Basic conversion operators for humidity, temperature and pressure

src/CSET/operators/__init__.py

@@ -34,12 +34,15 @@
     convection,
     ensembles,
     filters,
+    humidity,
     imageprocessing,
     mesoscale,
     misc,
     plot,
+    pressure,
     read,
     regrid,
+    temperature,
     transect,
     wind,
     write,
@@ -56,13 +59,16 @@
     "ensembles",
     "execute_recipe",
     "filters",
+    "humidity",
     "get_operator",
     "imageprocessing",
     "mesoscale",
     "misc",
     "plot",
+    "pressure",
     "read",
     "regrid",
+    "temperature",
     "transect",
     "wind",
     "write",

src/CSET/operators/_atmospheric_constants.py

@@ -0,0 +1,41 @@
+# © Crown copyright, Met Office (2022-2026) and CSET contributors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Constants for the atmosphere."""
+
+# Reference pressure.
+P0 = 1000.0  # hPa
+
+# Specific gas constant for dry air.
+RD = 287.0
+
+# Specific gas constant for water vapour.
+RV = 461.0
+
+# Specific heat capacity for dry air.
+CPD = 1005.7
+
+# Latent heat of vaporization.
+LV = 2.501e6
+
+# Reference vapour pressure.
+E0 = 6.1078  # hPa
+
+# Reference temperature.
+T0 = 273.15  # K
+
+# Ratio between mixing ratio of dry and moist air.
+EPSILON = 0.622
+
+# Ratio between specific gas constant and specific heat capacity.
+KAPPA = RD / CPD

src/CSET/operators/humidity.py

@@ -0,0 +1,176 @@
+# © Crown copyright, Met Office (2022-2026) and CSET contributors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Operators for humidity conversions."""
+
+import iris.cube
+
+from CSET._common import iter_maybe
+from CSET.operators._atmospheric_constants import EPSILON
+from CSET.operators.misc import convert_units
+from CSET.operators.pressure import vapour_pressure
+
+
+def specific_humidity_to_mixing_ratio(
+    cubes: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Convert specific humidity to mixing ratio."""
+    w = iris.cube.CubeList([])
+    for cube in iter_maybe(cubes):
+        mr = cube.copy()
+        mr = cube / (1 - cube)
+        mr.rename("mixing_ratio")
+        w.append(mr)
+    if len(w) == 1:
+        return w[0]
+    else:
+        return w
+
+
+def mixing_ratio_to_specific_humidity(
+    cubes: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Convert mixing ratio to specific humidity."""
+    q = iris.cube.CubeList([])
+    for cube in iter_maybe(cubes):
+        sh = cube.copy()
+        sh = cube / (1 + cube)
+        sh.rename("specific_humidity")
+        q.append(sh)
+    if len(q) == 1:
+        return q[0]
+    else:
+        return q
+
+
+def saturation_mixing_ratio(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate saturation mixing ratio."""
+    w = iris.cube.CubeList([])
+    for T, P in zip(iter_maybe(temperature), iter_maybe(pressure), strict=True):
+        mr = (EPSILON * vapour_pressure(T)) / ((P / 100.0) - vapour_pressure(T))
+        mr.units = "kg/kg"
+        mr.rename("mixing_ratio")
+        w.append(mr)
+    if len(w) == 1:
+        return w[0]
+    else:
+        return w
+
+
+def saturation_specific_humidity(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate saturation specific humidity."""
+    q = iris.cube.CubeList([])
+    for T, P in zip(iter_maybe(temperature), iter_maybe(pressure), strict=True):
+        sh = (EPSILON * vapour_pressure(T)) / (P / 100.0)
+        sh.units = "kg/kg"
+        sh.rename("specific_humidity")
+        q.append(sh)
+    if len(q) == 1:
+        return q[0]
+    else:
+        return q
+
+
+def mixing_ratio_from_RH(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+    relative_humidity: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate the mixing ratio from RH."""
+    w = iris.cube.CubeList([])
+    for T, P, RH in zip(
+        iter_maybe(temperature),
+        iter_maybe(pressure),
+        iter_maybe(relative_humidity),
+        strict=True,
+    ):
+        RH = convert_units(RH, "1")
+        mr = saturation_mixing_ratio(T, P) * RH
+        w.append(mr)
+    if len(w) == 1:
+        return w[0]
+    else:
+        return w
+
+
+def specific_humidity_from_RH(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+    relative_humidity: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate the mixing ratio from RH."""
+    q = iris.cube.CubeList([])
+    for T, P, RH in zip(
+        iter_maybe(temperature),
+        iter_maybe(pressure),
+        iter_maybe(relative_humidity),
+        strict=True,
+    ):
+        RH = convert_units(RH, "1")
+        sh = saturation_specific_humidity(T, P) * RH
+        q.append(sh)
+    if len(q) == 1:
+        return q[0]
+    else:
+        return q
+
+
+def relative_humidity_from_mixing_ratio(
+    mixing_ratio: iris.cube.Cube | iris.cube.CubeList,
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Convert mixing ratio to relative humidity."""
+    RH = iris.cube.CubeList([])
+    for W, T, P in zip(
+        iter_maybe(mixing_ratio),
+        iter_maybe(temperature),
+        iter_maybe(pressure),
+        strict=True,
+    ):
+        rel_h = W / saturation_mixing_ratio(T, P)
+        rel_h.rename("relative_humidity")
+        RH.append(rel_h)
+    if len(RH) == 1:
+        return RH[0]
+    else:
+        return RH
+
+
+def relative_humidity_from_specific_humidity(
+    specific_humidity: iris.cube.Cube | iris.cube.CubeList,
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Convert specific humidity to relative humidity."""
+    RH = iris.cube.CubeList([])
+    for Q, T, P in zip(
+        iter_maybe(specific_humidity),
+        iter_maybe(temperature),
+        iter_maybe(pressure),
+        strict=True,
+    ):
+        rel_h = Q / saturation_specific_humidity(T, P)
+        rel_h.rename("relative_humidity")
+        RH.append(rel_h)
+    if len(RH) == 1:
+        return RH[0]
+    else:
+        return RH

src/CSET/operators/pressure.py

@@ -0,0 +1,75 @@
+# © Crown copyright, Met Office (2022-2026) and CSET contributors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Operators for pressure conversions."""
+
+import iris.cube
+import numpy as np
+
+from CSET._common import iter_maybe
+from CSET.operators._atmospheric_constants import E0, KAPPA, P0
+from CSET.operators.misc import convert_units
+
+
+def vapour_pressure(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate the vapour pressure of the atmosphere."""
+    v_pressure = iris.cube.CubeList([])
+    for T in iter_maybe(temperature):
+        es = T.copy()
+        exponent = 17.27 * (T - 273.16) / (T - 35.86)
+        es.data[:] = E0 * np.exp(exponent.core_data())
+        es.units = "hPa"
+        es.rename("vapour_pressure")
+        v_pressure.append(es)
+    if len(v_pressure) == 1:
+        return v_pressure[0]
+    else:
+        return v_pressure
+
+
+def vapour_pressure_from_RH(
+    temperature: iris.cube.Cube | iris.cube.CubeList,
+    relative_humidity: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate the vapour pressure using RH."""
+    v_pressure = iris.cube.CubeList([])
+    for T, RH in zip(
+        iter_maybe(temperature), iter_maybe(relative_humidity), strict=True
+    ):
+        RH = convert_units(RH, "1")
+        vp = vapour_pressure(T) * RH
+        v_pressure.append(vp)
+    if len(v_pressure) == 1:
+        return v_pressure[0]
+    else:
+        return v_pressure
+
+
+def exner_pressure(
+    pressure: iris.cube.Cube | iris.cube.CubeList,
+) -> iris.cube.Cube | iris.cube.CubeList:
+    """Calculate the exner pressure."""
+    pi = iris.cube.CubeList([])
+    for P in iter_maybe(pressure):
+        PI = P.copy()
+        PI.data[:] = (P.core_data() / P0) ** KAPPA
+        PI.rename("exner_pressure")
+        PI.units = "1"
+        pi.append(PI)
+    if len(pi) == 1:
+        return pi[0]
+    else:
+        return pi