摘要:六盘山是西北重要的水源涵养林基地，干旱少雨制约了该地区农业和经济发展。作为该地区人工增雨技术研究的基础，本文利用WRF模式对2018年8月21日发生在宁夏南部六盘山区的一次降水天气过程进行了数值模拟。根据模拟结果结合实测资料，分析了造成此次强降水过程的有利环流形势场，重点讨论了山区降水云系的微物理结构以及降水形成机制。结果表明：降水是在高空槽配合低涡的动力场作用下形成的，受六盘山地形的阻挡作用，低层低涡系统移速落后于高空槽；垂直方向上云系呈现“催化—供给”的分层结构，但在云系不同部位，各层水凝物配置不同，导致冷暖云过程对降水的贡献差异；六盘山东部迎风坡降水强于西坡。霰粒子融化和云水碰并是地面降水的主要来源；碰冻过冷雨水是霰增长的主要过程。迎风坡云水层深厚，含水量高，一方面促进过冷层中霰粒子的碰冻增长过程，一方面为雨滴碰并增长提供充沛的云水条件，即同时增强了冷暖云降水过程。地形对云的发展和降水的形成有明显影响，当降低地形高度后，云水量减少，暖云过程减弱，同时也影响了霰粒子的增长过程。
关键词:六盘山/
数值模拟/
微物理结构/
降水机制
Abstract:The Liupan Mountain area is a water-conservation forest base in northwestern China; however, drought and lack of rain restrict the agricultural and economic development of this region. Through the weather research and forecasting model, a precipitation process that occurred in the Liupan Mountain area in southern Ningxia on August 21, 2018, was simulated as the basis of further research on enhancing the technology of artificial precipitation in this area. Based on observational data, a favorable circulation situation was analyzed, and the microphysical structure and precipitation formation mechanism in the precipitation cloud system were investigated. Results show that the weather system of this precipitation process developed in the dynamic field of high-altitude trough associated with low vortex, and the low vortex featured a slower movement compared with the high-altitude trough because of the blocking effect of the Liupan Mountain terrain. The vertical structure of cloud showed a remarkable “seeding-feeding” stratified structure; however, the vertical microstructure differed in different parts of the cloud system. This resulted in differences in the contributions of cold and warm-cloud processes to precipitation. In addition, the precipitation on the east windward side of the Liupan Mountain area was stronger than that on the west. Rain water was mainly produced by the melting of graupel and collection of cloud water. The accretion of supercooled rain was the main process of graupel growth. The layer of cloud water on the windward slope was deep, having high water content. This promoted the process of rain accretion by graupel in the supercooled layer and provided abundant cloud water for the coalescence growth process of raindrops, which enhanced both cold cloud and warm-cloud precipitation processes. The terrain had an impact on clouds development and precipitation formation; when the terrain height was reduced, the cloud water decreased, and consequently, the warm-cloud processes weakened, which also affected the graupel growth process.
Key words:Liupan Mountain/
Numerical simulation/
Microphysical structure/
Precipitation mechanism
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