2017年6月4—5日张掖市暴雨过程分析

Analysis of Heavy Rainfall Process in Zhangye City During June 4-5,2017

本文利用常规地面与高空观测资料、区域站降水资料、卫星云图和雷达资料对2017年6月4—5日张掖市暴雨过程进行分析。结果表明,此次暴雨过程呈北槽南涡型,是西北地区出现强降水的典型环流形势,500 h Pa低涡和低槽、700 h Pa切变线及地面冷锋造成强烈的上升运动,是此次过程的主要影响系统。中尺度分析表明,较好的抬升条件、充沛的水汽、大气层结处于不稳定状态,有利于强对流和强降水的发生。副热带西风急流云系和高原切变云系在河西上空合并发展,且稳定维持,造成张掖市暴雨天气。从雷达回波图可以看出,辐合线和强回波带稳定少动,维持在民乐县上空,是造成此次暴雨天气过程的主要原因。此次暴雨过程的物理量场表现较好,低层辐合、高层辐散的配置为降水提供了强烈的上升气流,而较强的上升运动为强降水的产生提供了必要的动力条件;500 h Pa和700 h Pa偏南暖湿气流将孟加拉湾和南海的水汽输送至河西地区以及水汽通量散度的辐合,均为降水提供了源源不断的水汽;假相当位温高能舌为强降水的发生发展提供了不稳定能量条件。

Using conventional surface and upper-air observation data, regional station precipitation data, satellite cloud map data and radar echo data, the heavy rain process in Zhangye City during June 4-5,2017 was analyzed.The results showed that the torrential rain process was a north trough and south vortex type, and it was a typical circulation in the northwest region where heavy rainfall occun＇ed.The vortex and low trough at 500 hPa, the shear line at 700 hPa and the ground cold front caused a strong ascending motion,which was the main influence system of this process.The mesoscale analysis showed that, better uplift conditions, abundant water vapor, and unstable atmospheric stratification were conducive to the occun＇ence of strong convection and heavy ranffall.The subtropical westerly jet cloud system and the plateau shear cloud system merged and developed over Hexi, and remained stable,causing heavy rain in Zhangye City.From the radar echo diagram,the convergence line and the strong echo zone were stable and remained above the Minle County,which was the main reason for the heavy rain weather process.The physical volume field dm＇ing the heavy rain process performed well.The low-level convergence and high-level divergence cmffiguration provided strong updrafts for precipitation, and the strong ascending movement provided the necessary dynamic conditions for the generation of heavy precipitation.The southerly warm-and-wet air at 500 hPa and 700 hPa which transported the water vapor from the Bay of Bengal and the South China Sea to the Hexi region, and the convergence of water vapor flux divergence,both provided a steady stream of water vapor.The high energy tongue provided an unstable energy condition for the occurrence and development of heavy precipitation.