华东中尺度地形对浙北暴雨影响的模拟研究

以一次梅雨降水为例，利用中尺度模式进行一系列中尺度地形对降水的增幅影响的敏感性试验。结果表明，中尺度地形对强降水区域的分布和强度有很大的影响，强降水中心位于地形附近，地形引起的１２小时降水增幅高达总降水的９０％以上；中尺度地形作为一种外界迫动，初始在低层形成气旋性辐合和水汽热量的集中，然后通过凝结潜热释放所造成的中高层增温和高层辐散，使得地形垂直环流加强和向上伸展。于是在降水、潜热释放与地形垂直环流之间出现一种正反馈机制，导致地形对降水的强烈增幅；同时午后下垫面加热所形成的不稳定层结也有利于地形垂直环流的不稳定发展，产生新的雨峰；初始场的中尺度扰动似乎在降水的地形性增幅中并不起明显作用。

THE SIMULATION STUDY OF THE MESO-SCALE OROGRAPHIC EFFECTS ON HEAVY RAIN IN EAST CHINA

n order to investigate the meso-scale orographic effects on heavy rain, we conduct a series of sensitivity experiments for a mei-yu case by using of a meso-scale model. It is found that the meso-scale mountain has significant influence on the location and intensity of heavy rain area, the center of heavy rain is located over the moutain area, the orographic increment of 12 hour accumulated rainfall accounts for about 90 per cent of the totals.The meso-scale mountain, as a foreign forcing, initiats cyclonic convergence and the concentration of heat and moisture in lower layer, then causes middle layer warming through latent heating, and high level anticyclonic divergence, which is favourable for the intensification and upward extension of the orographic vertical circulation. It is the positive feed-back mechanism among precipitation, latent heating and orographic vertical circulation that leads to the intense orographic increment of precipitation. Besides, the instability stratification caused by the afternoon ground heating also contributes to the development of orographic vertical circulation and the generation of new rainfall peak. The meso-scale disturbances on the initial fields seems not to play a significant role in the meso-scale orographic intensification of precipitation.