一次小雨转大雪天气过程的诊断分析

应用常规观测资料、雷达资料以及NCEP/NCAR再分析资料,对2012年12月29日宿迁市一次小雨转大雪天气过程进行了诊断分析.结果表明,这次小雨转大雪天气过程的影响系统属后倾槽结构,西路冷空气从低层锲入形成冷垫,850 hPa对应的西北急流（冷空气）和700～600 hPa西南急流（暖湿空气）交汇,造成了这次雨雪天气;低层辐合和高层辐散的抽吸作用以及锋面的抬升作用,使上升运动得以维持;南海水汽沿700～600 hPa西南急流向北输送,受北方冷空气阻挡,使得水汽在雨雪区辐合上升;地面至850 hPa有冷平流,使得低层迅速降温,700 hPa以上有暖平流,造成逆温层结,为雨转雪过程提供了有利的温度环境;另外,利用雷达径向速度和风廓线图可清晰反演低层风场的变化,进一步分析冷、暖平流对雨转雪的影响.

Analysis of the Weather Process from Light Rain to Heavy Snow

The weather process from light rain to heavy snow in Suqian on December 29, 2012 was analyzed ac- cording to conventional observation data, radar data and NCEP/NCAR reanalysis data. The results showed that tilting trough influenced this weather process, westward cool air formed cold layer from the bottom, 850 hPa westward jet stream （cold air） and 700-600 hPa southwest jet stream （warm wet air） met and caused the rain and snow; suction role of low- level convergence and high-level diver- gence, uplift role of frontal surface main- tained the ascending motion; water vapor from the South Sea moved to north along the 700-600 hPa southwest jet stream, but was blocked by north cold air, mois- ture lifted up in snow area; cold jet stream from ground to 850 hPa reduced temperature in the bottom layer, warm advection above 700 hPa caused stratifi- cation of temperature inversion, and pro- vided a favorable temperature environ- ment for the transition from rain to snow; in addition, radar radial velocity and wind profile were used to reflect the change of low-level wind field, and fur- ther analyze influence of cold and warm advection on the transition from rain to snow.