河西走廊西部一次暴雨过程的水汽特征分析

Analysis on Water Vapor Characteristics during a Rainstorm in Western Hexi Corridor

文章利用常规气象观测资料和GdAS、NCEP/NCAR再分析资料,对2019年5月5—7日河西走廊西部暴雨天气过程的水汽特征进行分析与讨论。结果表明:本次暴雨是由200 hPa高空急流、500 hPa短波槽、700 hPa低空急流和祁连山地形阻挡共同作用下产生的;降雨强盛时期暴雨区对流层低层维持6 g·kg^(-1)的比湿和80%以上相对湿度;水汽主要由两路异常远距离水汽通道输送,分别是蒙古高压低层偏东回流气流引导的偏东路径,南支槽以及高原切变引导的偏南路径;暴雨区水汽主要来源于对流层中低层东边界,中低层东边界水汽输入贡献率达81.2%;利用HYSPLIT模型后向72 h模拟发现,暴雨区水汽来源主要有3条路径,分别是低层偏东路径、中层偏南路径和高层偏西路径,对应的水汽源地为蒙古国东南部、新疆东部和里海;高层300 hPa干冷空气侵入中层,与中低层上升气流在暴雨区上空辐合交汇,对降水有一定的加强作用。

Based on conventional observation data,GdAS and NECP/NCAR reanalysis data,the characteristics of rainstorm water vapor in the west of Hexi corridor on 5-7 May 2019 were analyzed.The results are as follow:The rainstorm was produced by combined action of 200 hPa upper-level jet stream,500 hPa short-wave trough,700 hPa low-level jet stream and Qilian mountain terrain barrier;The specific humidity of 6 g·kg^(-1) and over 80%relative humidity were maintained in the lower troposphere of rainstorm area during the heavy rainfall;The water vapor was mainly transported by two abnormal long-distance water vapor channels,which were east path guided by easterly backflow in the low layer of Mongolian high pressure and south path jointly guided by southern branch trough and plateau shear;The water vapor over rainstorm area mainly came from the eastern boundary in middle-lower layer troposphere.The contribution rate of water vapor input at the east boundary of the middle-low layer was 81.2%;The backward 72h simulated results by HYSPLIT model showed that the water vapor sources in rainstorm area mainly consisted of three paths,which are the low layer east path,middle layer south path and high layer west path.The corresponding water vapor sources are southeastern Mongolia,eastern Xinjiang,and the Caspian Sea;The upper 300 hPa dry cold air invaded middle layer,converged and intermingled with the updraft from middle-lower layer over the rainstorm area,which had a certain strengthening effect on the precipitation.