一次高原涡和西南涡作用下强降水的回波结构和演变分析

Analysis of the echo structure and its evolution as shown in a severe precipitation event caused by the plateau vortex and the southwest vortex

中文关键词:  高原涡  西南涡  降水回波结构

英文关键词:Plateau vortex  Southwest vortex  Echo structure of precipitation

中文摘要:

      2009年7月30—31日，青藏高原东侧背风坡发生了一次持续性强降水过程。在高原涡和西南涡相继出现并相互作用的天气环境中，四川盆地内生成了3个中尺度对流系统。使用新一代天气雷达组网的反射率因子，美国环境预报中心（NCEP）再分析资料，以及热带测雨卫星搭载的测雨雷达（TRMM PR）反射率因子，可以得到这次暴雨的发展演变及其三维结构特征。通过与TRMM PR探测资料的对比验证，地基组网雷达的结果与其非常一致，基本能反映出对流系统的演变全貌，而在高原和山区地基雷达缺测的区域，测雨雷达探测资料可以做为补充。分析表明，降水落区的低层正涡度和水汽辐合上升与高层负涡度和水汽辐散相配合，是触发暴雨的有利条件。第1个降水系统位于高原涡东南侧，随着高原涡的移动衰亡移出盆地并最终消散，降水系统和高原涡在时间上有滞后相关，二者移动速度的突变较为一致；第2和第3个降水系统在西南涡出现的时段强烈发展，在局地停留维持并打通成为一条沿山脉走向的贯穿整个盆地的混合降水回波带，在西南涡发展至成熟阶段给四川盆地南部带来最大小时降水，降水系统和西南涡的相关无论在强度还是移速上都非常显著。在复杂的地形条件下，青藏高原和四川盆地相接处，降水云团的0℃层高度并未随地表发生明显变化，但降水云团进入盆地后，低于0℃层高度的降水粒子融化变为液相，使得云团从对流型降水变为分层结构的层云降水。

英文摘要:

      On 30 and 31 July 2009, a lasting severe rainfall occurred in the eastern lee of the Tibetan Plateau. There were three meso-scale convective systems in the Sichuan Basin, under the synoptic background that a plateau vortex and a southwest vortex had interacted at this region. The radar mosaic reflectivity data, NCEP reanalysis data and TRMM PR data are used to analyse its evolution and three-dimensional structure. By contrasting with TRMM PR, it is found that the radar mosaic has the same results and could describe the evolution of this event. In the plateau and the mountains with no mosaic data, TRMM PR could be used for supplement. The analysis results show that: at the precipitation area, positive vorticity at the middle and low levels and the moisture convergence upward motion matched high-level negative vorticity and water vapor divergence, which was a favorable condition to trigger severe rain. The first precipitation system is located southeast of the plateau vortex, moved toward the east with it and then dissipated. The precipitation has been found to lag the plateau vortex in terms of the intensity correlation, while its speed changed simultaneously with the vortex. The second and third precipitation systems have developed strongly during the existing stage of the southwest vortex, and then mixed into an echo belt throughout the basin along the mountains, causing the most severe rainfall in the southern basin. The intensity and movement of the precipitation system changed almost in the same time as those of the vortex. Under the complex terrain conditions with the mountains adjacent to the basin, the zero layers did not change significantly, but the cloud melted partially from ice to liquid when entering the basin and being under zero layers. This resulted precipitation in the change from convective cloud to straitform cloud with a stratified structure.