EPPT-2389: Calculation of localised svp

improver/psychrometric_calculations/condensation_trails.py

@@ -11,6 +11,9 @@
 
 from improver import BasePlugin
 from improver.constants import EARTH_REPSILON
+from improver.psychrometric_calculations.psychrometric_calculations import (
+    calculate_svp_in_air,
+)
 from improver.utilities.common_input_handle import as_cubelist
 
 
@@ -73,8 +76,32 @@ def _calculate_engine_mixing_ratios(
             / EARTH_REPSILON
         )
 
+    def _find_local_vapour_pressure(self, pressure_levels: np.ndarray) -> np.ndarray:
+        """
+        Calculate the local vapour pressure (svp) at the given pressure levels using the temperature and pressure data.
+
+        Args:
+            pressure_levels (np.ndarray): Pressure levels (Pa).
+
+        Returns:
+            np.ndarray: The localised vapour pressure at the given
+                pressure levels (Pa).
+        """
+        # Pressure levels has to be reshaped to match the temperature and humidity dimensions
+        pressure_levels_reshaped = np.reshape(
+            pressure_levels,
+            (len(pressure_levels),) + (1,) * (self.temperature.ndim - 1),
+        )
+        svp = calculate_svp_in_air(
+            temperature=self.temperature, pressure=pressure_levels_reshaped
+        )
+        return self.relative_humidity * svp
+
     def process_from_arrays(
-        self, temperature: np.ndarray, humidity: np.ndarray, pressure_levels: np.ndarray
+        self,
+        temperature: np.ndarray,
+        relative_humidity: np.ndarray,
+        pressure_levels: np.ndarray,
     ) -> np.ndarray:
         """
         Main entry point of this class for data as Numpy arrays
@@ -84,19 +111,22 @@ def process_from_arrays(
 
         Args:
             temperature (np.ndarray): Temperature data on pressure levels where pressure is the leading axis (K).
-            humidity (np.ndarray): Relative humidity data on pressure levels where pressure is the leading axis (kg kg-1).
+            relative_humidity (np.ndarray): Relative humidity data on pressure levels where pressure is the leading axis (kg kg-1).
             pressure_levels (np.ndarray): Pressure levels (Pa).
 
         Returns:
             np.ndarray: The calculated engine mixing ratios on pressure levels (Pa/K).
             This is a placeholder until the full contrail formation logic is implemented.
         """
         self.temperature = temperature
-        self.humidity = humidity
+        self.relative_humidity = relative_humidity
         self.pressure_levels = pressure_levels
         self.engine_mixing_ratios = self._calculate_engine_mixing_ratios(
             self.pressure_levels
         )
+        self.local_vapour_pressure = self._find_local_vapour_pressure(
+            self.pressure_levels
+        )
         return self.engine_mixing_ratios
 
     def process(self, *cubes: Union[Cube, CubeList]) -> Cube:

improver_tests/psychrometric_calculations/condensation_trails/test_CondensationTrailFormation.py

@@ -12,6 +12,9 @@
 from improver.psychrometric_calculations.condensation_trails import (
     CondensationTrailFormation,
 )
+from improver.psychrometric_calculations.psychrometric_calculations import (
+    calculate_svp_in_air,
+)
 from improver.synthetic_data.set_up_test_cubes import set_up_variable_cube
 
 LOCAL_MANDATORY_ATTRIBUTES = {
@@ -168,3 +171,55 @@ def test_engine_mixing_ratio(
     # Check that _calculate_engine_mixing_ratios works after process
     mixing_ratios = plugin._calculate_engine_mixing_ratios(pressure_levels)
     np.testing.assert_array_equal(mixing_ratios, expected_mixing_ratios)
+
+
+@pytest.mark.parametrize(
+    "temperature, relative_humidity, pressure_levels, expected_vapour_pressure",
+    [
+        # Test with multiple pressure levels
+        (
+            np.array([250.0, 260.0, 270.0], dtype=np.float32),
+            np.array([0.5, 0.6, 0.7], dtype=np.float32),
+            np.array([100000, 90000, 80000], dtype=np.float32),
+            calculate_svp_in_air(
+                np.array([250.0, 260.0, 270.0], dtype=np.float32),
+                np.array([100000, 90000, 80000], dtype=np.float32),
+            )
+            * np.array([0.5, 0.6, 0.7], dtype=np.float32),
+        ),
+        # Test with single pressure level
+        (
+            np.array([280.0], dtype=np.float32),
+            np.array([0.8], dtype=np.float32),
+            np.array([95000], dtype=np.float32),
+            calculate_svp_in_air(
+                np.array([280.0], dtype=np.float32),
+                np.array([95000], dtype=np.float32),
+            )
+            * np.array([0.8], dtype=np.float32),
+        ),
+    ],
+)
+def test_find_local_vapour_pressure(
+    temperature: np.ndarray,
+    relative_humidity: np.ndarray,
+    pressure_levels: np.ndarray,
+    expected_vapour_pressure: np.ndarray,
+) -> None:
+    """
+    Test that _find_local_vapour_pressure returns the expected local vapour pressure values.
+
+    This test sets the temperature and relative_humidity attributes on the plugin,
+    calls _find_local_vapour_pressure, and checks the output against expected values.
+
+    Args:
+        temperature (np.ndarray): Array of temperature values (K).
+        relative_humidity (np.ndarray): Array of relative humidity values (fraction).
+        pressure_levels (np.ndarray): Array of pressure levels (Pa).
+        expected_vapour_pressure (np.ndarray): Expected vapour pressure output (Pa).
+    """
+    plugin = CondensationTrailFormation()
+    plugin.temperature = temperature
+    plugin.relative_humidity = relative_humidity
+    result = plugin._find_local_vapour_pressure(pressure_levels)
+    np.testing.assert_allclose(result, expected_vapour_pressure)