+*Fix 3-equation ice-ocean flux iteration#972
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Fix the 3-equation iteration for the buoyancy flux between the ocean and an overlying ice-shelf when ICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIX is true and SHELF_3EQ_GAMMA it false. This code now uses proper bounding of the self-consistent solution, avoiding further amplifying the fluxes in the cases when the differences between the diffusivities of heat and salt to make the buoyancy flux destabilizing for finite turbulent mixing. Both the false-position iterations and the (appropriately chosen) Newton's method iterations have been extensively examined and determined to be working correctly via print statements that have subsequently been removed for efficiency. Previously, the code to determine the 3-equation solution for the buoyancy flux between the ocean and an ice shelf had been skipping iteration altogether or doing un-bounded Newton's method iterations with a sign error in part of the derivative, including taking the square root of negative numbers, leading to the issue described at NOAA-GFDL#945. That issue has now been corrected and can be closed once this commit has been merged into the dev/gfdl branch of MOM6. This commit also changes the names of the runtime parameters to correct the ice shelf flux iteration bugs from ICE_SHELF_BUOYANCY_FLUX_ITT_BUG and ICE_SHELF_SALT_FLUX_ITT_BUG to ICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIX and ICE_SHELF_SALT_FLUX_ITT_BUGFIX to avoid confusion with other ..._BUG parameters where `true` is to turn the bugs on, whereas here `true` fixes them. The old names are retained via `old_name` arguments to the `get_param()` calls, so no existing configurations will be disrupted by these changes. Additionally, an expression to determine a scaling factor to limit ice-shelf bottom slopes in `calc_shelf_driving_stress()` was refactored to avoid the possibility of division by zero. This commit will change (and correct) answers for cases with ICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIX set to true, but as these would often fail with a NaN from taking the square root of a negative value, it is very unlikely that any such configurations are actively being used, and there seems little point in retaining the previous answers. No answers are changed in cases that do not use an active ice shelf.
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## dev/gfdl #972 +/- ##
============================================
- Coverage 37.41% 37.37% -0.04%
============================================
Files 304 306 +2
Lines 93061 93793 +732
Branches 17860 17985 +125
============================================
+ Hits 34816 35053 +237
- Misses 51678 52140 +462
- Partials 6567 6600 +33 ☔ View full report in Codecov by Sentry. 🚀 New features to boost your workflow:
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Fix the 3-equation iteration for the buoyancy flux between the ocean and an overlying ice-shelf when
ICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIX = trueandSHELF_3EQ_GAMMA = false. This code now uses proper bounding of the self-consistent solution, avoiding further amplifying the fluxes in the cases when the differences between the diffusivities of heat and salt to make the buoyancy flux destabilizing for finite turbulent mixing. Both the false-position iterations and the (appropriately chosen) Newton's method iterations have been extensively examined and determined to be working correctly via print statements that have subsequently been removed for efficiency.Previously, the code to determine the 3-equation solution for the buoyancy flux between the ocean and an ice shelf had been skipping iteration altogether or doing un-bounded Newton's method iterations with a sign error in part of the derivative, including taking the square root of negative numbers, leading to the issue described at #945. That issue has now been corrected and can be closed once this commit has been merged into the dev/gfdl branch of MOM6.
This commit also changes the names of the runtime parameters to correct the ice shelf flux iteration bugs from
ICE_SHELF_BUOYANCY_FLUX_ITT_BUGandICE_SHELF_SALT_FLUX_ITT_BUGtoICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIXandICE_SHELF_SALT_FLUX_ITT_BUGFIXto avoid confusion with other..._BUGparameters wheretrueis to turn the bugs on, whereas heretruefixes them. The old names are retained viaold_namearguments to theget_param()calls, so no existing configurations will be disrupted by these changes.Additionally, an expression to determine a scaling factor to limit ice-shelf bottom slopes in
calc_shelf_driving_stress()was refactored to avoid the possibility of division by zero.This commit will change (and correct) answers for cases with
ICE_SHELF_BUOYANCY_FLUX_ITT_BUGFIXset to true, but as these would often fail with a NaN from taking the square root of a negative value, it is very unlikely that any such configurations are actively being used, and there seems little point in retaining the previous answers. No answers are changed in cases that do not use an active ice shelf.