山东半岛一次冷流暴雪过程的中尺度模拟与云微物理特征分析

本文以NCEP-FNL资料作为初始场和边界场,采用WRF中尺度模式对2010年12月29-30日发生在山东半岛的一次冷流暴雪过程进行数值模拟,并利用高时空分辨率模拟结果分析此次过程的中尺度特征和云微物理特征.模拟与分析结果表明,此次暴雪过程发生在较强的海气温差背景下,渤海海表对冷空气的增温增湿作用显著,通过湍流交换等作用向低层大气输送大量感热、潜热和水汽；水汽由渤海中部海域输送到山东半岛东北部地区,其上空水汽辐合层比较浅薄,集中在800 hPa以下,相对湿度饱和层和比湿高值维持的时间与强降雪时段一致；中尺度海岸锋的生消过程对冷流暴雪过程形成有着重要作用,水平方向上呈现为偏北风和偏西风的强辐合带,局地环流中的上升运动触发不稳定能量释放,直接决定暴雪的落区和强度,这是产生浅对流降雪的主要物理机制；云中水凝物粒子的高度在600 hPa以下,最大值出现在850～900 hPa之间与浅对流结构相对应；各水凝物粒子含量相差较大,以雪和霰最多.

Mesoscale Numerical Simulation and Cloud Microphysical Characteristics of a Cold Air Snowstorm in Shandong Peninsula

Based on the NCEP FNL data, the mesoscale model WRF is used to simulate the process of a cold air snowstorm occurred in Shandong Peninsula during 29-30 December 2010. High spatiotemporal resolution data from model output are adopted to analyze mesoscale and microphysical characteristics of the cold air snowstorm. The results indicate that this snowstorm occurs under the background of significant air sea temperature differences, furthermore heat and moisture are transported from the sea surface of Bohai sea to cold air, which is caused by turbulence. Vapor from the central part of Bohai Sea are transported to the northeast of Shandong Peninsula, where the moisture convergence layer is thin, below 800 hPa. The duration of the maximum value of specific humidity and the saturated layers of relative humidity is corresponding to the heavy snowfall period. The frontogenesis of mesoscale costal front, which shows a strong convergence zone of northerly and westerly winds in the horizontal structure, plays a significant role in the heavy snow process. The ascending motions in the local circumfluence of the costal front directly decide the area and intensity of the snowstorm. In addition, the updraft is the trigger of instable energy and the mechanism of shallow convective snow. The droplets distribute mainly below 600 hPa and their maximum appears in the 850-900 hPa, respectively, which agrees with the structure of the shallow convection. In addition, the contents of droplets are different from each other, among which the contents of snow and graupel are the most.