渤海西岸边界层东风与暴雪天气的机理分析

2008年12月20—21日和2010年1月3日天津地区分别出现了历史同期罕见的暴雪天气。为了提高对这种极端天气发生机理的认识,利用多种资料对这两次天气过程进行了分析。结果表明：两次暴雪过程均属于回流型降雪,但环流形势和影响系统的演变却不尽相同。影响系统分别为高空横槽（高空槽）、850 hPa切变（850 hPa低涡切变）和地面倒槽（地面气旋）,水汽源自700 hPa西南气流和边界层东风的水汽输送。由于两次过程均与边界层东风相伴,特别对渤海西岸边界层东风对降雪天气的影响和作用进行探讨,表明偏东风不仅为本地输送一定量级的水汽,同时这种具有冷湿特征的东风还会与内陆具有暖湿结构的偏南风形成地面辐合线,加强地面的动力抬升作用,产生上升运动,有利于雨雪天气的加强和维持,因此可以认为边界层东风对暴雪的发生发展起到了显著的作用。

Analysis of the mechanisms of boundary layer easterly wind and snowstorm over the western coast of the Bohai Sea

Rarely intense snowstorms occur on December 20-21,2008 and January 3,2010 respectively in Tianjin.These two weather processes were analyzed based on multiple data in order to understand the mechanism of this weather.The results indicate that two snowfall events are both backflow-type snowstorms despite synoptic patterns and major weather systems in each case are distinctly different.Main weather systems are the horizontal trough at the upper level,850 hPa shear and surface inverted trough（surface cyclone）.Moreover,southwesterly airflow in 700 hPa provides moisture condition.Two processes are both accompanied by boundary layer easterly wind.The easterly wind not only transports some moisture,but also produces the surface convergence line with the warm and damp southerly wind,which could strengthen the lifting action and could generate lifting motion.Therefore,it is favorable to strengthen and maintain this weather process.Boundary layer easterly wind is playing a significant role in the initiation and development of snowstorm.