新疆一次超极地寒潮天气分析

Analysis of a Super Polar Path Cold Wave in Xinjiang

利用常规天气资料、美国NCEP/NCAR 1°×1°网格点逐6 h再分析资料,运用天气学原理,对2012年1月16—21日新疆一次超极地路径寒潮天气过程进行分析和总结。结果表明:本次过程是一次极地冷空气向南爆发影响新疆的寒潮天气,属于乌拉尔山脊类里咸海长脊型;寒潮发生在极涡偏在东北半球,超长波为三波的大背景下。过程期间欧亚范围维持两槽一脊的经向环流,欧洲与西伯利亚地区均为深厚的低压系统,里咸海长脊与乌拉尔山脊同位相叠加形成经向度超过35个纬距的暖性闭合高压,即乌拉尔山阻塞高压。随着乌拉尔山阻高不断向东南方向衰退,脊前强的北风带推动西西伯利亚横槽转竖南压,引导极地冷空气向南爆发,造成新疆大范围的寒潮天气。冷空气入侵新疆前后海平面气压中心强度分别为1 047.5 hPa和1 071 hPa。强的冷平流是气温骤降的主要原因。中高层偏西急流与近地面风场辐合形成的垂直环流为降雪提供必要的动力条件。降雪过程中,南北疆中低层增湿明显。北疆降雪水汽来源于咸海和巴尔喀什湖,寒潮爆发后降雪成因归结于强的冷平流在动力作用下的冷凝降雪。数值预报性能检验来看,500 hPa高度场预报ECWMF较T639精准且稳定性高,气压场和850 hPa温度场预报T639优于ECWMF。

Based on conventional surface and upper data,NCEP 1 x 1 ~reanalysis data of every 6-h, in terms of the synoptic principle and the dynamic diagnosis,the cold wave during 16-21 January 2012 was analyzed.The results are as follows： the cold wave resulted from the polar cold air outbreak in Xinjiang, belong to the ridge developed in the Caspian Sea and Aral Sea of the Urals ridge class. The cold wave oecoured when super long wave were three waves, polar vortex was located in the Northeast Hemisphere in 100 hPa. two trough-one ridge of the meridional circulation was maintained in the Eurasian range during the cold wave, deep low pressure system located to the European mainland and the Siberia, The Ural blocking high was build up with the same phase interaction between the Caspian Sea-Aral Sea and the Urals ridge, the radial distance of atmospheric circulation larger than 35 zonal distance. When the Ural blocking high gradually declined,the stronger northerly wind in the front of the ridge were favorable to the revising of the transverse trough, meanwhile, the cold air moved southeastwards and invaded into Xinjiang. The greatest sea level pressure were 1 047.5 hPa and 1 071 hPa before and after the invasion of the cold wave.The main reason for the rapid air temperature decrease was the intense cold advection. The dynamic conditions of snowfall was derived from vertical circulation composed of the high-level west jet and the low-level convergence. During the snowfall,the humidity was significantly increased in the middle-low layer. Water vapor in the Northern Xinjiang comes from Aral Sea and Balqash. The latter snowfall was attributed to the condensate cooling under strong cold adveetion. By comparison, ECMWF model was expert in height of 500 hPa, T639 model were better at pressure and temperature forecast.