中文摘要：

2008年12月4～6日发生在渤海中东部及山东半岛地区的暴雪过程是一次异常强渤海海效应暴雪个例,利用中尺度数值模式RAMS4.4,以三维轨迹和物理量诊断分析相结合的方法研究了暴雪的三维运动结构及其演变特征。结果表明：（1）气块的三维轨迹分析揭示出各层冷空气进入渤海前后产生不同的运动路径,低层冷空气气块流经渤海时产生了上升运动,而中高层的气块基本不受影响,仍然维持原来的运动方向,表明暖海面对对流层低层冷空气的作用。（2）天气尺度系统产生的动力强迫与海效应两种作用相结合,是造成异常强降雪的重要原因。经向度大的高空槽发展、加深时,一方面槽前正涡度平流增强使得低空产生质量补偿辐合上升,为降雪提供了有利的动力条件;另一方面它引导冷空气向下向南爆发,造成海面上空温湿场垂直差异更大,形成较强的对流不稳定层结,海效应降雪增强,最强降雪就出现在高空槽影响期间。因此,高空槽是否过境可作为强降雪时段的预报着眼点。（3）对流层低层西北气流受到长白山南部及辽东半岛千山山脉的影响,转为东北风自渤海北部向南吹,在渤海与环境风场的西北风构成切变线,产生辐合上升运动,触发不稳定能量产生强降雪。在地面气压场上,相应的切变线表现为渤海至渤海海峡的等压线存在气旋性弯曲。该切变线是渤海海效应降雪的重要影响系统,其方向和位置决定了强降雪的落区及强度。（4）对流层中低层的垂直风向切变大小影响海效应降雪带的分布,垂直风向切变很小时使得低层热量和水汽汇合到狭窄的区域,有利于形成局地强降雪。

英文摘要：

Based on the simulated data of RAMS4.4 model,3-D trajectory analysis of air parcel and diagnosis,three-dimensional structure and development mechanism of an intense anomaly example of Bohai ocean-effect snowstorm which occurred in Shandong peninsula and Bohai on 4~16 December 2008 are analyzed.The results shows that the strong extremely cold air leads large difference between the sea and atmosphere.From 3-D trajectory analysis,the air parcel in Bohai low level goes upward,but the middle and upper air parcels remain the original direction.Dynamical force of weather scale system and ocean-effect play the common action on the snowstorm.Upper trough deepening has two actions.One,compensatory assending motion caused by positive vorticity advection is favorable to more snowfall.Another,it can lead cold air to outbreak southward.Then more instable layer will bring more ocean-effect snowstorm.In result,the strongest snowfall occurred during the upper trough influence.So it is the importance to this phenomenon in the forecast operation.In the low troposphere,shear line between the northwest and northeast wind decide the intensity and position of snowfall.What′s more,the weak vertical wind direction is helpful to form strong snowfall in local area.