Add MASS_WEIGHT_IN_PGF_VANISHED_ONLY to modify mass weighting in PGF

[claireyung]

This PR introduces the runtime variable MASS_WEIGHT_IN_PGF_VANISHED_ONLY
which has default False. If true, then the MASS_WEIGHT_IN_PRESSURE_GRADIENT
and MASS_WEIGHT_IN_PRESSURE_GRADIENT_TOP effect of weighting T/S integrals
in slanted grid cell FV PGF calculation is turned off if both sides of the
grid cell are nonvanished, where nonvanished means thickness greater than
RESET_INTXPA_H_NONVANISHED which defaults to 1e-6 m. Since the benefit of
MASS_WEIGHT_IN_PRESSURE_GRADIENT happens in vanished layers (creating a
fake PGF away from vanished layer, which is arrested by upwinded viscosity)
the benefit is still there, but now we can use MASS_WEIGHT_IN_PRESSURE_GRADIENT
for coordinates that also have slanted layers in the open ocean that are
not vanished, e.g. sigma coordinates or SIGMA_SHELF_ZSTAR coordinates in the
ice shelf where we DO trust T and S values. Additionally, this is required
near a grounding line in a 3D z-coord ice shelf as some strange looking
slanted non-vanished cells can emerge, and MWIPG being on would create fake PGFs
in non-vanished cells (and therefore generating spurious currents).

Recommend MASS_WEIGHT_IN_PGF_VANISHED_ONLY to be set to True, as well as
MASS_WEIGHT_IN_PRESSURE_GRADIENT and MASS_WEIGHT_IN_PRESSURE_GRADIENT_TOP
if you have vanishing layers with min thickness < 0.1m.

Also modifies MassWt_u and MassWt_v diagnostics to reflect usage
of MASS_WEIGHT_IN_PRESSURE_GRADIENT.

This commit should not change default answers since it defaults to False. However,
my implementation is not very efficient because it involves a lot of comparing
thicknesses and should probably be optimised.

I would appreciate suggestions to optimise this code!!

[Hallberg-NOAA]

Thank you for this new contribution. I appreciate where this is going, but I believe that there are dimensionally inconsistent expressions that need to be revisited, as identified in specific comments at the relevant lines. To evaluate the dimensional consistency of these expressions, you should verify that different values of H_RESCALE_POWER and Z_RESCALE_POWER give identical results.

There is also some inconsistent indenting in a few places.

Once these problems are corrected, I will be happy to accept this PR.

[codecov]

Codecov Report

Attention: Patch coverage is 21.97802% with 71 lines in your changes missing coverage. Please review.

Project coverage is 38.13%. Comparing base (83efb99) to head (63fedcd).
Report is 34 commits behind head on dev/gfdl.

Files with missing lines	Patch %	Lines
src/core/MOM_density_integrals.F90	18.51%	58 Missing and 8 partials ⚠️
src/core/MOM_PressureForce_FV.F90	50.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           dev/gfdl     #810      +/-   ##
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- Coverage     38.15%   38.13%   -0.02%     
============================================
  Files           296      296              
  Lines         87249    87400     +151     
  Branches      16284    16339      +55     
============================================
+ Hits          33287    33331      +44     
- Misses        47975    48067      +92     
- Partials       5987     6002      +15     

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[claireyung]

Thanks Bob! I think I have added your suggested changes. I tested the code on the sigma seamount, showing that

1. we can now use MASS_WEIGHT_IN_PRESSURE_GRADIENT for sigma seamount
2. I got the same answers (with the fix) using H_RESCALE_FACTOR and Z_RESCALE_FACTOR = +/- 140 for both Boussinesq and non-Boussinesq versions. I did this by comparing output of runs: https://gist.github.com/claireyung/c80d3b44bc1861fbdf20c180bcf73586

Please let me know if there are any further changes or verification I should be doing! Thanks

[Hallberg-NOAA]

This PR has now addressed all of the concerns that I had with the original version, and I am pleased to accept it. Thank you for this contribution.

[Hallberg-NOAA]

This PR has passed pipeline testing at https://gitlab.gfdl.noaa.gov/ogrp/mom6ci/MOM6/-/pipelines/26364 with the expected warnings about a new parameter in many MOM_parameter_doc files.