Add support for native ERA5 data in GRIB format

doc/quickstart/configure.rst

@@ -924,7 +924,7 @@ infrastructure. The following example illustrates the concept.
 .. _extra-facets-example-1:
 
 .. code-block:: yaml
-   :caption: Extra facet example file `native6-era5.yml`
+   :caption: Extra facet example file `native6-era5-example.yml`
 
    ERA5:
      Amon:

doc/quickstart/find_data.rst

@@ -107,18 +107,27 @@ The following native reanalysis/observational datasets are supported under the
 To use these datasets, put the files containing the data in the directory that
 you have :ref:`configured <config_options>` for the ``rootpath`` of the
 ``native6`` project, in a subdirectory called
-``Tier{tier}/{dataset}/{version}/{frequency}/{short_name}``.
+``Tier{tier}/{dataset}/{version}/{frequency}/{short_name}`` (assuming you are
+using the ``default`` DRS for ``native6``).
 Replace the items in curly braces by the values used in the variable/dataset
 definition in the :ref:`recipe <recipe_overview>`.
-Below is a list of native reanalysis/observational datasets currently
-supported.
 
-.. _read_native_era5:
+.. _read_native_era5_nc:
 
-ERA5
-^^^^
+ERA5 (in netCDF format downloaded from the CDS)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+ERA5 data can be downloaded from the Copernicus Climate Data Store (CDS) using
+the convenient tool `era5cli <https://era5cli.readthedocs.io>`__.
+For example for monthly data, place the files in the
+``/Tier3/ERA5/version/mon/pr`` subdirectory of your ``rootpath`` that you have
+configured for the ``native6`` project (assuming you are using the ``default``
+DRS for ``native6``).
 
-- Supported variables: ``cl``, ``clt``, ``evspsbl``, ``evspsblpot``, ``mrro``, ``pr``, ``prsn``, ``ps``, ``psl``, ``ptype``, ``rls``, ``rlds``, ``rsds``, ``rsdt``, ``rss``, ``uas``, ``vas``, ``tas``, ``tasmax``, ``tasmin``, ``tdps``, ``ts``, ``tsn`` (``E1hr``/``Amon``), ``orog`` (``fx``)
+- Supported variables: ``cl``, ``clt``, ``evspsbl``, ``evspsblpot``, ``mrro``,
+  ``pr``, ``prsn``, ``ps``, ``psl``, ``ptype``, ``rls``, ``rlds``, ``rsds``,
+  ``rsdt``, ``rss``, ``uas``, ``vas``, ``tas``, ``tasmax``, ``tasmin``,
+  ``tdps``, ``ts``, ``tsn`` (``E1hr``/``Amon``), ``orog`` (``fx``).
 - Tier: 3
 
 .. note:: According to the description of Evapotranspiration and potential Evapotranspiration on the Copernicus page
@@ -131,6 +140,85 @@ ERA5
   of both liquid and solid phases to vapor (from underlying surface and vegetation)."
   Therefore, the ERA5 (and ERA5-Land) CMORizer switches the signs of ``evspsbl`` and ``evspsblpot`` to be compatible with the CMOR standard used e.g. by the CMIP models.
 
+.. _read_native_era5_grib:
+
+ERA5 (in GRIB format available on DKRZ's Levante or downloaded from the CDS)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+ERA5 data in monthly, daily, and hourly resolution is `available on Levante
+<https://docs.dkrz.de/doc/dataservices/finding_and_accessing_data/era_data/index.html#era-data>`__
+in its native GRIB format.
+
+.. note::
+  ERA5 data in its native GRIB format can also be downloaded from the
+  `Copernicus Climate Data Store (CDS)
+  <https://cds.climate.copernicus.eu/datasets>`__.
+  For example, hourly data on pressure levels is available `here
+  <https://cds.climate.copernicus.eu/datasets/reanalysis-era5-pressure-levels?tab=download>`__.
+  Reading self-downloaded ERA5 data in GRIB format is experimental and likely
+  requires additional setup from the user like setting up the proper directory
+  structure for the input files and/or creating a custom :ref:`DRS
+  <config_option_drs>`.
+
+To read these data with ESMValCore, use the :ref:`rootpath
+<config_option_rootpath>` ``/pool/data/ERA5`` with :ref:`DRS
+<config_option_drs>` ``DKRZ-ERA5-GRIB`` in your configuration, for example:
+
+.. code-block:: yaml
+
+  rootpath:
+    ...
+    native6:
+      /pool/data/ERA5: DKRZ-ERA5-GRIB
+    ...
+
+The `naming conventions
+<https://docs.dkrz.de/doc/dataservices/finding_and_accessing_data/era_data/index.html#file-and-directory-names>`__
+for input directories and files for native ERA5 data in GRIB format on Levante
+are
+
+* input directories: ``{family}/{level}/{type}/{tres}/{grib_id}``
+* input files: ``{family}{level}{typeid}_{tres}_*_{grib_id}.grb``
+
+All of these facets have reasonable defaults preconfigured in the corresponding
+:ref:`extra facets<extra_facets>` file, which is available here:
+:download:`native6-era5.yml
+</../esmvalcore/config/extra_facets/native6-era5.yml>`.
+If necessary, these facets can be overwritten in the recipe.
+
+Thus, example dataset entries could look like this:
+
+.. code-block:: yaml
+
+  datasets:
+    - {project: native6, dataset: ERA5, timerange: '2000/2001',
+       short_name: tas, mip: Amon}
+    - {project: native6, dataset: ERA5, timerange: '2000/2001',
+       short_name: cl, mip: Amon, tres: 1H, frequency: 1hr}
+    - {project: native6, dataset: ERA5, timerange: '2000/2001',
+       short_name: ta, mip: Amon, type: fc, typeid: '12'}
+
+The native ERA5 output in GRIB format is stored on a `reduced Gaussian grid
+<https://confluence.ecmwf.int/display/CKB/ERA5:+data+documentation#ERA5:datadocumentation-SpatialgridSpatialGrid>`__.
+By default, these data are regridded to a regular 0.25°x0.25° grid as
+`recommended by the ECMWF
+<https://confluence.ecmwf.int/display/CKB/ERA5%3A+What+is+the+spatial+reference#heading-Interpolation>`__
+using bilinear interpolation.
+
+To disable this, you can use the facet ``automatic_regrid: false`` in the
+recipe:
+
+.. code-block:: yaml
+
+  datasets:
+    - {project: native6, dataset: ERA5, timerange: '2000/2001',
+       short_name: tas, mip: Amon, automatic_regrid: false}
+
+- Supported variables: ``albsn``, ``cl``, ``cli``, ``clt``, ``clw``, ``hur``,
+  ``hus``, ``o3``, ``prw``, ``ps``, ``psl``, ``rainmxrat27``, ``sftlf``,
+  ``snd``, ``snowmxrat27``, ``ta``, ``tas``, ``tdps``, ``toz``, ``ts``, ``ua``,
+  ``uas``, ``va``, ``vas``, ``wap``, ``zg``.
+
 .. _read_native_mswep:
 
 MSWEP
@@ -140,7 +228,10 @@ MSWEP
 - Supported frequencies: ``mon``, ``day``, ``3hr``.
 - Tier: 3
 
-For example for monthly data, place the files in the ``/Tier3/MSWEP/version/mon/pr`` subdirectory of your ``native6`` project location.
+For example for monthly data, place the files in the
+``/Tier3/MSWEP/version/mon/pr`` subdirectory of your ``rootpath`` that you have
+configured for the ``native6`` project (assuming you are using the ``default``
+DRS for ``native6``).
 
 .. note::
   For monthly data (``V220``), the data must be postfixed with the date, i.e. rename ``global_monthly_050deg.nc`` to ``global_monthly_050deg_197901-201710.nc``
@@ -642,6 +733,8 @@ first discuss the ``drs`` parameter: as we've seen in the previous section, the
 DRS as a standard is used for both file naming conventions and for directory
 structures.
 
+.. _config_option_drs:
+
 Explaining ``drs: CMIP5:`` or ``drs: CMIP6:``
 ---------------------------------------------
 Whereas ESMValCore will by default use the CMOR standard for file naming (please

esmvalcore/_provenance.py

@@ -4,6 +4,7 @@
 import logging
 import os
 from functools import total_ordering
+from pathlib import Path
 
 from netCDF4 import Dataset
 from PIL import Image
@@ -209,9 +210,10 @@ def _initialize_entity(self):
         """Initialize the entity representing the file."""
         if self.attributes is None:
             self.attributes = {}
-            with Dataset(self.filename, "r") as dataset:
-                for attr in dataset.ncattrs():
-                    self.attributes[attr] = dataset.getncattr(attr)
+            if "nc" in Path(self.filename).suffix:
+                with Dataset(self.filename, "r") as dataset:
+                    for attr in dataset.ncattrs():
+                        self.attributes[attr] = dataset.getncattr(attr)
 
         attributes = {
             "attribute:" + str(k).replace(" ", "_"): str(v)

esmvalcore/_recipe/recipe.py

@@ -37,6 +37,7 @@
     PreprocessorFile,
 )
 from esmvalcore.preprocessor._area import _update_shapefile_path
+from esmvalcore.preprocessor._io import GRIB_FORMATS
 from esmvalcore.preprocessor._multimodel import _get_stat_identifier
 from esmvalcore.preprocessor._regrid import (
     _spec_to_latlonvals,
@@ -227,6 +228,34 @@ def _get_default_settings(dataset):
     return settings
 
 
+def _add_dataset_specific_settings(dataset: Dataset, settings: dict) -> None:
+    """Add dataset-specific settings."""
+    project = dataset.facets["project"]
+    dataset_name = dataset.facets["dataset"]
+    file_suffixes = [Path(file.name).suffix for file in dataset.files]
+
+    # Automatic regridding for native ERA5 data in GRIB format if regridding
+    # step is not already present (can be disabled with facet
+    # automatic_regrid=False)
+    if all(
+        [
+            project == "native6",
+            dataset_name == "ERA5",
+            any(grib_format in file_suffixes for grib_format in GRIB_FORMATS),
+            "regrid" not in settings,
+            dataset.facets.get("automatic_regrid", True),
+        ]
+    ):
+        # Settings recommended by ECMWF
+        # (https://confluence.ecmwf.int/display/CKB/ERA5%3A+What+is+the+spatial+reference#heading-Interpolation)
+        settings["regrid"] = {"target_grid": "0.25x0.25", "scheme": "linear"}
+        logger.debug(
+            "Automatically regrid native6 ERA5 data in GRIB format with the "
+            "settings %s",
+            settings["regrid"],
+        )
+
+
 def _exclude_dataset(settings, facets, step):
     """Exclude dataset from specific preprocessor step if requested."""
     exclude = {
@@ -541,6 +570,7 @@ def _get_preprocessor_products(
         _apply_preprocessor_profile(settings, profile)
         _update_multi_dataset_settings(dataset.facets, settings)
         _update_preproc_functions(settings, dataset, datasets, missing_vars)
+        _add_dataset_specific_settings(dataset, settings)
         check.preprocessor_supplementaries(dataset, settings)
         input_datasets = _get_input_datasets(dataset)
         missing = _check_input_files(input_datasets)

esmvalcore/cmor/_fixes/fix.py

@@ -845,6 +845,8 @@ def _fix_time_bounds(self, cube: Cube, cube_coord: Coord) -> None:
         """Fix time bounds."""
         times = {"time", "time1", "time2", "time3"}
         key = times.intersection(self.vardef.coordinates)
+        if not key:  # cube has time, but CMOR variable does not
+            return
         cmor = self.vardef.coordinates[" ".join(key)]
         if cmor.must_have_bounds == "yes" and not cube_coord.has_bounds():
             cube_coord.bounds = get_time_bounds(cube_coord, self.frequency)