MOM6 Nodal modulation PR changes our baselines

[yichengt900]

The GFDL MOM6 Nodal Modulation PR #725 addresses several inconsistencies between open boundary tidal forcing and astronomical tidal forcing. One significant bug fix is the addition of the equilibrium phase to the SAL term, which was missing in the previous code. While this improves tidal modulation, it will unfortunately lead to unavoidable changes our baselines.

We will need to conduct several tests to ensure this change does not negatively impact our current regional configuration. Once we are satisfied with the results, we can update all the baselines and adjust some runtime parameter names as needed.

[andrew-c-ross]

It looks to me like the main change is the addition of nodal modulation to the astronomical forcing (previously it was only in the boundary forcing). It might be possible to reproduce the previous configuration if the nodal modulation was turned off in both.

[yichengt900]

Thanks, @andrew-c-ross. That aligns with my understanding after reviewing the code. Currently, we do enable nodal modulation for the tidal boundary forcing in both NWA12 and NEP10. This now also automatically enables nodal modulation for the astronomical forcing, as they share the same runtime parameters (TIDE_ADD_NODAL and TIDE_NODAL_REF_DATE) for consistency. I am running a short-term test case in NWA12 with this change and will let you know if I observe any negative impacts.

[yichengt900]

Ok, I’m happy to say that the results from the updated MOM6 with the nodal modulation PR generally align with the NWA published results. Even the Gulf Stream indices are performing well without additional fine-tuning, despite the inclusion of the new changes (nodal modulation and the impact of sulfate reduction on bottom oxygen), which altered the baselines. I plan to update both the MOM6 and COBALT tags, along with new baselines, to the main branch, probably by next week.