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<p>The Indian Ocean Dipole (IOD) is an important air-sea coupled system in the tropical Indian Ocean that plays a remarkable role in modulating agriculture, ecosystems and extreme climate in many regions of the world. One of the most pronounced biases in the IOD simulated by the previous generation of climate models is its excessively large amplitude. In this study, we show that the IOD amplitude bias persists and even increases in the latest CMIP6 models compared to the CMIP5 models. The overestimated IOD amplitude in CMIP6 is mainly due to stronger thermocline feedback in the tropical Indian Ocean. Specifically, the climatological thermocline in the southeastern equatorial Indian Ocean is shallower in the CMIP6 together with the biases in the mean SST and low-level winds. The shallower thermocline is conducive to a stronger thermocline feedback, leading to a stronger IOD amplitude. In addition, the positive wind-evaporation-SST feedback simulated by CMIP6 is stronger during the IOD developing phase, but weaker during the decaying phase. This leads to IOD developing more efficiently but decaying more slowly in CMIP6. Further, the amplitude of El Niño-Southern Oscillation and its influence on IOD are much stronger in CMIP6 than in CMIP5. These two factors also contribute to a greater bias of IOD amplitude in CMIP6. The results of this study provide a guideline for improving the ability of coupled climate models to simulate IOD in the future.</p>

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Origins of the overestimated Indian Ocean dipole amplitude in current coupled climate models

  • 期刊论文

  • 发表日期：

    2025年4月3日

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  • Xiaoming Ju,
  • Shangfeng Chen,
  • Wen Chen,
  • Renguang Wu,
  • Lin Chen,
  • Xin Cheng

摘要

The Indian Ocean Dipole (IOD) is an important air-sea coupled system in the tropical Indian Ocean that plays a remarkable role in modulating agriculture, ecosystems and extreme climate in many regions of the world. One of the most pronounced biases in the IOD simulated by the previous generation of climate models is its excessively large amplitude. In this study, we show that the IOD amplitude bias persists and even increases in the latest CMIP6 models compared to the CMIP5 models. The overestimated IOD amplitude in CMIP6 is mainly due to stronger thermocline feedback in the tropical Indian Ocean. Specifically, the climatological thermocline in the southeastern equatorial Indian Ocean is shallower in the CMIP6 together with the biases in the mean SST and low-level winds. The shallower thermocline is conducive to a stronger thermocline feedback, leading to a stronger IOD amplitude. In addition, the positive wind-evaporation-SST feedback simulated by CMIP6 is stronger during the IOD developing phase, but weaker during the decaying phase. This leads to IOD developing more efficiently but decaying more slowly in CMIP6. Further, the amplitude of El Niño-Southern Oscillation and its influence on IOD are much stronger in CMIP6 than in CMIP5. These two factors also contribute to a greater bias of IOD amplitude in CMIP6. The results of this study provide a guideline for improving the ability of coupled climate models to simulate IOD in the future.