Characterising surface discrepancies and vertical coherence of ocean temperature anomalies in CMIP6 HighResMIP during ENSO events

Golla, Sreevathsa, Hirschi, Joel, Mecking, Jennifer, Blaker, Adam and Marsh, Robert (2024) Characterising surface discrepancies and vertical coherence of ocean temperature anomalies in CMIP6 HighResMIP during ENSO events. AGU Fall Meeting 2024, , Washington, United States. 09 - 13 Dec 2024. 1 pp .

Abstract

Considering the widespread implications of El Niño-Southern Oscillation (ENSO) on global and regional climate, through atmospheric and oceanic teleconnections, understanding its changing inter-annual dynamics in the context of a warming climate is crucial. Therefore, evaluating the ability of current generation high-resolution climate models to accurately simulate the spatio-temporal characteristics and underlying dynamics of ENSO, is essential for improving future projections. In this study, we review and evaluate the representation of ENSO in several high-resolution coupled climate model simulations from the CMIP6 HighResMIP project, along with two ocean-only simulations forced with surface fluxes from atmospheric reanalyses. Our evaluation concentrates on the ability of current state-of-the-art models to represent central equatorial Pacific warming and cooling. We assess the representation of surface and sub-surface spatio-temporal characteristics of the equatorial Pacific Ocean temperature anomalies that define ENSO events against observation-based ocean temperature datasets. We observe a strong alignment in both the timing and vertical structure of temperature anomalies in the ocean-only model simulations with observations, particularly during strong ENSO events. The genesis of sub-surface anomalies and their further vertical propagation to the surface is well simulated in the atmosphere-forced ocean-only model runs. However, several high-resolution coupled model runs underestimated the magnitude of sub-surface temperature anomalies and showed significant diversity in representing typical ENSO characteristics. The vertical coherence of temperature anomalies was more pronounced in forced ocean-only simulations compared to coupled model runs. The underestimation of sub-surface temperature anomalies and the large diversity in characteristics in coupled model runs indicate potential shortcomings in accurately representing the genesis and evolution of temperature anomalies. Furthermore, potential hypotheses have been discussed to explain the observed model diversity and shortcomings of coupled model runs compared to the ocean-only model simulations.

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Contributors

Author: Sreevathsa Golla

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