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<p>This study aims to investigate the impact of the mid-high-latitude Eurasian intraseasonal oscillation (MHLE-ISO) on extreme hot days (EHDs) in the middle-lower reaches of the Yangtze River valley (MLRYR). Both the leading patterns over the mid-high latitudes and the surface air temperature (SAT) anomaly in the MLRYR exhibit significant intraseasonal periodicity of 10–30 days. The leading modes of the MHLE-ISO in boreal summer are characterized by southeastward propagation and a quasi-barotropic structure. Based on the ISO phases, it is found that the MHLE-ISO can modulate SAT and EHDs in the MLRYR. Phase 1 exhibits the highest SAT anomaly and phase 2 has the most EHDs, while phase 5 shows the lowest SAT anomaly and fewest EHDs. A diagnosis of the temperature budget reveals that EHDs are primarily driven by meridional temperature advection, adiabatic heating and diabatic heating. The advection of temperature by the meridional ISO flow, the descending motion anomaly induced by vorticity advection, and the changes in cloud cover and surface radiation linked to the MHLE-ISO circulation all play significant roles in temperature rise. The circulation comes from the MHLE region. The study also demonstrates that stronger ISO intensity enhances anomalous anticyclone in the MLRYR during phase 2, creating condition more favorable for EHDs. In contrast, the result for phase 5 is approximately a mirror image of phase 2.</p>

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Impact of mid-high-latitude Eurasian ISO on extreme hot days in the middle-lower reaches of the Yangtze River valley during boreal summer

  • 期刊论文

  • 发表日期：

    2026年3月16日

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  • Meiling Zhang,
  • Shuangyan Yang,
  • Zhiwei Zhu,
  • Tim Li

摘要

This study aims to investigate the impact of the mid-high-latitude Eurasian intraseasonal oscillation (MHLE-ISO) on extreme hot days (EHDs) in the middle-lower reaches of the Yangtze River valley (MLRYR). Both the leading patterns over the mid-high latitudes and the surface air temperature (SAT) anomaly in the MLRYR exhibit significant intraseasonal periodicity of 10–30 days. The leading modes of the MHLE-ISO in boreal summer are characterized by southeastward propagation and a quasi-barotropic structure. Based on the ISO phases, it is found that the MHLE-ISO can modulate SAT and EHDs in the MLRYR. Phase 1 exhibits the highest SAT anomaly and phase 2 has the most EHDs, while phase 5 shows the lowest SAT anomaly and fewest EHDs. A diagnosis of the temperature budget reveals that EHDs are primarily driven by meridional temperature advection, adiabatic heating and diabatic heating. The advection of temperature by the meridional ISO flow, the descending motion anomaly induced by vorticity advection, and the changes in cloud cover and surface radiation linked to the MHLE-ISO circulation all play significant roles in temperature rise. The circulation comes from the MHLE region. The study also demonstrates that stronger ISO intensity enhances anomalous anticyclone in the MLRYR during phase 2, creating condition more favorable for EHDs. In contrast, the result for phase 5 is approximately a mirror image of phase 2.