【作者】 杨成芳； 周兵； 陈优宽；

【Author】 Yang Chengfang1) Zhou Bing2) Chen Youkuan1) 1)(Shandong Meteorological Center, Jinan 250031) 2)(National Meteorological Center, Beijing 100081)

【机构】 山东省气象中心； 国家气象中心；

【摘要】 利用多普勒雷达资料和RAMS模式对2005年发生在山东半岛北部沿海的一次冷流暴雪进行了中尺度特征分析。结果表明:这次暴雪发生在西北气流、较大海气温差和半岛的丘陵地形特殊条件下,其降雪机制与美国大湖效应降雪类似。冷流暴雪在多普勒雷达速度图上表现为长生命史的逆风区。数值模拟结果显示,模式对沿海地区的冷流降雪过程具有较好的预报能力,可以很好地模拟出强冷流降雪的落区和大气环流形势的演变,证实了暴雪中尺度垂直环流的存在。暴雪出现在上升运动增强和逆风区维持的阶段。更多还原

【Abstract】 In this paper, detailed analysis was made to reveal the radar character and Mesoscale character of cold airflow snowstorm, by using the Yantai Doppler radar data located in north coastal area of Shandong Peninsula and Mesoscale Model RAMS on cold airflow snowstorm occurred on 6 December 2005 in Yantai. Long term Adverse Wind Regions were found in Doppler radar velocity images, which is the most remarkable character. Adverse Wind Regions had persisted for nearly six hours in integrated form. The corresponding strong base reflectivity in large range passed Yantai from North-west to South-east like a belt. Strong snow fell in the left of Adverse Wind Regions. The center of snowstorm located in the area of Adverse Wind Regions. The data from automatic meteorology observation station showed latitudinal shear front. Cyclonic circulation coincided with Adverse Wind Regions. Mesoscale Model RAMS could succeeded simulating the development of cold airflow snowstorm. The results showed that the model snowfall was agreement with the fact snowfall in the range, intensity and center. The model flow and temperature in every phrase and level greatly indicated the evolvement of background of cold airflow snowstorm. So the model results could be used for the mesoscale analysis. There was vergence and strong updraft at lower level while reversed in the mid level near Yantai. So a vertical circulation formed, which was good for more snowfall. Development of vertical wind, vertical velocity and relative vortex also proved the existence of the mesoscale vertical circulation. Adverse Wind Regions developed when updraft raised. Compared with summer rainstorm, The core of vertical updraft was evidently lower and their intensity were weaker. The hill in Shandong Peninsula lifted the updraft to trigger the snowstorm. Evolvement of cold air and wind indicated that snowfall formed when cold air from north met with warm and wet air near the surface of sea. Snowstorm occurred during the updraft raised and Adverse Wind Regions developed. So there were two conclusions. Firstly, north-west airflow, large sea-air temperature difference and special hill topography caused the snowstorm. Its mechanism was similar with the lake-effect snow events in the Great Lakes region of North America. When cold and dry air flew along the surface of warm sea, large sea-air temperature difference would exist, which caused unsteady in air layer. That was why low cloud produced snowfall. The distributing of snowfall was of remarkable regional character, which was related with special hill topography. Secondly, Shear in low layer and mesoscale vertical circulation was proved important to snowstorm. Special hill topography leaded to strong updraft, which was helpful to obvious snowfall. The core of updraft was lower than rainstorm. Snowstorm occurred during updraft increased and Adverse Wind Regions developed. Long term Adverse Wind Regions in Doppler radar velocity images showed Mesoscale ve更多还原