MOM6 PR test: gfdl-to-main-2025-09-25 on MC 25km RYF

[dougiesquire]

Testing of mom-ocean/MOM6#1680 on dev-MC_25km_jra_ryf.

Companion to ACCESS-NRI/ACCESS-OM3#164

[dougiesquire]

!test repro

[github-actions]

✅ The Bitwise Reproducibility Check Succeeded ✅

When comparing:

• MOM6-PR-test/gfdl-to-main-2025-09-25/dev-MC_25km_jra_ryf (checksums created using commit fc4e02e), against
• dev-MC_25km_jra_ryf (checksums in commit 81a7080)

Further information

The experiment can be found on Gadi at /scratch/tm70/repro-ci/experiments/access-om3-configs/fc4e02e1417675f81361305dca9808ecd83c54b3, and the test results at https://github.com/ACCESS-NRI/access-om3-configs/runs/56601437992.

The checksums generated by this !test command are found in the testing/checksum directory of https://github.com/ACCESS-NRI/access-om3-configs/actions/runs/19753502434/artifacts/4703280038.

The checksums compared against are found here https://github.com/ACCESS-NRI/access-om3-configs/tree/81a708018986dc87df1fd7061629643f0e6b68fe/testing/checksum

Test summary:
✅ test_repro_historical

[dougiesquire]

Note, I set the following parameters to preserve answers, because some defaults have changed relative to the version of MOM6 currently used in ACCESS-OM3:

- MASS_WEIGHT_IN_PRESSURE_GRADIENT_TOP = False !   [Boolean] default = False
+ MASS_WEIGHT_IN_PRESSURE_GRADIENT_TOP = False !   [Boolean] default = True
                                ! If true and MASS_WEIGHT_IN_PRESSURE_GRADIENT is true, use mass weighting when
                                ! interpolating T/S for integrals near the top of the water column in FV
                                ! pressure gradient calculations.
- NDIFF_ANSWER_DATE = 20240101    ! default = 20240101
+ NDIFF_ANSWER_DATE = 20240101    ! default = 99991231
                                ! The vintage of the order of arithmetic to use for the neutral diffusion.
                                ! Values of 20240330 or below recover the answers from the original form of the
                                ! neutral diffusion code, while higher values use mathematically equivalent
                                ! expressions that recover rotational symmetry.
- WAVE_INTERFACE_ANSWER_DATE = 20221231 ! default = 20221231
+ WAVE_INTERFACE_ANSWER_DATE = 20221231 ! default = 99991231
                                ! The vintage of the order of arithmetic and expressions in the surface wave
                                ! calculations.  Values below 20230101 recover the answers from the end of 2022,
                                ! while higher values use updated and more robust forms of the same expressions:
                                !    <  20230101 - Original answers for wave interface routines
                                !    >= 20230101 - More robust expressions for Update_Stokes_Drift
                                !    >= 20230102 - More robust expressions for get_StokesSL_LiFoxKemper
                                !    >= 20230103 - More robust expressions for ust_2_u10_coare3p5

However, when we actually bring these changes into ACCESS-OM3, we'll almost certainly want to accept the default changes (and corresponding answer changes).