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Fix derivation for sea ice extent (siextent) #2648

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Fix derivation for sea ice extent (siextent) #2648

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3f2cd5c
fixed derivation script for siextent
axel-lauer Nov 7, 2024
0373a94
Update siextent.py
axel-lauer Jan 28, 2025
7a1be2f
moved comments above statement
axel-lauer Jan 30, 2025
2a949ca
removed trailing whitespace
axel-lauer Jan 30, 2025
09bff8f
Merge branch 'main' into fix_siextent
sloosvel Jan 30, 2025
eb9cd61
Fix units in tests
sloosvel Jan 31, 2025
0c8beb9
updated siextent.py
axel-lauer Feb 21, 2025
1eaa6f0
Separate variables per project
sloosvel Feb 21, 2025
f03c1ef
Merge branch 'main' into fix_siextent
sloosvel Feb 21, 2025
f2499bd
Do not consider siconca
sloosvel Mar 10, 2025
6175831
Merge branch 'main' into fix_siextent
valeriupredoi May 15, 2025
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2 changes: 1 addition & 1 deletion esmvalcore/cmor/tables/custom/CMOR_siextent.dat
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Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@ modeling_realm: seaIce
! Variable attributes:
!----------------------------------
standard_name:
units: m2
units: 1
cell_methods: area: mean where sea time: mean
cell_measures: area: areacello
long_name: Sea Ice Extent
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24 changes: 14 additions & 10 deletions esmvalcore/preprocessor/_derive/siextent.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
"""Derivation of variable `sithick`."""
"""Create mask for derivation of variable `siextent`."""

import logging

Expand All @@ -14,14 +14,15 @@


class DerivedVariable(DerivedVariableBase):
"""Derivation of variable `siextent`."""
"""Create mask for derivation of variable `siextent`."""

@staticmethod
def required(project):
"""Declare the variables needed for derivation."""
"""Declare the variable needed for derivation."""
# 'sic' only is sufficient as there is already an entry

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esmvalcore/preprocessor/_derive/siextent.py#L22 

trailing whitespace (W291)
# in the mapping table esmvalcore/cmor/variable_alt_names.yml
required = [
{"short_name": "sic", "optional": "true"},
{"short_name": "siconca", "optional": "true"},
{"short_name": "sic"},
]
return required

Expand All @@ -30,11 +31,11 @@
"""Compute sea ice extent.

Returns an array of ones in every grid point where
the sea ice area fraction has values > 15 .
the sea ice area fraction has values > 15% .

Use in combination with the preprocessor
`area_statistics(operator='sum')` to weigh by the area and
compute global or regional sea ice extent values.
compute global or regional sea ice extent values (in m2).

Arguments
---------
Expand All @@ -48,16 +49,19 @@
sic = cubes.extract_cube(Constraint(name="sic"))
except iris.exceptions.ConstraintMismatchError:
try:
sic = cubes.extract_cube(Constraint(name="siconca"))
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If I remember correctly, siconca was added because some models were missing siconc, but I am not sure if that is still the case.

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That is right. In any case, I think it does not hurt to also try "siconca", so I would prefer to keep this here if that's fine.

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Well in that case, it looks like it needs to be re-added because tests are failing due to siconca not being required anymore.

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I justed updated that part a bit: 0c8beb9
I cannot get this preprocessor working for CMIP5 data, though, when adding {"short_name": "siconca", "optional": "true"},. Alternatively, I can remove the "siconca" part. Any advice would be highly appreciated...

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@sloosvel sloosvel Feb 21, 2025 •
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I tested with the latest commit 1eaa6f0 loading CMIP5 sic data, CMIP6 sic data and CMIP6 data that only has siconca available and it worked finding the data that is needed for each project:

datasets:

        - {dataset: GISS-E2-1-H, grid: gr} # CMIP6 sic data 
        - {dataset: GISS-E2-1-H, exp: piControl, grid: gn, timerange: '3180/3180'} # CMIP6 siconca data
        - {dataset: GISS-E2-H-CC, project: CMIP5, ensemble: r1i1p1, mip: OImon} # CMIP5 sic data

diagnostics:

  test:
    variables:
      siextent:
        project: CMIP6
        mip: SImon
        timerange: '2000/2000'
        derive: true
        exp: historical
        ensemble: r1i1p1f1
    scripts: null

Let me know if it works for you

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Thank you for looking into this, @sloosvel! I tried this and I don't think we found the optimum solution yet. If I add a CMIP6 dataset that provides both, siconc and siconca (e.g. MPI-ESM1-2-LR), I run into a shape error, e.g.

ValueError: Chunks do not add up to shape. Got chunks=((96,), (192,)), shape=(220, 256)

Also, our current solution does not support to process any observationally-based data (e.g. projects OBS, OBS6, ana4mips, obs4MIPs, native5, etc.). Here are some examples for observationally-based datasets that I tried:

  - {dataset: ESACCI-SEAICE, project: OBS6, tier: 2, type: sat, version: L4-SICONC-RE-SSMI-12.5kmEASE2-fv3.0-NH,
     supplementary_variables: [{short_name: areacello, mip: Ofx}]}
  - {dataset: HadISST, project: OBS, tier: 2, type: reanaly, version: '1', mip: OImon}
  - {dataset: CFSR, project: ana4mips, tier: 1, type: reanalysis, mip: OImon}

So maybe checking for if project == 'CMIP6' or project == 'OBS6' is enough and a plain else for all other cases in the required function? But then, there is still the shape problem.

Do you have an idea what we could do? I didn't expect this to be so complicated...

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You are right, trying to include siconca makes things too complicated. I checked and the issue was with only one dataset that was missing siconc. Maybe the data is available nowadays. I will remove the calls to siconca, since it's not worth it to include it just for one dataset.

sic = cubes.extract_cube(Constraint(name="siconc"))
except iris.exceptions.ConstraintMismatchError as exc:
raise RecipeError(
"Derivation of siextent failed due to missing variables "
"sic and siconca."
"sic and siconc."
) from exc

ones = da.ones_like(sic)
siextent_data = da.ma.masked_where(sic.lazy_data() < 15.0, ones)
siextent = sic.copy(siextent_data)
siextent.units = "m2"
siextent.units = "1" # unit is 1 as this is just a mask
# that has to be used with preprocessor

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# area_statistics(operator='sum') to

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# obtain the sea ice extent (m2)

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return siextent