From 48bff80650c4f5f645f0a34b97ea1fae77b7fbd7 Mon Sep 17 00:00:00 2001
From: Mathew Maltrud <maltrud@lanl.gov>
Date: Mon, 26 Feb 2024 11:28:29 -0600
Subject: [PATCH 1/3] add distinct passive tracer background vert diffusivity

---
 components/mpas-ocean/bld/build-namelist      |  2 ++
 .../namelist_defaults_mpaso.xml               |  2 ++
 .../namelist_definition_mpaso.xml             | 16 ++++++++++++++++
 components/mpas-ocean/src/Registry.xml        | 12 ++++++++++++
 .../shared/mpas_ocn_diagnostics_variables.F   |  6 ++++++
 .../mpas-ocean/src/shared/mpas_ocn_vmix.F     | 19 ++++++++++++++++++-
 6 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/components/mpas-ocean/bld/build-namelist b/components/mpas-ocean/bld/build-namelist
index 0b8d3c782fa7..238af2be2ab1 100755
--- a/components/mpas-ocean/bld/build-namelist
+++ b/components/mpas-ocean/bld/build-namelist
@@ -616,6 +616,8 @@ add_default($nl, 'config_use_cvmix');
 add_default($nl, 'config_cvmix_prandtl_number');
 add_default($nl, 'config_cvmix_background_scheme');
 add_default($nl, 'config_cvmix_background_diffusion');
+add_default($nl, 'config_cvmix_background_diffusion_passive_enable');
+add_default($nl, 'config_cvmix_background_diffusion_passive');
 add_default($nl, 'config_cvmix_background_viscosity');
 add_default($nl, 'config_cvmix_BryanLewis_bl1');
 add_default($nl, 'config_cvmix_BryanLewis_bl2');
diff --git a/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml b/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
index 4069eb144cff..d7e0485168c8 100644
--- a/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
+++ b/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
@@ -229,6 +229,8 @@
 <config_cvmix_prandtl_number>1.0</config_cvmix_prandtl_number>
 <config_cvmix_background_scheme>'constant'</config_cvmix_background_scheme>
 <config_cvmix_background_diffusion>0.0</config_cvmix_background_diffusion>
+<config_cvmix_background_diffusion_passive_enable>.false.</config_cvmix_background_diffusion_passive_enable>
+<config_cvmix_background_diffusion_passive>0.0</config_cvmix_background_diffusion_passive>
 <config_cvmix_background_viscosity>1.0e-4</config_cvmix_background_viscosity>
 <config_cvmix_BryanLewis_bl1>8.0e-5</config_cvmix_BryanLewis_bl1>
 <config_cvmix_BryanLewis_bl2>1.05E-4</config_cvmix_BryanLewis_bl2>
diff --git a/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml b/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
index 01456cd6583a..6b1026ea4d11 100644
--- a/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
+++ b/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
@@ -747,6 +747,22 @@ Valid values: Any positive real value.
 Default: Defined in namelist_defaults.xml
 </entry>
 
+<entry id="config_cvmix_background_diffusion_passive_enable" type="logical"
+	category="cvmix" group="cvmix">
+Enable different background vertical diffusion value for passive tracer quantities
+
+Valid values: .true. or .false.
+Default: Defined in namelist_defaults.xml
+</entry>
+
+<entry id="config_cvmix_background_diffusion_passive" type="real"
+	category="cvmix" group="cvmix">
+Background vertical diffusion applied to passive tracer quantities if enabled
+
+Valid values: Any positive real value.
+Default: Defined in namelist_defaults.xml
+</entry>
+
 <entry id="config_cvmix_background_viscosity" type="real"
 	category="cvmix" group="cvmix">
 Background vertical viscosity applied to horizontal velocity
diff --git a/components/mpas-ocean/src/Registry.xml b/components/mpas-ocean/src/Registry.xml
index f8b56c083d44..5524651cc185 100644
--- a/components/mpas-ocean/src/Registry.xml
+++ b/components/mpas-ocean/src/Registry.xml
@@ -477,6 +477,14 @@
 					description="Background vertical diffusion applied to tracer quantities"
 					possible_values="Any positive real value."
 		/>
+		<nml_option name="config_cvmix_background_diffusion_passive" type="real" default_value="1.0e-5" units="m^2 s^-1"
+					description="Background vertical diffusion applied to passive tracer quantities"
+					possible_values="Any positive real value."
+		/>
+		<nml_option name="config_cvmix_background_diffusion_passive_enable" type="logical" default_value=".false."
+					description="flag to enable using a different background vertical diffusion for passive tracers"
+					possible_values=".true. or .false."
+					/>
 		<nml_option name="config_cvmix_background_viscosity" type="real" default_value="1.0e-4" units="m^2 s^-1"
 					description="Background vertical viscosity applied to horizontal velocity"
 					possible_values="Any positive real value."
@@ -3085,6 +3093,10 @@
 			 description="vertical diffusion defined at the cell center (horizontally) and top (vertically)"
 			 packages="forwardMode;analysisMode"
 		/>
+		<var name="vertDiffPassiveTopOfCell" type="real" dimensions="nVertLevelsP1 nCells Time" units="m^2 s^-1"
+			 description="vertical diffusion defined at the cell center (horizontally) and top (vertically) for passive tracers"
+			 packages="forwardMode;analysisMode"
+		/>
 		<var name="bulkRichardsonNumber" type="real" dimensions="nVertLevels nCells Time" units="1"
 			 description="CVMix/KPP: bulk Richardson number"
 			 missing_value="FILLVAL" missing_value_mask="cellMask"
diff --git a/components/mpas-ocean/src/shared/mpas_ocn_diagnostics_variables.F b/components/mpas-ocean/src/shared/mpas_ocn_diagnostics_variables.F
index 567c3efc183c..b64890a25691 100644
--- a/components/mpas-ocean/src/shared/mpas_ocn_diagnostics_variables.F
+++ b/components/mpas-ocean/src/shared/mpas_ocn_diagnostics_variables.F
@@ -141,6 +141,7 @@ module ocn_diagnostics_variables
    type (field2DReal), pointer :: wettingVelocityField
 
    real (kind=RKIND), dimension(:,:), pointer :: vertDiffTopOfCell
+   real (kind=RKIND), dimension(:,:), pointer :: vertDiffPassiveTopOfCell
    real (kind=RKIND), dimension(:,:,:), pointer :: vertNonLocalFlux
    integer, dimension(:,:), pointer :: rediLimiterCount
    real (kind=RKIND), dimension(:,:,:), pointer :: activeTracerSurfaceFluxTendency
@@ -494,6 +495,8 @@ subroutine ocn_diagnostics_variables_init(domain, jenkinsOn, hollandJenkinsOn, e
                    vertViscTopOfCell)
          call mpas_pool_get_array(diagnosticsPool, 'vertDiffTopOfCell', &
                    vertDiffTopOfCell)
+         call mpas_pool_get_array(diagnosticsPool, 'vertDiffPassiveTopOfCell', &
+                   vertDiffPassiveTopOfCell)
          call mpas_pool_get_array(diagnosticsPool, 'vertAleTransportTop', &
                    vertAleTransportTop)
          call mpas_pool_get_array(diagnosticsPool, 'vertTransportVelocityTop', &
@@ -752,6 +755,7 @@ subroutine ocn_diagnostics_variables_init(domain, jenkinsOn, hollandJenkinsOn, e
          !$acc                   barotropicForcing,               &
          !$acc                   vertViscTopOfCell,               &
          !$acc                   vertDiffTopOfCell,               &
+         !$acc                   vertDiffPassiveTopOfCell,        &
          !$acc                   GMStreamFuncZonal,               &
          !$acc                   relativeVorticity,               &
          !$acc                   kineticEnergyCell,               &
@@ -999,6 +1003,7 @@ subroutine ocn_diagnostics_variables_destroy(err) !{{{
          !$acc                   barotropicForcing,               &
          !$acc                   vertViscTopOfCell,               &
          !$acc                   vertDiffTopOfCell,               &
+         !$acc                   vertDiffPassiveTopOfCell,        &
          !$acc                   GMStreamFuncZonal,               &
          !$acc                   relativeVorticity,               &
          !$acc                   kineticEnergyCell,               &
@@ -1204,6 +1209,7 @@ subroutine ocn_diagnostics_variables_destroy(err) !{{{
                  barotropicForcing,               &
                  vertViscTopOfCell,               &
                  vertDiffTopOfCell,               &
+                 vertDiffPassiveTopOfCell,        &
                  GMStreamFuncZonal,               &
                  relativeVorticity,               &
                  kineticEnergyCell,               &
diff --git a/components/mpas-ocean/src/shared/mpas_ocn_vmix.F b/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
index 87f23d65aa1f..4c96c6e952dc 100644
--- a/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
+++ b/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
@@ -1583,9 +1583,26 @@ subroutine ocn_vmix_implicit(dt, meshPool, statePool, forcingPool, scratchPool,
                !$acc enter data copyin(tracerGroupSurfaceFlux)
 #endif
 
-               call ocn_tracer_vmix_tend_implicit(dt, vertDiffTopOfCell, layerThickness, tracersGroup, &
+               if (trim(groupItr % memberName) /= 'activeTracers' .and. &
+                   config_cvmix_background_diffusion_passive_enable) then
+                      vertDiffPassiveTopOfCell = vertDiffTopOfCell - &
+                         config_cvmix_background_diffusion + config_cvmix_background_diffusion_passive
+#ifdef MPAS_OPENACC
+                      !$acc update host (vertDiffPassiveTopOfCell)
+#endif
+!maltrud debug
+ do k = 1, maxLevelCell(1)
+  write(*,*)' DEBUG01: ',k,vertDiffPassiveTopOfCell(k,1)
+ enddo
+
+                      call ocn_tracer_vmix_tend_implicit(dt, vertDiffPassiveTopOfCell, layerThickness, tracersGroup, &
+                        vertNonLocalFlux, tracerGroupSurfaceFlux,  &
+                        config_cvmix_kpp_nonlocal_with_implicit_mix, err)
+               else
+                      call ocn_tracer_vmix_tend_implicit(dt, vertDiffTopOfCell, layerThickness, tracersGroup, &
                         vertNonLocalFlux, tracerGroupSurfaceFlux,  &
                         config_cvmix_kpp_nonlocal_with_implicit_mix, err)
+               end if
 #ifdef MPAS_OPENACC
                !$acc exit data delete(tracerGroupSurfaceFlux)
 #endif

From 5c6fdd5928874825ea15f870314fb1a77e58decf Mon Sep 17 00:00:00 2001
From: Mathew Maltrud <maltrud@lanl.gov>
Date: Wed, 8 May 2024 12:01:12 -0500
Subject: [PATCH 2/3] added explicit k-loop for calculating vertDiffPassive

---
 .../mpas-ocean/src/shared/mpas_ocn_vmix.F     | 28 +++++++++++++++----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/components/mpas-ocean/src/shared/mpas_ocn_vmix.F b/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
index 4c96c6e952dc..5eefa945a68c 100644
--- a/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
+++ b/components/mpas-ocean/src/shared/mpas_ocn_vmix.F
@@ -1585,15 +1585,33 @@ subroutine ocn_vmix_implicit(dt, meshPool, statePool, forcingPool, scratchPool,
 
                if (trim(groupItr % memberName) /= 'activeTracers' .and. &
                    config_cvmix_background_diffusion_passive_enable) then
-                      vertDiffPassiveTopOfCell = vertDiffTopOfCell - &
+
+
+#ifdef MPAS_OPENACC
+                  !$acc parallel loop gang vector collapse(3) present(vertDiffPassiveTopOfCell, vertDiffTopOfCell)
+#else
+                  !$omp parallel
+                  !$omp do schedule(runtime) private(k, iTracer)
+#endif
+                  do iCell = 1, nCellsOwned
+                  do k = 2, maxLevelCell(iCell)
+                      vertDiffPassiveTopOfCell(k,iCell) = vertDiffTopOfCell(k,iCell) - &
                          config_cvmix_background_diffusion + config_cvmix_background_diffusion_passive
+                  end do
+                  end do
+#ifndef MPAS_OPENACC
+                  !$omp end do
+                  !$omp end parallel
+#endif
+
+
+
+
+
+
 #ifdef MPAS_OPENACC
                       !$acc update host (vertDiffPassiveTopOfCell)
 #endif
-!maltrud debug
- do k = 1, maxLevelCell(1)
-  write(*,*)' DEBUG01: ',k,vertDiffPassiveTopOfCell(k,1)
- enddo
 
                       call ocn_tracer_vmix_tend_implicit(dt, vertDiffPassiveTopOfCell, layerThickness, tracersGroup, &
                         vertNonLocalFlux, tracerGroupSurfaceFlux,  &

From b25883b1fec41c95bc5bd095afd3b023d89a108c Mon Sep 17 00:00:00 2001
From: Jon Wolfe <jonbob@lanl.gov>
Date: Thu, 9 May 2024 15:21:41 -0500
Subject: [PATCH 3/3] Make bld files consistent with mpaso Registry using
 automated scripts

---
 components/mpas-ocean/bld/build-namelist           |  4 ++--
 components/mpas-ocean/bld/build-namelist-section   |  4 +++-
 .../bld/namelist_files/namelist_defaults_mpaso.xml |  8 ++------
 .../namelist_files/namelist_definition_mpaso.xml   | 14 +++++++-------
 4 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/components/mpas-ocean/bld/build-namelist b/components/mpas-ocean/bld/build-namelist
index 238af2be2ab1..99bbb8c68edc 100755
--- a/components/mpas-ocean/bld/build-namelist
+++ b/components/mpas-ocean/bld/build-namelist
@@ -557,9 +557,9 @@ add_default($nl, 'config_Redi_constant_kappa');
 add_default($nl, 'config_Redi_maximum_slope');
 add_default($nl, 'config_Redi_use_slope_taper');
 add_default($nl, 'config_Redi_use_surface_taper');
+add_default($nl, 'config_Redi_limit_term1');
 add_default($nl, 'config_Redi_use_quasi_monotone_limiter');
 add_default($nl, 'config_Redi_quasi_monotone_safety_factor');
-add_default($nl, 'config_Redi_limit_term1');
 add_default($nl, 'config_Redi_min_layers_diag_terms');
 add_default($nl, 'config_Redi_horizontal_taper');
 add_default($nl, 'config_Redi_horizontal_ramp_min');
@@ -616,8 +616,8 @@ add_default($nl, 'config_use_cvmix');
 add_default($nl, 'config_cvmix_prandtl_number');
 add_default($nl, 'config_cvmix_background_scheme');
 add_default($nl, 'config_cvmix_background_diffusion');
-add_default($nl, 'config_cvmix_background_diffusion_passive_enable');
 add_default($nl, 'config_cvmix_background_diffusion_passive');
+add_default($nl, 'config_cvmix_background_diffusion_passive_enable');
 add_default($nl, 'config_cvmix_background_viscosity');
 add_default($nl, 'config_cvmix_BryanLewis_bl1');
 add_default($nl, 'config_cvmix_BryanLewis_bl2');
diff --git a/components/mpas-ocean/bld/build-namelist-section b/components/mpas-ocean/bld/build-namelist-section
index 28030392442d..bebd11c72b31 100644
--- a/components/mpas-ocean/bld/build-namelist-section
+++ b/components/mpas-ocean/bld/build-namelist-section
@@ -96,9 +96,9 @@ add_default($nl, 'config_Redi_constant_kappa');
 add_default($nl, 'config_Redi_maximum_slope');
 add_default($nl, 'config_Redi_use_slope_taper');
 add_default($nl, 'config_Redi_use_surface_taper');
+add_default($nl, 'config_Redi_limit_term1');
 add_default($nl, 'config_Redi_use_quasi_monotone_limiter');
 add_default($nl, 'config_Redi_quasi_monotone_safety_factor');
-add_default($nl, 'config_Redi_limit_term1');
 add_default($nl, 'config_Redi_min_layers_diag_terms');
 add_default($nl, 'config_Redi_horizontal_taper');
 add_default($nl, 'config_Redi_horizontal_ramp_min');
@@ -155,6 +155,8 @@ add_default($nl, 'config_use_cvmix');
 add_default($nl, 'config_cvmix_prandtl_number');
 add_default($nl, 'config_cvmix_background_scheme');
 add_default($nl, 'config_cvmix_background_diffusion');
+add_default($nl, 'config_cvmix_background_diffusion_passive');
+add_default($nl, 'config_cvmix_background_diffusion_passive_enable');
 add_default($nl, 'config_cvmix_background_viscosity');
 add_default($nl, 'config_cvmix_BryanLewis_bl1');
 add_default($nl, 'config_cvmix_BryanLewis_bl2');
diff --git a/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml b/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
index d7e0485168c8..8d7c8cdce7a7 100644
--- a/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
+++ b/components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml
@@ -146,15 +146,14 @@
 <config_Redi_maximum_slope>0.01</config_Redi_maximum_slope>
 <config_Redi_use_slope_taper>.true.</config_Redi_use_slope_taper>
 <config_Redi_use_surface_taper>.true.</config_Redi_use_surface_taper>
+<config_Redi_limit_term1>.true.</config_Redi_limit_term1>
 <config_Redi_use_quasi_monotone_limiter>.true.</config_Redi_use_quasi_monotone_limiter>
 <config_Redi_quasi_monotone_safety_factor>0.9</config_Redi_quasi_monotone_safety_factor>
-<config_Redi_limit_term1>.true.</config_Redi_limit_term1>
 <config_Redi_min_layers_diag_terms>0</config_Redi_min_layers_diag_terms>
 <config_Redi_min_layers_diag_terms ocn_grid="ARRM10to60E2r1">15</config_Redi_min_layers_diag_terms>
 <config_Redi_horizontal_taper>'ramp'</config_Redi_horizontal_taper>
 <config_Redi_horizontal_taper ocn_grid="SOwISC12to60E2r4">'RossbyRadius'</config_Redi_horizontal_taper>
 <config_Redi_horizontal_taper ocn_grid="ECwISC30to60E2r1">'RossbyRadius'</config_Redi_horizontal_taper>
-<!-- To do: ramp for WC but RossbyRadius for Cryo -->
 <config_Redi_horizontal_taper ocn_grid="IcoswISC30E3r5">'ramp'</config_Redi_horizontal_taper>
 <config_Redi_horizontal_ramp_min>20e3</config_Redi_horizontal_ramp_min>
 <config_Redi_horizontal_ramp_min ocn_grid="WCAtl12to45E2r4">30e3</config_Redi_horizontal_ramp_min>
@@ -180,7 +179,6 @@
 <config_GM_closure ocn_grid="WCAtl12to45E2r4">'constant'</config_GM_closure>
 <config_GM_closure ocn_grid="SOwISC12to60E2r4">'N2_dependent'</config_GM_closure>
 <config_GM_closure ocn_grid="ECwISC30to60E2r1">'N2_dependent'</config_GM_closure>
-<!-- To do: constant for WC but N2_dependent for Cryo -->
 <config_GM_closure ocn_grid="IcoswISC30E3r5">'constant'</config_GM_closure>
 <config_GM_constant_kappa>900.0</config_GM_constant_kappa>
 <config_GM_constant_kappa ocn_forcing="datm_forced_restoring" ocn_grid="oEC60to30v3wLI">600.0</config_GM_constant_kappa>
@@ -198,7 +196,6 @@
 <config_GM_spatially_variable_baroclinic_mode>3.0</config_GM_spatially_variable_baroclinic_mode>
 <config_GM_spatially_variable_baroclinic_mode ocn_grid="SOwISC12to60E2r4">1.0</config_GM_spatially_variable_baroclinic_mode>
 <config_GM_spatially_variable_baroclinic_mode ocn_grid="ECwISC30to60E2r1">1.0</config_GM_spatially_variable_baroclinic_mode>
-<!-- To do: 3.0 for WC but 1.0 for Cryo? -->
 <config_GM_spatially_variable_baroclinic_mode ocn_grid="IcoswISC30E3r5">3.0</config_GM_spatially_variable_baroclinic_mode>
 <config_GM_Visbeck_alpha>0.13</config_GM_Visbeck_alpha>
 <config_GM_Visbeck_max_depth>1000.0</config_GM_Visbeck_max_depth>
@@ -209,7 +206,6 @@
 <config_GM_horizontal_taper>'ramp'</config_GM_horizontal_taper>
 <config_GM_horizontal_taper ocn_grid="SOwISC12to60E2r4">'RossbyRadius'</config_GM_horizontal_taper>
 <config_GM_horizontal_taper ocn_grid="ECwISC30to60E2r1">'RossbyRadius'</config_GM_horizontal_taper>
-<!-- To do: ramp for WC but RossbyRadius for Cryo -->
 <config_GM_horizontal_taper ocn_grid="IcoswISC30E3r5">'ramp'</config_GM_horizontal_taper>
 <config_GM_horizontal_ramp_min>20e3</config_GM_horizontal_ramp_min>
 <config_GM_horizontal_ramp_min ocn_grid="WCAtl12to45E2r4">30e3</config_GM_horizontal_ramp_min>
@@ -229,8 +225,8 @@
 <config_cvmix_prandtl_number>1.0</config_cvmix_prandtl_number>
 <config_cvmix_background_scheme>'constant'</config_cvmix_background_scheme>
 <config_cvmix_background_diffusion>0.0</config_cvmix_background_diffusion>
-<config_cvmix_background_diffusion_passive_enable>.false.</config_cvmix_background_diffusion_passive_enable>
 <config_cvmix_background_diffusion_passive>0.0</config_cvmix_background_diffusion_passive>
+<config_cvmix_background_diffusion_passive_enable>.false.</config_cvmix_background_diffusion_passive_enable>
 <config_cvmix_background_viscosity>1.0e-4</config_cvmix_background_viscosity>
 <config_cvmix_BryanLewis_bl1>8.0e-5</config_cvmix_BryanLewis_bl1>
 <config_cvmix_BryanLewis_bl2>1.05E-4</config_cvmix_BryanLewis_bl2>
diff --git a/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml b/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
index 6b1026ea4d11..c2fac6fc35ce 100644
--- a/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
+++ b/components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml
@@ -747,19 +747,19 @@ Valid values: Any positive real value.
 Default: Defined in namelist_defaults.xml
 </entry>
 
-<entry id="config_cvmix_background_diffusion_passive_enable" type="logical"
+<entry id="config_cvmix_background_diffusion_passive" type="real"
 	category="cvmix" group="cvmix">
-Enable different background vertical diffusion value for passive tracer quantities
+Background vertical diffusion applied to passive tracer quantities
 
-Valid values: .true. or .false.
+Valid values: Any positive real value.
 Default: Defined in namelist_defaults.xml
 </entry>
 
-<entry id="config_cvmix_background_diffusion_passive" type="real"
+<entry id="config_cvmix_background_diffusion_passive_enable" type="logical"
 	category="cvmix" group="cvmix">
-Background vertical diffusion applied to passive tracer quantities if enabled
+flag to enable using a different background vertical diffusion for passive tracers
 
-Valid values: Any positive real value.
+Valid values: .true. or .false.
 Default: Defined in namelist_defaults.xml
 </entry>
 
@@ -2054,7 +2054,7 @@ Default: Defined in namelist_defaults.xml
 
 <entry id="config_n_ts_iter" type="integer"
 	category="split_timestep_share" group="split_timestep_share">
-number of large iterations over stages 1-3
+number of large iterations over stages 1-3; For the split_explicit_ab2 time integrator, this value only affects the first time step when it is not a restart run. For restart runs, this value has no effect on the split_explicit_ab2 time integrator.
 
 Valid values: any positive integer, but typically 1, 2, or 3
 Default: Defined in namelist_defaults.xml