甘肃陇南两次暴雨天气过程对比分析

Comparative analysis of two rainstorm cases in Longnan of Gansu Province

2017年8月甘肃陇南出现暴雨天气,礼县、武都气象站24 h降水量突破历史极值,极端性和局地性突出。应用欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第5代全球大气再分析产品ERA5、雷达资料及地面加密观测资料,对2017年8月6—7日、19—20日发生在甘肃省陇南地区的2次暴雨过程进行对比分析,重点讨论2次过程的环流背景以及强降水时段雷达反射率因子、径向速度、物理量特征。结果表明,2次暴雨过程均发生在西风槽偏北气流与中低层偏南暖湿气流交汇处,但是2次过程的主要影响系统及触发条件不同;雷达回波显示8月6—7日由冷式切变线引起的暴雨系统对流性较强,反射率因子值较高、中心高度较低,降水率较大,持续时间短;19—20日暖区降水的反射率因子值较低、中心高度较高,降水率较小,持续时间较长。

In August 2017,there were torrential rains in Longnan,Gansu Province.The 24-hour precipitation at the Li County and Wudu weather stations broke through the historical extreme values,with obvious extremes and localities.Based on ERA5 reanalysis data of the European Centre for Medium-Range Weather Forecasts,radar data and ground observation data,a comparative analysis of two heavy rain cases that occurred in Longnan,Gansu Province from 6 to 7 and from 19 to 20 August 2017 are carried out.The circula⁃tion background and the radar reflectivity factor,radial velocity and physical quantity characteristics of the heavy rainfall processes of the two cases are discussed emphatically.The results show that the two rainstorms all occurred at the intersection between the northerly airflow in the westerly trough and the southerly warm and humid airflow in the middle-lower layer,but the main impact systems and trig⁃gering conditions are different.The radar echo shows from August 6 to 7,the convective system caused by the cold shear line is stron⁃ger,with higher reflectivity factor,lower central height,higher precipitation rate and shorter duration.The reflectivity factor of precipita⁃tion in warm region from August 19 to 20 is lower,and its central height is higher,and the precipitation rate is smaller,and the precipi⁃tation process maintained for longer time.