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<p>The Pacific Meridional Mode (PMM) strongly modulates tropical cyclone (TC) genesis frequency over the southeastern part of the western North Pacific (SEWNP) under the present climate. Nevertheless, it remains unclear how the projected future changes in PMM under global warming will affect TC genesis over the western North Pacific (WNP). This study first evaluates the historical simulations of twenty models from the Coupled Model Intercomparison Project Phase 6 and then selects five best-performing models to conduct future projections. Results show robust dipole changes in PMM-driven TC genesis over the SEWNP, with increases in the northeastern SEWNP and decreases in the southwestern SEWNP during the peak TC season under the Shared Socioeconomic Pathway 5-8.5 warming scenario, indicating a northward shift of PMM-driven WNP TC genesis. Further analyses reveal that the El Niño-like PMM sea surface temperature (SST) warming and eastward retreat of the off-equatorial central Pacific warm SST anomalies strengthen the zonal SST gradient in the tropical central Pacific in a warmer climate, leading to the enhancement and northward shift of PMM-induced anomalous low-level cyclone. Anomalous low-level relative vorticity therefore shifts northward, accompanied by increased mid-level humidity and ascending motion, favoring more TC genesis in the northeastern SEWNP. Enhanced vertical wind shear is responsible for reduced TC genesis in the southwestern SEWNP.</p>

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Projected dipole changes in the Pacific meridional mode-induced tropical cyclone genesis over the Western North Pacific under global warming

  • 期刊论文

  • 发表日期：

    2025年10月17日

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  • Xiangjiang Wei,
  • Si Gao,
  • Wei Zhang

摘要

The Pacific Meridional Mode (PMM) strongly modulates tropical cyclone (TC) genesis frequency over the southeastern part of the western North Pacific (SEWNP) under the present climate. Nevertheless, it remains unclear how the projected future changes in PMM under global warming will affect TC genesis over the western North Pacific (WNP). This study first evaluates the historical simulations of twenty models from the Coupled Model Intercomparison Project Phase 6 and then selects five best-performing models to conduct future projections. Results show robust dipole changes in PMM-driven TC genesis over the SEWNP, with increases in the northeastern SEWNP and decreases in the southwestern SEWNP during the peak TC season under the Shared Socioeconomic Pathway 5-8.5 warming scenario, indicating a northward shift of PMM-driven WNP TC genesis. Further analyses reveal that the El Niño-like PMM sea surface temperature (SST) warming and eastward retreat of the off-equatorial central Pacific warm SST anomalies strengthen the zonal SST gradient in the tropical central Pacific in a warmer climate, leading to the enhancement and northward shift of PMM-induced anomalous low-level cyclone. Anomalous low-level relative vorticity therefore shifts northward, accompanied by increased mid-level humidity and ascending motion, favoring more TC genesis in the northeastern SEWNP. Enhanced vertical wind shear is responsible for reduced TC genesis in the southwestern SEWNP.