+Add runtime parameter KPP_LT_MLD_GUESS_MIN

  Added the new runtime parameter KPP_LT_MLD_GUESS_MIN to specify a previously
hard-coded lower limit on the estimate of the boundary layer depth used to
calculate the Langmuir number for some options with KPP.  By default all answers
are bitwise identical, but there is a new entry in the MOM_parameter_doc.all
files for some configurations with a KPP and Langmuir enhanced turbulence.

src/parameterizations/vertical/MOM_CVMix_KPP.F90

@@ -113,6 +113,9 @@ module MOM_CVMix_KPP
   logical :: LT_Vt2_Enhancement        !< Flags if enhancing Vt2 due to LT
   integer :: LT_VT2_METHOD             !< Integer for Vt2 LT method
   real    :: KPP_VT2_ENH_FAC           !< Factor to multiply by VT2 if Method is CONSTANT [nondim]
+  real    :: MLD_guess_min             !< The minimum estimate of the mixed layer depth used to
+                                       !! calculate the Langmuir number for Langmuir turbulence
+                                       !! enhancement with KPP [Z ~> m]
   logical :: STOKES_MIXING             !< Flag if model is mixing down Stokes gradient
                                        !! This is relevant for which current to use in RiB
 
@@ -460,6 +463,13 @@ logical function KPP_init(paramFile, G, GV, US, diag, Time, CS, passive)
     endif
   endif
 
+  if (CS%LT_K_ENHANCEMENT .or. CS%LT_VT2_ENHANCEMENT) then
+    call get_param(paramFile, mdl, "KPP_LT_MLD_GUESS_MIN", CS%MLD_guess_min,     &
+                   "The minimum estimate of the mixed layer depth used to calculate "//&
+                   "the Langmuir number for Langmuir turbulence enhancement with KPP.", &
+                   units="m", default=1.0, scale=US%m_to_Z)
+  endif
+
   call closeParameterBlock(paramFile)
 
   call get_param(paramFile, mdl, 'DEBUG', CS%debug, default=.False., do_not_log=.True.)
@@ -1120,10 +1130,10 @@ subroutine KPP_compute_BLD(CS, G, GV, US, h, Temp, Salt, u, v, tv, uStar, buoyFl
       enddo ! k-loop finishes
 
       if ( (CS%LT_K_ENHANCEMENT .or. CS%LT_VT2_ENHANCEMENT) .and. .not. present(lamult)) then
-        MLD_guess = max( 1.*US%m_to_Z, abs(CS%OBLdepthprev(i,j) ) )
+        MLD_guess = max( CS%MLD_guess_min, abs(CS%OBLdepthprev(i,j) ) )
         call get_Langmuir_Number(LA, G, GV, US, MLD_guess, uStar(i,j), i, j, &
                                  H=H(i,j,:), U_H=U_H, V_H=V_H, WAVES=WAVES)
-        CS%La_SL(i,j)=LA
+        CS%La_SL(i,j) = LA
       endif