2011年初湖南暴雪过程的成因和数值模拟分析

The Numerical Simulation Analysis and Causes of Snowstorm Occurring in Hunan Province,Early 2011

利用多种观测资料及NCEP再分析资料,对2011年1月17—20日湖南一次大范围暴雪过程进行了诊断分析,并使用WRF模式对其云微物理特征及降水相态转换机制进行数值模拟,旨在探讨本次强雨雪过程降水相态变化和暴雪形成及其发展成因。结果表明:乌拉尔山前部南下的冷空气与来自孟加拉湾及南海的暖湿气流在湖南长时间交汇产生锋生强迫,在静止锋区上界形成强辐合上升运动,是湖南大范围暴雪天气持续的主要原因;强烈的上升运动和持续的水汽辐合为本次暴雪过程提供了动力、水汽条件,"冷空气楔"上爬升的暖湿气流维持时间较长,是持续性大范围暴雪产生的重要热力条件;WRF模式能较好地模拟降雪量级及强降雪落区。雪粒子的产生和发展不仅与液水比含量大小有关,还与其上空冰晶的含量及分布密切相关,雪的凝华增长、冰晶向雪的自动转化和雨水与雪碰并成雪可能是本次降雪发生、发展最主要的物理过程,冰雪粒子大值中心及强上升运动区对预报强降雪带位置有较好的指示作用。

Based on various conventional observations, the NCEP reanalysis data, a largescale blizzard process in Hunan Province during 1720 January. 2011 was analyzed and the process was simulated on dynamic, water vapor, thermodynamic conditions, and cloud microphysical characteristics by the WRF nu merical 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 airflows 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 up ward 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 longduration 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 snowand 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.