芙蓉江上游一次特大暴雨成因及地形影响作用分析

Analysis of the Causes of a Extremely Heavy Rainstorm in the Upper Reaches of Furong River and the Role of Topographic Influence

为探究2021年8月8日遵义市区域性暴雨天气过程中芙蓉江上游局地特大暴雨成因及地形的影响作用,该文利用探空资料、地面自动站观测资料、多普勒雷达观测资料及ERA5再分析资料,采用常规诊断方法对此次过程进行了详细分析。结果表明:(1)受地形影响,强降雨集中发生在芙蓉江上游峡谷内,200 mm以上的降雨发生在峡谷左侧山脉上,100 mm以上的降雨发生在峡谷底部。(2)副高控制及南北两支水汽输送在遵义上空汇聚,形成高温高湿的大气环境,低层及地面锋区南压触发对流,夜间副高增强使低层系统长时间维持,导致区域性暴雨产生。(3)中心强度在55~60 dBz的低质心降水回波带长时间维持少动是造成本次区域性暴雨天气的直接原因。峡谷左侧山脉上的回波单体发展旺盛,回波顶高在15 km以上,具有悬垂结构及小尺度辐合区。能量耗尽后峡谷内中心强度在55 dBz的低质心降水回波发展导致峡谷底部出现大暴雨天气。(4)大气不稳定性最强时,系统长时间维持导致南北两股气流汇入峡谷中产生狭管效应,峡谷深处出现小尺度气旋性环流使对流增强,由此引发峡谷山脉上特大暴雨。不稳定能量耗散后,冷空气越过山脉叠加在峡谷底部暖空气之上,使大气不稳定增强,导致峡谷底部产生大暴雨。

To investigate the causes of localized extremely heavy rainfall in the upper part of Furong River and the influence of topography during the regional rainstorm in Zunyi City on August 8,2021,the heavy rain process was analyzed by conventional diagnostic methods based on the upper-air observation data,automatic station data,Doppler radar observation data and ERA5 hourly reanalysis data.The results show that:(1)the topographic distribution of heavy rainfall is distinctive,concentrated in the upper Furong River gorge,with more than 200 mm of rainfall occurring on the mountains to the left of the gorge and more than 100 mm at the bottom of the gorge.(2)The control of subtropical high pressure and the transport of water vapour from the north and south converge over Zunyi to form a high temperature and high humidity atmospheric environment,with convection triggered by the southward pressure of low-level and ground frontal areas,and the strengthening of subtropical high pressure at night to maintain the low-level system for a long time,leading to the generation of regional rainstorms.(3)The low-mass precipitation echo zone with a central intensity of 55~60 dBz maintaining little movement for a long time is the direct cause of this regional stormy weather.The echoes on the mountain range to the left of the canyon are highly developed,with the top height of the echoes above 15 km,with overhanging structures and small-scale convergence zones.The development of low-mass precipitation echoes with a central intensity of 55 dBz in the canyon after energy depletion resulted in heavy rainfall events at the bottom of the canyon.(4)At the height of atmospheric instability,the system is maintained over a long period of time resulting in the convergence of the north and south flows into the canyon creating a narrow tube effect and an enhanced convection due to small-scale cyclonic circulation deep in the canyon,which leads to exceptionally heavy rainfall over the canyon mountains.After the instability energy is dissipated,cold air crosses the mountain range and superimposes on the warm air at the bottom of the canyon,resulting in enhanced atmospheric instability and heavy rainfall at the bottom of the canyon.