cam6_4_174: Update MPAS dynamical core to version 8.4.0

.gitmodules

@@ -88,7 +88,7 @@
 	url = https://github.com/MPAS-Dev/MPAS-Model.git
         fxrequired = AlwaysRequired
         fxsparse = ../.mpas_sparse_checkout
-        fxtag = v8.2.1
+        fxtag = v8.4.0
 	fxDONOTUSEurl = https://github.com/MPAS-Dev/MPAS-Model.git
 
 [submodule "cosp2"]

bld/build-namelist

@@ -4398,7 +4398,6 @@ if ($dyn =~ /mpas/) {
     add_default($nl, 'mpas_coef_3rd_order');
     add_default($nl, 'mpas_smagorinsky_coef');
     add_default($nl, 'mpas_mix_full');
-    add_default($nl, 'mpas_epssm');
     add_default($nl, 'mpas_smdiv');
     add_default($nl, 'mpas_apvm_upwinding');
     add_default($nl, 'mpas_h_ScaleWithMesh');
@@ -4409,12 +4408,18 @@ if ($dyn =~ /mpas/) {
     add_default($nl, 'mpas_rayleigh_damp_u');
     add_default($nl, 'mpas_rayleigh_damp_u_timescale_days');
     add_default($nl, 'mpas_number_rayleigh_damp_u_levels');
+    add_default($nl, 'mpas_epssm_minimum');
+    add_default($nl, 'mpas_epssm_maximum');
+    add_default($nl, 'mpas_epssm_transition_bottom_z');
+    add_default($nl, 'mpas_epssm_transition_top_z');
     add_default($nl, 'mpas_apply_lbcs');
     add_default($nl, 'mpas_jedi_da');
     add_default($nl, 'mpas_do_restart');
     add_default($nl, 'mpas_print_global_minmax_vel');
     add_default($nl, 'mpas_print_detailed_minmax_vel');
     add_default($nl, 'mpas_print_global_minmax_sca');
+    add_default($nl, 'mpas_halo_exch_method');
+    add_default($nl, 'mpas_gpu_aware_mpi');
 
     # mpas_block_decomp_file_prefix should only be set when more than one task is used.
     # Otherwise the file is not used and should not be added to the input dataset file.

bld/namelist_files/namelist_defaults_cam.xml

@@ -3457,8 +3457,6 @@
 <mpas_coef_3rd_order          > 1.0D0 </mpas_coef_3rd_order>
 <mpas_smagorinsky_coef        > 0.125D0 </mpas_smagorinsky_coef>
 <mpas_mix_full                > .true. </mpas_mix_full>
-<mpas_epssm                   > 0.1D0 </mpas_epssm>
-<mpas_epssm hgrid="mpasa120" waccm_phys="1"> 0.5D0 </mpas_epssm>
 <mpas_smdiv                   > 0.1D0 </mpas_smdiv>
 <mpas_apvm_upwinding          > 0.5D0 </mpas_apvm_upwinding>
 <mpas_apvm_upwinding hgrid="mpasa120" waccm_phys="1"> 0.0D0 </mpas_apvm_upwinding>
@@ -3472,6 +3470,11 @@
 <mpas_rayleigh_damp_u         > .true. </mpas_rayleigh_damp_u>
 <mpas_rayleigh_damp_u_timescale_days> 5.0 </mpas_rayleigh_damp_u_timescale_days>
 <mpas_number_rayleigh_damp_u_levels> 5 </mpas_number_rayleigh_damp_u_levels>
+<mpas_epssm_minimum> 0.1D0 </mpas_epssm_minimum>
+<mpas_epssm_maximum> 0.1D0 </mpas_epssm_maximum>
+<mpas_epssm_maximum hgrid="mpasa120" waccm_phys="1"> 0.5D0 </mpas_epssm_maximum>
+<mpas_epssm_transition_bottom_z> 30000.0D0 </mpas_epssm_transition_bottom_z>
+<mpas_epssm_transition_top_z> 50000.0D0 </mpas_epssm_transition_top_z>
 <mpas_apply_lbcs> .false. </mpas_apply_lbcs>
 <mpas_jedi_da> .false. </mpas_jedi_da>
 <mpas_block_decomp_file_prefix hgrid="mpasa480">atm/cam/inic/mpas/mpasa480.graph.info.part.</mpas_block_decomp_file_prefix>
@@ -3487,6 +3490,9 @@
 <mpas_print_detailed_minmax_vel> .false. </mpas_print_detailed_minmax_vel>
 <mpas_print_global_minmax_sca  > .false. </mpas_print_global_minmax_sca>
 
+<mpas_halo_exch_method> mpas_halo </mpas_halo_exch_method>
+<mpas_gpu_aware_mpi> .false. </mpas_gpu_aware_mpi>
+
 <!-- ================================================================== -->
 <!-- Chemistry Rates Diagnostics                                        -->
 <!-- ================================================================== -->

bld/namelist_files/namelist_definition.xml

@@ -8810,8 +8810,8 @@ Default: 120000.0
 
 <entry id="mpas_visc4_2dsmag" type="real" category="mpas"
        group="nhyd_model" valid_values="">
-Scaling coefficient of delta_x^3 to obtain Del^4 diffusion coefficient in
-MPAS dycore.
+Coefficient multiplied by delta x^3 to obtain Del^4 physical hyperviscosity
+in MPAS dycore.
 Default: 0.05
 </entry>
 
@@ -8902,13 +8902,6 @@ MPAS dycore.
 Default: TRUE
 </entry>
 
-<entry id="mpas_epssm" type="real" category="mpas"
-       group="nhyd_model" valid_values="">
-Off-centering parameter for the vertically implicit acoustic integration in
-MPAS dycore
-Default: 0.1
-</entry>
-
 <entry id="mpas_smdiv" type="real" category="mpas"
        group="nhyd_model" valid_values="">
 3-d divergence damping coefficient in MPAS dycore.
@@ -8984,6 +8977,32 @@ damping linearly ramps to zero by layer number from the top
 Default: 3
 </entry>
 
+<entry id="mpas_epssm_minimum" type="real" category="mpas"
+       group="damping" valid_values="real values between 0 and 1">
+Value of epssm, the off-centering parameter for the vertically implicit acoustic integration,
+below transition zone.
+Default: 0.1
+</entry>
+
+<entry id="mpas_epssm_maximum" type="real" category="mpas"
+       group="damping" valid_values="real values between 0 and 1">
+Value of epssm, the off-centering parameter for the vertically implicit acoustic integration,
+above transition zone.
+Default: 0.5
+</entry>
+
+<entry id="mpas_epssm_transition_bottom_z" type="real" category="mpas"
+       group="damping" valid_values="positive real values">
+Height (in meters) above MSL for the bottom of transition zone for epssm.
+Default: 30000.0
+</entry>
+
+<entry id="mpas_epssm_transition_top_z" type="real" category="mpas"
+       group="damping" valid_values="positive real values">
+Height (in meters) above MSL for the top of transition zone for epssm.
+Default: 50000.0
+</entry>
+
 <entry id="mpas_apply_lbcs" type="logical" category="mpas"
        group="limited_area" valid_values="">
 Whether to apply lateral boundary conditions
@@ -9034,6 +9053,18 @@ dycore.
 Default: FALSE
 </entry>
 
+<entry id="mpas_halo_exch_method" type="char*512" category="mpas"
+       group="development" valid_values="mpas_dmpar,mpas_halo">
+Method to use for exchanging halos in MPAS dycore.
+Default: mpas_halo
+</entry>
+
+<entry id="mpas_gpu_aware_mpi" type="logical" category="mpas"
+       group="development" valid_values=".false.,.true.">
+Whether to use GPU-aware MPI for halo exchanges in MPAS dycore. GPU-aware MPI
+is only implemented for mpas_halo_exch_method = mpas_halo.
+Default: FALSE
+</entry>
 
 <!-- Dycore testing  -->
 

doc/ChangeLog

@@ -1,3 +1,126 @@
+Tag name: cam6_4_174
+Originator(s): kuanchihwang
+Date: 21 May 2026
+One-line Summary: Update MPAS dynamical core to version 8.4.0
+Github PR URL: https://github.com/ESCOMP/CAM/pull/1545
+
+Purpose of changes (include the issue number and title text for each relevant GitHub issue):
+
+This PR updates MPAS dynamical core from version 8.2.1 to 8.4.0. See the in-between release notes of MPAS for details.
+
+Closes #1479
+
+Describe any changes made to build system:
+
+M       src/dynamics/mpas/Makefile
+  * Update Makefile to fix build errors
+  * Remove unnecessary Makefile build target
+  * Add patches to fix crash in MPAS 8.4.0
+
+Describe any changes made to the namelist:
+
+M       bld/build-namelist
+M       bld/namelist_files/namelist_defaults_cam.xml
+M       bld/namelist_files/namelist_definition.xml
+  * Update namelist definitions, defaults, and input to accommodate MPAS 8.4.0
+
+List any changes to the defaults for the boundary datasets:
+
+None
+
+Describe any substantial timing or memory changes:
+
+None
+
+Code reviewed by: nusbaume
+
+List all files eliminated:
+
+None
+
+List all files added and what they do:
+
+A       src/dynamics/mpas/driver/0001-Fix-Fortran-standard-violation.patch
+A       src/dynamics/mpas/driver/0002-Add-missing-argument-intent.patch
+A       src/dynamics/mpas/driver/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
+  * Update MPAS dynamical core to version 8.4.0
+M       src/dynamics/mpas/dp_coupling.F90
+  * Add support for new deformation coefficients introduced in MPAS 8.4.0
+M       src/dynamics/mpas/driver/cam_mpas_subdriver.F90
+  * Remove deprecated variables that no longer exist
+  * Define new constituent indexes required by MPAS 8.4.0
+M       src/dynamics/mpas/driver/README
+  * Add patches to fix crash in MPAS 8.4.0
+M       src/dynamics/mpas/dycore
+  * Update MPAS dynamical core to version 8.4.0
+M       src/dynamics/mpas/dyn_comp.F90
+  * Update namelist definitions, defaults, and input to accommodate MPAS 8.4.0
+  * Add support for new deformation coefficients introduced in MPAS 8.4.0
+
+If there were any failures reported from running test_driver.sh on any test
+platform, and checkin with these failures has been OK'd by the gatekeeper,
+then copy the lines from the td.*.status files for the failed tests to the
+appropriate machine below. All failed tests must be justified.
+
+derecho/intel/aux_cam:
+  ERC_D_Ln9.mpasa120_mpasa120.F2000climo.derecho_intel.cam-outfrq9s_mpasa120 (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.F2000climo.derecho_intel.cam-outfrq9s_mpasa120 NLCOMP
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.F2000climo.derecho_intel.cam-outfrq9s_mpasa120 BASELINE /glade/campaign/cesm/community/amwg/cam_baselines/cam6_4_173_intel: DIFF
+  ERC_D_Ln9.mpasa120_mpasa120.FHISTC_LTso.derecho_intel.cam-outfrq9s_mpasa120 (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.FHISTC_LTso.derecho_intel.cam-outfrq9s_mpasa120 NLCOMP
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.FHISTC_LTso.derecho_intel.cam-outfrq9s_mpasa120 BASELINE /glade/campaign/cesm/community/amwg/cam_baselines/cam6_4_173_intel: DIFF
+  ERC_D_Ln9.mpasa120_mpasa120.QPC7.derecho_intel.cam-outfrq9s_mpasa120 (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.QPC7.derecho_intel.cam-outfrq9s_mpasa120 NLCOMP
+    FAIL ERC_D_Ln9.mpasa120_mpasa120.QPC7.derecho_intel.cam-outfrq9s_mpasa120 BASELINE /glade/campaign/cesm/community/amwg/cam_baselines/cam6_4_173_intel: DIFF
+
+  Expected namelist and answer changes due to MPAS version update.
+
+  Notes about SMS_D_Ln9_P1536x1.ne0CONUSne30x8_ne0CONUSne30x8_mt12.FCHIST.derecho_intel.cam-outfrq9s:
+  This test is flaky. It may sometimes fail with a "floating invalid" error in CTSM.
+
+derecho/nvhpc/aux_cam:
+  PASS.
+
+izumi/nag/aux_cam:
+  ERC_D_Ln9.mpasa480_mpasa480_mt232.FHS94.izumi_nag.cam-outfrq9s (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.FHS94.izumi_nag.cam-outfrq9s NLCOMP
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.FHS94.izumi_nag.cam-outfrq9s BASELINE /fs/cgd/csm/models/atm/cam/pretag_bl/cam6_4_173_nag: DIFF
+  ERC_D_Ln9.mpasa480_mpasa480_mt232.QPC7.izumi_nag.cam-outfrq9s_mpasa480 (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.QPC7.izumi_nag.cam-outfrq9s_mpasa480 NLCOMP
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.QPC7.izumi_nag.cam-outfrq9s_mpasa480 BASELINE /fs/cgd/csm/models/atm/cam/pretag_bl/cam6_4_173_nag: DIFF
+
+  Expected namelist and answer changes due to MPAS version update.
+
+  ERC_D_Ln9.f10_f10_mt232.FHIST_C5.izumi_nag.cam-outfrq3s_subcol (Overall: FAIL) details:
+    FAIL ERC_D_Ln9.f10_f10_mt232.FHIST_C5.izumi_nag.cam-outfrq3s_subcol COMPARE_base_rest
+
+  Pre-existing test failure. See https://github.com/ESCOMP/CAM/issues/1514.
+
+izumi/gnu/aux_cam:
+  ERC_D_Ln9.mpasa480_mpasa480_mt232.FHISTC_LTso.izumi_gnu.cam-outfrq9s_mpasa480 (Overall: DIFF) details:
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.FHISTC_LTso.izumi_gnu.cam-outfrq9s_mpasa480 NLCOMP
+    FAIL ERC_D_Ln9.mpasa480_mpasa480_mt232.FHISTC_LTso.izumi_gnu.cam-outfrq9s_mpasa480 BASELINE /fs/cgd/csm/models/atm/cam/pretag_bl/cam6_4_173_gnu: DIFF
+  ERS_Ln9_P24x1.mpasa480_mpasa480.F2000climo.izumi_gnu.cam-outfrq9s_mpasa480 (Overall: DIFF) details:
+    FAIL ERS_Ln9_P24x1.mpasa480_mpasa480.F2000climo.izumi_gnu.cam-outfrq9s_mpasa480 NLCOMP
+    FAIL ERS_Ln9_P24x1.mpasa480_mpasa480.F2000climo.izumi_gnu.cam-outfrq9s_mpasa480 BASELINE /fs/cgd/csm/models/atm/cam/pretag_bl/cam6_4_173_gnu: DIFF
+
+  Expected namelist and answer changes due to MPAS version update.
+
+CAM tag used for the baseline comparison tests if different than previous
+tag: cam6_4_173
+
+Summarize any changes to answers:
+
+In summary, this PR is answer-changing for tests that involve MPAS dynamical core.
+For tests that do not involve MPAS dynamical core, they are bit-for-bit.
+
+===============================================================
+
 Tag name: cam6_4_173
 Originator(s): pel, peverwhee, hplin
 Date: 15 May 2026