香港特大暴雨β中尺度线状对流三维结构研究

Research on the Three-Dimensional Structure of Meso-β-Scale Convective Systems in a Heavy Rain Process in Hong Kong

β中尺度狭窄线状对流系统是造成锋前暖区暴雨的主要角色，对其结构和机理的研究具有重要意义。作者使用高时空分辨率的多普勒雷达观测资料。对1998年6月8～9日香港暴雨过程中的β中尺度的狭窄线状雨带进行流场、回波强度和散度的时空四维结构的深入剖析。利用观测资料得到线状β中尺度对流系统的三维流场和水平散度结构。发现线状β中尺度对流系统的水平散度垂直配置与低层强降水回波之间存在一定的关系,并给出发展和成熟阶段中线状β中尺度对流系统的流场和散度场配置的基本结构。

The meso-scale convective system plays a key role in heavy rain processes. The research shows that the meso-β-scale convective system is the mainly system which directly cause the heavy rain in suitable large-scale environment. And the research on the structure of the meso-β-scale system and its developing mechanism become very important to understand such a heavy rainfall process. But until now, it is very difficult to analyze the meso-β-scale convective system based on routine observational data with lower resolution, so the Doppler radar data with high temporal and spatial resolution is used in such case. A four-dimensional structure analysis of the meso-scale convective systems in the heavy rainstorm process, which happened during 8 to 10 June 1998 in Hong Kong of China, is performed using the high-temporal and spatial resolution data observed by meteorological Doppler radar. This heavy rain process, with characteristics of great intensity, outbreak and small time scale, can be divided into three periods in which strong precipitation is observed. The following work is done to get the structures of the different systems. Firstly, the horizontal wind field retrieved from the Doppler radar data is verified and then the horizontal divergence is calculated. According to the Doppler radar reflectivity and horizontal wind field from 0300 UTC to 0600 UTC on 9 June, it is found that there are three strong reflectivity lines and a small but isolated meso-β-scale system field in the large-scale wind field. So, the dynamical structures of the three strong reflectivity lines during 0300 UTC to 0600 UTC 9 June are analysed in detail. The following conclusions are drawn from the research： 1） The convergence, including the convergence between the southwest wind and the south wind and the convergence between the southwest wind and the west wind, is the main reason for the strong precipitation. The three-dimensional wind and divergence structure of meso-β-scale convective systems is achieved for the first time. 2） The pattern between the strong reflectivity region and the horizontal convergence region of the meso-scale convective system at low level can be divided into two different situations. The situations are related with the vertical distribution of the horizontal divergence. And a sketch map to show the two situations is given in this paper.