一次超级单体分裂过程的雷达回波特征分析

Analysis of the splitting processes of the supercell storms based on the Doppler weather radar data

中文关键词:  分裂  左移超级单体  环境背景  雷达回波特征

英文关键词:Split  Left-moving supercell storm  Environmental conditions  Characteristics of radar echoes

中文摘要:

      2007年7月9日16—20时（北京时）在河北南部非常罕见地观测到了多个超级单体风暴在相近地点连续生成及分裂的过程。利用石家庄新乐SA型多普勒天气雷达资料、地面自动站及常规天气资料，对超级单体分裂过程及环境条件做了分析。表明这次的多个超级单体风暴是在强的对流有效位能和垂直风切变的环境条件下发生的。由于垂直风切变矢量方向随高度逆时针旋转，因此，分裂后左移的反气旋风暴得到加强，发展成为具有深厚中反气旋的左移超级单体风暴，而右移的气旋性风暴受到抑制，与理论研究结果一致。但也有不同之处，沿着地面高湿区内热力边界偏暖一侧移动的气旋性风暴没有受到明显抑制，有利的地面环境条件抵消了气旋性风暴受抑制的程度，使气旋性风暴能够持续更长的时间。该强烈发展的带有明显中反气旋的超级单体风暴具有低层钩状回波和入流缺口、中高层有界弱回波区及位于有界弱回波区之上的高层具有反射率因子核心和强烈风暴顶辐散，与经典的气旋式右移超级单体风暴的回波特征非常类似，除了是反气旋涡旋外，其回波特征与气旋式超级单体近似成镜像。风暴分裂是在单体形成不久的发展初期开始的。分裂先从中高层开始，然后迅速向下延伸。分裂后相对于0—6 km风切变矢量，左侧的单体为反气旋左移风暴，右侧的为气旋性右移风暴。

英文摘要:

      An infrequent process with several supercells generating and splitting at nearby places occurred on 9 July 2007 in the south of the Shijiazhuang region was observed. Based on the Doppler weather radar data from the Xinle station in the Shijiazhuang region, automatic weather station data and conventional weather data, the splitting process and environmental conditions of the splitting supercell storms were analyzed. The results showed that this supercell storm developed under an environmental condition with high convective available potential energy (CAPE) and strong vertical wind shear. Because the direction of vertical wind shear vector rotated counterclockwise with height, after the splitting, the left-moving anticyclonic storms were strengthened and turn into a left-moving supercell storm with deep meso-anticyclone, while the right-moving cyclonic ones were restrained. These results resembled theoretical study. At the same time, it was not in accordance with the theoretical study in some aspects, which include that, the cyclonic storms moving along the warm side of thermal boundary of high humidity region were not obviously restrained. That was because advantageous surface environmental conditions offset resistance of the cyclonic vortices, which made them lasted longer. The intensely developed supercell storm with obvious meso-anticyclone had features as hook echo and inflow notch at the low level, bounded weak echo region (BWER) at the middle-upper level and reflectivity core and strong storm top divergence at the upper level. These echo features were similar to classic cyclonic right-moving supersell except with anticyclone and the echo feature being approximate mirror image of cyclonic supercell storm. Storm splitting began at the initial stage of the formation of cells. The splitting occurred at the middle-upper level at first and then extended downward rapidly. After the division, relative to the 0-6 km wind shear vector, the left cells were anticyclonic left-moving storms and the right ones were cyclonic right-moving storms.