Fake PR for QG Leith Visc bug fix #10
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VarMix_CS%slope_x was being set with units of [Z L-1 ~> nondim], but described in comments as though it was simply [nondim], and then used in the (apparently unused?) calculate_slopes=.false. branch in calc_slope_functions_using_just_e as though its units actually were [nondim]. This commit corrects this inconsistency, while also rescaling the internal slope variables in that routine to also have the proper units of [Z L-1 ~> nondim]. In so doing, several rescaling factors could be eliminated from the calculations. In addition, the slopes used in calc_QG_Leith_viscosity were also being rescaled with the wrong factor or had dimensionally incorrect tiny values in some denominators, and this has been corrected as well. In testing this rescaling fix, a number of other bugs were identified with USE_QG_LEITH_VISC=True (as described at github.com/mom-ocean/issues/1590), so a fatal error message was added if this option is enabled. All answers in the MOM6-examples test suite are bitwise identical, but the code will now give a fatal error if USE_QG_LEITH_VISC=.true.
This commit includes a series of changes that get MOM6 to reproduce across
processor counts, layouts and restarts when USE_QG_LEITH_VISC = True. These
changes include:
- Expanding the halos to 2 in updates for h, tv%T and tv%S
- Adding a thermo_var_ptrs and a timestep argument to to the interfaces to
horizontal_viscosity and initialize_dyn_split_RK2
- Adding the new publicly visible routine calc_QG_slopes
- Adding the arguments slope_x and slope_y to calc_QG_Leith_viscosity and
avoiding the use of the VarMix%slope_[xy] elements in that routine
- Increasing some loop extents in calc_QG_Leith_viscosity
Note that several of the expansions of the halo sizes in updates or in some
of the calculations are not necessary if an extra halo update is included for
slope_x and slope_y after the call to calc_QG_slopes in horizontal_viscosity.
This extra halo update has also been included. As it stands, this commit is a
working draft intended for discussion; once there is a collective decision about
how to handle some of the options here, there should be some clean-up before
this code is merged into the main branch of MOM6. This commit includes several
changes to publicly visible interfaces, and it will change answers with
USE_QG_LEITH_VISC = True, but answers and output are bitwise identical in other
cases.
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This PR is for discussion only of the changes needed for the QG Leith viscosity to reproduce across PE count, layouts and restarts to address mom-ocean#1590.
An actual PR would go instead via the NOAA-GFDL: dev/gfdl, but some cleanup and conflict resolution is needed before this could occur.