ACCESS-OM2 v1.0: a global ocean–sea ice model at three resolutions

Andrew E Kiss,Andrew Mcc Hogg,Christopher Chapman,Matthew A Chamberlain,Peter Dobrohotoff,Abhishek Savita,Maxim Nikurashin,Russell Fiedler,Marshall L Ward,Gary B Brassington,Earl R Duran,Xihan Zhang,Peter R Oke,Paul Spence,James Munroe,Stephen M Griffies,Fanghua Wu,Océane Richet,Fabio Boeira Dias,Simon J Marsland,Andreas Klocker,Nicholas Hannah,Adele K Morrison,Aidan Heerdegen,Matthew H England,Gabriela S Pilo,Catia M Domingues,P̀etra Heil ,Kial Douglas Stewart ,R M Holmes

doi:10.5194/gmd-13-401-2020

Abstract

Abstract. We introduce ACCESS-OM2, a new version of the ocean–sea ice model of the Australian Community Climate and Earth System Simulator. ACCESS-OM2 is driven by a prescribed atmosphere (JRA55-do) but has been designed to form the ocean–sea ice component of the fully coupled (atmosphere–land–ocean–sea ice) ACCESS-CM2 model. Importantly, the model is available at three different horizontal resolutions: a coarse resolution (nominally 1∘ horizontal grid spacing), an eddy-permitting resolution (nominally 0.25∘), and an eddy-rich resolution (0.1∘ with 75 vertical levels); the eddy-rich model is designed to be incorporated into the Bluelink operational ocean prediction and reanalysis system. The different resolutions have been developed simultaneously, both to allow for testing at lower resolutions and to permit comparison across resolutions. In this paper, the model is introduced and the individual components are documented. The model performance is evaluated across the three different resolutions, highlighting the relative advantages and disadvantages of running ocean–sea ice models at higher resolution. We find that higher resolution is an advantage in resolving flow through small straits, the structure of western boundary currents, and the abyssal overturning cell but that there is scope for improvements in sub-grid-scale parameterizations at the highest resolution.

Highlights

The computational load of Australian Community Climate Earth System Simulator (ACCESS)-OM2 is dominated by MOM5, which typically comprises around 90 % of CPU time at the lower resolutions and 75 % of this time at 0.1◦ resolution
The strength of the Equatorial Undercurrent (EUC) core is within 10 % of observations, and its latitudinal width at 140◦ W is accurate in ACCESS-OM2-025 and ACCESSOM2-01 but somewhat too wide in ACCESS-OM2
The ACCESS-OM2 model suite is designed as a model hierarchy, with supported configurations at three different horizontal resolutions

Summary

Introduction

They form the oceanic component of coupled climate and Earth system models that are used for projecting future climate and can incorporate biogeochemical and ecosystem dynamics which extend the realm of application. They are needed for forecasting on shorter timescales – both forecasting in the ocean and for seasonal prediction of the ocean– sea ice–atmosphere state. Ocean–sea ice models can be used to quantitatively test, or experiment with, the dynamics of the climate system; such process studies have been invaluable in forming a broad understanding of the drivers of climate change and variability. While higherresolution models are becoming computationally feasible, the additional resolution does not necessarily result in improved simulations

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Conclusion