| 14 Oct 2025
Two-tier MOM6 Regional Modelling Suite of the East Australian Current System
Abstract. We present a new ultra-high resolution 1/30° (∼3 km) regional ocean model of the eastern Australian region and evaluate the performance of this model against two 1/10° (∼10 km) models as well as a suite of satellite and in situ observations. We evaluate model biases in the context of (i) submesoscale-permitting (∼3 km) vs. mesoscale-permitting (∼10 km) horizontal resolution and (ii) differences between version 5 and version 6 of the Modular Ocean Model (MOM5 vs. MOM6) to assess the added value in each case and determine the suitability of our higher resolution model for scientific research. There are some consistent biases shared by the two regional MOM6 configurations, and also in the higher resolution configuration that are not seen in the lower resolution models. These biases are further investigated with two sets of sensitivity experiments to understand the effect of submesoscale eddy parameterization and imposed dynamic viscosity at a submesoscale-permitting resolution. The high-resolution simulation has much higher variance compared to the lower resolution simulations across all evaluation metrics, indicating that the greater spectrum of length scales also manifests in more variability in the temporal domain. The two MOM6 regional configurations of differing resolution appear to be more aligned than the regional (MOM6) and global (MOM5) 1/10° configurations in most results, reflecting the substantial changes made to the MOM between version 5 and version 6. Importantly, we also show that higher resolution is not a panacea: in regions where key dynamics are quasi-linear and well-captured captured by coarser grids (e.g., the EAC jet), further refinement may offer limited benefit – and actually degrade the performance if parameterizations are not appropriately tuned.
General comment:
It is very difficult to make fair comparisons among three models: OM2-01(MOM5 0.1 degree global model), STHPAC10K(MOM6 0.1 degree large regional model), and EAC03K (MOM6 1/30 degree small regional model) because the model settings differ much among the three models. To properly assess the impact of a specific model setting, only the setting should be changed. Also, most results from EAC03K with the small domain appear to be largely influenced by STHPAC10K. The comparisons between MOM5 and MOM6 by using OM2-01 with the global domain and STHPAC10K with the regional domain is also complicated. A large portion of the manuscript is devoted to the non-fair comparisons. If the authors would like to show how EAC03 simulated EAC region well, they should focus on the topic. Therefore, I recommend that the authors should rewrite the entire manuscript.
I am not convinced that the parameterization of mixed layer eddies is implemented into 3km model. The model partially resolves submesoscales including mixed layer eddies as the author mentioned in the manuscript. The effect of the parameterization should be tested in the model at the coarser resolution that cannot resolve mixed layer eddies. Previous studies implemented the parameterization into the coarser models that do not resolve mixed layer eddies. Therefore, the authors should remove the sensitivity experiment of mixed layer eddy parameterization of 3km model.
Please explain about the surface momentum flux. The eddy variability (SSH variance) in the model is much influenced by how the surface momentum flux is estimated. The eddy killing (e.g. Zhai and Greatbatch, 2007; Renautl et al. 2016) should be considered when the eddy variability in the model is verified. If the surface ocean current is not considered, the eddy variability becomes relatively too strong.
Renault, L., M. J. Molemaker, J. C. McWilliams, A. F. Shchepetkin, F. Lemarié, D. Chelton, S. Illig, and A. Hall, 2016: Modulation of Wind Work by Oceanic Current Interaction with the Atmosphere. J. Phys. Oceanogr., 46, 1685–1704, https://doi.org/10.1175/JPO-D-15-0232.1.
Zhai, X., and R. J. Greatbatch (2007), Wind work in a model of the northwest Atlantic Ocean, Geophys. Res. Lett., 34, L04606, doi:10.1029/2006GL028907.
Specific comment:
Data availability is insufficient. Please clarify how to get the data.
Figure 3, 7, 9: Please clarify the units.