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<p>The Indian Ocean Dipole (IOD) is a pivotal factor in the interannual variability of the Indian Ocean (IO), influencing the climate of IO regions and beyond. An analysis of six-decade-long data has uncovered that intense tropical cyclones (TCs) that form in April over the Bay of Bengal (BoB) have the potential to advance the onset of positive Indian Ocean Dipole (pIOD) events by approximately 2–3&#xa0;weeks when compared to pIOD events that are linked to the El Niño-Southern Oscillation (ENSO) without the influence of April BoB TCs. Composite diagnostic analyses indicate that the energy dispersion of April BoB TCs gives rise to a Rossby wave train, which in turn induces an anticyclonic wind anomaly over the southeastern tropical IO (TIO). The resultant easterly and southeasterly wind anomalies enhance coastal upwelling off the Sumatra, resulting in a negative sea surface temperature anomaly (SSTA). The cold SSTA leads to the formation of an anomalous high-pressure system, which subsequently forces an anticyclonic circulation anomaly and sustains the upwelling. The wind-upwelling-SST positive feedback maintains the negative SSTA in the eastern pole area of the IOD. When combined with the slightly positive SSTA in the western pole area, this establishes the dipole mode earlier in the TIO. BoB TCs serve as a synoptic-scale trigger for interannual variability. This underlying mechanism presents a novel leading indicator for interannual climate events across the IO region.</p>

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Bay of Bengal tropical cyclones advance onset of positive Indian Ocean Dipole through coupled atmosphere–ocean processes

  • 期刊论文

  • 发表日期：

    2026年1月6日

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  • Zhi Li,
  • Yue Fang,
  • Lili Zeng

摘要

The Indian Ocean Dipole (IOD) is a pivotal factor in the interannual variability of the Indian Ocean (IO), influencing the climate of IO regions and beyond. An analysis of six-decade-long data has uncovered that intense tropical cyclones (TCs) that form in April over the Bay of Bengal (BoB) have the potential to advance the onset of positive Indian Ocean Dipole (pIOD) events by approximately 2–3 weeks when compared to pIOD events that are linked to the El Niño-Southern Oscillation (ENSO) without the influence of April BoB TCs. Composite diagnostic analyses indicate that the energy dispersion of April BoB TCs gives rise to a Rossby wave train, which in turn induces an anticyclonic wind anomaly over the southeastern tropical IO (TIO). The resultant easterly and southeasterly wind anomalies enhance coastal upwelling off the Sumatra, resulting in a negative sea surface temperature anomaly (SSTA). The cold SSTA leads to the formation of an anomalous high-pressure system, which subsequently forces an anticyclonic circulation anomaly and sustains the upwelling. The wind-upwelling-SST positive feedback maintains the negative SSTA in the eastern pole area of the IOD. When combined with the slightly positive SSTA in the western pole area, this establishes the dipole mode earlier in the TIO. BoB TCs serve as a synoptic-scale trigger for interannual variability. This underlying mechanism presents a novel leading indicator for interannual climate events across the IO region.