芜湖市一次引发严重内涝暴雨过程的水汽输送特征

Water vapor transport characteristics of a rainstorm process leading to severe urban waterlogging in Wuhu

基于自动气象观测站降水数据、中国降水数据集、ERA5再分析资料及NCEP/NCAR再分析数据,使用水汽收支分析、HYSPLIT后向轨迹追踪和水汽输送贡献率等方法对2022年6月5日凌晨芜湖市一次引发严重内涝暴雨过程的水汽输送特征进行了分析。结果表明:此次暴雨过程出现在200 hPa分流区和850 hPa低空急流左前方,500 hPa冷空气在低空急流出口北侧不断激发对流云团,形成强降水。高层辐散和低层辐合增强了水汽的水平辐合和垂直输送,西南低空急流持续加强,将水汽不断输送至暴雨区,为暴雨的出现提供了必要的水汽条件,使芜湖市在强降水发生前水汽充沛,湿层深厚且持续增湿。暴雨出现时大气可降水量、850 hPa比湿、水汽通量和水汽通量散度分别达到71.0 kg·m^(-2)、16.0 g·kg^(-1)、15.0 g·hPa^(-1)·cm^(-1)·s^(-1)和-3.0×10^(-6)g·cm^(-2)·hPa^(-1)·s^(-1)。850 hPa水汽通量散度的变化与暴雨的出现和强度变化有较好的对应关系,雨强最强时段可达-8.0×10^(-6)g·cm^(-2)·hPa^(-1)·s^(-1)。水汽收支和追踪分析结果显示:水汽流入主要发生在对流层低层的西边界和南边界,暴雨发生前流入层深厚,有向上的水汽垂直输送。整层水汽流入量约为56.0×10^(7)t·h^(-1),主要流入高度为850~700 hPa,单层流入量最大可达9.0×10^(7)t·h^(-1),水汽主要源自孟加拉湾和南海,其水汽通道轨迹占比为32.0%,水汽输送贡献率达55.4%。暴雨出现时水汽流入层降低,流入量减少,水汽垂直输送减弱,总水汽净流入集中在850 hPa,净流入量为1.0×10^(7)t·h^(-1)左右,水汽主要源自南海,其水汽通道轨迹占比为46.0%,水汽输送贡献率达60.3%。

This study aims to accumulate prediction experience of local rainstorm process,enhance understanding of heavy rainfall water vapor characteristics,and improve rainstorm prediction ability.Analyzing precipitation data from automatic meteorological observation stations,the China precipitation dataset,ERA5 reanalysis data,and NCEP/NCAR reanalysis data,we investigate the water vapor transport characteristics of a severe waterlogging rainstorm process in Wuhu City during the early morning of June 5,2022.Utilizing methods such as water vapor budget analysis,HYSPLIT backward trajectory tracking,and water vapor transport contribution rate analysis,our findings reveal that the rainstorm occurred in the 200 hPa diverging area and the left front of the 850 hPa low-level jet stream.The continuous impacts of the 500 hPa cold air on the low-level jet stream triggered convective cloud clusters,resulting in strong precipitation.The high-level divergence and low-level convergence enhanced horizontal convergence and vertical transport of water vapor,while the southwest low-level jet stream strengthened and transported water vapor to the rainstorm area,providing the necessary conditions for the occurrence of the rainstorm.Consequently,Wuhu City had abundant water vapor before the heavy rainfall event,with a deep and continuously humidified wet layer.The total column water increased by 4.1 kg·m^(-2)in 6 hours,with the rainstorm occurring at the highest value of continuous water vapor increase.During the rainstorm,key parameters such as total column water,specific humidity of 850 hPa,water vapor flux,and water vapor flux divergence reached significant levels,correlating well with the intensity of rainstorm.Our analysis attributes these conditions to the strengthening southwest low-level jet stream from the Bay of Bengal to the lower reaches of the Yangtze River,continuously transporting water vapor to Wuhu City.After the rainstorm,water vapor quantities decreased significantly.The results of the water vapor budget and water vapor tracking analysis showed that before the rainstorm occurred,water vapor inflow mainly occurred at the western and southern boundaries of the lower troposphere.The inflow layer was deep,and there was upward vertical transport of water vapor.The quantity of water vapor inflow into the entire layer was approximately 56.0×10^(7)t·h^(-1),with a main inflow height of 850—700 hPa.The maximum quantity of water vapor inflow into a single layer could reach 9.0×10^(7)t·h^(-1),originating mainly from 1000 meters above the Bay of Bengal and the South China Sea,with their water vapor channel trajectory accounting for 32.0%and their water vapor transport contribution rate of 55.4%.The other two sources of water vapor in the northwest passage were 7000 meters above the Baltic Sea and 3000 meters below the Ural River.When the rainstorm occurred,the main inflow layer decreased to 850 hPa,and the southern boundary turned to outflow at 700 hPa.The inflow of the entire layer decreased to about 21.0×10^(7)t·h^(-1),weakening vertical water vapor transport,with the total net inflow height of water vapor concentrated at 850 hPa and a net inflow quantity of about 1.0×10^(7)t·h^(-1).The water vapor mainly originated from 1000 meters above the South China Sea,with their water vapor channel trajectory accounting for 46.0%and their water vapor transport contribution rate of 60.3%.The other two sources of water vapor in the northwest passage were over 2000 meters east of the lower reaches of the Ural River and over 7000 meters above the Norwegian Sea.The Bay of Bengal and the South China Sea were the main sources of water vapor during the rainstorm.The study underscores that while water vapor conditions are essential for rainstorm formation,other factors such as trigger mechanisms and impact system locations are crucial in understanding waterlogging events.Future research should focus on integrating multi-source detection data to enhance rainstorm prediction and early warning capabilities.