2009年晚秋河北特大暴雪多普勒雷达特征分析

Analysis on Doppler Radar Feature of Snowstorm in Hebei in Late Autumn of 2009

利用石家庄新乐CINRAD/SA雷达资料、加密自动站资料和四维变分同化风场反演资料,分析了2009年11月10-12日河北地区发生的有历史记录以来的特大暴雪天气过程。结果表明,这次特大暴雪过程可分为切变线回流降雪和西风槽降雪两个阶段。切变回流降雪回波为对流性层云和积云的混合云,西风槽降雪回波为层状云且无零度层亮带,对流性降雪回波的垂直结构与盛夏暴雨回波结构类似,是产生这次极端降雪的重要原因;径向速度场分布存在"牛眼"特征、零等速度线出现"S"形、反"S"形和不连续线。当同时出现暖平流、风向辐合及风速辐合时,降雪维持;当同时出现暖平流、风向辐散及风速辐散时,降雪减弱;从地面到1.2km的边界层内存在边界层辐合线,垂直风切变的辐合抬升使垂直运动增强、降雪强度增大。

Using the Xinle CINRAD radar data in Shijiazhuang, dense-automatic station data, and four-dimensional variation data assimilation of wind retrieval, the strongest snowstorm occurred in Hebei Province from 10 to 12 November 2009, which is a new record in its meteorological history, are analyzed. The result shows that the snowstorm is divided into two phases.. Shear line with return flow and westerly trough snow. It is found that shear line with return flow snowfall echo is convective mixed cumulostratus. The westerly trough echo are stratiform clouds without bright bands. The vertical structure of convective snowfall echo is similar to that of summer rainfall echo, which is the most important reason for this ex- treme event. The radial velocity field exists ＇bovine-eye~ feature, zero velocity line appears ＇S^-, anti ＇S^- shaped and discontinuous zero line. When the the warm advection with wind-direction and wind-speed con- vergence appear, the snowfall starts to enhance, while the warm advection with wind-direction and wind- speed divergence appear, the snowfall starts to abate. Boundary layer convergence line exists from the ground to 1.2 km boundary layer. The convergent uplifting of vertical wind shear enhances the vertical motion and snowfall strengthing.