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

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.

Resolving and Parameterising the Ocean Mesoscale in Earth System Models

“…In CMIP6 models, the approach at the eddypresent resolution varies between models. For example, at 1/4°resolution, different model families make different choices about the use of GM [36,37]. This is also an issue in eddy-rich models but at higher latitudes than in eddypresent models.…”

Insights into projected changes in marine heatwaves from a high-resolution ocean circulation model

“…While the higher values in OFAM3 may suggest an overestimated variability in these eddy-rich regions, we believe that the actual biases are smaller than indicated here. Previous studies suggest systematic negative biases of SST variability represented in gridded observation-based SST analysis products 13,23,24 . Specifically, these studies report a systematic underestimate of eddy kinetic energy in the Southern Ocean by as much as 60-70% when calculated from gridded altimetry data because of interpolation, which smooths variability, compared to along-track data.…”

“…Although these models are useful in assessing the impacts of ongoing climate change on MHWs at the global scale, the spatial resolution of many of these models is too coarse to resolve mesoscale processes that play a substantial role in the dynamics of the ocean 12 . In particular, western boundary currents are regions of intense eddy activity where high-resolution models simulate the historical mean state and variability better than the coarse-resolution models 13 . This includes the simulation of MHWs 14 .…”

The Atlantic Meridional Overturning Circulation in High‐Resolution Models

“…A major bottleneck that currently applies to ocean/ocean‐atmosphere models is the limit in scalability of the model performance as the number of processors used is increased. When the number of cores is increased to O(10000‐20000), performance starts to plateau and increasing the core number even further is detrimental to model performance (e.g., Kiss et al, 2020; Koldunov et al, ). Unless there is a step change in processor technology (such as quantum computing, e.g., Arute et al, ; Steane, 1998) in the near future, one can assume that the next generation(s) of HPCs will consist of massively parallel machines with millions of cores becoming commonplace.…”