北京地区深秋季节一次对流性暴雨天气中尺度分析

Meso-scale Analysis of Heavy Rainfall Event Occurred in the Late Autumn 2007 in Beijing

使用加密自动站、微波辐射计和风廓线仪等探测资料,详细分析了深秋季节(2007年10月27日)发生在北京地区的一次强对流局地暴雨过程的天气系统结构特征,探讨系统的发生发展机制。分析表明,此次局地暴雨天气是在高空冷槽和地面冷锋系统相配合的有利的大尺度环流背景下,地形和热岛效应共同作用产生的中尺度系统造成的。前人对夏季暴雨的研究结果可以很好地解释此次秋季强对流天气的发生发展机理,低层偏东气流与北京西部山脉的相互作用使得气旋式涡度增加,产生中低层垂直风切变,使山脉迎风坡的降水增强。城市热岛形成的城区与郊区之间的水平温度梯度在迎风坡强迫产生的中尺度垂直切变是对流性局地强降水发生发展的重要条件。吹向迎风坡的风速与降水强度之间存在正反馈过程,这也是局地降水增强的可能因素。此次秋季过程主要是较强冷空气与较好的水汽条件配合造成,而夏季强对流过程则多是在高温高湿条件下弱冷空气入侵造成。

To analyse the characteristics of the synoptic system structure as well as the characteristics of the occurrence and development mechanism of a strong convective rainstorm process took place in Beijing in the late autumn （October 27, 2007） based on the AWS, microwave radiometer and wind profiler data. Analysis indicates that in the context of the favorable large-scale circulation background composed by upper cold trough and surface cold front, the meso-scale systems caused by the special topography and heat island effect leads to the heavy rainfall directly. Previous research achievements about the strong convection in summer can be used to explain the physical mechanism of occurrence and development of the severe convective weather. The interaction between the low-level easterly airstreams and the western mountains of Beijing increases the cyclonic vorticity. This results in the formation of the lower vertical wind shear and enhances the precipitation on the windward slop. The horizontal temperature gradient between the western suburbs and the down-town caused by the urban heat island effect leads to the vertical wind shear on the windward slope, and this is an important factor to enhance the local heavy rainfall. At the same time, the positive feedback process between the wind speed of the wind blowing to the windward slop and the precipitation intensity maybe also is a main factor to enhance the local precipitation. Comparing with the strong convection events in summer, there are some obvious differences on the occurrence and development of the weather systems, which happened in fall is mainly caused by the strong cold air and better water conditions, while the process is weak under the conditions of high temperature and humidity, as well as＂ the invasion of weakly cold air in summer.