河西走廊西部一次极端暴雨成因分析

Analysis on the Formation Mechanism of an Extreme Rainstorm in the West of Hexi Corridor

利用常规观测资料、自动加密气象站观测资料、FY-2G卫星云图资料、嘉峪关多普勒雷达探测资料、NCEP/NCAR1°×1°再分析资料和全球同化系统(GDAS)资料,并使用HYSPLIT模式模拟了暴雨区上空气块的后向轨迹,对2019年6月20日河西走廊西部极端暴雨天气的成因进行分析。结果表明:极端暴雨是在欧亚大陆中高纬稳定维持“两槽两脊”的大尺度环流背景下,高原低涡长时间稳定在河西走廊西部上空,偏东低空急流和高空急流耦合以及祁连山北坡地形阻挡共同作用下造成的;异常强盛的偏东低空急流受祁连山北坡地形阻挡叠加边界层偏西风侵入,在暴雨区触发和加强对流系统发展,产生短时强降水;水汽主要经对流层中低层偏东路径和中高层偏南路径输送至暴雨区上空,偏东路径水汽输送强度明显偏大,对暴雨贡献显著;西北地区东部和柴达木盆地是此次暴雨过程重要的近距离水汽源地,大部分气块途经时获得了水汽,比湿和相对湿度明显增大。

The formation mechanism of the extreme rainstorm in the west of Hexi Corridor on June 20,2019 was analyzed by using HYSPLIT to simulate the backward trajectory of the air mass over the rainstorm area,based on conventional observation data,automatic encryption station observation data,FY-2G satellite cloud image data,Jiayuguan Doppler radar data,NCEP/NCAR 1°×1°reanalysis data,and GDAS(Global Data Assimilation System)data.The results were as follows:The extreme rainstorm was mainly caused by the long-term existence of the stable plateau vortex over the western Hexi Corridor,the coupling of easterly low-level jet stream with the upper-level jet stream,and the topological barrier of the northern slope of the Qilian Mountains under the large-scale circulation background characterized“two-trough and two-ridge”in the middle and high latitude region of Eurasia.The abnormal strong easterly low-level jet was blocked by the northern slope of the Qilian Mountains and invaded by the westerly wind in boundary layer,which triggered and strengthened convection in the rainstorm area and produced short-time heavy rain.The water vapor was mainly transported to rainstorm area by east path in the middle-lower troposphere and south path in the middle-upper troposphere.The water vapor transported in the east path was obviously greater,which made a significant contribution to the rainstorm.The eastern of Northwest China and the Qaidam Basin were two important and close sources of water vapor during this rainstorm,where most of air masses could gain water vapor by passing through,while the specific humidity and relative humidity increased obviously.