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Fixed an incorrect area used to calculate cell-centered ocean surface velocity under the ice shelf, which can impact the calculation of ice-shelf friction velocity. Added missing flags to some allocate_surface_state calls so that sfc_state%taux_shelf and sfc_state%tauy_shelf are allocated. This is required for the surface-stress-based (rather than surface-velocity-based) calculation of ice-shelf friction velocity. Also added taux_shelf and tauy_shelf as diagnostics for the ocean surface stress under the ice shelf.

@Hallberg-NOAA Hallberg-NOAA added bug Something isn't working answer-changing A change in results (actual or potential) labels Dec 8, 2025
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@Hallberg-NOAA I ended up removing the taux_shelf and tauy_shelf diagnostics entirely, as I only needed them during debugging to figure out that sfc_state%taux_shelf and sfc_state%tauy_shelf were not being allocated, which this PR fixes. I believe this PR should be good to go

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This simpler PR looks to me like it is ready to go.

I would note that this corrects an obvious symmetry-breaking bug that will change answers in some cases with an ice shelf using USTAR_SHELF_FROM_VEL = True without adding a bug-fix flag. I do not think that such configurations are widely used (or else the symmetry breaking should have been detected earlier), so this may be a case where no bug recovery option is needed, but we might come to regret this decision later.

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Upon further reflection, Alex and I decided that we should probably follow the standard MOM6 process and add a runtime bug-fix flag around the code correcting this bug, so that answers are not changed by default.

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This final change addresses all the concerns I had previously.

@Hallberg-NOAA Hallberg-NOAA added Parameter change Input parameter changes (addition, removal, or description) and removed answer-changing A change in results (actual or potential) labels Dec 9, 2025
Fixed an incorrect area used to calculate cell-centered ocean surface velocity under the ice_shelf, which can impact the calculation of ice-shelf friction velocity. Added missing flags to some allocate_surface_state calls so that sfc_state%taux_shelf and sfc_state%tauy_shelf are allocated. This is required for the surface-stress-based (rather than surface-velocity-based) calculation of ice-shelf friction velocity. Also added taux_shelf and tauy_shelf as diagnostics for the surface stress under the ice shelf.
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This PR passed pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/mom6ci/MOM6/-/pipelines/29558.

@Hallberg-NOAA Hallberg-NOAA merged commit c008a01 into NOAA-GFDL:dev/gfdl Dec 9, 2025
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