北京地形和热岛效应对一次β中尺度暴雨的作用

针对2010年7月9日北京地区一次典型的β中尺度暴雨过程,利用常规天气观测资料、地面加密自动站资料、风廓线雷达数据以及VDRAS（Variational Doppler Radar Analysis System）提供的精细化分析资料,研究了本次过程中地形、热岛效应以及两者相互作用对暴雨的影响。研究表明：地形的抬升作用对暴雨有明显的增强作用,降水过程中有地形雨带的生成;降水前城区热岛效应明显,由此造成的风场垂直切变和边界层辐合为β中尺度系统提供了有利的触发和加强条件,边界层辐合线的位置对暴雨落区有一定的指示意义;降水在西部山前城区发生后低层偏东风与降水之间形成了明显的正反馈,是β中尺度暴雨得以维持和发展的重要机制。

Effects of Topography and Urban Heat to a Meso-β Torrential Rain in Beijing Area

The west and north parts of Beijing area are mountainous and the urban heat island effect is obvious in Beijing area,these may influence the distribution and intensity of the rainfall.Using the intensified observation and analysis data including wind profile data,temperature elements of surface automatic weather stations(AWS),the wind distribution and vertical divergence of Variational Doppler Radar Analysis System(VDRAS),the effects of topography and urban heat island on a meso-βtorrential rain in Beijing area are studied in the afternoon on July 9,2010.Result shows:(1) When the wind is toward the mountain,the rainfall gets stronger at the windward slope;(2) The urban heat effect is obvious before the rainfall begins,the convergence at low levels because of the effect is about 1000 m high,and at the same time the temperature gradient caused by the urban heat effect can cause vertical wind shear,so that both the convergence of low level and the vertical wind shear can lead to the grow and development of the convective system;(3) Once strong convective precipitation begins on the windward slope,the positive feedback between rainfall intensity and southeast wind velocity appears,and the process is an essential condition to form meso-βscale torrential rain.