青藏高原夏季对流云微物理特征和降水形成机制

青藏高原对我国天气、气候和水循环过程有重要影响。利用第三次青藏高原大气科学试验（TIPEX-Ⅲ）2014年7月在那曲地区的飞机观测数据,研究青藏高原夏季对流云和降水的微物理特征及降水形成机制。飞机探测的云系主要为初生或发展阶段的冰水混合云,云滴数浓度低于平原、海洋地区1~2个量级,云内存在大量大云滴和雨滴,过冷水含量高。大粒子（D≥50 μm）数浓度量级为100~101 L-1,云内上升气流速度集中在1~4 m·s-1。青藏高原云滴谱主要呈双峰型,云内冰相粒子多为密实、不透明的霰粒子,云内凇附过程显著。云内暖雨过程产生的大云滴和雨滴有利于冰相过程,尤其是凇附过程的产生,使得青藏高原云更易产生降水。此外,残留云系与对流云有着较为类似的微物理特征。

Microphysical Characteristics and Precipitation Formation Mechanisms of Convective Clouds over the Tibetan Plateau in Summer

Tibetan Plateau (TP) has high impact on weather, climate, and water cycle of China, and it also affects the flood and drought in south China by modulating the onset and retreat of the Asian monsoon. However, owning to the lack of direct observations, the knowledge of microphysical characteristics and mechanisms inside the clouds over TP is still seriously lacking. During the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-Ⅲ), field observations is carried out in the summer of 2014, which employed ground-based and airborne instruments. By using the aircraft measurements collected during the TIPEX-Ⅲ, the microphysical characteristics and precipitation formation mechanisms of summertime clouds are studied. The results show that clouds detected by the aircraft are mainly newly born or developing mixed-phase convective clouds, as well as some residual clouds. The maximum and average concentrations of cloud drops are 1.1×105 L-1 and (9±10)×103 L-1, respectively, and the order of magnitude is 104 L-1, which is lower than clouds of plain and maritime regions by 1-2 orders. The maximum concentration for larger cloud particles is 28.82 L-1, and the order of magnitude is 100-101 L-1, which is also lower than other regions. The maximum liquid and total water content are 0.25 g·m-3 and 1.33 g·m-3, respectively, and the order of magnitude is 10-1-100 g·m-3, with abundant supercooled liquid water content in the clouds. The uplifting velocity distributes mainly in the range of 1-4 m·s-1 with a maximum of 4.3 m·s-1, indicating the convective clouds over the TP are weaker than other regions. The cloud drop size distributions (DSD) are mostly bimodal with different second peaks at the larger end, and some of the DSDs are unimodal, which are mainly found in newly borne clouds. There are more large cloud drops and drizzles in the clouds over the TP, which is the result of active warm rain processes. And the ice particles mainly consist of opaque and dense graupels as well as some needles and plates, indicating active rimming processes. The warm rain processes do not generate rain directly, but contribute to the subsequent glaciation and rimming processes, leading to the quick formation of precipitation over the TP. The residual clouds show similar ice characteristics with convective clouds, but much drier and weaker, and they also maintain small amount of supercooled liquid water.