国家自然科学基金资助项目40905059, 中国气象科学研究院基本科研业务费专项资金面上项目2008Y001, 国家自然科学基金资助项目41075099
2008年1月中下旬, 我国南方经历了四次历史罕见的冰冻雨雪天气。本文针对2008年1月25~29日的一次典型冻雨天气过程, 在实测资料、NCEP再分析资料综合分析的基础上, 利用中国气象科学研究院 (CAMS) 中尺度云分辨模式对1月28日~29日的冻雨天气过程进行了数值模拟, 研究了冰冻天气形成的大气层结及云系冻雨区云的宏微观结构特征, 初步分析了冻雨形成的云微物理过程及云物理成因。结果表明, 深厚而稳定的逆温层和低空冷层的存在是大范围冻雨出现的直接原因。此次南方冰冻过程中, 湖南和贵州两地冻雨形成的云物理机理不同, 不同冻雨区上空为两种不同类型的云, 对应两种不同的云微物理结构和大气层结结构。湖南冻雨区云层较厚, 云顶温度较低, 属于混合相云, 云中高层存在丰富的冰相粒子 (雪的比含水量最大)。湖南冻雨在 "冷—暖—冷" 层结下, 通过 "冰相融化过程" 形成, 即在锋面之上的对流层中层水汽辐合中心内形成的雪, 从高空落入暖层, 雪融化形成雨, 再下落到冷层后, 形成过冷雨滴, 最后接触到温度低于 0℃的物体或降落到地面上, 迅速冻结形成冻雨。而贵州冻雨区云层较薄, 云顶温度较高, 属于暖云, 中高层基本无冰相粒子, 低层为云水和雨水 (云水的比含水量最大)。贵州冻雨是在 "暖—冷" 层结下通过 "过冷暖雨过程" 形成的。即水汽沿锋面抬升, 在对流层中低层的水汽辐合中心内, 经过冷却凝结成云滴, 通过碰并云滴增长的雨滴下落到低空冷层, 形成的过冷却雨滴直接冻结形成冻雨。
Southern China suffered four severe freezing rain and snow storm processes during January 2008. In this paper, a classical freezing rain process during 25-29 January 2008 was selected as a research case. Characteristics of stratification structure and cloud physics of the freezing rain were analyzed. Combining with observation, the freezing rain process during 28-29 January 2008 was simulated by the CAMS (Chinese Academy of Meteorological Sciences) mesoscale cloud model. The authors studied characteristics of micro-macroscale structure of cloud system over the freezing rain area and initially analyzed the microphysical process in the cloud and the mechanism of freezing rain formation. The results show that, the stable and thicker melting layer and cold layer at low levels was direct cause that the wide range of freezing rain appeared. Two different types of clouds existed over different freezing rain areas in this freezing rain process. Two types of clouds have different characteristics of stratification structure and cloud physics and mechanism of freezing rain formation. Clouds over the Hunan Province freezing rain area belonged to mixed-phase cloud: the cloud thickness was deeper, the cloud top temperature was lower, and in the clouds there were large amount of ice-phase particles. Under the consideration of stratification ("cold-warm-cold" layer), the freezing rain over Hunan Province was formed by ice-crystal mechanisms (the melting process). That is, the freezing rain developed as the falling snow encounters a layer of warm air, and then the snow completely melted and became rain. As the rain continued to fall, it passed through a thin layer of cold air just above the surface, cooled to a temperature below freezing, and formed supercooled drops. When the supercooled raindrop dropped and struck the ground, or anything else below 0℃, they instantly freeze, forming the freezing rain. However, clouds over the Guizhou Province freezing rain area belonged to warm clouds: the cloud thickness was thinner, the cloud top temperature was higher, and in the clouds there were little ice-phase particles. Under the consideration of stratification ("warm-cold" layer), the freezing rain over Guizhou Province was formed by supercooled warm-rain processes (collision-coalescence process). Supercooled raindrops developed by microscopic cloud droplets collecting one another as they fall. Ice processes were not involved in the formation of these raindrops.
陶玥,史月琴,刘卫国.2008年1月南方一次冰冻天气中冻雨区的层结和云物理特征.大气科学,2012,36(3):507~522 TAO Yue, SHI Yueqin, LIU Weiguo. Characteristics of Stratification Structure and Cloud Physics of the Freezing Rain over Southern China in January 2008. Chinese Journal of Atmospheric Sciences (in Chinese),2012,36(3):507~522复制