摘要:2014年5月31日北京发生一次雷暴大风过程。以雷达资料同化结果为初始场，对此次过程进行高分辨率数值模拟。采用非静力平衡和非地转平衡的经向动量方程和质量权重动能方程，利用模拟资料，对雷暴大风过程中经向动量和质量权重动能进行收支分析，以此来研究雷暴过程中对流层中低层动量通量和动能通量输送特征，讨论地面大风的可能成因。分析结果表明，在对流层中低层，经向动量通量散度是影响经向动量局地变化的主要强迫项。雷暴系统后部的入流把中低层的经向动量倾斜向下输送，系统前部对流云区中低层的下沉气流也向下输送经向动量。这两支下传动量通量先后与近地面经向动量的水平通量汇合，向系统前沿输送经向动量。在北京西北部地形阻挡作用下，经向动量通量在系统前端近地面辐合，促进那里的经向动量局地增长，有利于增强那里的南风。质量动能收支的特征与经向动量收支类似，在近地面层质量动能的局地变化主要是由质量动能通量散度引起的。系统后部入流把中层质量动能向下传输到近地面层，然后与近地面质量动能的水平通量汇合，向系统前沿输送质量动能。相对来说，近地面层经向动量和质量动能的水平通量比下传通量更重要，这主要与低层较强的东南急流有关。
关键词:雷暴大风/
经向动量/
质量权重动能/
动量下传
Abstract:A thunderstorm is a severe convective weather that can result in weather disaster.To analyze the possible reason for surface gusts associated with thunderstorms, a high resolution numerical simulation of a severe thunderstorm occurred in Beijing on 31 May 2014 was carried out.Based on the equations of momentum and mass weighted kinetic energy, the budget of meridional momentum and kinetic energy was investigated with the simulation output data.The fluxes transport of meridional momentum and mass kinetic energy was examined.It was shown that local changes of meridional momentum and mass kinetic energy near the surface were primarily dominated by the divergence of meridional momentum and mass kinetic energy fluxes.In the middle and lower troposphere, the rear inflow in the stratiform zone and the descending flow in the convective zone transported downwards meridional momentum and mass kinetic energy, which were converged with horizontal fluxes of meridional momentum and mass kinetic energy near the surface.The converged fluxes were then horizontally transported to the front of the convective zone.Blocked by topography to the northwest of Beijing, the combined fluxes converged in the front, and intensified the southerly wind gust on the ground.Similar to meridional momentum, local changes in mass kinetic energy near the surface were primarily dominated by the divergence of mass kinetic energy flux.The rear inflow in the middle troposphere brought mass kinetic energy downward to the ground layer, and merged with the horizontal flux of mass kinetic energy near the surface.Relatively speaking, the horizontal flux of the meridional momentum and the mass kinetic energy of the near ground layer are mainly related to strong low-level southeasterly jet and more important than the downward flux transport.
Key words:Thunderstorm/
Meridional momentum/
Mass kinetic energy/
Downward transportation of momentum
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