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

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 formation 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 evolution characteristics of snowstorm clouds, and combined with NECP FNL data, forming locations and moving features of different processes are classified. In addition, routine observation is used to analyze the corresponding 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 dominant 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 unstable 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 distributes at 2 km height, and additionally the maximum and average values of ice effective radius is about 120 μm and 91 μm, respectively.