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Add ability to smoothly turn off the MLE scheme for deep mixed layers #443

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Add ability to smoothly turn off the MLE scheme for deep mixed layers #443

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a79a968
Taper MLE depth
iangrooms Jun 11, 2026
37385e5
syntax
iangrooms Jun 11, 2026
bfc37bc
Merge branch 'dev/ncar' into taper_mld_mle
iangrooms Jul 23, 2026
22cedee
Merge branch 'dev/ncar' into taper_mld_mle
iangrooms Aug 15, 2026
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39 changes: 39 additions & 0 deletions src/parameterizations/lateral/MOM_mixed_layer_restrat.F90
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,11 @@ module MOM_mixed_layer_restrat
!! the mixed-layer [nondim].
real :: MLE_MLD_stretch !< A scaling coefficient for stretching/shrinking the MLD used in
!! the MLE scheme [nondim]. This simply multiplies MLD wherever used.
real :: MLE_TAPER_FN_DEPTH !< The mixed layer depth in the FFH and Bodner schemes can be tapered.
!! H is replaced by H / (1 + (H/H0)**P) where H0 is MLE_TAPER_FN_DEPTH.
!! [Z ~> m]
integer :: MLE_TAPER_FN_POWER !< The mixed layer depth in the FFH and Bodner schemes can be tapered.
!! H is replaced by H / (1 + (H/H0)**P) where P is MLE_TAPER_FN_POWER.

! The following parameters are used in the Bodner et al., 2023, parameterization
logical :: use_Bodner = .false. !< If true, use the Bodner et al., 2023, parameterization.
Expand Down Expand Up @@ -326,6 +331,13 @@ subroutine mixedlayer_restrat_OM4(h, uhtr, vhtr, tv, forces, dt, h_MLD, VarMix,
"No MLD to use for MLE parameterization.")
endif

! Smoothly turn off the scheme by reducing the MLD when the MLD is greater than CS%MLE_TAPER_FN_DEPTH
if ((CS%MLE_TAPER_FN_POWER > 0) .and. (CS%MLE_TAPER_FN_DEPTH > 0.)) then
do j=js-1,je+1 ; do i=is-1,ie+1
MLD_fast(i,j) = MLD_fast(i,j) / (1. + (MLD_fast(i,j)/CS%MLE_TAPER_FN_DEPTH)**CS%MLE_TAPER_FN_POWER)
enddo ; enddo
endif

! Apply time filter (to remove diurnal cycle)
if (CS%MLE_MLD_decay_time>0.) then
if (CS%debug) then
Expand Down Expand Up @@ -933,6 +945,13 @@ subroutine mixedlayer_restrat_Bodner(CS, G, GV, US, h, uhtr, vhtr, tv, forces, d
CS%MLD_filtered(i,j) = little_h(i,j)
enddo ; enddo

! Smoothly turn off the scheme by reducing the MLD when the MLD is greater than CS%MLE_TAPER_FN_DEPTH
if ((CS%MLE_TAPER_FN_POWER > 0) .and. (CS%MLE_TAPER_FN_DEPTH > 0.)) then
do j=js-1,je+1 ; do i=is-1,ie+1
little_h(i,j) = little_h(i,j) / (1. + (little_h(i,j)/CS%MLE_TAPER_FN_DEPTH)**CS%MLE_TAPER_FN_POWER)
enddo ; enddo
endif

! Calculate "big H", representative of the mixed layer depth, used in B22 formula (eq 27).
if (CS%MLD_grid) then
do j=js-1,je+1 ; do i=is-1,ie+1
Expand All @@ -951,6 +970,14 @@ subroutine mixedlayer_restrat_Bodner(CS, G, GV, US, h, uhtr, vhtr, tv, forces, d
CS%MLD_growing_Tfilt, CS%MLD_decaying_Tfilt, dt)
enddo ; enddo
endif

! Smoothly turn off the scheme by reducing the MLD when the MLD is greater than CS%MLE_TAPER_FN_DEPTH
if ((CS%MLE_TAPER_FN_POWER > 0) .and. (CS%MLE_TAPER_FN_DEPTH > 0.)) then
do j=js-1,je+1 ; do i=is-1,ie+1
big_H(i,j) = big_H(i,j) / (1. + (big_H(i,j)/CS%MLE_TAPER_FN_DEPTH)**CS%MLE_TAPER_FN_POWER)
enddo ; enddo
endif

do j=js-1,je+1 ; do i=is-1,ie+1
CS%MLD_filtered_slow(i,j) = big_H(i,j)
enddo ; enddo
Expand Down Expand Up @@ -1713,6 +1740,8 @@ logical function mixedlayer_restrat_init(Time, G, GV, US, param_file, diag, CS,
CS%fl_from_file = .false.
CS%MLD_grid = .false.
CS%Cr_grid = .false.
CS%MLE_TAPER_FN_POWER = 0
CS%MLE_TAPER_FN_DEPTH = 0.0

call get_param(param_file, mdl, "DEBUG", CS%debug, default=.false., do_not_log=.true.)
call get_param(param_file, mdl, "DEFAULT_ANSWER_DATE", default_answer_date, &
Expand All @@ -1724,6 +1753,16 @@ logical function mixedlayer_restrat_init(Time, G, GV, US, param_file, diag, CS,
call get_param(param_file, mdl, "USE_STANLEY_ML", CS%use_Stanley_ML, &
"If true, turn on Stanley SGS T variance parameterization "// &
"in ML restrat code.", default=.false.)
call get_param(param_file, mdl, "MLE_TAPER_FN_DEPTH", CS%MLE_TAPER_FN_DEPTH, &
"Mixed layer (and mixing-layer) depths in the MLE restratification "//&
"schemes are replaced by H / (1 + (H/H0)**P) when "//&
"P=MLE_TAPER_FN_POWER > 0 and H0=MLE_TAPER_FN_DEPTH > 0.", &
units="m", default=0., scale=US%m_to_Z)
call get_param(param_file, mdl, "MLE_TAPER_FN_POWER", CS%MLE_TAPER_FN_POWER, &
"The power of H/H0 in the MLE mixed-layer depth tapering. "//&
"Any positive integer may be used, but even integers are more "//&
"efficient to calculate. Very large values may lead to numerical "//&
"instabilities.", default=0)
if (CS%use_Stanley_ML .and. .not.stoch_eos) then
call MOM_error(FATAL, "mixedlayer_restrat_init: USE_STANLEY_ML requires STOCH_EOS")
endif
Expand Down
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