綦江流域一次致洪暴雨的夜间突发机制
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国家自然科学基金气象联合基金重点项目(U2242202)、重庆市技术创新与应用发展专项面上项目(CSTB2022TIAD-GPX0031)、四川省科技计划项目(2023YFS0430)、重庆市自然科学基金面上项目(CSTB2022NSCQ-MSX0665)、重庆市气象部门业务技术攻关项目(YWJSGG-202408)、中国气象局创新发展专项(CXFZ2024J001)共同资助


Analysis of Nocturnal Enhancement Mechanism of a Flood-Triggering Rainstorm in Qijiang Basin
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    摘要:

    利用多源观测资料和ERA5再分析资料,通过分析2020年6月19—22日引发綦江流域破纪录洪水的暴雨过程,研究了此次西南涡暴雨的夜间增强机制,结果表明:①降水在夜间至清晨加强,具有显著的日变化特征。过程分为3个阶段,第3阶段云顶亮温更低、云团移动传播更慢,致使降水和对流更强、持续时间更长。②暴雨发生在西太平洋副热带高压北侧的浅槽背景下,由深厚西南涡、稳定维持的低空急流和地面辐合线导致。对流初生时,辐合线附近为高温高湿的强不稳定环境,地面偏北风经地形抬升后汇入盆地-高原次级环流的上升支,触发对流。③四川盆地和云贵高原北部的低空非地转风每日顺时针偏转,均在夜间转为偏南风并加强,在高原上强于盆地。夜间低空风场在盆地为次地转、高原为超地转,形成暖式切变和风速辐合。非地转风水汽通量昼负夜正,而地转风水汽通量总体为正值,使实际风水汽通量在夜间显著增大。以上日变化有利于水汽积聚和辐合抬升,造成夜雨增幅。④动量平衡方程的平流项和非地转项在夜间转为正值或正值增大,且在高原上强于盆地,使前者水平风在夜间增幅更大,形成风速梯度和辐合。非地转效应对此次夜雨增强有重要作用。

    Abstract:

    Using multi-source observation data and ERA5 reanalysis data, a rainstorm that triggers a record-breaking flood in Qijiang Basin (QB) from June 19 to 22, 2020, is analysed. The nocturnal enhancement mechanism of precipitation brought by Southwest Vortex is hereafter studied. The results show that: (1) The rainstorm, exhibiting significant daily variation, intensified during the night and early morning. The whole process was divided into three stages. At the third stage, the MCSs showed lower Blackbody Brightness Temperature (TBB), moved and propagated more slowly, and resulted in stronger precipitation and convection with longer duration. (2) Under the background of a weak trough in the westerly to the north of the Western Pacific Subtropical High, the rainstorm was caused by a strong Southwest Vortex, a stable low-level jet, and a convergence line on the surface. At the stage of convection initiation, an unstable environment with high temperature and humidity was formed near the convergence line. Meanwhile, the northerly wind on the surface was forced to lift by terrain, then joined the updraft of basin-plateau secondary vertical circulation, and later triggered convection. (3) The low-level ageostrophic wind above Sichuan Basin (SB) and northern Yunnan-Guizhou Plateau (YGP) rotated clockwise every day, both turned southerly and strengthened at night, and was stronger above YGP than above SB. The nocturnal low-level wind, being sub-geostrophic above SB and super-geostrophic above YGP, caused warm shear and flow convergence. Additionally, the water vapour flux transported by ageostrophic wind was negative during the day and positive at night, while the water vapour flux transported by geostrophic wind remained positive all day, resulting in a significant positive increase in the water vapour flux transported by actual wind at night. The above daily variations were conducive to water vapour accumulation and flow convergence, which eventually led to the intensification of precipitation. (4) The advection and ageostrophic terms in the momentum balance equation became positive or increased at night, and were greater above YGP than above SB. The horizontal wind on YGP therefore intensified, wind speed gradient and convergence were formed as a result. The ageostrophic effect played an important role in the nocturnal enhancement mechanism of precipitation.

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朱岩,翟丹华,邓承之,张焱,李佳.綦江流域一次致洪暴雨的夜间突发机制[J].气象科技,2025,53(3):391~404

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  • 收稿日期:2024-04-17
  • 定稿日期:2025-03-20
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  • 在线发布日期: 2025-06-27
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