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<p>In September 2024, the Yangtze River Basin (YRB) in China experienced a record-breaking extreme high temperature event (EHTE), with regional mean SAT anomalies reaching + 3.5&#xa0;°C and a return period of 110 years, highlighting the emerging risks of early-autumn extremes. Diagnostic analyses and numerical experiments reveal that the event resulted from the combined effect of multi-scale atmospheric circulation anomalies. In the upper troposphere, an anticyclone dominated the northern YRB; at mid–lower levels, an intensified and northwestward-displaced Western Pacific Subtropical High (WPSH) persisted, accompanied by anomalous meridional circulation with strong subsidence over the basin. The above circulation configuration suppressed cloud cover and increased downward shortwave radiation, thereby strengthening surface net radiation and increasing the upward sensible heat flux from land to air to raise SAT. Further dynamical tracing shows that concurrent warm SST anomalies in the North Atlantic and Caribbean contributed to the excitation of a downstream Rossby wave train, forming the upper-level anticyclone over the YRB. Meanwhile, intensified convection over the South China Sea (SCS) induced a negative-phase PJ-like wave train and descending motion, reinforcing WPSH anomalies. Numerical experiments confirm that Atlantic SST and SCS heating can independently reproduce the corresponding wave trains and circulation anomalies. Overall, this study highlights the synergistic role of Atlantic SST and SCS convection via distinct teleconnection processes in shaping the three-dimensional circulation that led to the unprecedented early-autumn EHTE over the YRB, thereby deepening our understanding of the mechanisms behind nontraditional-season extreme climate events.</p>

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Extreme multi-source forcings reshape three-dimensional circulation to drive the record-breaking Early-Autumn 2024 heat event over the Yangtze River Basin

  • 期刊论文

  • 发表日期：

    2025年11月24日

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  • Haihong Yang,
  • Shujuan Hu,
  • Yao Sheng,
  • Ziyang Yu,
  • Wenxin Zhang,
  • Jianjun Peng,
  • Deqian Li

摘要

In September 2024, the Yangtze River Basin (YRB) in China experienced a record-breaking extreme high temperature event (EHTE), with regional mean SAT anomalies reaching + 3.5 °C and a return period of 110 years, highlighting the emerging risks of early-autumn extremes. Diagnostic analyses and numerical experiments reveal that the event resulted from the combined effect of multi-scale atmospheric circulation anomalies. In the upper troposphere, an anticyclone dominated the northern YRB; at mid–lower levels, an intensified and northwestward-displaced Western Pacific Subtropical High (WPSH) persisted, accompanied by anomalous meridional circulation with strong subsidence over the basin. The above circulation configuration suppressed cloud cover and increased downward shortwave radiation, thereby strengthening surface net radiation and increasing the upward sensible heat flux from land to air to raise SAT. Further dynamical tracing shows that concurrent warm SST anomalies in the North Atlantic and Caribbean contributed to the excitation of a downstream Rossby wave train, forming the upper-level anticyclone over the YRB. Meanwhile, intensified convection over the South China Sea (SCS) induced a negative-phase PJ-like wave train and descending motion, reinforcing WPSH anomalies. Numerical experiments confirm that Atlantic SST and SCS heating can independently reproduce the corresponding wave trains and circulation anomalies. Overall, this study highlights the synergistic role of Atlantic SST and SCS convection via distinct teleconnection processes in shaping the three-dimensional circulation that led to the unprecedented early-autumn EHTE over the YRB, thereby deepening our understanding of the mechanisms behind nontraditional-season extreme climate events.