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Unphysical ocean temperatures due to Redi diagonal terms #4784

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mark-petersen opened this issue Feb 9, 2022 · 0 comments · Fixed by #4785
Closed

Unphysical ocean temperatures due to Redi diagonal terms #4784

mark-petersen opened this issue Feb 9, 2022 · 0 comments · Fixed by #4785
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@mark-petersen
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An unphysical warming to 60C on the Indonesian coast occurs in the WC14 MPAS-Ocean stand-alone spin-up. This does not occur in E3SM simulations, but it may be covered up by surface fluxes, or cause unrealistic surface fluxes in shallow ocean columns.

See full description in MPAS-Dev/compass#308

@mark-petersen mark-petersen self-assigned this Feb 9, 2022
jonbob added a commit that referenced this issue Mar 17, 2022
… (PR #4785)

Turn off Redi diagonal terms for shallow columns

The MPAS-Ocean Redi diagonal terms are not guaranteed to produce bounded
tracer fields, and in practice produce growing temperatures in a few
ocean columns with fewer than 5 vertical cells in particular
simulations. Redi is meant for isopycnal mixing in the deep ocean, so
not applying Redi diagonal terms in very shallow regions is an
acceptable solution. The problematic behavior is described in
MPAS-Dev/compass#308.

Here we add the flag config_Redi_min_layers_diag_terms. Redi diagonal
terms (2 and 3) are turned off from layer 1 through
config_Redi_min_layers_diag_terms-1, and on from
config_Redi_min_layers_diag_terms through nVertLevels.

If config_Redi_min_layers_diag_terms is set to 1, Redi will be applied
as before this PR, and simulations should compare bit-for-bit or machine
precision to previous simulations.

We are adding the default config_Redi_min_layers_diag_terms=6 (no Redi
applied in columns with 5 or fewer vertical cells). I found in
sensitivity tests that values of 5 and 6 produce no non-monotonic
warming in the problematic case of WC14 ocean-only spin-up with no
surface forcing and rough bathymetry (the most challenging case, see
MPAS-Dev/compass#308) but a value of 4 produces increasing temperatures.

Fixes #4784
[NML]
[non-BFB]
@jonbob jonbob closed this as completed in 6f7d0ba Mar 18, 2022
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