新疆伊犁一次大风降雪天气的成因分析

Cause Analysis of a Gale and Snowfall in Yili, Xinjiang

采用常规观测资料、NCEP逐6小时再分析资料(0.25˚ ×0.25˚、1.0˚ ×1.0˚)、FY-2G卫星相当黑体温度资料,综合分析2021年1月22日至25日伊犁的大风降雪降温天气过程。此次天气的大尺度环流背景为500 hPa黑海高压脊推动深厚的西西伯利亚低槽东移南压影响伊犁。地面冷高压以西方路径入侵伊犁,冷锋两侧较强的气压梯度、变压梯度是造成大风的主要原因,850 hPa强烈的冷平流利于气压梯度的加大与维持。强降雪期间,2 g∙kg−1比湿线伸至850 hPa以上,湿层较厚,水汽通量散度辐合中心位于850 hPa及以下。850 hPa强烈的冷平流和低空西风急流利于降雪增强并维持。FY-2G卫星相当黑体温度TBB演变分析表明,降雪最强时段,TBB在−48℃~−52℃之间,TBB梯度较大。

A gale, snowfall and decreased temperature weather process from 22nd to 25th January 2021 in Yili was synthetically diagnosed based on conventional observation data, NCEP daily reanalysis data (0.25˚ ×0.25˚, 1.0˚ ×1.0˚), and FY-2G satellite Black Body Temperature data. The large-scale circulation background of this weather is that the 500 hPa black sea high ridge pushes the deep west Si-berian low trough eastward and influences Yili. The surface cold high invaded Yili with the western path, and the strong pressure gradient and pressure gradient on both sides of the cold front were the main reasons for the strong winds. The strong cold advection at 850 hPa was conducive to the increase and maintenance of pressure gradient. During heavy snowfall, the specific humidity line of 2 g∙kg−1 extends to more than 850 hPa, the wet layer is thicker, and the convergence center of moisture flux divergence is located at and below 850 hPa. The strong cold advection and low westerly jet at 850 hPa were conducive to the enhancement and maintenance of snowfall. The TBB evolution analysis of fairly black body temperature of FY-2G satellite shows that TBB is between −48˚C and −52˚C during the period of heaviest snowfall, with a large TBB gradient.