ENSO teleconnections in eddy-rich climate models

Abstract. We examine how ENSO atmospheric teleconnections are represented in a novel suite of coupled simulations with eddy-resolving ocean and high-resolution atmosphere, at an unprecedented grid spacing of ∼10 km in both components. The single-member, multi-decadal experiments have been performed under a coordinated protocol within the European Eddy-RIch Earth System Models (EERIE) project using three different models.

To assess the performance of the EERIE models, we design tailored metrics to encapsulate and quantify different aspects of the ENSO teleconnections: direct tropical response, Rossby wave sources, extra-tropical tropospheric and stratospheric anomalies, and surface impacts. The metrics are based on linear regressions on the Niño3.4 index of several atmospheric fields in early- and late winter. Additionally, we apply the same diagnostics to a set of complementary atmosphere-only simulations run at lower resolution (∼30 km, 10 members) and high resolution (∼10 km, 1 member), which allow to isolate the impact of atmospheric resolution and estimate the internal variability.

We find mixed results in the EERIE coupled simulations compared to previous generation eddy-parametrized and eddy-permitting models (maximum ∼25 km in both atmosphere and ocean). The performance, though overall positive, varies by season, region, and model configuration and a systematic improvement does not emerge clearly. Similarly, the atmosphere-only experiments also indicate limited advances from the increased atmospheric resolution. However, potential benefits may be hindered by the large uncertainty in the ENSO response due to internal variability and sampling.