局地低矮地形对华南暴雨影响的数值试验

Numerical Experiment of the Effect of Local Low Terrain on Heavy Rainstorm of South China

为了探讨华南地区常见的局地喇叭口、迎风坡地形对暴雨的影响,选取云开山地到珠三角平原之间的地理范围为研究区域,利用中尺度气象模式进行三组地形试验,研究了一次特大暴雨过程中局地地形对强降雨的影响。结果表明,移去云开山地,原山地迎风坡的雨带北抬,对应雨量增加带,24h增值超过100mm;增加云开山地的高度,则会出现反"C"形雨量增加带;对于南北向的喇叭口地形,越往北降雨增幅越明显。地形试验表明,华南地区数百米的山地可影响到对流层中上层环流变化;通过改变局地地形,在特定区域将造成近地层辐合与上升运动的增强,有时甚至形成垂直方向的正向闭合环流圈,从而引起局地中尺度对流的发展,造成暴雨增幅;地形的改变将促使近地层风场发生改变,对中尺度而言,先发生变化的风场会引起涡度等要素随之改变,最终导致暴雨落区的变化。

In order to investigate the influence on the Southern China rainstorm from the local trumpet-shaped terrain and the windward slope terrain, the geographic range between the Yunkai Mountain and the Pearl River delta plain are selected as study area, and three groups of terrain test are carried out by using mesoscale meteorological models. If the Yunkai Mountain was taken off, the original rain belt would move northwardly, with an increment of rainfall larger than 100 mm·（24h）-1. When the height of Yunkai Mountain was increased, a rainfall increasing belt with a reverse ‘C’ shape would appear. The terrain of several hundred meters can affect the middle-upper troposphere circulation. The enhancements of boundary layer convergence and ascending motion can emerge in certain region through local terrain changes. Sometimes it even forms a positive closed circulation of vertical direction, which causes the development of local convection. In terms of the mesoscale system, the topographic changes will firstly lead to the changes in surface wind field, the changing wind field will cause vorticity and other physical elements changes, and eventually lead to the changes on precipitation.