南疆西部一次罕见大暴雪过程分析

Analysis on Rare Snowstorm in West of Southern Xinjiang

利用高分辨率卫星资料、多普勒雷达产品、常规观测和再分析资料,分析了2011年2月25-28日南疆西部一次历史罕见大暴雪天气过程的多尺度特征和物理量配置。结果表明:中亚低涡是此次大暴雪天气过程的主要影响系统,强降雪期间高、低空风场配置与夏季南疆西部典型暴雨过程类似。冬季低空偏东急流中心最大风速超过20 m·s^(-1)较为罕见。南疆西部三面环山,低空偏东急流先于高空西南急流12 h在南疆盆地东部建立,有利于将南疆盆地东部的水汽向西输送并在南疆西部汇合;受地形影响低层气流向西汇合过程中也有利于垂直上升运动的生成。大暴雪过程中存在偏西、偏东和偏南三支异常水汽输送,其中偏东水汽输送最为重要。两个β中尺度云团是造成大暴雪的主要系统,强降雪出现在云团内部局地增强阶段。大暴雪过程中以层状云雷达回波为主,局地回波强度梯度较大、边界清晰,具有一定短时弱对流特征。

Based on the data of FY-2E Stationary Meteorological Satellite from China Meteorological Agency(CMA),Doppler radar products,the reanalysis dataset from the NCEP/NCAR reanalysis project and convention observation,the caused mechanism of a rare snowstorm event in the west of southern Xinjiang was analyzed.The results show that the rare snowstorm occurred on the background of central Asia trough to south cutting cortex low.The favorable configuration of three jet streams in snowstorm is similar as in rainstorm.It is unusual that the low-level jet's speed exceeds 20 m·s^(-1) in winter.The formation time of low-level jet earlier than the highlevel jet 12 hours plays an important role in the snowstorm.Favorable configuration about the jet streams of higher southwest and lower east to provide the power and water condition for the snowstorm.Water vapor source payments calculation analyses show that there are three parts of water vapor sources,the first is thick central Asian vortex itself carry water vapor form southwest airflow,the second is by east of airflow water vapor concentration and convergence form southern basin on middle low level,the third is conveying the relay water vapor that warm-moist from the coastal margin of southeast China.The water vapor transmission from the east airflow is more than others.The two meso-β-scale cold clouds are the main systems for the severe snowstorm.The mesoscale cloud enhanced in local is the direct effect of heavy snow.The main radar echo during the snowstorm is stratiform cloud.In local place the radar echo intensity gradient is large and has the short-term weak convection characteristic.