乌鲁木齐“4.24”短时降水和冰雹中小尺度特征对比分析

Comparative analysis on the medium and small scale characteristics of the “4.24” short-term rain and hail storms in Urumqi

利用常规资料以及NCEP再分析、微波辐射计、风廓线雷达、GPS大气可降水量及卫星红外云图资料,对2016年4月24日清晨和傍晚乌鲁木齐分别出现的短时降水和冰雹天气进行对比分析。结果表明:(1)短时降水和冰雹天气均与500 hPa中纬度低槽东移有关,短时降水发生在500 hPa槽底偏西急流、低层偏北气流形势下;冰雹发生在高、低空一致西北急流形势下。(2)在低空急流触发下产生短时降水,降水期间存在远距离水汽输送;乌鲁木齐前期短时降水是冰雹发生前低层增湿的主要原因,低空急流向底层下传是冰雹触发的关键因子。(3)短时降水和冰雹均发生在中尺度对流云团TBB梯度最大处;冰雹云内上升气流异常强盛,其温度和水汽密度廓线陡升较短时降水期间更加剧烈。

A short-term rain and hail storm,respectively,occurred before the early morning and the evening on 24 April 2016 in Urumqi.Comparative analysis on the medium and small scale characteristics of the short-term rain and hail storms were made by using conventional data,NCEP reanalysis data with 1°×1°resolution,microwave radiometerdata,wind profile radardata,GPS atmospheric precipitation water vapor and satellite infrared cloud image.The results are as follows.(1)The short-term rain and hail storms were associated with eastward trough at mid-latitude on 500 hPa.Short-term rainfall occurred under the situation of 500 hPa westerly jet at the trough bottom and low-level north air flow.The hail occurred undert he situation of northwest stream jet which consistently exists in both low-and high levels.(2)The short-term rainfall was triggered by low-level jet,which providesa long distance water vapor transport.The low-level moistening before hail occurred was associated with the prior short-term rainfall,and the hail was triggered by the downward transport of low-level jet.(3)Both the short-term rain and hail storms occurred where TBB has maximum gradient.Abnormal updraft within the hail cloud was stronger.Its temperature and water vapor density profiles rised more dramatically than those in the short-term rain storm.