MPAS-Dev/MPAS-Model: MPAS Version 8.4.0

This release of MPAS introduces new capabilities and improvements in the MPAS-Atmosphere model and its supporting software infrastructure, and it is the first release to provide the foundation for CheMPAS-A, a chemistry capability for MPAS-Atmosphere. Notable changes are listed below.

MPAS-Atmosphere Initialization:

• Fix an issue in snow initialization over areas covered by seaice. (PR #1438)

• Introduce namelist control over the vertical coordinate configuration for real-data case initialization. Two new namelist options may now be specified in the &vertical_grid namelist group in the namelist.init_atmosphere file:

  • config_hybrid_coordinate (default: true) Whether to employ a hybrid vertical coordinate
  • config_hybrid_top_z (default: 30000 m) Height at which coordinate surfaces become constant height surfaces

  Additionally, the smoothing coefficient formula for the hybrid coordinate now uses the transition height instead of the model top height. (PR #1382)

• Add computation of the edgeNormalVectors, cellTangentPlane, and localVerticalUnitVectors fields for MPAS-A initialization case 13 (CAM-MPAS 3-d grid) to better support alternative initialization workflows for CAM-MPAS. (PR #1351)

MPAS-Atmosphere Dynamics:

• Implement an initial Large-Eddy Simulation (LES) capability. Similar to WRF, it contains two subgrid turbulence models -- a diagnostic Turbulent Kinetic Energy (TKE) formulation based on a 3-d Smagorinsky formulation, and a 1.5-order prognostic TKE formulation. These formulations generally follow the implementation in WRF (see the WRF Technical Note Version 4, sections 4.2.3 and 4.2.4 for a description of the formulations). (PR #1404)

• Generalize the epssm parameter, allowing level-dependent values to be specified through four new namelist options:

  • config_epssm_minimum (default value: 0.1)
  • config_epssm_maximum (default value: 0.5)
  • config_epssm_transition_bottom_z (default value: 30000.0)
  • config_epssm_transition_top_z (default value: 50000.0)

  The epssm parameter is an off-centering coefficient for the vertically semi-implicit acoustic / gravity-wave integration, and it was previously specified as a single, constant value using the config_epssm namelist option. (PR #1381)

• Add the capability to turn off microphysics tendencies above a specified height with a new namelist option, config_microphysics_top, in the &physics namelist group. Ignoring tendencies from the microphysics at upper levels has been found to alleviate some instabilities in deep-domain (i.e., model tops above the stratopause) MPAS-Atmosphere simulations. (PR #1380)

• Optimize OpenACC data movement throughout the MPAS-A dycore, so that the majority of fields are transferred to the device at the start of a dynamics step and from the device at the end of a dynamics step. (PR #1315)

• Remove the scaling of the gravity-wave absorbing layer coefficient (dss) by the local mesh size. Previously, the absorbing layer coefficient was scaled by dx/dx_fine, and for large values of dx/dx_fine, instabilities have been encountered associated with this scaling of the absorbing layer coefficient. (PR #1379)

MPAS-Atmosphere Physics:

• Correct an issue with high q2 values over urban cells in Noah-MP. (PR #1383)

• Fix crashes when using the CAM SW radiation scheme. (PR #1391)

• Fix an indexing typo in mpas_atmphys_interface.F, where evapprod(k,k) was used instead of evapprod(k,i). The fix corrects diagnostic output, but should not affect the model state or simulation results. (PR #1396)

• Correct the units designations of the gravity wave drag diagnostics variables dusfcg, dvsfcg, dtaux3d, and dtauy3d in the atmosphere core's Registry.xml file. (PR #1378)

MPAS-Atmosphere Misc.:

• Remove PV diagnostic fields from the default "output" stream for MPAS-Atmosphere, reducing the size of the default "history" netCDF files by ~20%. (PR #1428)

• Modify the MPAS-Atmosphere CMake build system to use manage_externals to obtain specific tags from the https://github.com/NCAR/MMM-physics.git and https://github.com/NOAA-GSL/UGWP.git repositories, rather than simply obtaining the HEAD of the default branch. This modification corrects build failures when using CMake. (PR #1421)

CheMPAS-A:

• Enable linking with the MUSICA-Fortran library to support development of chemistry capabilities based on MICM and TUV-x. (PR #1309)

• Add a new namelist group, &musica, with a single option, config_micm_file, to control the MICM configuration in MPAS-Atmosphere. The new namelist group is only included in the namelist.atmosphere file (and therefore, only recognized) when MPAS is compiled with support for the MUSICA library. (PR #1376)

• Introduce directory structure and stub modules for MUSICA, and more broadly, for chemistry options in the atmosphere core. (PR #1360)

  New directories and modules include:

    src/
      core_atmosphere/
        chemistry/              <--|
          mpas_atm_chemistry.F  <--|
          musica/               <--| new in this release
            mpas_musica.F       <--|

Infrastructure:

• Introduce the ability to partition meshes "online" at model startup using the PT-Scotch library. (PR #1364)

• Enable execution of halo exchanges directly on GPU-resident fields when MPAS is linked with an MPI library that is GPU-aware. To enable GPU-aware halo exchanges, a new namelist option, config_gpu_aware_mpi, in the &development namelist group must be set to true at runtime. (PR #1355)

• Improve support for using an external ESMF library through a new build option, MPAS_ESMF. (PR #1405)

• Set the default PnetCDF header alignment to 128 KiB when creating new output files with SMIOL. This has been found to fix I/O issues when overwriting existing model output files under certain conditions. (PR #1386)

• Fix an issue with macro expansion with newer Intel oneAPI compilers by adding a flag for the intel build target to change the order of macro expansion in the Fortran pre-processor. This change in macro expansion order fixes an issue with some nested macro use in MPAS. (PR #1392)

• Fix a buffer overflow in the streaminfo_query function in the mpas_stream_inquiry module , where the local array c_attname was allocated without space for a C null character. (PR #1352)

Known Issues:

• MPAS-Atmosphere results using different OpenMP thread counts are not reproducible.

• Bit-reproducible restarts and bit-reproducible results using different MPI task counts require reduced optimization with the GNU and Intel oneAPI compilers (-O1 appears to work).

• With config_les_model = '3d_smagorinky', turning off all compiler optimizations appears to be necessary for bit-reproducibility.

• MPAS-Atmosphere results differ when using an external ESMF library.

Acknowledgements: Thanks to Dan Rosen (@danrosen25), Zhe Zhang (@CharlesZheZhang), Mike Toy (@mdtoyNOAA), @Yi-ChuanLO, David Fillmore (@dwfncar), and Matt Dawson (@mattldawson) for their contributions to this release.