Update ISMIP7 processing to handle OCX forcing

[trhille]

Update ismip7_forcing test group to handle OCX forcing, which has a slightly different directory structure from other forcings. Extrapolate forcings into missing data cells before interpolating to MALI mesh. Also unify the structure for ismip7_forcing output with that expected as input for ismip7_run.

Checklist

• User's Guide has been updated
• Developer's Guide has been updated
• Documentation has been built locally and changes look as expected
• Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

[Copilot]

🟡 Changes recommended

Unresolved critical output-layout and NetCDF encoding issues, along with API and input-validation issues, block approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR adds OCX reanalysis support to ISMIP7 forcing processing, including AIS/GrIS source handling, missing-cell extrapolation, and updated output organization.

Changes:

• Adds OCX configurations and AIS ocean-choice handling.
• Centralizes extrapolation before remapping.
• Updates forcing layouts and user/developer documentation.

File summaries

File	Change / final review notes
docs/users_guide/landice/test_groups/ismip7_forcing.rst	Documents OCX inputs and outputs. Nit (1 vote): AIS ocean and atmosphere outputs use inconsistent directories, so the documented ocx_forcing_path is not directly runnable.
docs/developers_guide/landice/test_groups/ismip7_forcing.rst	Updates developer guidance. Nits (1 vote each): Qualify EN4 as GrIS-only, document the AIS choice layout, and update the stale fracture helper reference.
docs/developers_guide/landice/api.rst	Registers the shared remapping helper.
compass/landice/tests/ismip7_forcing/remap_utils.py	Adds shared extrapolation logic. Critical (1 vote): Source encodings may be incompatible with NETCDF3_64BIT_DATA; clear or replace them before writing temporary files.
compass/landice/tests/ismip7_forcing/ocean_thermal/process_thermal_forcing.py	Handles OCX ocean sources and choices. Critical (3 votes): AIS ocean output is not co-located with atmosphere output and cannot be consumed directly by ismip7_run. Moderate (2 votes): Invalid tokens combined with all bypass validation.
compass/landice/tests/ismip7_forcing/ismip7_forcing.cfg	Adds ocean-choice configuration.
compass/landice/tests/ismip7_forcing/ismip7_forcing_ocx_gis.cfg	Adds a GrIS OCX configuration.
compass/landice/tests/ismip7_forcing/ismip7_forcing_ocx_ais.cfg	Adds an AIS OCX configuration.
compass/landice/tests/ismip7_forcing/ice_sheet_params.py	Adds OCX parameter overrides. Nit (1 vote): The module description incorrectly says all OCX runs use EN4; qualify this for GrIS and document AIS choices.
compass/landice/tests/ismip7_forcing/fracture/remap_utils.py	Removes duplicated extrapolation code. Moderate (1 vote): Removing the documented helper path can break downstream imports; retain a compatibility re-export or explicitly handle the breaking change.
compass/landice/tests/ismip7_forcing/fracture/process_lake_properties.py	Uses the shared extrapolation helper.
compass/landice/tests/ismip7_forcing/fracture/process_excess_melt.py	Uses the shared extrapolation helper.
compass/landice/tests/ismip7_forcing/atmosphere/process_temperature.py	Adds OCX handling and extrapolation.
compass/landice/tests/ismip7_forcing/atmosphere/process_temperature_gradient.py	Adds OCX handling and extrapolation.
compass/landice/tests/ismip7_forcing/atmosphere/process_smb.py	Adds OCX handling and extrapolation.
compass/landice/tests/ismip7_forcing/atmosphere/process_smb_gradient.py	Adds OCX handling and extrapolation.
compass/landice/tests/ismip7_forcing/atmosphere/process_runoff.py	Adds OCX handling and extrapolation.

Review details

Suppressed comments (5)

compass/landice/tests/ismip7_forcing/fracture/remap_utils.py:5

• This removes fracture.remap_utils.extrapolate_source, which was a documented API entry before this PR. Internal imports are updated, but downstream callers importing that path will now get ImportError; please keep a compatibility re-export here or explicitly handle this as a breaking API change.

import xarray as xr
from mpas_tools.io import write_netcdf

compass/landice/tests/ismip7_forcing/ice_sheet_params.py:36

• The module-level description says every OCX run uses EN4 for the ocean, but the AIS override below deliberately sets ocean_model to None and uses per-choice ocean products. Qualify EN4 to GrIS and document the AIS choice layout so this description matches get_params().

# Overrides applied for the OCX (reanalysis) scenario. OCX has no distinct
# ESM model: it uses fixed reanalysis products (RACMO for the atmosphere and
# EN4 for the ocean) at data version v1. When scenario is 'OCX' the [ismip7]
# model option is ignored and these sources are used instead.

docs/developers_guide/landice/test_groups/ismip7_forcing.rst:35

• This paragraph says OCX always sets ocean_model = EN4, but _OCX_OVERRIDES['ais'] sets it to None and uses the choice-based ocean layout; EN4 is only the GrIS source. Qualify these source names by ice sheet and document the AIS choice layout here, otherwise developers may construct the wrong filename/path.

When ``scenario = OCX``, ``get_params`` applies a set of OCX overrides on top
of the ice-sheet defaults: data version ``v1``, the ocean file-name grid token
(e.g. ``ocean-1000m``), and the fixed reanalysis sources (``atm_model`` =
``RACMO2.3p2-ERA`` and ``ocean_model`` = ``EN4``). The processing steps use

docs/developers_guide/landice/test_groups/ismip7_forcing.rst:37

• The helper was moved to compass.landice.tests.ismip7_forcing.remap_utils, but the fracture section later in this same guide still documents extrapolate_source under fracture.remap_utils (lines 175-177). Update that reference so the developer guide does not direct readers to a symbol that no longer exists.

they are set, so the OCX ``model`` option is ignored. This keeps OCX handling

docs/users_guide/landice/test_groups/ismip7_forcing.rst:100

• This layout description is not true for AIS OCX: the changed AIS branch writes ocean output under OCX_<choice> while atmosphere output is under OCX. Consequently, directing ocx_forcing_path to {output_base_path}/OCX does not provide a runnable AIS forcing set. Update the documented OCX layout after aligning the producer and consumer.

The ``group`` directory is ``{model}_{scenario}`` for the ESM scenarios and
``{scenario}`` (i.e. ``OCX``) for OCX, whose atmosphere and ocean use
different sources (``RACMO2.3p2-ERA`` and ``EN4``) but must share one
directory. To feed :ref:`landice_ismip7_run`, point its ``forcing_basepath``
at ``output_base_path`` for ESM scenarios, or its ``ocx_forcing_path`` at
``{output_base_path}/OCX`` for OCX.

• Files reviewed: 17/17 changed files
• Comments generated: 3
• Review effort level: Lite

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