Update 2 Adds new ocean to ice coupling fields for frazil ice formation by njeffery · Pull Request #559 · E3SM-Project/Omega

njeffery · 2026-09-16T16:40:19Z

Updated version of #535

Fixes double counting of ocean heat flux during frazil ice formation.
For the ocean to ice coupler fields, Fioo_q now only contains the melt potential while Fioo_frazilh contains the heat from frazil ice formation. frazilh and q are combined in ice_comp_mct to reproduce the sea ice freezingMeltingPotential

Fioo_q is removed from driver-mct as it is no longer a heat flux.
A new flag, config_use_accumulated_frazil_energy default false, is added to the ocean model. Default retains the latent heat definition of frazil energy.
config_use_accumulated_frazil_energy = true uses the accumulatedFrazilHeat variable from frazil formation.

Tested in XS_2x5 GMPAS runs in 2 configurations:

config_use_accumulated_frazil_energy = true ; config_frazil_coupling_type = 'omega-fluxes'
and
default: config_use_accumulated_frazil_energy = false ; config_frazil_coupling_type = 'external'

Both completed successfully.

Test 1 was compared with darin's codebase from the previous PR (darincomeau@ea24e0f). Restart files at the end of day 11 showed differences in only 4 fields: o2x_ox_Fioo_frazilh, budg_dataG, o2x_ox_Fioo_q, and freezingMeltingPotential.

Differences in o2x_ox_Fioo_frazilh and freezingMeltingPotential were round off level only.
Differences in o2x_ox_Fioo_q, were all negative, as expected.
Differences in budg_dataG, also expected, were significant in regions of frazil ice formation.

Part of the frazil implementation documentation (sections 1.3-1.5). Currently here: https://www.overleaf.com/project/68896a760125362ca62587d1

Copilot

🟡 Changes recommended

There are verified correctness issues in diagnostics/logging and potential out-of-bounds writes due to unguarded optional coupler indices.

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Pull request overview

This PR updates MPAS-Ocean ↔ MPAS-Seaice frazil coupling to avoid double-counting ocean heat flux by splitting melt potential (Fioo_q) from frazil-formation heat (Fioo_frazilh) and adding explicit frazil salt/heat coupling fields through the drivers and registries.

Changes:

Add/rename ocean→ice frazil coupling flux fields (mass/salt/heat) and route them into MPAS-Seaice Icepack thermodynamics.
Add config_use_accumulated_frazil_heat to optionally couple accumulated frazil energy rather than latent-heat-from-mass.
Update MCT diagnostics/budget accounting to incorporate the new frazil salt/heat fields.

File summaries

File	Description
driver-moab/shr/seq_flds_mod.F90	Update frazil salt field metadata from “production” to “flux”.
driver-mct/shr/seq_flds_mod.F90	Add/rename frazil salt/heat flux metadata for MCT coupler field lists.
driver-mct/main/seq_diag_mct.F90	Extend diagnostic budgets to include frazil salt/heat fields and indices.
components/mpas-seaice/src/shared/mpas_seaice_initialize.F	Allow `config_frazil_coupling_type='omega-fluxes'`.
components/mpas-seaice/src/shared/mpas_seaice_icepack.F	Plumb frazil mass/salt/heat flux arrays into Icepack thermodynamics call.
components/mpas-seaice/src/Registry.xml	Register new ocean-coupling vars (frazilMassFlux/SaltFlux/HeatFlux) and allow omega-fluxes option.
components/mpas-seaice/driver/mpassi_cpl_indices.F	Clarify comments for frazil coupling indices.
components/mpas-seaice/driver/ice_comp_mct.F	Combine melt potential and frazil heat into `freezingMeltingPotential`; conditionally use omega-fluxes fields.
components/mpas-seaice/cime_config/buildnml	Add new frazil coupling vars to namelist-generated stream/var lists.
components/mpas-seaice/bld/namelist_files/namelist_definition_mpassi.xml	Document omega-fluxes as a valid frazil coupling type.
components/mpas-ocean/src/shared/mpas_ocn_frazil_forcing.F	Accumulate frazil latent energy (`accumulatedFrazilIceEnergy`) alongside mass/salt.
components/mpas-ocean/src/Registry.xml	Add `config_use_accumulated_frazil_heat` and register `accumulatedFrazilIceEnergy`.
components/mpas-ocean/src/analysis_members/Registry_conservation_check.xml	Minor description fix for conservation-check frazil heat flux variable.
components/mpas-ocean/src/analysis_members/mpas_ocn_conservation_check.F	Switch conservation-check frazil heat computation to use accumulated frazil energy.
components/mpas-ocean/driver/ocn_comp_mct.F	Export separate frazil heat flux vs melt potential and reset accumulated frazil energy each coupling interval.
components/mpas-ocean/bld/namelist_files/namelist_definition_mpaso.xml	Document new `config_use_accumulated_frazil_heat` namelist entry.
components/mpas-ocean/bld/namelist_files/namelist_defaults_mpaso.xml	Provide default `.false.` for `config_use_accumulated_frazil_heat`.
components/mpas-ocean/bld/build-namelist-section	Add new namelist option to generated defaults list.
components/mpas-ocean/bld/build-namelist	Add new namelist option to generated defaults list.

Review details

Files reviewed: 19/19 changed files
Comments generated: 3
Review effort level: Lite

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cbegeman

Thanks for the quick turnaround on this. Your G-case comparison looks promising! Most of the code changes were clear to me, I just have one question below about the frazil mass/salt adjust term.

cbegeman · 2026-09-16T19:52:28Z

      freezingMeltingPotential,    &
+      frazilMassFlux,              &
+      frazilSaltFlux,              &
+      frazilHeatFlux    ,          &


Suggested change

frazilHeatFlux , &

frazilHeatFlux, &

cbegeman · 2026-09-16T19:59:41Z

            i2x_i(index_i2x_Fioi_melth  ,n) = oceanHeatFlux(i)
            i2x_i(index_i2x_Fioi_swpen  ,n) = oceanShortwaveFlux(i)
-            i2x_i(index_i2x_Fioi_meltw  ,n) = oceanFreshWaterFlux(i)
+            i2x_i(index_i2x_Fioi_meltw  ,n) = oceanFreshWaterFlux(i) + frazilMassAdjust(i)/ailohi


Can you help me understand this addition? Is Fioi_frazil one of the coupling fields that is never used by the ocean model? So, prior to this change, were we neglecting to include the frazil mass adjustment?

Using Fioi_frazil would be a cleaner way to separate the sources of fresh water fluxes. For now, it's not being used and that term is included in meltw.

Got it. Thanks!

cbegeman · 2026-09-16T21:16:28Z

            i2x_i(index_i2x_Fioi_melth  ,n) = oceanHeatFlux(i)
            i2x_i(index_i2x_Fioi_swpen  ,n) = oceanShortwaveFlux(i)
-            i2x_i(index_i2x_Fioi_meltw  ,n) = oceanFreshWaterFlux(i)
+            i2x_i(index_i2x_Fioi_meltw  ,n) = oceanFreshWaterFlux(i) + frazilMassAdjust(i)/ailohi


Has meltw always failed to include the frazil mass adjustment? Or is there a change to where (through which variable) frazil mass adjustment is applied? Similar questions apply to the frazil salt adjustment below

No. Since defined, it's been included in meltw. That term was dropped at some point along this effort, I think when Fioi_frazil was added.

I think I initially made the change to move frazilMassAdjust to Fioi_frazil when the field was first added, but it required more changes to ocn_comp_mct. The current configuration is what was done originally, as @njeffery said. The same is true for the salt flux from the frazil mass adjustment, which is added to Fioi_salt.

Thank you for clarifying. Sounds good.

Copilot

🟡 Changes recommended

MPAS-Ocean exports Fioo_frazils without guarding against a zero (missing) coupler-field index, which can cause out-of-bounds writes at runtime.

Get a fresh assessment by requesting another Copilot review.

Review details

Suppressed comments (1)

components/mpas-ocean/driver/ocn_comp_mct.F:3427

index_o2x_Fioo_frazils can be 0 (perrWith='quiet' lookup), but this keepFrazil=.false. path still writes o2x_o(index_o2x_Fioo_frazils, n) whenever index_o2x_Fioo_frazil /= 0. Guard the frazils assignment separately to avoid out-of-bounds indexing.

             if (index_o2x_Fioo_frazil /= 0) then
                o2x_o(index_o2x_Fioo_frazil, n) = 0.0_RKIND
                o2x_o(index_o2x_Fioo_frazils, n) = 0.0_RKIND
             endif

Files reviewed: 19/19 changed files
Comments generated: 2
Review effort level: Lite

njeffery · 2026-09-16T22:34:01Z

+             if (index_o2x_Fioo_frazil /= 0) then
+                o2x_o(index_o2x_Fioo_frazil, n) = accumulatedFrazilIceMass(i) / ocn_cpl_dt
+                o2x_o(index_o2x_Fioo_frazils, n) = accumulatedFrazilIceMass(i)/ 1000.0_RKIND * &
+                   config_frazil_sea_ice_reference_salinity / ocn_cpl_dt
+             endif


Will work with just the one check. Fioo_frazil and Fioo_frazils are used together. If one is defined, then the other needs to be. This is not true for Fioo_q and Fioo_frazilh.

njeffery · 2026-09-16T22:32:36Z

+		<nml_option name="config_use_accumulated_frazil_energy" type="logical" default_value=".false."
+					description="If true, send the total energy accumulated from frazil ice formation to the sea ice model, otherwise use the latent heat."
+					possible_values=".true. or .false."
+		/>


Updated the PR description

karapeterson · 2026-09-16T23:56:33Z

Have looked at the changes here and they look good to me. Was trying to get the Moab diagnostics working, but have had some bugs. Am rebuilding and rerunning now and will attach a diff once I confirm things are working correctly.

karapeterson · 2026-09-17T16:26:41Z

moab_cpl_changes.patch

Attached is patch with Moab coupler changes consistent with the mct changes. This will probably be needed as it seems that Moab is becoming the default coupler. @njeffery let me know if you'd like to add this here or if I should create a different PR. The changes were tested in a G-case with this PR.

njeffery · 2026-09-17T18:48:12Z

Thanks @karapeterson ! I'll implement those now.

njeffery · 2026-09-17T18:58:25Z

@karapeterson : How do I turn on MOAB to test?

rljacob · 2026-09-17T19:34:23Z

Use --driver moab in create_newcase. Or remove "Vmct" from the testname.

rljacob · 2026-09-17T19:38:18Z

You'll also have to merge #523 in to your local clone.

karapeterson · 2026-09-17T19:53:37Z

Thanks @njeffery and @rljacob for the instructions. When I ran the test, I was using MPAS-ocean and had not included #523

…i_cpl_indices.F,seq_flds_mod.F90

add index_x2i_Fioo_frazilh (frazil heat flux from ocean) add index_x2i_Fioi_frazil (frazil mass flux from sea ice) add index_x2i_Fioi_frazils (frazil salt flux from sea ice) add index_x2i_Fioi_frazilh (frazil heat flux from sea ice) All added to mpassi_cpl_indices.F and seq_flds_mod.F90. Fioi_frazil and Fioi_frazils added to ice_comp_mct.F

Updates Icepack submodule to frazil coupling branch Adds ocean-ice coupling fields: frazil salt flux (Fioo_frazils) frazil enthalpy flux (Fioo_frazilh) defined consistent with freezingMeltPotential To use, set config_frazil_coupling_type to ‘omega-fluxes’ Backwards compatible with mpas-ocean for config_frazil_coupling_type = ‘external’ Stealth

Sea ice initialize now allows for the config_frazil_coupling_type option: "omega-fluxes"

Sea ice initialize NOW allows for config_frazil_coupling_type option: “omega-fluxes”

Removes double counting of frazil energy in coupler budget. Corrects possible but in temperature tendency of frazil melt. nBFB

Adds optional formulation in frazil.

Revert to original formulation with comments.

1. Initialized frazilMassFlux to 0 for SOM 2. Corrected indexing of component-level salt budget sum 3. Type in comment 4. Corrected definition of Fioo_frazils in MOAB to be consistent with mct

Also removes redundant write in coupler diagnostics Clean up confusing comments in ocean conservation member

Co-authored-by: Carolyn Begeman <cbegeman@lanl.gov>

Makes the following changes to be consistent with salt/energy flux name convention: 1. Fioi_frazil to Fioi_frazilm 2. Fioo_frazil to Fioo_frazilm

darincomeau · 2026-10-01T21:36:18Z

Thanks @njeffery for the rebase - I just rebased the seaice-coupling branch onto develop so this PR looks right again.

andrewdnolan · 2026-10-01T23:50:37Z

Also, 'frazil' needs to be changed to 'frazilm' in Omega's drirver code. With this diff:

diff --git a/components/omega/src/drivers/coupled/omega_cpl_indices.F90 b/components/omega/src/drivers/coupled/omega_cpl_indices.F90
index 3c762a1e44..abe632731a 100644
--- a/components/omega/src/drivers/coupled/omega_cpl_indices.F90
+++ b/components/omega/src/drivers/coupled/omega_cpl_indices.F90
@@ -81,7 +81,7 @@ contains
       export_field_names(7) = "So_dhdy"
       export_field_names(8) = "Faoo_h2otemp"
       export_field_names(9) = "Fioo_q"
-      export_field_names(10) = "Fioo_frazil"
+      export_field_names(10) = "Fioo_frazilm"
 
       ! get mct_avect_index value for each export field name
       call get_indices_from_names( &

I can get SMS_Vmct_Ln9.TL319_EC30to60E2r2.GOMEGA-JRA1p5.chrysalis_intel to pass, without these changes we'll get runtime failures. (Thanks @darincomeau for bringing this to my attention).

Since that file hasn't been changes as part of this PR I can comment there directly and/or suggest changes.

Flagged in gnu compilation

Fioo_frazil to Fioo_frazilm in omega. Needed for SMS_Vmct_Ln9.TL319_EC30to60E2r2.GOMEGA-JRA1p5.chrysalis_intel to pass.

njeffery · 2026-10-05T15:19:06Z

@andrewdnolan and @darincomeau : I fixed the formatting issue in seq_diag_mct and pushed the frazil to frazilm change in omega.

njeffery requested review from cbegeman, darincomeau, erinethomas, karapeterson and proteanplanet and a lite review from Copilot September 16, 2026 16:40

Copilot started reviewing on behalf of njeffery September 16, 2026 16:41

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Copilot AI reviewed Sep 16, 2026

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Comment thread components/mpas-ocean/driver/ocn_comp_mct.F

Comment thread components/mpas-ocean/src/analysis_members/mpas_ocn_conservation_check.F Outdated

Comment thread driver-mct/main/seq_diag_mct.F90

cbegeman reviewed Sep 16, 2026

View reviewed changes

njeffery requested a lite review from Copilot September 16, 2026 22:23

Copilot started reviewing on behalf of njeffery September 16, 2026 22:23

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Copilot AI reviewed Sep 16, 2026

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andrewdnolan reviewed Sep 22, 2026

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Comment thread driver-mct/shr/seq_flds_mod.F90

darincomeau mentioned this pull request Sep 28, 2026

UPDATE - Adds new ocean to ice coupling fields for frazil ice formation #535

Closed

erinethomas and others added 9 commits September 29, 2026 12:13

add index_x2i_Fioo_frazils (frazil salt flux) to ice_comp_mct.F,mpass…

6fbd75f

…i_cpl_indices.F,seq_flds_mod.F90

adding o2x_Fioo_frazilh/o2x_Fioo_frazils to mpaso

4b63826

Enable variable salinity coupling inputs for sea ice

543f448

Updating icepack submodule 9.2.26

97550f5

Add budgeting in mct coupler for new coupling fields.

9a4de09

Fix bugs leading to build errors.

833ae50

Update sea ice config checks

13db738

Sea ice initialize now allows for the config_frazil_coupling_type option: "omega-fluxes"

njeffery and others added 17 commits September 29, 2026 12:13

Corrects update sea ice config options

961366e

Sea ice initialize NOW allows for config_frazil_coupling_type option: “omega-fluxes”

Fixes salt flux units error

a142bc4

Make frazil energy consistent with the ocean energy change

6c686e7

Removes double counting of frazil energy in coupler budget. Corrects possible but in temperature tendency of frazil melt. nBFB

fixed type introduced in last commit

f292121

Corrections to ensure BFB

ba610a2

Adds optional formulation in frazil.

Clean up ocean frazil routine

540ebe4

Revert to original formulation with comments.

corrects typo in frazil routine

7754efc

Remove redundant newFrazilEnergy

cbe81bf

Added copilot suggestions

9ecd1da

1. Initialized frazilMassFlux to 0 for SOM 2. Corrected indexing of component-level salt budget sum 3. Type in comment 4. Corrected definition of Fioo_frazils in MOAB to be consistent with mct

Splits ocean coupling of freezemelt potential into frazil heat and melt

15d3cb4

Clean up coupler diagnostics for frazil

51d8b83

Adds index checks for perrWith indices

b3dc930

Also removes redundant write in coupler diagnostics Clean up confusing comments in ocean conservation member

Update components/mpas-ocean/src/Registry.xml

3bf13b6

Co-authored-by: Carolyn Begeman <cbegeman@lanl.gov>

Changed registry field name and description

661ebaf

Removes space

893e102

Adds coupling diagnostics for moab

19f2d6d

Renamed frazil mass coupling fluxes

69b15d1

Makes the following changes to be consistent with salt/energy flux name convention: 1. Fioi_frazil to Fioi_frazilm 2. Fioo_frazil to Fioo_frazilm

njeffery force-pushed the njeffery/frazil-coupling branch from a735fde to 69b15d1 Compare September 29, 2026 17:18

darincomeau force-pushed the seaice-coupling branch from f1c42f8 to d02fe6f Compare October 1, 2026 21:35

andrewdnolan reviewed Oct 1, 2026

View reviewed changes

Comment thread driver-mct/main/seq_diag_mct.F90 Outdated

njeffery added 2 commits October 5, 2026 10:11

Corrects formatting in seq_diag_mct.F90

271d434

Flagged in gnu compilation

Changes frazil mass coupler name for consistency with mpassi

a107f9b

Fioo_frazil to Fioo_frazilm in omega. Needed for SMS_Vmct_Ln9.TL319_EC30to60E2r2.GOMEGA-JRA1p5.chrysalis_intel to pass.

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njeffery commented Sep 16, 2026 •

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