Added derivation of hfns

esmvalcore/cmor/tables/custom/CMOR_hfns.dat

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+SOURCE: CMIP6
+!============
+variable_entry:    hfns
+!============
+modeling_realm:    atmos
+!----------------------------------
+! Variable attributes:
+!----------------------------------
+standard_name:
+units:             W m-2
+cell_methods:      time: mean
+cell_measures:     area: areacella
+long_name:         Surface Net Heat Flux
+!----------------------------------
+! Additional variable information:
+!----------------------------------
+dimensions:        longitude latitude time
+out_name:          hfns
+type:              real
+positive:          up
+!----------------------------------

esmvalcore/preprocessor/_derive/hfns.py

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+"""Derivation of variable `hfns`."""
+
+from iris import NameConstraint
+
+from ._baseclass import DerivedVariableBase
+
+
+class DerivedVariable(DerivedVariableBase):
+    """Derivation of variable `hfns`."""
+
+    @staticmethod
+    def required(project):
+        """Declare the variables needed for derivation."""
+        required = [
+            {
+                'short_name': 'hfls',
+            },
+            {
+                'short_name': 'hfss',
+            },
+        ]
+        return required
+
+    @staticmethod
+    def calculate(cubes):
+        """Compute surface net heat flux."""
+        hfls_cube = cubes.extract_cube(NameConstraint(var_name='hfls'))
+        hfss_cube = cubes.extract_cube(NameConstraint(var_name='hfss'))
+
+        hfns_cube = hfls_cube + hfss_cube
+        hfns_cube.units = hfls_cube.units
+
+        return hfns_cube

tests/unit/preprocessor/_derive/test_hfns.py

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+"""Test derivation of ``hfns``."""
+import numpy as np
+import pytest
+from iris.cube import CubeList
+
+from esmvalcore.preprocessor._derive import hfns
+
+from .test_shared import get_cube
+
+
+@pytest.fixture
+def cubes():
+    """Input cubes for derivation of ``xch4``."""
+    hfls_cube = get_cube([[[1.0]]], air_pressure_coord=False,
+                         standard_name='surface_upward_latent_heat_flux',
+                         var_name='hfls', units='W m-2')
+    hfss_cube = get_cube([[[1.0]]], air_pressure_coord=False,
+                         standard_name='surface_upward_sensible_heat_flux',
+                         var_name='hfss', units='W m-2')
+    return CubeList([hfls_cube, hfss_cube])
+
+
+def test_hfns_calculate(cubes):
+    """Test function ``calculate``."""
+    derived_var = hfns.DerivedVariable()
+    out_cube = derived_var.calculate(cubes)
+    assert out_cube.shape == (1, 1, 1)
+    assert out_cube.units == 'W m-2'
+    assert out_cube.coords('time')
+    assert out_cube.coords('latitude')
+    assert out_cube.coords('longitude')
+    np.testing.assert_allclose(out_cube.data, [[[2.0]]])
+    np.testing.assert_allclose(out_cube.coord('time').points, [0.0])
+    np.testing.assert_allclose(out_cube.coord('latitude').points, [45.0])
+    np.testing.assert_allclose(out_cube.coord('longitude').points, [10.0])
+
+
+def test_hfns_required():
+    """Test function ``required``."""
+    derived_var = hfns.DerivedVariable()
+    output = derived_var.required(None)
+    assert output == [
+        {'short_name': 'hfls'},
+        {'short_name': 'hfss'},
+    ]