渤海海效应暴雪云特征的观测分析

Observational Analysis of Cloud Characteristics of the Bohai Sea-effect Snowstorms

利用静止卫星(GMS5,GOES-9,MTSAT)红外数据与CloudSat卫星云剖面雷达数据、NCEP FNL分析资料与常规观测资料,对2001—2010年发生的12次渤海海效应暴雪过程中云的演变特征、渤海热力作用与暴雪云团垂直结构及相态组成进行了观测分析。发现不同生成源地的暴雪云通常在渤海上快速发展,云中多存在水平范围可达100~300 km的密实条状或块状云团,其下对应主要降雪区域;暴雪云生成源地可分为渤海湾及莱州湾附近、渤海中部、辽东湾附近3种,暴雪云在海上移动主要受850 hPa风场影响;渤海暖海面与其上冷空气间的热量、水汽交换形成的不稳定层结条件,导致暴雪云进一步发展;暴雪云发展旺盛时期高度可达4 km,其冰水含量最大值达600 mg·m^(-3)且主要集中在2 km高度附近,平均值可达303 mg·m^(-3),冰粒子有效半径最大值约为120μm,平均值约为91μm。

Sea-effect snowstorm is a kind of typical local disastrous weather phenomena in winter of Shandong Province. The pioneering researches on snowstorm clouds usually focus on the period of snowfalls, but studies on their for- mation and development stages are rare. The clouds over the northern Shandong Peninsula usually are the southern edge of the sea-effect snowstorm clouds, and its evolution is closely relative to the main clouds over the Bohai Sea. 12 sea-effect snowstorm events during 2001--2010 over the Bohai Sea are investigated. First, stationary satellites （GMS-5, GOES-9, MTSAT） infrared data is used to investigate the evolu- tion characteristics of snowstorm clouds, and combined with NECP FNL data, forming locations and mov- ing features of different processes are classified. In addition, routine observation is used to analyze the cor- responding relationship between snow and snowstorm clouds and the influence of the diabatic heating effect over the Bohai Sea. Finally, cloud profiling radar data of CloudSat are used to analyze the vertical structure and compositions of snowstorm clouds. The snowstorm clouds with different origins usually grow rapidly over the Bohai Sea, and among the clouds there are dense clouds with horizontal scale of 100--300 km in form of strips or a bulk, which is closely relative to the snowfall areas. The snowstorm clouds during their initial stages can be classified into three main categories according to their forming locations, near the Bohai Bay and the Laizhou Bay, the central part of the Bohai Sea, and near the Liaodong Bay. The movements of snowstorm clouds depend on winds at 850 hPa, and its domi- nant directions of movements can be classified into three types, by reference to the Bohai Strait move from west to east, from northwest to southeast, and from north to south, and finally the clouds reach the upper air of the northern Shandong Peninsula, which leads to its snowfalls. As cold winds move across long expanses of warmer water, the heat and moisture transport from the Bohai Sea warm surface upwards to its above cold air, defined as the Bohai sea-effect, results in the unsta- ble conditions over the Bohai Sea. And meanwhile, the unstable conditions improve the shallow convection to .intense, which results in the snowstorm clouds. The height of mature sea-effect snowstorm clouds can reach 4 km or so, and its ice-water mixture content has an average value of about 303 mg · m-3 , its maximum is about 600 mg ·m-3 and mainly distrib- utes at 2 km height, and additionally the maximum and average values of ice effective radius is about 120μm and 91 μm, respectively.