青海东南部一次局地强对流天气成因分析

An Analysis of the Causes of a Local Strong Convective Weather in the Southeast of Qinghai

利用常规气象观测资料、自动站资料、云图和数值预报资料,对2009年7月20暴雨天气进行分析。结果表明:这是一次伴有局地冰雹、雷暴和大风的强对流天气,短时强降水造成的局地暴雨,降水持续时间短且集中。天气形势是副热带高压西北侧西南暖湿气流午后热对流造成的;地面中小尺度辐合线以及午后热力抬升共同触发。Tlogp图反映上干下湿,能量CAPE值达98.8 J/kg,有强的不稳定,风场为强盛的西南风。水汽充沛,暴雨区处于西南暖湿气流水汽输送带中,地面露点增达14℃,为全省中心,比湿大值在东南部中心达11 g/kg,水汽通量辐合较强[-14 g/(m·s)],自青海湖向(东南)暴雨区移动。暴雨区在降水过程中地面至高空均为强上升区,上升气流强且深厚。午后副高外围生成的对流云带东移,中小尺度对流云团合并,TBB高值中心达220 k。EC模式预报副热带高压整体偏东,与实况差异大,在今后的预报中,注意模式预报误差。

Using conventional meteorological observation data,automatic station data,cloud images and numerical forecast data to analyze the heavy rain on July 20,2009,the results showed that:this was a severe convective weather accompanied by local hail,thunderstorms and strong winds,local heavy rain caused by short-term heavy rainfall,and the rainfall duration was short and concentrated.The weather situation is caused by the afternoon thermal convection of the warm humid air from the southwest on the northwest side of the subtropical high;the surface meso-small-scale convergence line and the afternoon thermal uplift are both triggered.The Tlogp diagram reflects the upper and lower wetness,the energy CAPE value is 98.8 J/kg,there is strong instability,and the wind field is a strong southwest wind.Water vapor is abundant.The rainstorm area is located in the southwest warm and humid air vapor conveyor belt.The ground dew point has increased to 14℃.It is the center of the province.The specific humidity is 11 g/kg in the southeast center.The water vapor flux has a strong convergence[-14/g(m·s)],moving from Qinghai Lake to the(southeast)heavy rain area.During the precipitation process,the rainstorm area is a strong ascending area from the ground to the upper air,and the updraft is strong and deep.In the afternoon,the convective cloud belt generated on the periphery of the subtropical high moves eastward,and the small and medium-sized convective cloud clusters merges,and the TBB high-value center reaches 220 k.The EC model forecasts the subtropical high to be easterly as a whole,which is quite different from the actual situation.In future forecasts,attention should be paid to model forecast errors.