Fix logic for setting KV_ML_INVZ2 from KVML

- We were reading KV_ML_INVZ2 without logging, then checking for KVML
  and finally logging based on a combination of the two. This had the side
  affect that we get warnings about not using KVML even if KVML was not
  present.
- The fix checks for KVML first, and then changes the default so that
  when KVML=1e-4 is replaced by KV_ML_INVZ2=1e-4 we end up with no
  warnings and KVML can be obsoleted safely.
  Note: this commit alone does not remove all warnings from the MOM6-examples
  suite because we still need to fix the MOM_input that still use KVML
- KVML needs to be unscaled since it is the default for KV_ML_INVZ2
- tc3 used KVML and has been corrected.

.testing/tc3/MOM_input

@@ -283,10 +283,10 @@ HMIX_FIXED = 20.0               !   [m]
 KV = 1.0E-04                    !   [m2 s-1]
                                 ! The background kinematic viscosity in the interior.
                                 ! The molecular value, ~1e-6 m2 s-1, may be used.
-KVML = 0.01                     !   [m2 s-1] default = 1.0E-04
-                                ! The kinematic viscosity in the mixed layer.  A typical
-                                ! value is ~1e-2 m2 s-1. KVML is not used if
-                                ! BULKMIXEDLAYER is true.  The default is set by KV.
+KV_ML_INVZ2 = 0.01              !   [m2 s-1] default = 0.0
+                                ! An extra kinematic viscosity in a mixed layer of thickness HMIX_FIXED, with
+                                ! the actual viscosity scaling as 1/(z*HMIX_FIXED)^2, where z is the distance
+                                ! from the surface, to allow for finite wind stresses to be transmitted through.
 HBBL = 10.0                     !   [m]
                                 ! The thickness of a bottom boundary layer with a
                                 ! viscosity of KVBBL if BOTTOMDRAGLAW is not defined, or

src/parameterizations/vertical/MOM_vert_friction.F90

@@ -2156,6 +2156,7 @@ subroutine vertvisc_init(MIS, Time, G, GV, US, param_file, diag, ADp, dirs, &
 # include "version_variable.h"
   character(len=40)  :: mdl = "MOM_vert_friction" ! This module's name.
   character(len=40)  :: thickness_units
+  real :: Kv_mks ! KVML in MKS
 
   if (associated(CS)) then
     call MOM_error(WARNING, "vertvisc_init called with an associated "// &
@@ -2339,30 +2340,22 @@ subroutine vertvisc_init(MIS, Time, G, GV, US, param_file, diag, ADp, dirs, &
 
   CS%Kvml_invZ2 = 0.0
   if (GV%nkml < 1) then
-    call get_param(param_file, mdl, "KV_ML_INVZ2", CS%Kvml_invZ2, &
-                 "An extra kinematic viscosity in a mixed layer of thickness HMIX_FIXED, "//&
-                 "with the actual viscosity scaling as 1/(z*HMIX_FIXED)^2, where z is the "//&
-                 "distance from the surface, to allow for finite wind stresses to be "//&
-                 "transmitted through infinitesimally thin surface layers.  This is an "//&
-                 "older option for numerical convenience without a strong physical basis, "//&
-                 "and its use is now discouraged.", &
-                 units="m2 s-1", default=-1.0, scale=US%m2_s_to_Z2_T, do_not_log=.true.)
-    if (CS%Kvml_invZ2 < 0.0) then
-      call get_param(param_file, mdl, "KVML", CS%Kvml_invZ2, &
+    call get_param(param_file, mdl, "KVML", Kv_mks, &
                  "The scale for an extra kinematic viscosity in the mixed layer", &
-                 units="m2 s-1", default=0.0, scale=US%m2_s_to_Z2_T, do_not_log=.true.)
-      if (CS%Kvml_invZ2 >= 0.0) &
-        call MOM_error(WARNING, "KVML is a deprecated parameter. Use KV_ML_INVZ2 instead.")
+                 units="m2 s-1", default=-1.0, do_not_log=.true.)
+    if (Kv_mks >= 0.0) then
+      call MOM_error(WARNING, "KVML is a deprecated parameter. Use KV_ML_INVZ2 instead.")
+    else
+      Kv_mks = 0.0
     endif
-    if (CS%Kvml_invZ2 < 0.0) CS%Kvml_invZ2 = 0.0
-    call log_param(param_file, mdl, "KV_ML_INVZ2", CS%Kvml_invZ2, &
+    call get_param(param_file, mdl, "KV_ML_INVZ2", CS%Kvml_invZ2, &
                  "An extra kinematic viscosity in a mixed layer of thickness HMIX_FIXED, "//&
                  "with the actual viscosity scaling as 1/(z*HMIX_FIXED)^2, where z is the "//&
                  "distance from the surface, to allow for finite wind stresses to be "//&
                  "transmitted through infinitesimally thin surface layers.  This is an "//&
                  "older option for numerical convenience without a strong physical basis, "//&
                  "and its use is now discouraged.", &
-                 units="m2 s-1", default=0.0, unscale=US%Z2_T_to_m2_s)
+                 units="m2 s-1", default=Kv_mks, scale=US%m2_s_to_Z2_T)
   endif
 
   if (.not.CS%bottomdraglaw) then