*Non-Boussinesq revision of diabatic_driver #430
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This commit completes the non-Boussinesq revision of the diabatic_driver code. The revised code uses thickness_to_dz and works with internal variables in vertical distances in the denominator of diffusive flux calculations in diabatic_ALE_legacy, diabatic_ALE and layered_diabatic. The code now uses find_ustar to extract the friction velocities passed to KPP_compute. The (tiny) boundary layer tracer diffusivity is also rescaled to [H2 T-1]. With this set of changes, all implicit references to Boussinesq reference density are eliminated from the calculations in diabatic_driver when in non-Boussinesq mode. A total of 14 thickness rescaling factors were cancelled out, and there are 15 new or renamed variables in the diabatic routines. 4 new checksum calls are also added to diabatic_ALE_legacy to assist in debugging. Because GV%Z_to_H is an exact power of 2 in Boussinesq mode, all answers are bitwise identical in that mode, but in non-Boussinesq mode the use of the layer averaged specific volume to convert thicknesses to vertical distances leads to changing answers.
Hallberg-NOAA
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@@ Coverage Diff @@
## dev/gfdl #430 +/- ##
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Coverage 38.05% 38.06%
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Files 269 269
Lines 77024 77047 +23
Branches 14221 14223 +2
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+ Hits 29314 29329 +15
- Misses 42394 42400 +6
- Partials 5316 5318 +2
... and 1 file with indirect coverage changes 📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more |
| @@ -145,8 +146,8 @@ module MOM_diabatic_driver | |||
| !! diffusivity of Kd_min_tr (see below) were operating. | |||
| real :: Kd_BBL_tr !< A bottom boundary layer tracer diffusivity that | |||
| !! will allow for explicitly specified bottom fluxes | |||
| !! [H Z T-1 ~> m2 s-1 or kg m-1 s-1]. The entrainment at the bottom is at | |||
| !! least sqrt(Kd_BBL_tr*dt) over the same distance. | |||
| !! [H2 T-1 ~> m2 s-1 or kg2 m-4 s-2]. The entrainment at the | |||
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NB units should be kg m-1 s-1 ?
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In this case, Kd_BBL_tr has weird units because it is being used (by multiplying by the timestep and taking a the square root) to set a minimal smoothing thickness for tracers at the bottom. Kd_BBL_tr is effectively a diffusivity times a density in non-Boussinesq mode. In this case we are effectively using a prescribed density - the same one (RHO_KV_CONVERT) as is being used to convert diffusivities from [m2 s-1] to [kg m-1 s-1] in non-Boussinesq mode.
Were we being more precise, this density that is being multiplied by a near-bottom diffusivity would probably be a density averaged over a near-bottom thickness, and perhaps that averaging thickness itself would be determined by sqrt(Kd_BBL * rho_avg), but this then becomes an implicit, iteratively solved equation that hardly seems like it would worth the extra complexity and cost.
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Gaea regression: https://gitlab.gfdl.noaa.gov/ogrp/MOM6/-/pipelines/20223 ✔️ |
This commit completes the non-Boussinesq revision of the diabatic_driver code. The revised code uses thickness_to_dz and works with internal variables in vertical distances in the denominator of diffusive flux calculations in diabatic_ALE_legacy, diabatic_ALE and layered_diabatic. The code now uses find_ustar to extract the friction velocities passed to KPP_compute. The (tiny) boundary layer tracer diffusivity is also rescaled to [H2 T-1]. With this set of changes, all implicit references to Boussinesq reference density are eliminated from the calculations in diabatic_driver when in non-Boussinesq mode.
A total of 14 thickness rescaling factors were cancelled out, and there are 15 new or renamed variables in the diabatic routines. 4 new checksum calls are also added to diabatic_ALE_legacy to assist in debugging.
Because GV%Z_to_H is an exact power of 2 in Boussinesq mode, all answers are bitwise identical in that mode, but in non-Boussinesq mode the use of the layer averaged specific volume to convert thicknesses to vertical distances leads to changing answers.