摘要:第三次青藏高原科学试验针对高原夏季云和降水物理过程开展了大量观测研究，为进一步揭示高原云微物理结构、云中水分转化和区域水分收支特征，本文采用中尺度数值预报模式（WRF）并结合高原试验期间的各种观测资料，对那曲观测试验区2014年7月5~6日的一次较为典型的夏季对流云降水过程进行了数值模拟研究。结果表明WRF模式能够基本再现高原夏季对流云的发展演变过程以及降水的日变化特征。模拟结果显示高原夏季对流云中具有较高的过冷云水和霰粒子含量，冰相过程在高原云和降水的形成和发展中具有十分重要的作用，地面降水主要由霰粒子融化产生。暖雨过程对降水的直接贡献很小，但在霰胚形成中具有十分重要的作用。霰粒子胚胎的形成主要来源于冰晶与过冷雨滴的撞冻过程，雪粒子和过冷雨水的碰冻转化及过冷雨滴的均质冻结贡献相对较小。霰粒子的增长过程在12 km（-40℃）以上层主要依靠对冰晶、雪粒子的聚并收集过程，而在其下层的增长过程主要依赖对过冷云水的凇附增长，对雪粒子的聚并收集和凝华增长过程较小。高原那曲地区净水汽收支为正，日平均降水转化率可达20.75%，接近长江下游地区，高于华北、西北地区。该地区日降水再循环率为10.92%，说明局地蒸发的水汽对高原降水的水汽来源具有一定的贡献，但高原降水的90%仍然由外界输入的水汽转化形成。
关键词:青藏高原/
数值模拟/
云微物理/
水分转化与收支/
降水再循环率
Abstract:Intensive observational studies on clouds and precipitation have been conducted in the project of the Third Tibetan Plateau Atmospheric Scientific Experiment. In order to further reveal cloud microphysical structure, water transformation in clouds and regional water budget properties over the plateau, a relatively typical convective precipitation process on July 5-6, 2014 in the Naqu region is investigated using mesoscale numerical prediction model (WRF) combined with observational data collected during the experiment. The results indicate that WRF model could reproduce the general characteristics of cloud process and diurnal variation of precipitation over the plateau. The modeling results show that there were large amounts of supercooled cloud water and graupel particles in the summer convective clouds over the plateau. The ice process played a critical role in the development of clouds and precipitation over the plateau. The surface precipitation mainly formed by the melting of graupel particles. Although the warm cloud microphysical process had small direct contribution to the formation of surface precipitation, it had an important contribution to the formation of graupel embryos. The accretion transformation process of ice crystal with supercooled raindrops contributed to the production of graupel particles and its growth mainly relied on the riming process for supercooled cloud water. The net water vapor budget was positive at Naqu over the plateau and the mean daily conversion rate from vapor to precipitation was as high as 20.75%, which is close to that in the downstream of the Yangtze river and higher than that in northern and northwestern China. The contribution of daily mean surface evaporation to precipitation, i.e., precipitation recycling, was 10.92%, indicating that 90% of the rainfall was from the conversion of water vapor outside, although local evaporation of water vapor had a certain contribution to the water vapor source of the rainfall over the plateau.
Key words:Tibetan Plateau/
Numerical simulation/
Cloud microphysics/
Water transformation and budget/
Precipitation recycling
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