Abstract:

Using the conventional meteorological data and NCEP reanalysis data, the heavy snow process in the middle of Shanxi Province on 19 April 2013 was analyzed. The results show that the co-existence of plateau trough on 500 hPa, low vortex shear line at low level, ground return airflow and Hetao cyclone provided advantageous flow pattern configuration for snowstorm. The southwest jet(SWJ) on 700 hPa, the southeast jet (SEJ) on 850 hPa and the eastly jet (EJ) on 925 hPa provided the strong water vapor transport and supplement together. The coupling of the northwest jet (NWJ) on 500 hPa and northeasterly severe airflow on 850 hPa, the positive vorticity transport at high level, the tilt vertical structure of lower-level convergence and upper-level divergence made ascending motion enhancement and triggered the release of unstable energy at low level, which led to occurrence of the snowstorm. The change of low level and near surface temperature, the drop of 0 ℃ level height, increase of  inversion layer depth and vertical wind shear were important indexes to judge the change of precipitation phases and enhance of snowfall intensity during the process.

Key words:  heavy snow , configuration of flow pattern, jet, inclined structure, precipitation phases

摘要：

利用常规气象观测资料和NCEP全球再分析资料，对2013年4月19日出现在山西中部的一次暴雪天气过程进行了综合分析。结果表明：高原槽、低空低涡切变线、地面回流以及河套气旋等的共同存在为暴雪天气提供了有利的流型配置；700 hPa西南急流、850 hPa偏东南急流和925 hPa偏东急流为此次暴雪天气提供了强的水汽输送和补充；500 hPa偏西北急流和850 hPa偏东北强气流耦合加强，且高层正涡度输送以及低层辐合、高层辐散的倾斜垂直结构使得上升运动加强，触发低层不稳定能量释放，导致暴雪天气的发生。低层和近地层温度变化、0 ℃层高度下降、逆温层增厚以及垂直风切变加大是判断此次降水过程相态变化和降雪强度增强的重要指标。

关键词: 暴雪, 流型配置, 急流, 倾斜结构, 降水相态