The ACCESS-CM2 climate model with a higher resolution ocean-sea ice component (1/4°)

Abstract. A new configuration of the Australian Community Climate and Earth System Simulator coupled model, ACCESS-CM2, with a higher resolution ocean-sea ice component at 0.25° is introduced. The higher resolution ACCESS-CM2-025 model was developed to better represent the ocean mesoscale and expand the scope of climate modelling research applications. The individual model components have not been changed compared with ACCESS-CM2-1, the existing lower resolution version of the model at 1°, which was one of Australia's contributions to the World Climate Research Program's Coupled Model Intercomparison Project Phase 6 (CMIP6). This paper assesses the simulated climate for a 500 years present-day run in ACCESS-CM2-025 against observations, the lower resolution ACCESS-CM2-1 model, and two ocean-sea ice models using the same model components and comparable grid resolutions but with prescribed atmospheric forcing. ACCESS-CM2-025 is more energetic and performs better in regions of elevated ocean mesoscale variability such as at western boundary currents. The higher resolution ACCESS-CM2-025 also features a more realistic ENSO life cycle and seasonality, with a reduced biennality, which is common in the lower resolution ACCESS-CM2-1. Both ACCESS-CM2 models share many biases, particularly near the sea surface and also affecting sea ice coverage, reflecting insufficiency in the atmospheric model component. While ACCESS-CM2-025 exhibits improved time-mean deep convection, sea ice, and mixed layer depth in the North Atlantic, it also experiences multidecadal variability, which is evident in many variables, including the Atlantic Meridional Overturning Circulation.