西天山南麓两次暴雪过程对比分析

Comparative Analysis of Two Blizzard Processes in the South Slope of the Western Tianshan Mountains

利用常规气象观测、FY-4A卫星及ERA5再分析数据,对比分析2021年2月25—27日(过程I)和4月1—4日(过程II)西天山南麓阿克苏地区拜城县2次暴雪过程成因。结果表明:两次暴雨过程均在中亚低值系统影响下发生,300 hPa偏西急流、500 hPa低涡(低槽)、850 hPa偏东急流、地面冷高压冷锋及暴雪区上空垂直环流的发展是形成暴雪的主要动力机制;均有偏西和西南路径的水汽输送,水汽强辐合出现在700 hPa;降雪期间TBB极值、<-30℃的维持时间及>-5℃对降雪量级、持续时间及降水相态预报有指示意义。不同点主要表现在:过程I为中亚低槽快速东移型,偏东急流仅在850 hPa,急流强度较弱且位置偏南;过程II为中亚低涡缓慢东移型,700、850 hPa有明显偏东急流且持续时间长,位置西伸至阿克苏地区北部;过程II上升运动中心更接近暴雪中心,且强度强、伸展高、持续时间长,冷暖交汇更剧烈,偏东水汽输送明显且辐合强度更强、辐合持续时间更长。

This study used the data of conventional observation,FY-4A satellite and ERA5 reanalysis,and analyzed the causative factors behind two heavy snowfall events that occurred in Baicheng County from February 25 to 27,2010(process I)and from April 1 to 4,2010(process II).The results show that both snowstorms are caused by Central Asian low-pressure system,300 hPa westerly jet,500 hPa vortex(trough),850 hPa easterly jet,surface cold high pressure,cold front and vertical circulation over blizzard areas are the main dynamic mechanism of two snowstorms;water vapor is transported from west and southwest path,the strong convergence of water vapor at 700 hPa,during the period of snowfall,the extremes of TBB,the maintenance times of TBB less than-30℃and the occurrence of TBB greater than-5℃provide reliable indications for predicting the orders,duration and phase of snowfall.The differences of two snowstorms are as follows:process I is characterized by the rapidly eastward-moving of the Central Asian trough with easterly jet streams confined to 850 hPa,the jet is weaker and locates southward.In contrast,Process II is characterized by the slow eastward-moving of Central Asian vortex,significant easterly jets appear at 700 hPa and 850 hPa for a long duration,the jets are located in northern Aksu.Compared to process I,the upward movement center of process II is closer to blizzard center,process II has stronger ascending motion intensity,the higher extension height and longer duration;there is more intense cold-warm convergence.Additionally,there is a more pronounced easterly water vapor transport with stronger convergence and a more prolonged duration.