山区地形对暴雨的影响

本文分析了各种不同的自然条件下山区地形对暴雨的影响，指出山区复杂下垫面的热力和动力作用对暴雨有触发、加强或削弱、消亡的影响，在不同的区域地理背景下，地形的影响各不相同，在相同的地理背景下，不同的地形形态对暴雨的影响也有较大差异，地形性强迫抬升和辐合是触发暴雨和使之加强的重要机制，地形性辐射和下沉区对应暴雨的低频区，背区波暴雨过程在西北、华北的冷锋天气过程中较为多见，夏季山区局地对流性暴雨过程在凌晨

INFLUENCE OF TOPOGRAPHY ON STORM RAINFALL

In this article. we analyse the influence of complex mountain surface layer on the formation and distribution of storm rainfall. The results show that topographically induced convergence and upward motion is one of the most important mechanism that may cause and strengthen storm rainfall. In moist regions, precipitation of storm rainfall caused by topography is much more than in less moist regions.In the humid region. leeward slope is usually dry with little or no rainfall, that is the so called rain shadow. In the semi-humid region with strong stable air passing over niountain. there is a high frenquency of leeward wave storm rainfall. In this srtuation. leeward wave storm rainfall is about eight times of that of windword slope. In the arid region. local gale may occur on leeward slope with little or no rainfall.Local thermal circulation and land-water circulation may cause cyclonic convergence with violent convective motion which can motivate nocturnal storm rainfall in the semi-humid region. In humid region, however. it may cause storm rainfall which is very strong but only lasts a short time.This kind of storm rainfall is dangerous but difficult to predict.In the mountain valleys. the moist warm air flows more paralell to the valley. storm rainfall is more easy to form or become strong. On the contrary. with air flow direction perpendicular to valley direction, the valley will be filled by dry and relatively hot air with no rainfall.