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Add ISMIP7 fracture test case for shelf-collapse pathways - #975

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Add ISMIP7 fracture test case for shelf-collapse pathways#975
trhille wants to merge 7 commits into
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landice/ismip7_fracture

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@trhille

@trhille trhille commented Aug 13, 2026

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Add a 'fracture' test case to the ismip7_forcing test group that processes the ISMIP7 surface-melt-driven ice shelf collapse forcing (AIS) via three pathways, each as its own step:

  • process_excess_melt (Path A): remaps the excess meltwater field. Reconstructs x/y coordinates and corrects the y-axis orientation of the source file before conservative remapping.
  • process_lake_properties (Path B): remaps supraglacial lake mean depth and area fraction (Grau et al. 2025) via bilinear remapping.
  • process_shelf_collapse (Path C): remaps the annual ice shelf collapse mask via neareststod, rounding to 0/1.

Add per-pathway remap-method config options and documentation.

Checklist

  • User's Guide has been updated
  • Developer's Guide has been updated
  • API documentation in the Developer's Guide (api.rst) has any new or modified class, method and/or functions listed
  • Documentation has been built locally and changes look as expected: https://portal.nersc.gov/cfs/fanssie/trhille/compass-docs-PR975/html/
  • Document (in a comment titled Testing in this PR) any testing that was used to verify the changes

Add a 'fracture' test case to the ismip7_forcing test group that
processes the ISMIP7 surface-melt-driven ice shelf collapse forcing
(AIS) via three pathways, each as its own step:

- process_excess_melt (Path A): remaps the excess meltwater field.
  Reconstructs x/y coordinates and corrects the y-axis orientation of
  the source file before conservative remapping.
- process_lake_properties (Path B): remaps supraglacial lake mean depth
  and area fraction (Grau et al. 2025) via bilinear remapping.
- process_shelf_collapse (Path C): remaps the annual ice shelf collapse
  mask via neareststod, rounding to 0/1.

Add per-pathway remap-method config options and documentation.
Each fracture step returns early without processing its file when its
[ismip7_fracture] remapping-method option is set to None. This lets a
user process only the pathways whose source files are available,
without adding separate enable/disable flags.
Capture the integer years from the time coordinate before renaming the
time dimension to Time, since the rename also renames the coordinate
variable. Drop the leftover Time coordinate from the output.
Convert the excess melt field from mm w.e. yr-1 to kg m-2 s-1 using
1 mm w.e. = 1 kg m-2 and a 365-day year, consistent with other MALI
mass fluxes.
@trhille

trhille commented Aug 13, 2026

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Testing

Processing these files took less than one minute on one Perlmutter node.
CESM2-WACCM ssp5-8.5 shelf collapse mask:

shelf_collapse_mask.mov

CESM2-WACCM ssp5-8.5 lake depth and area:

lakes.mov

CESM2-WACCM ssp5-8.5 excess surface melt:

excess_melt.mov

Move the duplicated extrapolation and rename/xtime boilerplate from the
three fracture steps into a shared remap_utils module (extrapolate_source,
open_rename_and_trim, add_xtime_and_write). The step-specific logic
(unit conversion, mask rounding, per-variable attrs) stays in each step.
@trhille
trhille requested a review from matthewhoffman August 13, 2026 18:51
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