| Liupan Mountain area is an important water conservation forest base in the eastern part of northwest China,with abundant cloud water resources to be developed.In order to carry out weather modification operation scientifically,it is necessary to deeply study the microphysical structure and precipitation formation mechanism of the precipitating cloud system in this area.Based on the daily observational precipitation data,the spatial-temporal distribution of precipitation in Liupan Mountain area was analyzed.Using the Weather Research and Forecasting(WRF)model,two precipitation processes(July 1-2 and August 21-22,2018)occurred in Liupan Mountain area in southern Ningxia was simulated.Based on the simulation results and the observational data,the favorable circulation situation was analyzed during the two weather processes,and the evolution process,microphysical structure and precipitation formation mechanism in the precipitating cloud system on August 21 were mainly discussed.In addition,orographic sensitive experiments were designed to explore the impacts of the Liupan Mountain on the formation of clouds and precipitation.The main conclusions are as follows:The average annual precipitation in the Liupan Mountain area was about 518 mm,and the precipitation in the east side of the mountain was significantly higher than that in the west side.The precipitation in summer accounts for 50-60% of the annual precipitation.The cloud system on July 01-02 was formed under the joint action of the westerly trough and the low-level shear line,and the cloud system on August 21-22 developed in the dynamic field of aloft trough associated with low vortex.In both processes,the system moved from northwest to southeast,and the cumulative precipitation on the east side of the mountain was higher than that on the west side.The sensitivity studies of the cloud microphysics scheme(Morrison2 scheme,Thompson scheme,WSM6 scheme,Lin scheme)indicated that the precipitation process simulated by Lin scheme was closer to the actual precipitation.The low vortex on August 21 gradually fell behind the aloft trough,because of the blocking effect of the Liupan Mountain terrain.The easterly airflow accumulated in front of the mountain,forming a strong orographic cloud belt along the terrain.The vertical structure of cloud basically satisfied “seeding-feeding” stratified structure,but the microstructure of each layer was different in different parts of the cloud system,resulting in the difference of contribution of various microphysical processes to precipitation.Collision-coalescence process of cloud water and melting of graupel were the main sources of rain water,and the growth of graupel was mainly due to the accretion of supercooled rain.The clouds on the east slope developed upward,forming a rich cloud water layer and enhancing both the cold and warm cloud processes.The terrain had significant impacts on the low-level flow field and vapor flux divergence field.Under the dynamic force of terrain,the wind direction deflected,forming the convergence and divergence zone near the mountain range,and affecting the movement and development of the low level weather system.In addition,the Liupan Mountain terrain blocked water vapor transportation of the lower level,causing moisture convergence and motion on the east slope,which provided the water vapor conditions for the precipitation on the east windward slope.If leveling the terrain,precipitation on the east side decreased,and the center of heavy precipitation moved to the west.If the height of Liupan Mountain increased to 1.25 times,the updraft on the east slope was enhanced,which promoted the cloud body to develop upwards,and the supercooled water increased,so that the graupel grew rapidly,and the ice crystals and snow particles in the upper layer also increased slightly,which eventually leaded to the enhancement of ground precipitation. |
PDF Full Text Request