ismip7_forcing

The landice/ismip7_forcing test group processes (i.e., remaps and renames) the atmospheric and ocean thermal forcing data of the Ice Sheet Model Intercomparison for CMIP7 (ISMIP7) protocol. The processed data is used to force MALI in its simulations under the ISMIP7 experimental protocol. The test group supports both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GrIS), controlled by a single ice_sheet config option.

The test group includes three test cases: atmosphere, ocean_thermal, and fracture.

  • The atmosphere test case has five steps: process_smb, process_temperature, process_smb_gradient, process_temperature_gradient, and process_runoff.

  • The ocean_thermal test case has one step: process_thermal_forcing. For AIS this produces 3D thermal forcing (with 30 ocean depth layers); for GrIS it produces 2D (depth-averaged) thermal forcing. The step can also process the observational ocean thermal forcing climatology (Zhou et al.) for AIS, controlled by the process_ocean_climatology config option.

  • The fracture test case has three steps: process_excess_melt (Path A), process_lake_properties (Path B), and process_shelf_collapse (Path C). It processes the ISMIP7 surface-melt-driven ice shelf collapse forcing (AIS only).

(For more details on the steps of each test case, see atmosphere, ocean_thermal, and fracture.)

Usage

To use this test group, users need to:

  1. Provide a MALI mesh file onto which the source data will be remapped.

  2. Set the ice_sheet config option to either ais or gis.

  3. Provide the path to the ISMIP7 forcing data (base_path_ismip7).

  4. Run the atmosphere test case for each model and scenario combination.

  5. Run the ocean_thermal test case for each model and scenario combination.

  6. Run the fracture test case (AIS only) for each model and scenario combination to process the surface-melt-driven ice shelf collapse pathways (excess melt, lake properties, and the ice shelf collapse mask).

Example user config files are provided in the source tree for local testing:

  • compass/landice/tests/ismip7_forcing/ismip7_forcing_test.cfg (AIS-focused example)

  • compass/landice/tests/ismip7_forcing/ismip7_forcing_test_gis.cfg (GrIS-focused example)

These files contain machine-specific absolute paths and are intended as templates, not portable defaults. Copy one and edit paths and options for your environment before using it with compass setup ... -f USER.cfg.

The AIS example enables both ocean processing modes and uses a 2015-2300 processing window for both atmosphere and ocean thermal scenario forcing. The GrIS example enables scenario ocean processing only and uses 1980-2015.

Input Data

ISMIP7 forcing data is organized by variable and version. The expected directory structure under base_path_ismip7 is:

For AIS atmosphere (2km, polar stereographic EPSG:3031):

acabf/v2/acabf_AIS_{model}_{scenario}_SDBN1-2000m_v2_{year_range}.nc
ts/v2/ts_AIS_{model}_{scenario}_SDBN1-2000m_v2_{year_range}.nc
dacabfdz/v2/dacabfdz_AIS_{model}_{scenario}_SDBN1-2000m_v2_{year_range}.nc
dtsdz/v2/dtsdz_AIS_{model}_{scenario}_SDBN1-2000m_v2_{year_range}.nc
mrro/v2/mrro_AIS_{model}_{scenario}_SDBN1-2000m_v2_{year_range}.nc

For AIS ocean thermal (8km, 30 depth levels, decade files):

ocean/tf/v3/tf_AIS_{model}_{scenario}_ocean_v3_{start_year}-{end_year}.nc

For AIS ocean thermal climatology (8km, 30 depth levels, static):

{base_path_climatology}/tf/v3/tf_AIS_obs_ocean_climatology_*.nc

For AIS fracture / ice shelf collapse mask (8km, annual, Path C):

fracture/v2/ice_shelf_collapse_mask_*.nc

For GrIS atmosphere (1km, polar stereographic EPSG:3413):

acabf/v2/acabf_GrIS_{model}_{scenario}_SDBN1-1000m_v2_{year}.nc
ts/v2/ts_GrIS_{model}_{scenario}_SDBN1-1000m_v2_{year}.nc
dacabfdz/v2/dacabfdz_GrIS_{model}_{scenario}_SDBN1-1000m_v2_{year}.nc
dtsdz/v2/dtsdz_GrIS_{model}_{scenario}_SDBN1-1000m_v2_{year}.nc
mrro/v2/mrro_GrIS_{model}_{scenario}_SDBN1-1000m_v2_{year}.nc

For GrIS ocean thermal (same 1km grid, 2D, yearly files):

ocean/tf/v2/tf_GrIS_{model}_{scenario}_ocean_v2_{year}.nc

config options

The ismip7_forcing test group uses four config sections. The default values are:

# config options for ismip7 forcing data
[ismip7]

# Ice sheet: ais (Antarctic) or gis (Greenland)
ice_sheet = NotAvailable

# Base path to the input ISMIP7 forcing files
base_path_ismip7 = NotAvailable

# Base path to the MALI mesh
base_path_mali = NotAvailable

# Base path to which output forcing files are saved
output_base_path = NotAvailable

# Name of climate model (e.g., CESM2-WACCM, MRI-ESM2-0)
model = NotAvailable

# Scenario (e.g., historical, ssp126, ssp370, ssp585)
scenario = NotAvailable

# Name of the MALI mesh (used in output file naming)
mali_mesh_name = NotAvailable

# MALI mesh file name
mali_mesh_file = NotAvailable

# Number of MPI tasks for ESMF_RegridWeightGen
esmf_ntasks = 128

# Whether to process time-varying ocean thermal forcing (ESM scenario data)
process_ocean_thermal = true

# Whether to process observational ocean thermal forcing climatology
process_ocean_climatology = true

# config options for ismip7 atmosphere forcing
[ismip7_atmosphere]

# Remapping method: bilinear, neareststod, conserve
method_remap = conserve

# Start year for processing
start_year = 1850

# End year for processing
end_year = 2014

# config options for ismip7 ocean thermal forcing
[ismip7_ocean_thermal]

# Remapping method: bilinear, neareststod, conserve
method_remap = bilinear

# Start year for processing
start_year = 1850

# End year for processing
end_year = 2014

# config options for ismip7 ocean thermal forcing climatology
[ismip7_ocean_climatology]

# Remapping method: bilinear, neareststod, conserve
method_remap = bilinear

# Base path to observational climatology data
base_path_climatology = /path/to/ISMIP7/forcing/AIS/obs/zhou_annual_06_nov

# config options for ismip7 fracture (Path C, ice shelf collapse) forcing
[ismip7_fracture]

# Remapping method for each pathway. Set a method to None to skip
# processing that pathway's file.

# Remapping method for the ice shelf collapse mask (Path C).
# neareststod preserves the 0/1 mask values
method_remap_shelf_collapse = neareststod

# Remapping method for the excess meltwater field (Path A), a flux
method_remap_excess_melt = conserve

# Remapping method for the supraglacial lake properties (Path B)
method_remap_lake_properties = bilinear

# Version subdirectory of the fracture forcing data
version = v2

# Start year for processing
start_year = 1850

# End year for processing
end_year = 2014

All NotAvailable options must be overridden in a user config file passed at setup time (e.g., compass setup ... -f my_ismip7.cfg).

The boolean options process_ocean_thermal and process_ocean_climatology control which processing paths are executed when the ocean_thermal test case is run. Both default to true. Set one to false in your user config to skip that processing path.

atmosphere

The landice/ismip7_forcing/atmosphere test case processes the ISMIP7 atmosphere forcing fields and remaps them from the native polar stereographic grid to the MALI unstructured mesh.

Steps:

  • process_smb: Remaps the surface mass balance (acabf) field. The output variable is sfcMassBal.

  • process_temperature: Remaps the surface temperature (ts) field, clipped to a maximum of 273.15 K. The output variable is surfaceAirTemperature.

  • process_smb_gradient: Remaps the SMB lapse rate (dacabfdz) field. The output variable is sfcMassBalLapseRate.

  • process_temperature_gradient: Remaps the temperature lapse rate (dtsdz) field. The output variable is surfaceAirTemperatureLapseRate.

  • process_runoff: Remaps the ice sheet runoff (mrro) field. The output variable is ismip6Runoff.

ocean_thermal

The landice/ismip7_forcing/ocean_thermal test case processes the ISMIP7 ocean thermal forcing (tf) and remaps it from the native polar stereographic grid to the MALI unstructured mesh.

The step supports two processing modes, controlled by boolean config options in the [ismip7] section:

  • Scenario (time-varying) data (process_ocean_thermal = true): Processes ESM-driven thermal forcing for a given model/scenario combination.

  • Observational climatology (process_ocean_climatology = true): Processes the static Zhou et al. observational thermal forcing climatology (AIS only). This is a time-invariant 3D field referenced to 1995-2024.

Both modes can be enabled simultaneously.

For AIS scenario data, thermal forcing is 3D with 30 vertical ocean layers. The input files span decades (e.g., 1850-1859). The output variable is ismip6shelfMelt_3dThermalForcing with dimension nISMIP6OceanLayers. Associated depth coordinate variables ismip6shelfMelt_zOcean and ismip6shelfMelt_zBndsOcean are also produced.

For AIS climatology data, the output is the same 3D thermal forcing field but without a Time dimension, producing a single static file.

For GrIS, thermal forcing is 2D (depth-averaged), with monthly temporal resolution and yearly input files. The output variable is ismip6_2dThermalForcing.

fracture

The landice/ismip7_forcing/fracture test case processes the ISMIP7 surface-melt-driven ice shelf collapse forcing (AIS only). It implements the three ISMIP7 pathways as separate steps, each remapping annual fields from the native 8km polar stereographic grid onto the MALI unstructured mesh.

All three source files are discovered from the fracture/{version}/ subdirectory of base_path_ismip7.

Each pathway is run independently and can be skipped by setting its remapping-method config option to None in the [ismip7_fracture] section (for example, method_remap_excess_melt = None skips Path A). This is useful when only some of the pathway source files are available.

  • process_excess_melt (Path A): Remaps the excess meltwater field (melt + rain after firn air content depletion), matching excess_melt_*.nc. The output variable is ismip7ExcessMelt (converted from mm w.e. yr-1 to SI units of kg m-2 s-1) and is written to {output_base_path}/excess_melt/{model}_{scenario}/. Conservative remapping is used by default since this is a flux. This source file has no x/y coordinate variables and its array is flipped along the y axis relative to the other fracture files, so the step reconstructs the source grid (borrowing x/y from a sibling fracture file and flipping the data to match) before remapping.

  • process_lake_properties (Path B): Remaps the supraglacial lake mean depth and area fraction from the Grau et al. (2025) parameterization, matching lake_properties_*.nc. The output variables are ismip7LakeDepth (m) and ismip7LakeAreaFraction (unitless), written to {output_base_path}/lake_properties/{model}_{scenario}/. Bilinear remapping is used by default.

  • process_shelf_collapse (Path C): Remaps the annual ice shelf collapse mask, matching ice_shelf_collapse_mask_*.nc. An ice shelf grid cell is flagged as collapsed (mask value 1) when excess meltwater, computed after firn air content depletion, exceeds 72.5 mm/yr for 10 consecutive years; otherwise the mask value is 0. The mask is applied on floating areas only, similar to ISMIP6, and ice shelves collapse on January 1st of each year. The remapping uses neareststod by default so that the 0/1 mask values are preserved, and the remapped mask is rounded to 0/1. The output variable is calvingMask with an accompanying xtime variable, and the result is written to {output_base_path}/shelf_collapse/{model}_{scenario}/.

All three pathways produce continuous fields (Paths A and B) or a discrete mask (Path C) with an accompanying xtime variable. 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.