2014年夏季青藏高原云和降水微物理特征的数值模拟研究

为了加强对青藏高原（高原）云和降水微物理特征的深入认识，采用高分辨率中尺度数值预报模式（WRF），对第三次青藏高原大气科学试验2014年7月3-25日发生的6次不同强度云和降水过程进行了数值模拟分析。研究结果表明:（1）青藏高原夏季云和降水过程具有独特性。高原夏季对流的促发机制主要是午后高原加热造成的，云和降水具有明显的日变化。午夜后，对流性降水一般转化为层状云降水，具有明显的0℃层回波亮带，并且会产生强降水。大部分对流云云顶高度超过15 km（海拔高度），最大上升气流速度为10-40 m/s。（2）6次云过程中均具有高过冷云水含量，主要分布在0—-20℃层，冰晶含量主要分布在-20℃层以上的区域，强盛的对流云中，可出现在-40℃层以上区域；雨水集中分布在融化层之下，说明其主要依赖降水性冰粒子的融化过程；雪和霰粒子含量高，分布范围广，说明云中冰相过程非常活跃。（3）高原夏季云中水凝物的转化过程和降水的形成机理具有明显特点。霰粒子的融化过程是地面雨水的主要来源，暖雨过程对降水的直接贡献很小，但通过暖雨过程形成的过冷雨滴的异质冻结过程对云中霰胚的形成十分重要。霰粒子的增长主要依靠凇附过程以及聚并雪晶的增长过程。 

Numerical studies on microphysical properties of clouds and precipitation in the summer of 2014 over the Tibetan Plateau

In order to improve the understanding of microphysical properties of clouds and precipitation over the Tibetan Plateau, six cloud and precipitation processes with different intensities during the Third Tibetan Plateau Atmospheric Scientific Experiment from 3 to 25 July 2014 in the Naqu region of the Tibetan Plateau are investigated using the mesoscale numerical prediction model (WRF) with high resolution. The results indicate that the summer clouds and precipitation processes over the TP have some unique properties. The initiation process of clouds is closely associated with strong solar radiation heating in the daytime and the summer clouds and precipitation show an obvious diurnal variation. Generally, convective clouds would transform into stratiform-like clouds with an obvious bright band and often produce strong rainfall in the midnight. The maximum cloud top can reach more than 15 km above the sea level (ASL) and the velocity of updraft ranges from 10 m/s to 40 m/s. The simulations show high amount of supercooled water content primarily located between 0℃ and -20℃ layer in all the six cases. Ice crystals mainly form above -20℃ layer and even appear above -40℃ layer in the strong convective clouds. Rain water mostly appears below the melting layer, indicating that its formation mainly depends on the melting process of precipitating ice particles. Snow and graupel particles have the characteristics of high content and deep vertical distribution, showing that the ice process is very active in the development of clouds and precipitation. The transformation of hydrometeors and formation of precipitation over the plateau exhibit some obvious characteristics. Surface precipitation is mainly formed by the melting of graupel particles. Although the warm cloud microphysical process makes small direct contribution to the formation of surface precipitation, it makes important contribution to the formation of supercooled raindrops, which are essential for the formation of graupel embryos through heterogeneous freezing process. The growth of graupel particles mainly relies on the riming process with supercooled cloud water and aggregation of snow particles.