Diagnostic fixes to speed, dudt, and dvdt #931
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Recent testing showed a difference in the time derivative diagnostics dudt, dvdt, dhdt for symmetric and non-symmetric grids. The issue appears to be be due to assumed 1-indexing within the `register_time_deriv` functions of MOM_diagnostics, due to use of pointers without explicit start index. This was causing an error in `calculate_derivs`, which assume standard grid indexing. There was no error in non-symmetric mode, which assumes 1-indexing (when global indexing is disabled, as default), but was creating off-by-one errors in symmetric mode for the u and v time derivaties, which typically start at 0 for the x and y axes, respectively. The dhdt diagnostic was unaffected, since h-points always use 1-indexing. This also affected the dKE/dt diagnostic, since they used dudt and dvdt. We resolve this by introducing a lower bound input argument to `register_time_deriv` and use this to define the start index for the various p3d pointers. This is a minor API change which only affects the dudt, dvdt, and dhdt diagnostics, and may change the dudt and dvdt symmetric grid diagnostics.
The speed diagnostic currently requires an interpolation of u and v onto the h-points. On non-symmetric grids, this was causing an error on the west and south boundaries, since the compute loops in `extract_surface_state` did not update the boundaries, which are used in the speed calculation. We resolve this by extending the loops from G%IscB, which only includes the boundary on symmetric grids, to isc-1, which always include the boundaries. This assumes a nonzero halo, and that the halos of u and v have been updated.
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Tests are running here: https://gitlab.gfdl.noaa.gov/ogrp/MOM6/pipelines/8178 |
marshallward
changed the title
speed, dudt, and dvdt
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GitLab PR tests have all passed. |
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The
speeddiagnostic was incorrect on non-symmetric grids, due to missinguandvvalues on the west and south boundaries. This was fixed by explicitly extending loops fromIscBtoisc-1andJscBtojsc-1, i.e. iterating over the same indices for both grid types.The
dudtanddvdtloops were incorrect on symmetric grids, due to pointer arrays being incorrectly 1-indexed. This did not affect non-symmetric grids, which already start at 1. But symmetric grids, which start at 0, were offsetting all values to the west (foru) or south (forv) by one, and omitting the eastmost or northmost values. Thedhdtdiagnostic was unaffected, since h-points are unchanged across symmetric and non-symmetric.These commits will change the values of these diagnostics, but the dynamics are bitwise reproducible.