Made ICON output UGRID-compliant (on-the-fly) #1664

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Merged

zklaus merged 26 commits into main from icon2ugrid

Feb 1, 2023

doc/quickstart/find_data.rst

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@@ Expand Up / @@ -363,6 +363,32 @@ Key Description Default value if not specified @@
                   file                          default DRS is used)
     ============= ============================= =================================
+    ESMValCore automatically makes native ICON data `UGRID
+    <https://ugrid-conventions.github.io/ugrid-conventions/>`__-compliant when
+    loading the data.
+    The UGRID conventions provide a standardized format to store data on
+    unstructured grids, which is required by many software packages or tools to
+    work correctly.
+    An example is the horizontal regridding of native ICON data to a regular grid.
+    While the built-in :ref:`unstructured_nearest scheme <built-in regridding
+    schemes>` can handle unstructured grids not in UGRID format, using more complex
+    regridding algorithms (for example provided by the
+    :doc:`iris-esmf-regrid:index` package through :ref:`generic regridding
+    schemes`) requires the input data in UGRID format.
+    The following code snippet provides a preprocessor that regrids native ICON
+    data to a 1°x1° grid using `ESMF's first-order conservative regridding
+    algorithm <https://earthsystemmodeling.org/regrid/#regridding-methods>`__:
+    .. code-block:: yaml
+       preprocessors:
+         regrid_icon:
+           regrid:
+             target_grid: 1x1
+             scheme:
+               reference: esmf_regrid.experimental.unstructured_scheme:regrid_unstructured_to_rectilinear
+               method: conservative
     .. hint::
        To use the :func:`~esmvalcore.preprocessor.extract_levels` preprocessor on
@@ Expand Down @@

doc/recipe/preprocessor.rst

            
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    @@ -932,17 +932,17 @@ arguments is also supported. The call function for such schemes must be defined
  
    The `regrid` module will automatically pass the source and grid cubes as inputs

    of the scheme. An example of this usage is

    the :func:`~esmf_regrid.schemes.regrid_rectilinear_to_rectilinear`

    scheme available in :doc:`iris-esmf-regrid:index`:git 

    scheme available in :doc:`iris-esmf-regrid:index`:

    .. code-block:: yaml

        preprocessors:

          regrid_preprocessor:

            regrid:

              target_grid: 2.5x2.5

              scheme:

                reference: esmf_regrid.schemes:regrid_rectilinear_to_rectilinear

                mdtol: 0.7

      preprocessors:

        regrid_preprocessor:

          regrid:

            target_grid: 2.5x2.5

            scheme:

              reference: esmf_regrid.schemes:regrid_rectilinear_to_rectilinear

              mdtol: 0.7

    .. _ensemble statistics:

environment.yml

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@@ Expand Up / @@ -17,7 +17,7 @@ dependencies: @@
       - geopy
       - humanfriendly
       - importlib_resources
-      - iris>=3.2.1
+      - iris>=3.4.0
       - iris-esmf-regrid
       - isodate
       - jinja2
@@ Expand Down @@

esmvalcore/cmor/_fixes/icon/_base_fixes.py

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@@ Expand Up / @@ -88,6 +88,7 @@ def get_horizontal_grid(self, cube): @@
             # Download file if necessary
             logger.debug("Attempting to download ICON grid file from '%s' to '%s'",
                          grid_url, grid_path)
+            self.CACHE_DIR.mkdir(parents=True, exist_ok=True)
             with requests.get(grid_url, stream=True,
                               timeout=self.TIMEOUT) as response:
                 response.raise_for_status()
@@ Expand Down @@

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