2013年2月一次雷暴伴降雪天气过程分析

利用常规气象观测资料、ECMWF 0.5°×0.5°的6 h再分析资料和多普勒天气雷达探测资料,综合分析了2013年2月18日夜间至19日凌晨发生在江淮地区的雷暴伴降雪天气过程。结果表明,高层低槽东移、中层在江淮之间有切变线东移南压,低层以及地面为冷高压控制,是此次雷暴伴降雪天气过程发生时的天气背景;此次雷暴是在稳定的层结下产生的,不再满足不稳定层结这一雷暴发生的三要素之一。中层有较强的西南急流带,急流带随着系统的南移而向南收缩,其辐合带南移的速度快于急流向南收缩的速度,雷暴主要发生在急流的北侧边缘附近的辐合带内,辐合位于800 hPa以上的气层内,主要位于650～600 hPa。此次雷暴过程中,近地层和中层出现了相反的冷暖平流交替,雷雨发生时段,近地层为冷平流控制,850 hPa以上暖平流迅速加强,这也导致在中层出现了较强的上升气流,暖平流和上升气流的突然加强为雷暴的发生提供了动力触发条件;西南急流为降水地区提供了良好的水汽输送环境,另外,对流的发展、强烈的上升运动使得水汽向高层输送,整个中高层均有较为充足的水汽,为对流提供了较好的水汽条件。此次雷暴伴降雪天气过程中,对流回波的强度较弱,为30～35 dBz,顶高较低,大部分回波低于6 km,且干湿层边界明显。

Analysis on a Weather Process of a Thunderstorm with Snow in February 2013

The causes for a thunderstorm with snow in Jianghuai area in Feb.18-19,2013 were analyzed based on the conventional meteorological observation data,ECMWF reanalysis data per 6 hours and the data of Doppler weather radar.The results showed that： in the upper atmosphere there is a low trough eastward,in the middle layer the shear line in Jianghuai area eastwards and southwards,in the lower layer and ground is a cold high pressure,this is the weather background of the thunderstorm with snow.It happened on the stable layer,so it no longer content with unstable layer that is one of three elements of thunderstorm formation.There is strong southwest jet zone in middle layer,contraction south and moving to south.the velocity of the belt of convergency is faster than the jet flow.The thunderstorm occurred mainly in the north,near the edge of the convergence zone in the jet,air convergence in 800hPa above,mainly located at the height of 650hPa ～ 600hPa.The surface layer and the middle layer appeared opposite cold and warm advection alternately,thunderstorm occurred in the near surface layer,cold advection in control,850hPa above the warm advection strengthened quickly,this also causes in the middle layer showed a strong rising air currents,warm advection and updraft suddenly to strengthen the thunderstorm occurrence provides dynamic triggering conditions.Southwest jet for precipitation area provides good water vapor environment,due to the development of convection,strong ascending motion allows water vapor to senior transportation,makes the entire senior have relatively abundant water vapor,provides better water vapor condition for convection.The process of this thunderstorm with snow weather,weak intensity of convective echo top height is 30dBZ ～ 35dBZ,low echo,most less than 6 kilometers,wet and dry layer boundary was obviously.