+Obsoleted 9 parameters, including BETTER_BOUND_KH

  Obsoleted 9 runtime parameters that always take the same value, as agreed upon
in a MOM6 consortium wide conversations on June 2, 2025, and added tests to
catch these parameters in MOM_obsolete_params.  The parameters that were
obsoleted include BETTER_BOUND_KH, BETTER_BOUND_AH, USE_DIABATIC_TIME_BUG,
FIX_UNSPLIT_DT_VISC_BUG, CFL_BASED_TRUNCATIONS, ICE_SHELF_BUOYANCY_FLUX_ITT_BUG,
ICE_SHELF_SALT_FLUX_ITT_BUG and KD_BACKGROUND_VIA_KDML_BUG.  The runtime
parameter MAXVEL still exists, but it is logged in a different order than
before, changing the contents of the MOM_parameter_doc files. All answers are
bitwise identical in cases that run, but cases that use these parameters will
experience a fatal error.

Author: Hallberg-NOAA

src/core/MOM.F90

@@ -314,8 +314,6 @@ module MOM
   logical :: useMEKE                 !< If true, call the MEKE parameterization.
   logical :: use_stochastic_EOS      !< If true, use the stochastic EOS parameterizations.
   logical :: useWaves                !< If true, update Stokes drift
-  logical :: use_diabatic_time_bug   !< If true, uses the wrong calendar time for diabatic processes,
-                                     !! as was done in MOM6 versions prior to February 2018.
   real :: dtbt_reset_period          !< The time interval between dynamic recalculation of the
                                      !! barotropic time step [T ~> s]. If this is negative dtbt is never
                                      !! calculated, and if it is 0, dtbt is calculated every step.
@@ -840,15 +838,9 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
 
   rel_time = 0.0
   do n=1,n_max
-    if (CS%use_diabatic_time_bug) then
-      ! This wrong form of update was used until Feb 2018, recovered with CS%use_diabatic_time_bug=T.
-      CS%Time = Time_start + real_to_time(US%T_to_s*int(floor(rel_time+0.5*dt+0.5)))
-      rel_time = rel_time + dt
-    else
-      rel_time = rel_time + dt ! The relative time at the end of the step.
-      ! Set the universally visible time to the middle of the time step.
-      CS%Time = Time_start + real_to_time(US%T_to_s*(rel_time - 0.5*dt))
-    endif
+    rel_time = rel_time + dt ! The relative time at the end of the step.
+    ! Set the universally visible time to the middle of the time step.
+    CS%Time = Time_start + real_to_time(US%T_to_s*(rel_time - 0.5*dt))
     ! Set the local time to the end of the time step.
     Time_local = Time_start + real_to_time(US%T_to_s*rel_time)
 
@@ -878,16 +870,12 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
       endif
 
       end_time_thermo = Time_local
-      if (dtdia > dt .and. .not. CS%use_diabatic_time_bug) then
+      if (dtdia > dt) then
         ! If necessary, temporarily reset CS%Time to the center of the period covered
         ! by the call to step_MOM_thermo, noting that they begin at the same time.
-        ! This step was missing prior to Feb 2018, and is skipped with CS%use_diabatic_time_bug=T.
         CS%Time = CS%Time + real_to_time(0.5*US%T_to_s*(dtdia-dt))
-      endif
-      if (dtdia > dt .or. CS%use_diabatic_time_bug) then
         ! The end-time of the diagnostic interval needs to be set ahead if there
         ! are multiple dynamic time steps worth of thermodynamics applied here.
-        ! This line was not conditional prior to Feb 2018, recovered with CS%use_diabatic_time_bug=T.
         end_time_thermo = Time_local + real_to_time(US%T_to_s*(dtdia-dt))
       endif
 
@@ -903,8 +891,7 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
       CS%t_dyn_rel_thermo = -dtdia
       if (showCallTree) call callTree_waypoint("finished diabatic_first (step_MOM)")
 
-      if (dtdia > dt .and. .not. CS%use_diabatic_time_bug) & ! Reset CS%Time to its previous value.
-        ! This step was missing prior to Feb 2018, recovered with CS%use_diabatic_time_bug=T.
+      if (dtdia > dt) & ! Reset CS%Time to its previous value.
         CS%Time = Time_start + real_to_time(US%T_to_s*(rel_time - 0.5*dt))
     endif ! end of block "(CS%diabatic_first .and. (CS%t_dyn_rel_adv==0.0))"
 
@@ -1004,8 +991,7 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
 
       ! If necessary, temporarily reset CS%Time to the center of the period covered
       ! by the call to step_MOM_thermo, noting that they end at the same time.
-      ! This step was missing prior to Feb 2018, and is skipped with CS%use_diabatic_time_bug=T.
-      if (dtdia > dt .and. .not. CS%use_diabatic_time_bug) &
+      if (dtdia > dt) &
         CS%Time = CS%Time - real_to_time(0.5*US%T_to_s*(dtdia-dt))
 
       ! Apply diabatic forcing, do mixing, and regrid.
@@ -1024,8 +1010,7 @@ subroutine step_MOM(forces_in, fluxes_in, sfc_state, Time_start, time_int_in, CS
       endif
 
       ! Reset CS%Time to its previous value.
-      ! This step was missing prior to Feb 2018, and is skipped with CS%use_diabatic_time_bug=T.
-      if (dtdia > dt .and. .not. CS%use_diabatic_time_bug) &
+      if (dtdia > dt) &
         CS%Time = Time_start + real_to_time(US%T_to_s*(rel_time - 0.5*dt))
     endif
 
@@ -2732,11 +2717,6 @@ subroutine initialize_MOM(Time, Time_init, param_file, dirs, CS, &
                default=default_answer_date, do_not_log=non_Bous)
   if (non_Bous) CS%answer_date = 99991231
 
-  call get_param(param_file, "MOM", "USE_DIABATIC_TIME_BUG", CS%use_diabatic_time_bug, &
-                 "If true, uses the wrong calendar time for diabatic processes, as was "//&
-                 "done in MOM6 versions prior to February 2018. This is not recommended.", &
-                 default=.false.)
-
   call get_param(param_file, "MOM", "SAVE_INITIAL_CONDS", save_IC, &
                  "If true, write the initial conditions to a file given "//&
                  "by IC_OUTPUT_FILE.", default=.false.)

src/core/MOM_dynamics_unsplit.F90

@@ -634,9 +634,6 @@ subroutine initialize_dyn_unsplit(u, v, h, tv, Time, G, GV, US, param_file, diag
   character(len=48) :: flux_units
   ! This include declares and sets the variable "version".
 # include "version_variable.h"
-  logical :: use_correct_dt_visc
-  logical :: test_value  ! This is used to determine whether a logical parameter is being set explicitly.
-  logical :: explicit_bug, explicit_fix ! These indicate which parameters are set explicitly.
   integer :: isd, ied, jsd, jed, nz, IsdB, IedB, JsdB, JedB
   isd = G%isd ; ied = G%ied ; jsd = G%jsd ; jed = G%jed ; nz = GV%ke
   IsdB = G%IsdB ; IedB = G%IedB ; JsdB = G%JsdB ; JedB = G%JedB
@@ -655,33 +652,6 @@ subroutine initialize_dyn_unsplit(u, v, h, tv, Time, G, GV, US, param_file, diag
   call log_version(param_file, mdl, version, "")
 
   call get_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", CS%dt_visc_bug, &
-                 "If false, use the correct timestep in the viscous terms applied in the first "//&
-                 "predictor step with the unsplit time stepping scheme, and in the calculation "//&
-                 "of the turbulent mixed layer properties for viscosity with unsplit or "//&
-                 "unsplit_RK2.  If true, an older incorrect value is used.", &
-                 default=.false., do_not_log=.true.)
-  ! This is used to test whether UNSPLIT_DT_VISC_BUG is being actively set.
-  call get_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", test_value, default=.true., do_not_log=.true.)
-  explicit_bug = CS%dt_visc_bug .eqv. test_value
-  call get_param(param_file, mdl, "FIX_UNSPLIT_DT_VISC_BUG", use_correct_dt_visc, &
-                 "If true, use the correct timestep in the viscous terms applied in the first "//&
-                 "predictor step with the unsplit time stepping scheme, and in the calculation "//&
-                 "of the turbulent mixed layer properties for viscosity with unsplit or "//&
-                 "unsplit_RK2.", default=.true., do_not_log=.true.)
-  call get_param(param_file, mdl, "FIX_UNSPLIT_DT_VISC_BUG", test_value, default=.false., do_not_log=.true.)
-  explicit_fix = use_correct_dt_visc .eqv. test_value
-
-  if (explicit_bug .and. explicit_fix .and. (use_correct_dt_visc .eqv. CS%dt_visc_bug)) then
-    ! UNSPLIT_DT_VISC_BUG is being explicitly set, and should not be changed.
-    call MOM_error(FATAL, "UNSPLIT_DT_VISC_BUG and FIX_UNSPLIT_DT_VISC_BUG are both being set "//&
-                   "with inconsistent values.  FIX_UNSPLIT_DT_VISC_BUG is an obsolete "//&
-                   "parameter and should be removed.")
-  elseif (explicit_fix) then
-    call MOM_error(WARNING, "FIX_UNSPLIT_DT_VISC_BUG is an obsolete parameter.  "//&
-                   "Use UNSPLIT_DT_VISC_BUG instead (noting that it has the opposite sense).")
-    CS%dt_visc_bug = .not.use_correct_dt_visc
-  endif
-  call log_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", CS%dt_visc_bug, &
                  "If false, use the correct timestep in the viscous terms applied in the first "//&
                  "predictor step with the unsplit time stepping scheme, and in the calculation "//&
                  "of the turbulent mixed layer properties for viscosity with unsplit or "//&

src/core/MOM_dynamics_unsplit_RK2.F90

@@ -581,9 +581,6 @@ subroutine initialize_dyn_unsplit_RK2(u, v, h, tv, Time, G, GV, US, param_file,
   character(len=48) :: flux_units
   ! This include declares and sets the variable "version".
 # include "version_variable.h"
-  logical :: use_correct_dt_visc
-  logical :: test_value  ! This is used to determine whether a logical parameter is being set explicitly.
-  logical :: explicit_bug, explicit_fix ! These indicate which parameters are set explicitly.
   integer :: isd, ied, jsd, jed, nz, IsdB, IedB, JsdB, JedB
   isd = G%isd ; ied = G%ied ; jsd = G%jsd ; jed = G%jed ; nz = GV%ke
   IsdB = G%IsdB ; IedB = G%IedB ; JsdB = G%JsdB ; JedB = G%JedB
@@ -618,33 +615,6 @@ subroutine initialize_dyn_unsplit_RK2(u, v, h, tv, Time, G, GV, US, param_file,
                  units="nondim", default=0.0)
 
   call get_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", CS%dt_visc_bug, &
-                 "If false, use the correct timestep in the viscous terms applied in the first "//&
-                 "predictor step with the unsplit time stepping scheme, and in the calculation "//&
-                 "of the turbulent mixed layer properties for viscosity with unsplit or "//&
-                 "unsplit_RK2.  If true, an older incorrect value is used.", &
-                 default=.false., do_not_log=.true.)
-  ! This is used to test whether UNSPLIT_DT_VISC_BUG is being explicitly set.
-  call get_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", test_value, default=.true., do_not_log=.true.)
-  explicit_bug = CS%dt_visc_bug .eqv. test_value
-  call get_param(param_file, mdl, "FIX_UNSPLIT_DT_VISC_BUG", use_correct_dt_visc, &
-                 "If true, use the correct timestep in the viscous terms applied in the first "//&
-                 "predictor step with the unsplit time stepping scheme, and in the calculation "//&
-                 "of the turbulent mixed layer properties for viscosity with unsplit or "//&
-                 "unsplit_RK2.", default=.true., do_not_log=.true.)
-  call get_param(param_file, mdl, "FIX_UNSPLIT_DT_VISC_BUG", test_value, default=.false., do_not_log=.true.)
-  explicit_fix = use_correct_dt_visc .eqv. test_value
-
-  if (explicit_bug .and. explicit_fix .and. (use_correct_dt_visc .eqv. CS%dt_visc_bug)) then
-    ! UNSPLIT_DT_VISC_BUG is being explicitly set, and should not be changed.
-    call MOM_error(FATAL, "UNSPLIT_DT_VISC_BUG and FIX_UNSPLIT_DT_VISC_BUG are both being set "//&
-                   "with inconsistent values.  FIX_UNSPLIT_DT_VISC_BUG is an obsolete "//&
-                   "parameter and should be removed.")
-  elseif (explicit_fix) then
-    call MOM_error(WARNING, "FIX_UNSPLIT_DT_VISC_BUG is an obsolete parameter.  "//&
-                   "Use UNSPLIT_DT_VISC_BUG instead (noting that it has the opposite sense).")
-    CS%dt_visc_bug = .not.use_correct_dt_visc
-  endif
-  call log_param(param_file, mdl, "UNSPLIT_DT_VISC_BUG", CS%dt_visc_bug, &
                  "If false, use the correct timestep in the viscous terms applied in the first "//&
                  "predictor step with the unsplit time stepping scheme, and in the calculation "//&
                  "of the turbulent mixed layer properties for viscosity with unsplit or "//&

src/diagnostics/MOM_obsolete_params.F90

@@ -82,6 +82,9 @@ subroutine find_obsolete_params(param_file)
   call obsolete_real(param_file, "HALOCLINE_FILTER_LENGTH")
   call obsolete_real(param_file, "HALOCLINE_STRAT_TOL")
 
+  call obsolete_logical(param_file, "ICE_SHELF_BUOYANCY_FLUX_ITT_BUG", .true.)
+  call obsolete_logical(param_file, "ICE_SHELF_SALT_FLUX_ITT_BUG", .true.)
+
   ! Test for inconsistent parameter settings.
   split = .true. ; test_logic = .false.
   call read_param(param_file,"SPLIT",split)
@@ -108,10 +111,23 @@ subroutine find_obsolete_params(param_file)
   call obsolete_real(param_file, "MIN_Z_DIAG_INTERVAL")
   call obsolete_char(param_file, "Z_OUTPUT_GRID_FILE")
 
+  call obsolete_logical(param_file, "CFL_BASED_TRUNCATIONS", .true.)
+  call obsolete_logical(param_file, "KD_BACKGROUND_VIA_KDML_BUG", .false.)
+  call obsolete_logical(param_file, "USE_DIABATIC_TIME_BUG", .false.)
+
   call read_param(param_file, "INTERPOLATE_SPONGE_TIME_SPACE", test_logic)
   call obsolete_logical(param_file, "NEW_SPONGES", warning_val=test_logic, &
                         hint="Use INTERPOLATE_SPONGE_TIME_SPACE instead.")
 
+  test_logic = .true. ; call read_param(param_file, "BOUND_KH", test_logic)
+  call obsolete_logical(param_file, "BETTER_BOUND_KH", warning_val=test_logic, hint="Use BOUND_KH alone.")
+  test_logic = .true. ; call read_param(param_file, "BOUND_AH", test_logic)
+  call obsolete_logical(param_file, "BETTER_BOUND_AH", warning_val=test_logic, hint="Use BOUND_AH alone.")
+
+  test_logic = .false. ; call read_param(param_file, "UNSPLIT_DT_VISC_BUG", test_logic)
+  call obsolete_logical(param_file, "FIX_UNSPLIT_DT_VISC_BUG", warning_val=(.not.test_logic), &
+                        hint="Use UNSPLIT_DT_VISC_BUG instead, but with the reversed meaning.")
+
   call obsolete_logical(param_file, "SMOOTH_RI", hint="Instead use N_SMOOTH_RI.")
 
   call obsolete_logical(param_file, "INTERNAL_TIDE_CORNER_ADVECT", .false.)

src/ice_shelf/MOM_ice_shelf.F90

@@ -197,8 +197,6 @@ module MOM_ice_shelf
                                          !! divided by the von Karman constant VK. Was 1/8.
   real :: Vk                             !< Von Karman's constant - dimensionless
   real :: Rc                             !< critical flux Richardson number.
-  logical :: buoy_flux_itt_bug           !< If true, fixes buoyancy iteration bug
-  logical :: salt_flux_itt_bug           !< If true, fixes salt iteration bug
   real :: buoy_flux_itt_threshold        !< Buoyancy iteration threshold for convergence
 
   !>@{ Diagnostic handles
@@ -615,7 +613,7 @@ subroutine shelf_calc_flux(sfc_state_in, fluxes_in, Time, time_step_in, CS)
                 ! This is Newton's method without any bounds.  Should bounds be needed?
                 wB_flux_new = wB_flux - (wB_flux_new - wB_flux) / dDwB_dwB_in
                 ! Update wB_flux
-                if (CS%buoy_flux_itt_bug) wB_flux = wB_flux_new
+                wB_flux = wB_flux_new
               enddo !it3
             endif
 
@@ -688,8 +686,6 @@ subroutine shelf_calc_flux(sfc_state_in, fluxes_in, Time, time_step_in, CS)
                 Sbdry(i,j) = Sbdry_it
               endif ! Sb_min_set
 
-              if (.not.CS%salt_flux_itt_bug) Sbdry(i,j) = Sbdry_it
-
             endif ! CS%find_salt_root
 
           enddo !it1
@@ -1686,10 +1682,6 @@ subroutine initialize_ice_shelf(param_file, ocn_grid, Time, CS, diag, Time_init,
   call get_param(param_file, mdl, "ICE_SHELF_RC", CS%Rc, &
                  "Critical flux Richardson number for ice melt ", &
                  units="nondim", default=0.20)
-  call get_param(param_file, mdl, "ICE_SHELF_BUOYANCY_FLUX_ITT_BUG", CS%buoy_flux_itt_bug, &
-                 "Bug fix of buoyancy iteration", default=.true.)
-  call get_param(param_file, mdl, "ICE_SHELF_SALT_FLUX_ITT_BUG", CS%salt_flux_itt_bug, &
-                 "Bug fix of salt iteration", default=.true.)
   call get_param(param_file, mdl, "ICE_SHELF_BUOYANCY_FLUX_ITT_THRESHOLD", CS%buoy_flux_itt_threshold, &
                  "Convergence criterion of Newton's method for ice shelf "//&
                  "buoyancy iteration.", units="nondim", default=1.0e-4)