The Numerical Simulation Analysis and Causes of Snowstorm Occurring in Hunan Province, Early 2011
Based on various conventional observations, the NCEP reanalysis data, a large scale blizzard process in Hunan Province during 17-20 January. 2011 was analyzed and the process was simulated on dynamic, water vapor, thermodynamic conditions, and cloud microphysical characteristics by the WRF numerical model. The purpose was attempted to discuss the phase transformation of precipitation and the causes for the formation and development of this snowstorm process. The results indicate that, the cold air coming from Ural Mountains and the warm wet air flows coming from the Bay of Bengal and the South China Sea, were meeting with in Hunan for a long time and causing frontogenesis forcing, then strong upward motion was made in the stationary front area. Therefore, the sustained snowstorms took place in Hunan area. Meanwhile, strong upward movement and continuing moisture convergence provided water and power conditions for the snowstorm process, the warm and wet airflow was keeping on the cold air for long time, which provides significant thermal conditions for the long duration snowstorm. Good simulations of snowstorm areas and amount were achieved by model WRF. The formation and development of snow particle were connecting with not only liquid water content, but also the content of ice particle. The main physical process of this snowstorm was probably the deposition growth of snow, the automatic transformation from ice crystal to snow and the collision between rain and snow. The bigger value center of ice snow particulate and the strong upward movement area have indicative significance for the forecast of heavy snowfall.