the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Jan 2026
Assessing resolution sensitivity in coupled climate simulations with AWI-CM3
Abstract. In this study, we evaluate the performance of the latest version of the Alfred Wegener Institute Climate Model, AWI-CM3, in two configurations at different resolutions, demonstrating that higher spatial resolution substantially enhances the model’s ability to reproduce key climate variables and processes. The medium-resolution configuration consistently reduces climatological biases compared to both the low-resolution setup and the CMIP6 (Coupled Model Intercomparison Project, phase 6) multi-model mean, particularly in polar regions and areas characterized by strong mesoscale dynamics. Improvements are especially notable in the simulation of sea ice variability, ocean circulation, and ocean-atmosphere interactions. The medium-resolution simulation also exhibits greater interannual variability, which may reflect a more realistic representation of underlying processes, but whose implications will need to be fully assessed with multiple ensemble members. We conclude that long-term, eddy-permitting climate projections offer promising avenues for reducing structural uncertainties in future climate projections. As global modeling efforts move toward CMIP7 and beyond, our results highlight the importance of pursuing medium-resolution strategies in parallel with improved physical parameterizations and ensemble-based evaluation to more robustly capture the nonlinearities of the Earth system.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-5061', Anonymous Referee #1, 11 Mar 2026
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RC2: 'Comment on egusphere-2025-5061', Anonymous Referee #2, 16 Mar 2026
This paper investigates the impact of model resolution in coupled simulations using the AWI-CM3 model, which is one of the CMIP6-participating models. The model was run in two configurations: a lower-resolution setup (LR; atmosphere: ~102 to 120 km with 91 vertical levels; ocean: CORE2, 20 to 100 km) and a higher, medium-resolution setup (MR; atmosphere: ~32 to 38 km with 137 levels; ocean: DART, 4.5 to 25 km). The higher resolution permits ocean eddy-resolving capability. The paper covers a variety of evaluations to examine performance changes due to the increased resolution. The authors find that increased resolution leads to improved model performance overall. I believe the paper is well written and the scope fits the journal. However, before publication, readers would benefit from a revised manuscript, including the following.
Section 2: What is the simulation period? I assume that is identical to the CMIP6 Historical experiment protocol, but it may be worth noting it clearly in the text.
Table 1: I suggest adding the equivalent resolution information in km for the atmospheric and ocean grids, which will help improving the clarity of the configuration.
Fig. 1: I suggest use “LR” and “MR” or “lower” and “higher” for the 2nd and 3rd column titles, as the readers may not familiar with “CORE2” and “DART” terminologies thus have to revisit the text where they were defined.
Fig. 2: I suggest adding a color bar. Also, readers would benefit from knowing exact variables used in the figure. Some abbreviated variable names on the y-axis may not be very straightforward especially for those who are not in the field (e.g., mlotst, thetao, so, etc), although some were described in the text (line 155-170). I suggest providing full names of the variables (recommended) in a comprehensive way (like a table in the supplementary) and point to where they could be found from the figure caption.
Line 151-153: Regarding the overall score, some arbitrary is unavoidable depending the selection of variables and regions, and there has been long debates about defining the “overall score” in the community. I recommend discussing about such limitation of the overall score.
Fig 6: I find a mismatch between the figure and the interpretating text, and it puzzles me. It looks like the color bar to be the opposite of the interpretation of the result in the section 3.3. For example, lines 254-255 describes about the observed sea ice loss in the central Arctic (Fig. 6g) where in the figure, most of the Arctic sea is colored in red, in which according to the color bar, it indicates positive SIC trend, thus increasing sea ice. I encourage the authors double check the figure to make sure what it shows.
Fig 11. I recommend using the same configuration name (LR, MR) throughout the paper for consistency. I also wonder the lines from LR, MR, and OBS could be superimposed to same space and make comparison easier.
Citation: https://doi.org/10.5194/egusphere-2025-5061-RC2 -
AC1: 'Reply on RC2', Martina Zapponini, 18 Mar 2026
We thank the reviewer for the careful and constructive evaluation of our manuscript, and for the positive assessment of its scope and clarity. We appreciate the helpful suggestions provided. Below, we address each comment in detail.
- Section 2: We thank the reviewer for this suggestion. The simulation protocol was already described in the manuscript (lines 108–114); however, we have now introduced a dedicated subsection to improve the accessibility of the information.
- Table 1: The horizontal grid spacing ranges (in km) have now been included in the table.
- We have revised the figure and its caption to improve clarity.
- Figure 2: We thank the reviewer for the suggestions to improve the readability of the heatmaps. We have now added a colorbar to the figure and included a table mapping variable names in the Supplementary Figures.
- Lines 151–153: We agree with the reviewer that the overall score should be interpreted with caution. We have therefore added a clarification later in the manuscript (lines 178–181):
“While this overall score provides a useful summary of model performance, it involves an inherent degree of arbitrariness, as it depends on the selection of variables and regions. It is therefore interpreted alongside the individual diagnostics presented below, rather than as a standalone measure of model skill.”
- Figure 6: We thank the reviewer for pointing out this issue. The colorbar was inadvertently reversed and has now been corrected.
- Figure 11: We thank the reviewer for this suggestion. We have updated the configuration names and colors to ensure consistency with the rest of the analysis. We have, however, retained the three-column layout. As the time series can be noisy, overlaying them can make the comparison less clear. We believe that the current layout clearly highlights the main point of the comparison: the correspondence in variability in the MR configuration, which is also present in reanalysis and observations, but absent in the LR configuration.
The revised versions of the figures are provided in the attached files for reference.
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AC1: 'Reply on RC2', Martina Zapponini, 18 Mar 2026
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General comments:
The paper provides a useful overview of the coupled AWI-CM3 model, providing a near direct comparison between two model resolutions, as well as evaluation against observations/re-analysis and CMIP6. Particular attention is given to polar climate, where increased resolution has a larger impact on mesoscale processes unresolved by coarser resolution. The comparison is between a pair of simulations from 1950 - 2100, with most of the emphasis on evaluation of biases relative to present-day observations or reanalysis, rather than on future projections. Overall this is a well-written and clearly understandable manuscript that provides a very useful benchmark for the AWI-CM3 model and the impact of increased resolution.
Specific comments:
Each model is run for 250 years from initialization in repeat 1950 conditions, with the first 100 years considered spinup and subsequent 150 years as control. It would be useful to have some mention of the model’s level of equilibrium during this control period, and/or see metrics. Figure 3 shows some of this; the global SST and 2m air temperatures seem to be in equilibrium in the control, but maybe some of the sea ice metrics have a trend during the control? Is the ocean steadily gaining or losing heat during the control? In Figure 7d the AMOC time series appear to be declining from 1950, was this trend also in the control?