Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?

Lee, Jiwoo; Planton, Yann; Gleckler, P. J.; Sperber, Kenneth R.; Guilyardi, Éric; Wittenberg, Andrew T.; McPhaden, Michael J.; Pallotta, Giuliana

doi:10.1029/2021gl095041

Cited by 34 publications

(16 citation statements)

References 69 publications

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“…While the purpose of this study is to provide a detailed overview of ENSO projections in all available SMILEs, it is useful to provide some observational context. We note that a detailed comparison of ENSO characteristics in both CMIP models and SMILEs can be found in the following studies for a large range of ENSO metrics, and we do not repeat this here (Planton et al, 2021;Lee et al, 2021). We do, however, compare model-simulated and observed El Niño and La Niña composites (Figure S1 & S2).…”

Section: Datasetsmentioning

confidence: 97%

The future of the El Niño-Southern Oscillation: Using large ensembles to illuminate time-varying responses and inter-model differences

Maher

Wills²,

DiNezio³

et al. 2022

Preprint

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Abstract. Future changes in the El Niño–Southern Oscillation (ENSO) are uncertain, both because future projections differ between climate models and because the large internal variability of ENSO clouds the diagnosis of forced changes in observations and individual climate model simulations. By leveraging 14 single model initial-condition large ensembles (SMILEs), we robustly isolate the time evolving response of ENSO sea surface temperature (SST) variability to anthropogenic forcing from internal variability in each SMILE. We find non-linear changes in time in many models and considerable inter-model differences in projected changes in ENSO and the mean-state tropical Pacific zonal SST gradient. We demonstrate a linear relationship between the change in ENSO SST variability and the tropical Pacific zonal SST gradient although forced changes in the tropical Pacific SST gradient often occur later in the 21st century than changes in ENSO SST variability, which can lead to departures from the linear relationship. Single forcing SMILEs show a potential contribution of anthropogenic forcing (aerosols and greenhouse gases) to historical changes in ENSO SST variability, while the observed historical strengthening of the tropical Pacific SST gradient sits on the edge of the model spread for those models for which single forcing SMILEs are available. Our results highlight the value of SMILEs for investigating time-dependent forced responses and inter-model differences in ENSO projections. The non-linear changes in ENSO SST variability found in many models demonstrate the importance of characterising this time-dependent behaviour, as it implies that ENSO impacts may vary dramatically throughout the 21st century.

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Section: Datasetsmentioning

confidence: 97%

The future of the El Niño-Southern Oscillation: Using large ensembles to illuminate time-varying responses and inter-model differences

Maher

Wills²,

DiNezio³

et al. 2022

Preprint

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show abstract

“…Additionally, a recent study by Lee et al. (2021) has suggested that large (≥50) ensembles are needed to robustly capture the baseline ENSO characteristics and physical processes. Given the large uncertainties in the IPCC AR5 model projections of ENSO intensity and the need of large ensembles, it would be important to apply the current framework to the state‐of‐art IPCC AR6 model large ensemble simulations to further tackle this scientific question.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

The Impacts of a Weakened Atlantic Meridional Overturning Circulation on ENSO in a Warmer Climate

Liu

Pinto

Fedorov

et al. 2023

Geophysical Research Letters

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This study quantifies the impacts of the Atlantic Meridional Overturning Circulation (AMOC) on the El Niño–Southern Oscillation (ENSO) under anthropogenic warming by comparing climate change model simulations with declining and fixed strengths of the overturning. After the 1980s, a weakened AMOC is shown to reduce the strength of the annual cycle of sea surface temperature (SST) in the eastern equatorial Pacific and induce anomalous cross‐equatorial northerly winds there, which strengthens ENSO variability by about 11%. An analysis of the Bjerknes stability index reveals that this intensification of ENSO results mainly from enhanced Ekman upwelling feedback due to amplified atmospheric wind response to SST anomalies and oceanic upwelling response to equatorial wind stress anomalies. The weakened AMOC also promotes the occurrence of Central Pacific El Niño events and reduces ENSO skewness. These AMOC impacts on ENSO magnitude and complexity throughout the twenty‐first century are however smaller than ENSO variations expected from internal climate variability.

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“…Other wave-coupled effects, such as the effect of surface wave Stokes drift on air-sea momentum and heat fluxes, the effect of sea spray from wave breaking on air-sea heat fluxes, and the effect of SST diurnal cycle on air-sea heat and gas fluxes,-were also introduced to the climate models. Lee et al (2021) comprehensively evaluated all 59 CMIP6 climate models on their performance in reconstructing historical ENSO events, and FIO-ESM v2.0 ranked No. 1 among them (from their Figure S1).…”

Section: Ocean-to-climate Model Development and Applicationsmentioning

confidence: 99%

“…Lee et al. (2021) comprehensively evaluated all 59 CMIP6 climate models on their performance in reconstructing historical ENSO events, and FIO‐ESM v2.0 ranked No. 1 among them (from their Figure S1).…”

Section: Ocean‐to‐climate Model Development and Applicationsmentioning

confidence: 99%

Ocean Waves in Large‐Scale Air‐Sea Weather and Climate Systems

Babanin

2023

JGR Oceans

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Ocean surface gravity waves are mechanical water waves propagating along the sea interface, with heights from centimeters to more than 10 m. They are one of the most significant dynamic processes in the upper ocean which have received a lot of attention in the fluid mechanics and ocean science community, starting from Stokes (1847) and peaking about half a century ago (e.g., see Yuan and Huang (2012) for a review). When moderate-to-strong wind blows over the sea surface, most of the energy and momentum are first transported to surface waves, to support their growth (e.g., Kudryavtsev & Makin, 2001), before those are passed to the ocean through wave breaking and wave-turbulence interactions (Babanin, 2011). That is, the waves are the "sink" of the energy and momentum flux for the low atmosphere and the "source" for the upper ocean, and play an important role in redistribution of the air-sea energy and momentum fluxes at the space-time scale of the storms. Moreover, such energy and momentum balance is not quite dependent on the instantaneous and local wind, because the waves are integral of the wind over large scales. Furthermore, in large areas dominated by swells, the waves can be unrelated to the local wind altogether, and in fact can be responsible for generating the local winds (e.g., Hanley et al., 2010).

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Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?

Cited by 34 publications

References 69 publications

The future of the El Niño-Southern Oscillation: Using large ensembles to illuminate time-varying responses and inter-model differences

The future of the El Niño-Southern Oscillation: Using large ensembles to illuminate time-varying responses and inter-model differences

The Impacts of a Weakened Atlantic Meridional Overturning Circulation on ENSO in a Warmer Climate

Ocean Waves in Large‐Scale Air‐Sea Weather and Climate Systems

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