2020年11月乌鲁木齐机场一次强降雪天气过程及特征分析

Analysis of the Weather Process and Characteristics of a Heavy Snowfall at Urumqi Airport in November 2020

摘要: 利用常规气象观测资料、NECP FNL 0.25˚ × 0.25˚再分析数据、微波辐射计等资料，对2020年11月29日~30日乌鲁木齐机场强降雪天气过程的环流形势、水汽条件及动力条件等方面进行分析。结果表明：此次强降雪天气主要是巴湖低涡槽、中高层西南急流、低层西北急流、低层风切变、地面弱冷锋和地形强迫抬升等系统共同作用造成。降雪前，来自阿拉伯海和黑海的水汽在里海以东汇合后，随西南急流入侵北疆，随后由低层西北急流接力输送影响天山北麓一带。低空850 hPa上θ_se高值中心、低层逆温的存在，有利于强降雪区的不稳定能量累积。强降雪期间，机场低层850 hPa位于θ_se等值线相对密集处的能量锋区内，低层逆温被中层冷空气侵入，不稳定能量释放。高层辐散、中低层辐合和垂直次级环流形成和加强使降雪增幅，高层辐散中心、中低层辐合中心出现的时段与强降雪时段重合。

Abstract: Using conventional meteorological observation data, NECP FNL 0.25˚ × 0.25˚ reanalysis data, mi-crowave radiometer and other data, the circulation situation, water vapor conditions and dynamic conditions of heavy snowfall weather at Urumqi Airport from November 29 to 30, 2020 were analyzed. The results show that the heavy snowfall is mainly caused by the combined effect of the low vortex trough of Ba Lake, the middle and upper southwest jet stream, the low northwest jet stream, the low-level wind shear, the weak cold front on the ground and the forced lifting of the terrain. Before snowfall, water vapor from the Arabian Sea and the Black Sea converges east of the Caspian Sea, invades northern Xinjiang with the southwest jet stream, and is then relayed by the low-level northwest jet stream to affect the northern foothills of the Tianshan Mountains. The presence of high θ_se center and low-level temperature inversion on 850 hPa at low altitude is conducive to the unstable energy accumulation in heavy snowfall areas. During the heavy snowfall, the low level of the airport 850 hPa is located in the energy front area at the relatively dense θ_se contour, and the low-level temperature inversion is invaded by the cold air in the middle layer, and the unstable energy is released. High-level divergence, middle and low-level convergence and vertical secondary circulation increase the snowfall amplitude, and the periods of high-level divergence centers, mid-dle and low-level convergence centers coincide with the heavy snowfall periods.