| Intensive observational studies on clouds and precipitation have been conducted in the project of the Third Tibetan Plateau Atmospheric Scientific Experiment(TIPEX-III).In order to further reveal cloud and precipitation microphysical structure,water transformation in clouds and regional water budget properties over the plateau,seven cloud and precipitation processes(3-4 July,5-6 July,9-10 July,13-14 July,20-21 July,21-22 July,24-25 July)with different intensities on 3 July to 25 July,2014 in the Naqu region of the Tibetan Plateau were investigated using cloud-resolving mesoscale numerical prediction model(WRF)combined with observational data collected during the experiment.Sensitivity experiments of different cloud microphysical schemes(Lin scheme,WSM6 scheme,Goddard scheme,Thompson scheme and Morrison scheme)on a relatively typical convective precipitation process on 5-6 July,2014 were conducted.The sensitivity studies indicate that the Lin microphysical scheme may better reflect the structure and evolution characteristics of convective clouds than other schemes in the central Tibetan Plateau,and it can also better reflect the complex airflow distribution structure in the clouds and echo bright feature.In addition,the 24-hour accumulated rainfall in the Naqu area simulated by the Lin microphysical scheme was closer to the actual rainfall at the Naqu station.The results of the simulated six clouds and precipitation processes indicate that the summer clouds and precipitation processes over the TP had some unique properties.The initiation processes of clouds were closely associated with daytime strong solar radiation heating and the summer clouds and precipitation showed an obvious diurnal variation.The convective clouds were generally transformed into the stratiform-like clouds with an obvious bright band and often produced stronger rainfall in the midnight.The maximum cloud top could reach more than 15 km above sea level(ASL)and updrafts were ranged from 10 m/s to 40 m/s.The modeled all six cases had high amount of supercooled water content primarily located between 0 ? and-20 ? layers.Ice crystals were mainly formed above-20 ? layer and even appeared above-40 ? layer in the strong convective clouds.Rain water mostly appeared under the melting layer,indicating that its formation mainly depended on the melting process of precipitating ice particles.Snow and graupel particles had the characteristics of high content and deep vertical distribution,showing that the ice process was very active in the development of clouds and precipitation.The transformation of hydrometeor and formation of precipitation over the plateau has some obvious characteristics.The surface precipitation was mainly formed by the melting of graupel particles.Although the warm cloud microphysical process had small direct contribution in the formation of surface precipitation,it had an important contribution on the formation of supercooled raindrops,which were essential to form graupel embryos through heterogeneous freezing processes.Graupel particle growth mainly relied on the riming process with supercooled cloud water and aggregation of snow particles.The research on the characteristics of the water budget of Naqu area shows that 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 34.21%,which was higher than most regions surrounding the plateau and corresponded to the frequent convective clouds and precipitation processes over the plateau in the summer.The contribution of daily mean surface evaporation to precipitation i.e.precipitation recycling,was 15.39%,indicating that approximately 85%rainfall was from the conversion of water vapor outside though the local evaporation of water vapor had a certain contribution to the water vapor source of the rainfall over the plateau. |
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