Institute of Atmospheric Physics,Chinese Academy of Sciences
The WRF model was used to numerically simulate the heavy snowfall process in the Ili River Valley and the Northern slope of Tianshan Mountains on November 30, 2018, and 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 causes an increase in surface pressure and an increase in the dry air mass in column, which leads 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 Tianshan Mountains North Slope, the perturbation vertical pressure gradient force on the windward slope is larger, and the perturbation dry air buoyancy is smaller, which promotes the upward movement; On the leeward slope, the perturbation vertical pressure gradient force and the perturbation air buoyancy form a downward total force produces sinking acceleration, which causes the leeward slope strong sinking gale. The work done by the perturbation vertical pressure gradient force is basically opposite to the work done by the perturbation dry air buoyancy. On leeward slope, the work items of the perturbation vertical air pressure gradient force and the comprehensive force are to suppress the vertical kinetic energy, when 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 perturbation vertical pressure gradient force and the perturbation dry air buoyancy work items mainly appear in the middle and low layers, the water material drag force work items are mainly located in the lower layers, and the comprehensive force work in flat terrain is significantly less than that in complex terrain.