一次中亚低涡造成的新疆暴雪天气过程分析

Analysis on a heavy snow by central Asian vortex in Xinjiang

利用实况观测资料、EC/T639数值模式预报资料和NCEP1°×1°再分析资料,对2012年2月一次由中亚低涡造成的冬季新疆西部地区典型暴雪天气过程的环流特征和物理量场进行了综合分析。结果表明:此次暴雪天气过程属欧洲脊发展、中亚低涡东移造成的新疆西部及天山北坡的降雪过程。200 hPa西南急流使高层辐散,起到"抽气机"作用;500 hPa偏南气流与700 hPa东风急流为暴雪提供了水汽和热量的输送,同时加强了抬升运动;高层辐散、低层辐合以及较强的上升运动是暴雪发生的动力条件,上升运动的强盛发展阶段对应降雪强度最大时段;水汽的垂直输送导致局地比湿显著增大,深厚的湿层和强烈的水汽辐合为暴雪提供了充沛的水汽条件;云图上"干侵入"出现的时间与位置可以大致判断强降雪出现的时间和位置。

Based on the observational data, EC/T639 numerical prediction data and NCEP1 °× 1 ° reanalysis data at 6 h-interval, the circulation characteristics and physical quantity fields of the heavy snow caused by central Asian vortex in western Xinjiang in February are discussed comprehensively. The results show that the development of the Europe ridge and central Asian vortex＇s movement towards Xin- jiang brought about the heavy snow in western Xinjiang and the north slope of Tianshan Mountain. The southwestly jet at 200 hPa worked as an air pump, making airflow at 500 hPa and southeastly jet at 700 hPa provided upper-level divergence appear; the southly enough water vapor and heat for the heavy snow and strengthened the necessary ascending motion as well. Upper-level divergence,low-level conver- gence and strong ascending motion were all dynamic conditions for the heavy snow; the period of the heaviest snow was coincident with the strongest ascending motion. The vertical transportation of water va- por caused the increase of the local specific humidity, and the deep wet layer and the strong water vapor convergence provided abundant moisture for the heavy snow. The time and position of the dry intrusion in satellite cloud pictures can be used as an indicator in forecasting the heavy snow.