“21·7”河南暴雨水汽源地追踪和定量贡献分析

Tracking and Quantitative Contribution Analyses of Moisture Sources of Rainstorm in Henan Province in July 2021

2021年7月19~22日,河南省部分地区出现极端暴雨(简称“21·7”河南暴雨),造成严重城市内涝和人员伤亡。本文借助降水观测资料和再分析数据,分析了此次暴雨过程的大尺度环流形势,并利用拉格朗日轨迹追踪模式FLEXPART及水汽源区定量贡献分析方法,考察了暴雨过程的水汽源地、输送路径和源区水汽定量贡献。结果表明:此次暴雨期间以及暴雨发生前数天,东亚地区500 hPa环流形势极为稳定,西太平洋副热带高压(简称副高)异常偏北,与北侧高压脊连通、位置少动,欧亚大陆高空槽偏西,东亚中高纬环流显著平直,暴雨过程期间,热带气旋“烟花”和“查帕卡”与副高等持续协同影响,建立明显水汽输送通道,提供充足水汽,河南暴雨区维持显著近地面湿区和高可降水量;向前追踪数天发现,暴雨区目标气块主要来自西北太平洋和中国南海等地,且所处大气高度较低,此外,还有少量气块来自日本海附近和欧亚大陆中部(所处高度相对较高);定量贡献分析显示,水汽主要来自河南南侧中国中东部大陆(D)和西北太平洋(F),前者水汽贡献率(52.59%)达后者(25.51%)2倍以上,此外,河南暴雨区(T,3.68%)、中南半岛—中国南海(E,3.32%)和暴雨区北侧亚洲大陆(B,2.28%)也有一定贡献;目标气块在D区域水汽摄取量最大,略高于F区域,但前者沿途损耗率明显低于后者,造成D区域水汽贡献显著高于后者;B区域水汽摄取量略高于E区域,但其沿途损耗和未释放部分占比之和高于后者,导致后者水汽贡献相比略高;此外,T区域也有不可忽视的降水再循环率;延长向前追踪天数后,目标气块轨迹和各源区水汽摄取与贡献率相对变化不大,但所有源区水汽总贡献明显提升,可见,对于类似此次河南极端特大暴雨的强降水过程的水汽来源追踪而言,适当延长追踪天数十分必要。

Extreme rainstorms occurred in some regions of Henan Province from 19 July to 22 July 2021(referred to as“21·7”Henan rainstorm),causing severe urban waterlogging and casualties.Precipitation observation data and reanalysis data were used to analyze the large-scale circulation situations of this heavy rainfall.The moisture sources,transport paths,and quantitative contribution of each source area were also examined using the Lagrangian trajectory tracking model(FLEXPART)and the areal source-receptor attribution method.The results showed that the 500-hPa circulation in East Asia was extremely stable during the rainstorm and several days before the rainstorm.Connected with the northern high pressure ridge,the western Pacific subtropical high pressure(referred to as the sub-high)was unusually northward,with less movement.Meanwhile,the Eurasian high trough was westward,and the circulation in the middle and high latitudes of East Asia was significantly flat.During the rainstorm,tropical cyclones“In-Fa”and“Cempaka”continued to have synergistic effects with sub-high,establishing obvious water vapor transport channels and providing sufficient moisture.The rainstorm areas in Henan Province retained considerable near-surface wet regions and high precipitable water.Tracking forward for several days,the target particles in the rainstorm area mainly originated from the Northwest Pacific Ocean,the South China Sea,and other places and were located at relatively low atmospheric levels.Additionally,a few particles,which could be traced back to the vicinity of the Sea of Japan and central Eurasia,were at relatively high altitudes.Quantitative contribution analyses indicated that the moisture primarily originated from the continent of eastern–central China south of Henan(D)and the northwestern Pacific Ocean(F),with the contribution of the former(52.59%)twice more than that of the latter(25.51%).In addition,the moisture from the Henan rainstorm area(T,3.68%),Indo–China Peninsula–South China Sea(E,3.32%),and the Asian continent north of the storm area(B,2.28%)also contributed.The water vapor uptake of the target particles was the largest in region D,which was slightly higher than that in region F,but the rate of moisture loss along the former was clearly lower than that of the latter,resulting in significantly higher moisture contribution in region D than in region F.Although the moisture intake in region B was somewhat higher than that in region E,the sum of the moisture loss along the way and the unreleased part was higher than the latter,leading to a greater moisture contribution in region E.Moreover,region T had a non-negligible precipitation recycling rate.When the number of forward tracking days was extended,the trajectories of target particles,water vapor uptake,and contribution rate of each source had relatively minimal changes,but the total contribution of moisture from all source areas significantly increased.Thus,the number of days for the tracking of moisture sources for heavy precipitation events,such as this extreme rainfall in Henan,can be extended.