Add rescaling paramter to KD Shear

Add a parameted (beta) to rescale the distance to the nearest solid
boundary that is used within calculation of kappa shear. While rescaling
this value is unphysical, this adjustment can be thought of as not
allowing shear instabilities to grow up to the full distance to the
nearest boundary because of other turbulent processes which would disrupt
their growth.

src/parameterizations/vertical/MOM_kappa_shear.F90

@@ -54,6 +54,10 @@ module MOM_kappa_shear
   real    :: lambda2_N_S     !<   The square of the ratio of the coefficients of
                              !! the buoyancy and shear scales in the diffusivity
                              !! equation, 0 to eliminate the shear scale [nondim].
+  real    :: beta            !<   A coefficient to rescale the distance to the nearest 
+                             !! solid boundary. This adjustment is to account for 
+                             !! regions where 3 dimensional turbulence prevents the 
+                             !! growth of shear instabilies [nondim].
   real    :: TKE_bg          !<   The background level of TKE [Z2 T-2 ~> m2 s-2].
   real    :: kappa_0         !<   The background diapycnal diffusivity [H Z T-1 ~> m2 s-1 or Pa s]
   real    :: kappa_seed      !<   A moderately large seed value of diapycnal diffusivity that
@@ -794,7 +798,9 @@ subroutine kappa_shear_column(kappa, tke, dt, nzc, f2, surface_pres, hlay, dz_la
   do K=nzc,2,-1
     dist_from_bot = dist_from_bot + dz_lay(k)
     h_from_bot = h_from_bot + hlay(k)
-    I_L2_bdry(K) = ((dist_from_top(K) + dist_from_bot) * (h_from_top(K) + h_from_bot)) / &
+    !I_L2_bdry(K) = ((dist_from_top(K) + dist_from_bot) * (h_from_top(K) + h_from_bot)) / &
+    !               ((dist_from_top(K) * dist_from_bot) * (h_from_top(K) * h_from_bot))
+    I_L2_bdry(K) = 1/(CS%beta*CS%beta)*((dist_from_top(K) + dist_from_bot) * (h_from_top(K) + h_from_bot)) / &
                    ((dist_from_top(K) * dist_from_bot) * (h_from_top(K) * h_from_bot))
   enddo
 
@@ -1918,6 +1924,11 @@ function kappa_shear_init(Time, G, GV, US, param_file, diag, CS)
                  "Set this to 0 (the default) to eliminate the shear scale. "//&
                  "This is only used if USE_JACKSON_PARAM is true.", &
                  units="nondim", default=0.0, do_not_log=just_read)
+  call get_param(param_file, mdl, "LZ_RESCALE", CS%beta, &
+                 "A coefficient to rescale the distance to the nearest solid boundary. "//& 
+                 "This adjustment is to account for regions where 3 dimensional turbulence "//&  
+                 "prevents the growth of shear instabilies [nondim].", &
+                 units="nondim", default=1.0) 
   call get_param(param_file, mdl, "KAPPA_SHEAR_TOL_ERR", CS%kappa_tol_err, &
                  "The fractional error in kappa that is tolerated. "//&
                  "Iteration stops when changes between subsequent "//&