复杂地形强降雪过程中垂直运动诊断分析

利用WRF模式对2018年11月30日伊犁河谷和天山北坡强降雪过程进行数值模拟，并分析复杂地形强降雪过程垂直速度和垂直动能变化机制。研究表明，冷锋过境造成地表气压升高，干空气气柱质量增大，从而导致垂直气压梯度力和干空气气柱浮力发生变化，进而引起垂直运动发生发展。垂直速度局地时间变化主要取决于扰动垂直气压梯度力、水物质拖曳力和扰动干空气浮力。在天山北坡，气流过山时，迎风坡的扰动垂直气压梯度力较大，扰动干空气浮力较小，二者合力促进上升运动；在背风坡，扰动垂直气压梯度力和扰动空气浮力形成向下的合力，产生下沉加速度，导致背风坡下沉大风。扰动垂直气压梯度力做功和扰动干空气浮力做功情况基本相反，背风坡扰动垂直气压梯度力和综合强迫做功项抑制垂直动能，扰动干空气浮力和水物质拖曳力做功项增强垂直动能。此外，扰动垂直气压梯度力和扰动干空气浮力做功项主要出现在中低层，水物质拖曳力做功项主要位于低层，平缓地形处的综合强迫做功明显小于地形复杂处。

Diagnosis and Analysis of Vertical Motion during Complex Topographical Heavy Snowfall

The WRF (Weather Research and Forecasting) model was used to numerically simulate the heavy snowfall process that occurred on 30 November 2018, in the Ili River valley and the northern slope of the Tianshan mountains and to analyze the vertical velocity and vertical kinetic energy change mechanism of heavy snowfall under complex terrain. Studies have shown that the passage of a cold front increases the surface pressure and the dry air mass in the column, leading to changes in the vertical pressure gradient force and the dry air column buoyancy, which in turn causes the development of vertical motion. The local time variation of vertical velocity mainly depends on the perturbation vertical pressure gradient force, drag force of the water substance, and perturbation dry air buoyancy. When the airflow crosses the north slope of the Tianshan mountains, the perturbation vertical pressure gradient force on the windward slope becomes larger, and the perturbation dry air buoyancy becomes smaller, promoting the upward movement. On the leeward slope, the perturbation vertical pressure gradient force and the perturbation air buoyancy form a downward total force produce sinking acceleration, which results in a strong sinking gale of the leeward slope. The work done by the perturbation vertical pressure gradient force is basically contrary to the work done by the perturbation dry air buoyancy. On the leeward slope, the work items of the perturbation vertical air pressure gradient force and the comprehensive force are to suppress the vertical kinetic energy, while the work item of the perturbation dry air buoyancy and the drag force of the water substance enhances the vertical kinetic energy. In addition, the work items of the perturbation vertical pressure gradient force and the perturbation dry air buoyancy mainly appear in the middle and low layers, the work items of the water material drag force are mainly located in the lower layers, and the comprehensive force work in flat terrain is significantly less than that in complex terrain.