川西高原一次强对流天气过程的中尺度特征分析

Analysis on the Mesoscale Characteristics of a Severe Convection Process over Western Sichuan Plateau

利用常规、非常规观测资料和NCEP1°×1°再分析资料,分析了2016年7月21日川西高原中部甘孜州一次强对流天气的环境条件和中尺度对流特征。结果表明:(1)地面中尺度辐合线是本次强对流天气过程的主要触发系统。过程期间,高原切变线东移伴随中上层干冷空气扩散南下以及低层暖湿气流北上,整个气层形成“上冷下暖”的不稳定结构并有明显的垂直风切变,有利于强对流的发生。(2)卫星云图上可识别出典型的MCS结构,其对流中心强度TBB在-70℃以下,这些TBB≤-70℃的对流中心与强对流天气区域对应较好,对预报具有较好的指示意义。(3)雷达回波强度最大值为60 dBZ,最大回波顶高为16 km,雷达径向速度图上可识别出弱中尺度气旋。大气垂直累积液态含水量最大值超过55 kg·m^(-2),为强降水的发生提供了充沛的水汽条件。

Based on conventional observation data,regional automatic station data,Doppler weather radar products,FY4A satellite cloud images,NCEP 1°×1°reanalysis data and so on,the environmental conditions and mesoscale convective characteristics of a strong convective weather in Ganzi Prefecture on July 21,2016 were analyzed.Results are as follows:(1)The shear line of the plateau moved eastwards,accompanied by the diffusion of cold air in the middle and upper layers and the northward movement of warm and wet air in the lower layers.The combination of the systems made the whole layer form an unstable structure of“upper-layer-cold and the lower-layer-warm”and strong vertical wind shear,which was conducive to the occurrence of strong convection.(2)The typical MCS structure could be identified on the satellite cloud image,and its convective center strength TBB was below-70℃.The convective centers with TBB≤-70℃corresponded well with the strong convective weather area,which had a good indication for the forecast.(3)The strongest value of radar echo intensity could reach above 60 dBZ,and the maximum echo top height could reach above 16km.Weak mesoscale cyclones could be identified in the radial velocity diagram of radar.The maximum liquid water content accumulated vertically in the atmosphere exceeded 55 kg·m^(-2),which provided abundant water vapor conditions for the occurrence of heavy precipitation.