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<p>This study compares the interannual sea surface temperature (SST) variability in the equatorial Pacific between versions 1 and 2 of the Ocean Model Intercomparison Project (OMIP), using six ocean general circulation models participating in both OMIPs. The main distinction between OMIP1 and OMIP2 lies in the atmospheric forcing: CORE-II for OMIP1 and JRA55-do for OMIP2. The availability of two OMIPs using similar models, but different wind forcing, provides us with the opportunity to identify the impact of different aspects of the wind forcing on El Niño-Southern Oscillation (ENSO) with a relatively high statistical confidence, due to the multi-model nature of the OMIP simulations. OMIP1 shows 12.6% (15.5%) higher interannual SST variability than OMIP2 in the NINO3 (NINO3.4) region. Two hypotheses are explored to explain this disparity: (1) differences in the interannual variability of wind forcing, and (2) differences in the mean-state of wind forcing. Compared to OMIP2, OMIP1 shows stronger interannual zonal wind stress variability in the western equatorial Pacific, as well as stronger off-equatorial interannual zonal wind stress and wind stress curl variability. This enhanced interannual wind stress variability in OMIP1 leads to larger off-equatorial and eastern equatorial Pacific interannual sea surface height variability. The larger thermocline depth variations in the eastern equatorial Pacific in OMIP1 can account for a large fraction of the differences in interannual SST variability between the two OMIPs. Targeted sensitivity experiments confirm that most of the differences in interannual SST variability between the two OMIPs originate from the differences in wind stress interannual variability. The analysis of the climatological wind stress reveals stronger easterlies in OMIP1, particularly between 150<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation>W and 90<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation>W and 5<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation>S to 15<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(^{\circ }\)</EquationSource> </InlineEquation>N. This enhances Ekman divergence, interior equatorward geostrophic transport, and equatorial upwelling in OMIP1. Even though the thermocline feedback also depends on the climatological upwelling, the mean-state differences between the two OMIPs account only for a small fraction of the differences in interannual SST variability. Results also show that ocean models forced with JRA55-do tend to better represent the interannual variability and mean-state of the tropical Pacific Ocean.</p>

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Impact of wind forcing on the equatorial Pacific interannual variability in Ocean Model Intercomparison Project (OMIP) simulations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月2日

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  • Arthur Prigent,
  • Riccardo Farneti,
  • Fred Kucharski,
  • Antonietta Capotondi,
  • Joke F. Lübbecke

摘要

This study compares the interannual sea surface temperature (SST) variability in the equatorial Pacific between versions 1 and 2 of the Ocean Model Intercomparison Project (OMIP), using six ocean general circulation models participating in both OMIPs. The main distinction between OMIP1 and OMIP2 lies in the atmospheric forcing: CORE-II for OMIP1 and JRA55-do for OMIP2. The availability of two OMIPs using similar models, but different wind forcing, provides us with the opportunity to identify the impact of different aspects of the wind forcing on El Niño-Southern Oscillation (ENSO) with a relatively high statistical confidence, due to the multi-model nature of the OMIP simulations. OMIP1 shows 12.6% (15.5%) higher interannual SST variability than OMIP2 in the NINO3 (NINO3.4) region. Two hypotheses are explored to explain this disparity: (1) differences in the interannual variability of wind forcing, and (2) differences in the mean-state of wind forcing. Compared to OMIP2, OMIP1 shows stronger interannual zonal wind stress variability in the western equatorial Pacific, as well as stronger off-equatorial interannual zonal wind stress and wind stress curl variability. This enhanced interannual wind stress variability in OMIP1 leads to larger off-equatorial and eastern equatorial Pacific interannual sea surface height variability. The larger thermocline depth variations in the eastern equatorial Pacific in OMIP1 can account for a large fraction of the differences in interannual SST variability between the two OMIPs. Targeted sensitivity experiments confirm that most of the differences in interannual SST variability between the two OMIPs originate from the differences in wind stress interannual variability. The analysis of the climatological wind stress reveals stronger easterlies in OMIP1, particularly between 150 \(^{\circ }\) W and 90 \(^{\circ }\) W and 5 \(^{\circ }\) S to 15 \(^{\circ }\) N. This enhances Ekman divergence, interior equatorward geostrophic transport, and equatorial upwelling in OMIP1. Even though the thermocline feedback also depends on the climatological upwelling, the mean-state differences between the two OMIPs account only for a small fraction of the differences in interannual SST variability. Results also show that ocean models forced with JRA55-do tend to better represent the interannual variability and mean-state of the tropical Pacific Ocean.