xco2 derivation (#913)

* xco2 derivation

* Fix some spelling mistakes

* Change xch4 to xco2 #2

Co-authored-by: Valeriu Predoi <valeriu.predoi@gmail.com>

Author: bettina-gier

esmvalcore/preprocessor/_derive/xco2.py

@@ -0,0 +1,37 @@
+"""Derivation of variable ``xco2``."""
+
+from iris import Constraint
+
+from ._baseclass import DerivedVariableBase
+from ._shared import column_average
+
+
+class DerivedVariable(DerivedVariableBase):
+    """Derivation of variable ``xco2``."""
+
+    @staticmethod
+    def required(project):
+        """Declare the variables needed for derivation."""
+        required = [
+            {'short_name': 'co2'},
+            {'short_name': 'hus'},
+            {'short_name': 'zg'},
+            {'short_name': 'ps'},
+        ]
+        return required
+
+    @staticmethod
+    def calculate(cubes):
+        """Calculate the column-averaged atmospheric CO2 [1e-6]."""
+        co2_cube = cubes.extract_strict(
+            Constraint(name='mole_fraction_of_carbon_dioxide_in_air'))
+        print(co2_cube)
+        hus_cube = cubes.extract_strict(Constraint(name='specific_humidity'))
+        zg_cube = cubes.extract_strict(Constraint(name='geopotential_height'))
+        ps_cube = cubes.extract_strict(Constraint(name='surface_air_pressure'))
+
+        # Column-averaged CO2
+        xco2_cube = column_average(co2_cube, hus_cube, zg_cube, ps_cube)
+        xco2_cube.convert_units('1')
+
+        return xco2_cube

tests/unit/preprocessor/_derive/test_xco2.py

@@ -0,0 +1,58 @@
+"""Test derivation of ``xco2``."""
+import iris
+import numpy as np
+import pytest
+
+import esmvalcore.preprocessor._derive.xco2 as xco2
+
+from .test_shared import get_cube
+
+
+@pytest.fixture
+def cubes():
+    """Input cubes for derivation of ``xco2``."""
+    co2_cube = get_cube([[[[1.0]], [[2.0]]]], air_pressure_coord=True,
+                        standard_name='mole_fraction_of_carbon_dioxide_in_air',
+                        var_name='co2', units='1e-6')
+    hus_cube = get_cube([[[[0.2]], [[0.2]]]], air_pressure_coord=True,
+                        standard_name='specific_humidity', var_name='hus',
+                        units='%')
+    zg_cube = get_cube([[[100.0]]], air_pressure_coord=False,
+                       standard_name='geopotential_height', var_name='zg',
+
+                       units='m')
+    ps_cube = get_cube([[[100000.0]]], air_pressure_coord=False,
+                       standard_name='surface_air_pressure', var_name='ps',
+                       units='Pa')
+    return iris.cube.CubeList([co2_cube, hus_cube, zg_cube, ps_cube])
+
+
+def test_xco2_calculate(cubes):
+    """Test function ``calculate``."""
+    derived_var = xco2.DerivedVariable()
+    out_cube = derived_var.calculate(cubes)
+    assert out_cube.shape == (1, 1, 1)
+    assert out_cube.units == '1'
+    assert out_cube.coords('time')
+    assert out_cube.coords('air_pressure')
+    assert out_cube.coords('latitude')
+    assert out_cube.coords('longitude')
+    np.testing.assert_allclose(out_cube.data, [[[1.85e-6]]])
+    np.testing.assert_allclose(out_cube.coord('time').points, [0.0])
+    np.testing.assert_allclose(out_cube.coord('air_pressure').points, 85000.0)
+    np.testing.assert_allclose(out_cube.coord('air_pressure').bounds,
+                               [[80000.0, 90000.0]])
+    np.testing.assert_allclose(out_cube.coord('latitude').points, [45.0])
+    np.testing.assert_allclose(out_cube.coord('longitude').points, [10.0])
+
+
+def test_xco2_required():
+    """Test function ``required``."""
+    derived_var = xco2.DerivedVariable()
+    output = derived_var.required(None)
+    assert output == [
+        {'short_name': 'co2'},
+        {'short_name': 'hus'},
+        {'short_name': 'zg'},
+        {'short_name': 'ps'},
+    ]