Modify ERA5 fixes to support data produced by the new GRIB to netcdf converter version of ECMWF (#3030)

Co-authored-by: Manuel Schlund <32543114+schlunma@users.noreply.github.com>

Author: jlenh

esmvalcore/cmor/_fixes/native6/era5.py

@@ -4,6 +4,7 @@
 import logging
 
 import numpy as np
+from cf_units import Unit
 from iris.cube import CubeList
 from iris.util import reverse
 
@@ -515,7 +516,7 @@ def fix_metadata(self, cubes):
 class AllVars(Fix):
     """Fixes for all variables."""
 
-    def _fix_coordinates(  # noqa: C901
+    def _fix_coordinates(  # noqa: C901,PLR0912
         self,
         cube,
     ):
@@ -540,13 +541,22 @@ def _fix_coordinates(  # noqa: C901
                 ]
             coord = cube.coord(axis=axis)
             if axis == "T":
-                coord.convert_units("days since 1850-1-1 00:00:00.0")
+                coord.convert_units(
+                    Unit(
+                        "days since 1850-1-1 00:00:00.0",
+                        calendar=coord.units.calendar,
+                    ),
+                )
             if axis in ("X", "Y", "Z"):
                 coord.convert_units(coord_def.units)
             coord.standard_name = coord_def.standard_name
             coord.var_name = coord_def.out_name
             coord.long_name = coord_def.long_name
             coord.points = coord.core_points().astype("float64")
+            # For now, remove "stored_direction" attribute introduced by the
+            # new netCDF converter from ECMWF for ERA5 data if missing.
+            if coord.name() == "latitude":
+                coord.attributes.pop("stored_direction", None)
             if (
                 not coord.has_bounds()
                 and len(coord.core_points()) > 1

tests/integration/cmor/_fixes/native6/test_era5.py

@@ -72,6 +72,17 @@ def _era5_latitude():
     )
 
 
+def _era5_latitude_w_direction():
+    return DimCoord(
+        np.array([90.0, 0.0, -90.0]),
+        standard_name="latitude",
+        long_name="latitude",
+        var_name="latitude",
+        units=Unit("degrees"),
+        attributes={"stored_direction": "decreasing"},
+    )
+
+
 def _era5_longitude():
     return DimCoord(
         np.array([0, 180, 359.75]),
@@ -1577,3 +1588,38 @@ def test_unstructured_grid(unstructured_grid_cubes):
     assert lon.bounds is None
 
     assert fixed_cube.attributes["GRIB_PARAM"] == "(1, 1)"
+
+
+@pytest.fixture
+def cube_latitude_w_direction():
+    """Sample cube with latitude coordinate with direction."""
+    time = DimCoord(
+        [-31, 0, 31],
+        standard_name="time",
+        units="days since 1850-01-01",
+    )
+    cube = Cube(
+        _era5_data("mon"),
+        standard_name="air_temperature",
+        units="K",
+        dim_coords_and_dims=[
+            (time, 0),
+            (_era5_latitude_w_direction(), 1),
+            (_era5_longitude(), 2),
+        ],
+    )
+    return CubeList([cube])
+
+
+def test_latitude_w_direction(cube_latitude_w_direction):
+    """Test removal of latitude stored_direction attribute."""
+    fixed_cubes = fix_metadata(
+        cube_latitude_w_direction,
+        "tas",
+        "native6",
+        "era5",
+        "Amon",
+    )
+    assert len(fixed_cubes) == 1
+    fixed_cube = fixed_cubes[0]
+    assert fixed_cube.coord("latitude") == _cmor_latitude()