ismip7_forcing

The ismip7_forcing test group (compass.landice.tests.ismip7_forcing.Ismip7Forcing) processes (i.e., remaps and renames) the atmospheric and ocean thermal forcing data of the Ice Sheet Model Intercomparison for CMIP7 (ISMIP7) protocol from its native polar stereographic grid to the MALI unstructured mesh. The test group supports both AIS and GrIS via the ice_sheet config option. It includes three test cases: atmosphere, ocean_thermal, and fracture.

framework

The shared config options for the ismip7_forcing test group are described in ismip7_forcing in the User’s Guide.

ice_sheet_params

The module compass.landice.tests.ismip7_forcing.ice_sheet_params defines a dictionary of ice-sheet-specific parameters (projection, file naming prefix, grid resolution, data version, ocean dimensionality) and provides the function compass.landice.tests.ismip7_forcing.ice_sheet_params.get_params() to retrieve them based on the ice_sheet config option.

configure

The module compass.landice.tests.ismip7_forcing.configure validates that all required config options in the [ismip7] section have been set by the user (i.e., are not NotAvailable).

Repository-local example user configs are available at compass/landice/tests/ismip7_forcing/ismip7_forcing_test.cfg (AIS) and compass/landice/tests/ismip7_forcing/ismip7_forcing_test_gis.cfg (GrIS). These are intended for development/testing and include environment-specific paths.

create_mapfile

The module compass.landice.tests.ismip7_forcing.create_mapfile defines a unified framework for creating SCRIP and mapping files. The function compass.landice.tests.ismip7_forcing.create_mapfile.build_mapping_file() creates a SCRIP file from the input polar stereographic grid using the create_scrip_file_from_planar_rectangular_grid command from MPAS-Tools, then generates a mapping file via ESMF_RegridWeightGen. The projection is automatically determined from the ice_sheet config option using ice_sheet_params.

Test cases

atmosphere

The compass.landice.tests.ismip7_forcing.atmosphere.Atmosphere test case processes the ISMIP7 atmosphere forcing fields. It contains five steps: SMB, temperature, their respective gradients, and runoff. Each step discovers input files matching the ice-sheet-specific naming pattern, builds or reuses a mapping file, remaps each input file with ncremap, and combines/renames the results to MALI conventions.

Steps:

ocean_thermal

The compass.landice.tests.ismip7_forcing.ocean_thermal.OceanThermal test case processes the ISMIP7 ocean thermal forcing. It contains a single step, ProcessThermalForcing, which handles both AIS (3D, decade-spanning files) and GrIS (2D, yearly files) by branching on the ocean_3d parameter from ice_sheet_params.

The run() method dispatches to two sub-methods based on the boolean config options process_ocean_thermal and process_ocean_climatology in the [ismip7] section:

  • _run_scenario(): Processes time-varying ESM scenario data (model + scenario combination). Uses config from [ismip7_ocean_thermal].

  • _run_climatology(): Processes the static observational climatology (Zhou et al., AIS only). Uses config from [ismip7_ocean_climatology]. The TF version (currently v3) is hard-coded.

For AIS scenario data, the step:

  • Remaps thermal forcing preserving 30 vertical ocean layers

  • Produces ismip6shelfMelt_3dThermalForcing (dims: Time × nCells × nISMIP6OceanLayers)

  • Includes depth coordinate variables ismip6shelfMelt_zOcean and ismip6shelfMelt_zBndsOcean

For AIS climatology data, the step:

  • Extrapolates fill values, remaps, and renames to MALI conventions

  • Produces ismip6shelfMelt_3dThermalForcing (dims: nCells × nISMIP6OceanLayers) — no Time dimension

For GrIS, the step:

  • Remaps 2D monthly thermal forcing

  • Produces ismip6_2dThermalForcing (dims: Time × nCells)

fracture

The compass.landice.tests.ismip7_forcing.fracture.Fracture test case processes the ISMIP7 surface-melt-driven ice shelf collapse forcing (AIS only). It implements the three ISMIP7 pathways as independent steps, each discovering its source file from the fracture/{version}/ subdirectory of base_path_ismip7, building or reusing a mapping file, remapping with ncremap, and renaming the result to MALI conventions with an accompanying xtime variable. Per-pathway remapping methods are set in the [ismip7_fracture] config section. Setting a pathway’s remapping-method option to None causes that step to return early without processing its file, which is useful when only some pathway source files are available.

Steps:

  • ProcessExcessMelt (Path A) — excess_melt → ismip7ExcessMelt. The excess melt file lacks x/y coordinate variables and its array is flipped along the y axis relative to the other fracture files (it was produced with CDO). The _prepare_source_grid() method borrows x/y from a sibling fracture file, flips the data to match (raising if the flipped lat does not match the sibling grid), and writes a reconstructed source file. The field is then extrapolated (nearest neighbor, filling NaNs) and remapped conservatively by default (it is a flux).

  • ProcessLakeProperties (Path B) — lake_depth → ismip7LakeDepth and fraction_lake_area → ismip7LakeAreaFraction. Both variables are extrapolated and remapped in a single ncremap call (bilinear by default).

  • ProcessShelfCollapse (Path C) — mask → calvingMask. Remapped with neareststod by default and rounded to 0/1 so the discrete collapse mask is preserved.

The annual source fields use an integer year/time coordinate with units="year" (not CF-compliant), so each step opens the data with decode_times=False and constructs xtime at January 1st of each year.

Shared remapping helpers used by the fracture steps live in compass.landice.tests.ismip7_forcing.fracture.remap_utils: extrapolate_source (nearest-neighbor fill of NaNs on the source grid), open_rename_and_trim (open a remapped file, rename dimensions/variables to MALI conventions, and restrict to the requested year range), and add_xtime_and_write (add the xtime variable, drop auxiliary remapping variables, and write the output).

The output variable names for Paths A and B (ismip7ExcessMelt, ismip7LakeDepth, ismip7LakeAreaFraction) are descriptive placeholders and may need to be aligned with the MALI Registry once the corresponding model input fields are defined.