湾附近转向的西南水汽与南支槽前的西南气流在西南地区汇合北上,再与西风槽前西南水汽结合;强降雪出现在700 hPa水汽通量中心西北侧等值线密集区且风向气旋性辐合的偏南气流区域。(3)强降雪伴随山西上空深厚湿层、500 hPa以下明显水汽辐合,以及800 hPa以上对流层中强上升气流,而上升区下是明显的下沉气流,这是由低空偏东风的契入产生的。(4)强降雪期间300 hPa西风急流不断东移南压,山西位于其入口区右侧,出现强辐散,有利于地面河套倒槽发展、维持,以及垂直上升运动的增强。

Based on conventional surface and sounding observation data,NCEP 1° × 1° reanalysis data,a snowstorm structure with low-level eastern wind in Shanxi Province from 28 to 29 November 2011 is researched. The results are following:( 1) This weather process is developed by the joint influence of upper westerly trough,shear lines in lower level,ground return-flow and inverse trough. The northeaster wind occurs from 925 hPa to850 hPa upper Shanxi about 18 h before the snowstorm,the northeaster wind occurs on surface in Shanxi about12 h before the snowstorm,and it is strong during the snowstorm; The low-level northeaster wind is cold and dry before the snow,and it is a wet-cold pad during the snow.( 2) The water vapor of this snowstorm comes from the southwest water vapor emerging in southuest China and transport northward,this emerging southwest flow comes from the southwest wind in the front of South Westerly Trough and the turning of east flow in Beibu Gulf which comes from Western Pacific,then it is combined with the southwest flow in the front of the westerly trough. The heavy snow occurs in the area of south wind of the wind convergence on 700 hPa where is on the northwest of the vapor flux center and has dense isolines.( 3) The heavy snow accompanies with the deep wet layer,the obvious vapor flux convergence under 500 hPa and strong updraft current upper 800 hPa in the troposphere upper Shanxi area,under 800 hPa it has obvious downdraft current which is caused by the low-level eastern wind.( 4) The westerly jet on 300 hPa moves eastward and goes down southward among the heavy snow,Shanxi is located on the right of the jet's entrance region and occurs strong divergence,which impels the development and maintenance of the inverse trough of the Great Bend of the Yellow River on surface,and may cause stronger updraft current in the area of heavy snow.