Add use_standard_grid option for CORDEX datasets (#3059)

Author: bouweandela

doc/recipe/overview.rst

@@ -109,6 +109,7 @@ For example, a datasets section could be:
       - {dataset: CanESM2, project: CMIP5, exp: historical, ensemble: r1i1p1, start_year: 2001, end_year: 2004}
       - {dataset: UKESM1-0-LL, project: CMIP6, exp: historical, ensemble: r1i1p1f2, start_year: 2001, end_year: 2004, grid: gn}
       - {dataset: ACCESS-CM2, project: CMIP6, exp: historical, ensemble: r1i1p1f2, timerange: 'P5Y/*', grid: gn}
+      - {dataset: CCLM4-8-17, project: CORDEX, domain: EUR-11, driver: CNRM-CERFACS-CNRM-CM5, exp: historical, ensemble: r1i1p1, institute: CLMcom, rcm_version: v1, timerange: '2001/2004'}
       - {dataset: EC-EARTH3, alias: custom_alias, project: CMIP6, exp: historical, ensemble: r1i1p1f1, start_year: 2001, end_year: 2004, grid: gn}
       - {dataset: CMCC-CM2-SR5, project: CMIP6, exp: historical, ensemble: r1i1p1f1, timerange: '2001/P10Y', grid: gn}
       - {dataset: HadGEM3-GC31-MM, project: CMIP6, exp: dcppA-hindcast, ensemble: r1i1p1f1, sub_experiment: s2000, grid: gn, start_year: 2000, end_year, 2002}
@@ -378,6 +379,89 @@ When using the ``timerange`` tag to specify the start and end points, possible v
 Note that this section is not required, as datasets can also be provided in the
 Diagnostics_ section.
 
+CORDEX datasets
+---------------
+
+The horizontal coordinates of CORDEX data are often not accurate. Therefore,
+the tool provides the option to specify that the standard CORDEX grid for the
+domain should be used instead of the grid defined in the files. This can be
+enabled by adding ``use_standard_grid: true`` and disabled by adding
+``use_standard_grid: false`` to the dataset definition of the CORDEX data.
+
+For example:
+
+.. code-block:: yaml
+
+  datasets:
+    - dataset: CCLM4-8-17
+      rcm_version: v1
+      driver: CNRM-CERFACS-CNRM-CM5
+      institute: CLMcom
+      project: CORDEX
+      domain: EUR-11
+      exp: historical
+      ensemble: r1i1p1
+      use_standard_grid: true
+
+will use the standard CORDEX grid for the EUR-11 domain, as defined by the
+`py-cordex <https://py-cordex.readthedocs.io>`_ package for datasets on a
+rotated pole grid. For datasets on a Lambert conformal grid, ESMValCore provides
+an algorithm to calculate the standard grid, but this only works if the
+`grid mapping <https://cfconventions.org/Data/cf-conventions/cf-conventions-1.13/cf-conventions.html#grid-mappings-and-projections>`_
+is correct.
+
+This feature is disabled by default, but enabled by default for models with
+known issues through the default
+`CORDEX extra facets file <https://github.com/ESMValGroup/ESMValCore/blob/main/esmvalcore/config/configurations/defaults/extra_facets_cordex.yml>`__.
+
+.. warning::
+
+  If ``use_standard_grid: true`` is used, the tool will overwrite the existing grid
+  information. It is recommended to visualize the resulting data and compare it
+  to easily recognizable features (e.g. coastlines) to make sure the grid is
+  correct before using it in an aggregated manner.
+
+  Example Python script to visualize the grid of a CORDEX dataset and compare it
+  to coastlines:
+
+  .. code-block:: python
+
+      from esmvalcore.dataset import Dataset
+      import iris.quickplot
+      import matplotlib.pyplot as plt
+
+      ds = Dataset(
+          short_name="sftlf",
+          mip="fx",
+          project="CORDEX",
+          domain="EUR-11",
+          dataset="ALADIN63",
+          driver="CNRM-CERFACS-CNRM-CM5",
+          institute="CNRM",
+          exp="historical",
+          ensemble="r1i1p1",
+          rcm_version="v2",
+          use_standard_grid=True,
+      )
+      cube = ds.load()
+
+      plt.figure()
+      iris.quickplot.pcolormesh(
+          cube,
+          coords=["projection_x_coordinate", "projection_y_coordinate"],
+      )
+      plt.gca().coastlines()
+
+      plt.figure()
+      iris.quickplot.pcolormesh(
+          cube,
+          coords=["longitude", "latitude"],
+      )
+      plt.gca().coastlines()
+
+      plt.show()
+
+
 .. _`yaml`: https://yaml.org/refcard.html
 
 .. _Preprocessors:

esmvalcore/cmor/_fixes/cordex/cnrm_cerfacs_cnrm_cm5/aladin53.py

@@ -0,0 +1,32 @@
+"""Fixes for rcm ALADIN53 driven by CNRM-CERFACS-CNRM-CM5."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from esmvalcore.cmor.fix import Fix
+
+if TYPE_CHECKING:
+    from collections.abc import Sequence
+
+    from iris.cube import Cube
+
+
+class Sftlf(Fix):
+    """Fixes for sftlf."""
+
+    def fix_metadata(self, cubes: Sequence[Cube]) -> Sequence[Cube]:
+        for cube in cubes:
+            cube.units = "1"
+            cube.convert_units(self.vardef.units)
+        return cubes
+
+
+class Ts(Fix):
+    """Fixes for ts."""
+
+    def fix_metadata(self, cubes: Sequence[Cube]) -> Sequence[Cube]:
+        for cube in cubes:
+            cube.units = "deg_C"
+            cube.convert_units(self.vardef.units)
+        return cubes