基于加密自动站、风廓线、微波辐射计等多种稠密观测资料，结合多普勒天气雷达变分同化分析系统(VDRAS)反演的对流层低层热力动力场，对2009年7月29日发生在北京香山地区的局地暴雨过程(简称“7.29”过程)进行了综合分析。结果表明：该过程是一次典型的局地新生雷暴引发的γ中尺度局地大暴雨过程，其发生发展突然、持续时间短、局地性强、降水强度大；降水环境场上，较低的抬升凝结高度和自由对流高度使得新生雷暴的触发不需要太强的辐合抬升机制；北京北部山区雷暴冷池出流形成的300 m左右厚度的边界层偏北风与环境场偏南风的辐合，对香山雷暴的新生起到关键触发作用，有利的局地水汽条件为香山雷暴产生强降水提供了充沛的水汽；香山雷暴发生后，由于缺乏雷暴冷池出流与环境低层垂直风切变的相互作用，导致香山雷暴难以获得有组织的进一步发展，在其发展成熟后很快消亡；复杂地形在对流发生发展过程中具有十分重要的作用，一方面在雷暴新生前期通过山前辐合抬升起到触发机制作用，另一方面对大气垂直上升运动起到增幅作用。%Based on a variety of intensive observational data including intensified automatic surface weather observation system, wind profil-er and microwave radiometer, and combined with the thermodynamic and dynamic fields retrieved by the Variational Doppler Radar Analysis System (VDRAS), we have conducted a comprehensive analysis of a local heavy rain event occurred around Xiangshan in Beijing on 29 July 2009 (hereinafter referred to as“7.29”event). The results show that the“7.29”event is caused by a newly-born meso-γscale thunderstorm with formation and development being abrupt, short life history, highly localized and high precipitation rate. Looking from the early stage envi-ronment, unstable atmospheric condition with low lifting condensation level (LCL) and free convection level (LCF) makes the initiation of the newly-born thunderstorm not need much convergence lifting mechanism. The convergence between the southerly in environment field and the northerly from cold outflow that extended to 300 m above the surface, which happened in the northern mountain area of Beijing, is a key factor for the initiation of the Xiangshan thunderstorm. Favorable local water vapor environment supplies sufficient moisture for formation of the“7.29”event. After the initiation of the Xiangshan thunderstorm, due to the lack of the interaction between favorable low-level wind shear and the strong cold outflow produced by the convection itself, it dies out rapidly since it becomes difficult to get systematically further development after its maturation. In addition, the complicated terrain also shows an important role during the formation and development of convection. On the one hand it plays a triggering role for the initiation of the newly-born thunderstorm by topographic forcing effect. On the other hand, it plays an enhancement role for the vertical ascending movement of air for the convections.
展开▼
