Characteristics Of Convective Clouds, Precipitation And Raindrop Size Distribution In Summer Season Over Tibetan Plateau

The Tibetan plateau has an important impact on regional water cycle, ecosystem, disastrous weather formation, and climate change. China has conducted the Third Tibetan Plateau Experiment-Observation of Boundary Layer and Troposphere(2014~2017) project in order to reveal the physical process of meteorology and atmosphere over the Tibetan plateau. The observational instruments for cloud and precipitation processes in this field experiment include the C-band continuous wave radar, Ka-band millimeter wave cloud radar, ground-based raindrop disdrometer, lidar ceilometer etc. In this paper, the characteristics of convective clouds and precipitation as well as raindrop size distribution were analyzed by using observed data and FY-2E satellite TBB data from Jul. 1st to Aug. 31 st, 2014. The result shows that the convective activities mainly distributed in the central and southeast part of the Tibetan plateau and the precipitation has a quasi-two-week cycle during the observational period. The reflectivity of radar during observational period is relatively weaker, especially concerning to severe convections. There is always a bright band of melting layer in the the echo of radar, which is 780 m from ground. The mean cloud-top height is around 11.5 km(ASL), and its maximum value exceeds 19 km. The mean cloud-base height is 2.38 km(ABL). Precipitation has mainly shortlasting(20 min~1 h) and showery(≤5 mm/h) properties, and the mean precipitation intensity is around 1.2 mm/h. The result also shows that the raindrop size distribution over the Tibetan plateau is wider than that over plain at the same latitude and season, because of which the rain falls more easily over the plateau than that over plain. Gama distribution is suitable for the raindrop size distribution over the Tibetan plateau more than M-P distribution. Due to the solar heating effect over the plateau, both convective clouds and precipitation processes have obvious daily variation. Convections first begin before midday, reaching their maximum before night, after that the convective activities get weaker while precipitation remains high, then at late night the precipitation begin to dissipate, and to the morning the clouds die out. What’s more, due to the special atmospheric structure, even though there are continuous convections, they are relatively weaker.