Update MPAS dynamical core to version 8.4.0 by kuanchihwang · Pull Request #495 · ESCOMP/CAM-SIMA

kuanchihwang · 2026-04-24T19:09:31Z

Tag name (required for release branches)

TBD

Originator(s)

kuanchihwang

Description (include the issue title, and the keyword ['closes', 'fixes', 'resolves'] followed by the issue number)

This PR updates MPAS dynamical core from version 8.3.1 to 8.4.0. See the release notes for details.

Notably, the new Large Eddy Simulation (LES) capability in MPAS is experimentally supported under CAM-SIMA, at the price of increased complexity in constituent handling. However, due to the object-oriented design of MPAS subdriver, this complexity is entirely contained within the subdriver layer and does not affect other parts of CAM-SIMA. This capability is disabled by default, and can be enabled manually through namelist options.

A future PR is planned to refactor the dyn_mpas_define_scalar subroutine in MPAS subdriver to keep its complexity and scope in check.

Describe any changes made to the build system

src/dynamics/mpas/assets/Makefile.in.CESM has been modified to suppress harmless but potentially confusing errors in build logs.

Describe any changes made to the namelist

mpas_epssm

This namelist option has been deprecated and set to 0.0. Setting it to any values other than 0.0 triggers a compatibility warning.

mpas_epssm_maximum, mpas_epssm_minimum, mpas_epssm_transition_bottom_z, mpas_epssm_transition_top_z

These new namelist options provide more fine-grained control on the off-centering parameter for the vertically implicit acoustic integration.

mpas_gpu_aware_mpi

Whether to use GPU-aware MPI for halo exchanges.

mpas_les_model, mpas_les_surface, mpas_mix_scalars, mpas_surface_drag_coefficient, mpas_surface_heat_flux, mpas_surface_moisture_flux

These new namelist options control the new LES capability in MPAS.

List any changes to the defaults for the input datasets (e.g., boundary datasets)

None

List all files eliminated and why

None

List all files added and what they do

A       src/dynamics/mpas/assets/0001-Fix-Fortran-standard-violation.patch
A       src/dynamics/mpas/assets/0002-Add-missing-argument-intent.patch
A       src/dynamics/mpas/assets/0003-Avoid-implicit-save-attribute.patch
  * Add patches to fix crash in MPAS 8.4.0

List all existing files that have been modified, and describe the changes

M       .gitmodules
M       src/dynamics/mpas/dycore
  * Update MPAS dynamical core to version 8.4.0
M       src/dynamics/mpas/assets/generate_namelist_definition.py
M       src/dynamics/mpas/namelist_definition_mpas_dycore.xml
  * Update namelist definition file and script for MPAS dynamical core
M       src/dynamics/mpas/assets/Makefile.in.CESM
  * Suppress harmless errors in build logs
M       src/dynamics/mpas/driver/dyn_mpas_subdriver.F90
  * Remove deprecated variables that no longer exist
  * Rework constituent handling in MPAS subdriver to support new LES capability

Regression tests

derecho/aux_sima_gnu

SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 (Overall: DIFF) details:
  FAIL SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 NLCOMP
  FAIL SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: DIFF
SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 (Overall: DIFF) details:
  FAIL SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 NLCOMP
  FAIL SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_gnu.cam-outfrq_analy_ic_cam4 BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: DIFF
SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_gnu.cam-outfrq_kessler_mpas_derecho (Overall: DIFF) details:
  FAIL SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_gnu.cam-outfrq_kessler_mpas_derecho NLCOMP
  FAIL SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_gnu.cam-outfrq_kessler_mpas_derecho BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_gnu: DIFF

Expected answer changes due to MPAS version update.

SMS_Ln9.ne3pg3_ne3pg3_mg37.FADIAB.derecho_gnu.cam-outfrq_se_cslam (Overall: FAIL) details:
  FAIL SMS_Ln9.ne3pg3_ne3pg3_mg37.FADIAB.derecho_gnu.cam-outfrq_se_cslam RUN time=15

Known failing test.

derecho/aux_sima_intel

SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 (Overall: DIFF) details:
  FAIL SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 NLCOMP
  FAIL SMS_D_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_intel: DIFF
SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 (Overall: DIFF) details:
  FAIL SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 NLCOMP
  FAIL SMS_Ln9.mpasa120_mpasa120.QPC4.derecho_intel.cam-outfrq_analy_ic_cam4 BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_intel: DIFF
SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_intel.cam-outfrq_kessler_mpas_derecho (Overall: DIFF) details:
  FAIL SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_intel.cam-outfrq_kessler_mpas_derecho NLCOMP
  FAIL SMS_Ln9.mpasa480_mpasa480.FKESSLER.derecho_intel.cam-outfrq_kessler_mpas_derecho BASELINE /glade/campaign/cesm/community/amwg/sima_baselines/latest_intel: DIFF

Expected answer changes due to MPAS version update.

SMS_Ln9.ne3pg3_ne3pg3_mg37.FKESSLER.derecho_intel.cam-outfrq_se_cslam_multitape (Overall: NLFAIL) details:
  FAIL SMS_Ln9.ne3pg3_ne3pg3_mg37.FKESSLER.derecho_intel.cam-outfrq_se_cslam_multitape NLCOMP

Known failing test.

derecho/aux_sima_nvhpc

Pass.

The patches are being contributed to upstream MPAS. We have to keep them for now until the next MPAS release.

…bility

nusbaume

Thanks for bringing in the latest version of MPAS @kuanchihwang! I have a question, an optional clean-up request, and some requests to eventually provide some unit labels for MPAS namelist entries, but nothing that is strictly required for this particular PR.

Of course if you have any questions or concerns with any of my requests then just let me know. Thanks again!

nusbaume · 2026-05-12T03:14:11Z

@@ -0,0 +1,45 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001


Just double-checking that these three patch files won't be needed once MPAS PR MPAS-Dev/MPAS-Model#1448 has been merged?

nusbaume · 2026-05-12T16:24:25Z

+        character(strkind), pointer :: config_les_model
        integer :: mesh_format
        integer, pointer :: num_scalars
+        logical :: mpas_without_les


Should this logical be promoted to a variable within mpas_dynamical_core_type? That way we only need to query the config_les_model variable pointer once.

nusbaume · 2026-05-12T16:25:56Z

+        call self % get_variable_pointer(config_les_model, 'cfg', 'config_les_model')
+
+        mpas_without_les = (trim(adjustl(config_les_model)) == 'none')
+
+        nullify(config_les_model)


If we promote mpas_without_les to an mpas_dynamical_core_type variable then these lines are no longer needed.

nusbaume · 2026-05-12T16:40:06Z

+    <entry id="mpas_epssm_transition_bottom_z">
+        <category>mpas</category>
+        <desc>
+            Height MSL of bottom of transition zone for epssm


Should this say "above" here?

Suggested change

Height MSL of bottom of transition zone for epssm

Height above MSL of bottom of transition zone for epssm

nusbaume · 2026-05-12T16:47:13Z

+        <values>
+            <value>30000.0</value>
+        </values>


Can we add a units tag here to indicate what the units are for the height number (I am guessing meters)?

Suggested change

<values>

<value>30000.0</value>

</values>

<units>m</units>

<values>

<value>30000.0</value>

</values>

I realize this file is created with a script, so if it is too difficult to add this at the moment then I am happy to open an issue and figure out a better, script-driven method later.

nusbaume · 2026-05-12T16:48:32Z

+            Height MSL of top of transition zone for epssm
+        </desc>
+        <group>mpas_damping</group>
+        <type>real</type>
+        <values>
+            <value>50000.0</value>
+        </values>


Update description and add units element here as well (if doable)?

Suggested change

Height MSL of top of transition zone for epssm

</desc>

<group>mpas_damping</group>

<type>real</type>

<values>

<value>50000.0</value>

</values>

Height above MSL of top of transition zone for epssm

</desc>

<group>mpas_damping</group>

<type>real</type>

<units>m</units>

<values>

<value>50000.0</value>

</values>

nusbaume · 2026-05-12T17:04:06Z

+            <value>0.0</value>
+        </values>
+    </entry>
+    <entry id="mpas_surface_heat_flux">


Eventually can we add a units element for this entry as well? I am guessing it is something like m K s-1 but could be wrong. Again I am happy to push this off to future work given that there is a script involved.

nusbaume · 2026-05-12T17:05:13Z

+            <value>0.0</value>
+        </values>
+    </entry>
+    <entry id="mpas_surface_moisture_flux">


Eventually can we add a units element for this entry as well? I am guessing it is something like m kg kg-1 s-1 but could be wrong. Again I am happy to push this off to future work given that there is a script involved.

kuanchihwang added 6 commits April 24, 2026 12:29

Update MPAS dynamical core to version 8.4.0

d59713d

Suppress harmless errors in build logs

e87d52c

Add patches to fix crash in MPAS 8.4.0

93d5b89

The patches are being contributed to upstream MPAS. We have to keep them for now until the next MPAS release.

Update namelist definition file and script for MPAS dynamical core

3554b36

Remove deprecated variables that no longer exist

85af071

Rework constituent handling in MPAS subdriver to support new LES capa…

353430c

…bility

kuanchihwang temporarily deployed to CI-tests-on-CIRRUS April 24, 2026 19:09 — with GitHub Actions Inactive

kuanchihwang marked this pull request as ready for review April 24, 2026 19:17

kuanchihwang requested review from mgduda and nusbaume April 24, 2026 19:19

Merge branch 'development' into develop/mpas-dycore-8.4.0

a7ed1d9

kuanchihwang temporarily deployed to CI-tests-on-CIRRUS May 1, 2026 20:01 — with GitHub Actions Inactive

nusbaume approved these changes May 12, 2026

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Update MPAS dynamical core to version 8.4.0#495

Update MPAS dynamical core to version 8.4.0#495
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		@@ -0,0 +1,45 @@
		From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

	Height MSL of bottom of transition zone for epssm
	Height above MSL of bottom of transition zone for epssm

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kuanchihwang commented Apr 24, 2026

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Description (include the issue title, and the keyword ['closes', 'fixes', 'resolves'] followed by the issue number)

Describe any changes made to the build system

Describe any changes made to the namelist

List any changes to the defaults for the input datasets (e.g., boundary datasets)

List all files eliminated and why

List all files added and what they do

List all existing files that have been modified, and describe the changes

Regression tests

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