2021年11月18~20日乌鲁木齐机场长时间降雪特征分析
Analysis of Long-Term Snowfall Characteristics of Urumqi Airport from November 18 to 20, 2021

文章利用乌鲁木齐机场自动气象观测系统观测资料及美国环境预报中心(NCEP)的FNL (Final Operational Global Analysis) 0.25 × 0.25再分析资料对2021年11月18~20日乌鲁木齐机场连续降雪天气过程进行研究分析，总结此类天气过程特征，为今后预报长时间降雪提供一定的参考意见，结果表明：1) 此次连续降雪出现在中亚低涡位置偏北，稳定少动，不断分裂弱短波影响新疆地区的环流背景。2) 当水汽通量散度在700 hPa以下出现明显的辐合中心时，有利于出现中雪；当相对湿度集中在某一时段500 hPa以下，值高于85%以上时，配合暖平流，有利于持续性降雪。3) 高层辐散，低层辐合的形势有利于抽吸作用，上升运动加强，提供有利的动力条件，冷平流快速南下有利于乌鲁木齐机场出现中雪。低层辐散、高层辐合不利于抬升机制，有利于降雪结束。4) 云系结构紧密，强度强，移速快时，降水时间较短，但降水集中且降水量较大；云系结构松散，强度弱，移动缓慢，降水时间较长，但量级偏小。
This paper uses the observation data of Urumqi airport automatic meteorological observation system and FNL (Final Operational Global Analysis) 0.25 of American Environmental Prediction Center (NCEP) × 0.25 reanalysis data to study and analyze the continuous snowfall weather process of Urumqi airport from November 18 to 20, 2021, summarize the characteristics of such weather process, and pass some reference opinions for predicting long-term snowfall in the future. Results show: 1) The continuous snowfall is mainly due to the northward position of the Central Asian vortex, which is stable and less moving, and constantly splitting the weak short wave to affect Xinjiang; 2) When the divergence of water vapor flux is below 700 hPa, there is an obvious convergence center, which is conducive to moderate snow. When the relative humidity is concentrated below 500 hPa in a certain period, and the relative humidity is higher than 85%, combined with warm advection, it is conducive to continuous snowfall; 3) The situation of high-level divergence and low-level convergence is conducive to suction, strong updraft and good dynamic conditions. The rapid southward movement of cold advection is also conducive to moderate snow in Urumqi airport; Low level divergence and high-level convergence are not conducive to the lifting mechanism and conductive to the end of snowfall; 4) The cloud system is dense, complete and strong, but the moving speed is fast, the precipitation time is short, but the precipitation is concentrated and the precipitation is large; The cloud system is scattered, the intensity is weak, the moving speed is slow, and the precipitation time is long, but the magnitude is small.