From 2751720fc7216d8f2d0c221bdbfae080e55311b3 Mon Sep 17 00:00:00 2001
From: Manuel Schlund <32543114+schlunma@users.noreply.github.com>
Date: Tue, 23 Jan 2024 13:32:02 +0100
Subject: [PATCH] Added special unit conversion m -> DU for total column ozone
 (toz) (#2270)

---
 doc/recipe/preprocessor.rst                   |  2 ++
 esmvalcore/preprocessor/_units.py             | 14 +++++---
 .../preprocessor/_units/test_convert_units.py | 34 +++++++++++++++++++
 3 files changed, 46 insertions(+), 4 deletions(-)

diff --git a/doc/recipe/preprocessor.rst b/doc/recipe/preprocessor.rst
index fdac9ec7da..8412ceba3f 100644
--- a/doc/recipe/preprocessor.rst
+++ b/doc/recipe/preprocessor.rst
@@ -2335,6 +2335,8 @@ Currently, the following special conversions are supported:
 
 * ``precipitation_flux`` (``kg m-2 s-1``) --
   ``lwe_precipitation_rate`` (``mm day-1``)
+* ``equivalent_thickness_at_stp_of_atmosphere_ozone_content`` (``m``) --
+  ``equivalent_thickness_at_stp_of_atmosphere_ozone_content`` (``DU``)
 
 .. hint::
    Names in the list correspond to ``standard_names`` of the input data.
diff --git a/esmvalcore/preprocessor/_units.py b/esmvalcore/preprocessor/_units.py
index 4f435b7f86..069cef1a6d 100644
--- a/esmvalcore/preprocessor/_units.py
+++ b/esmvalcore/preprocessor/_units.py
@@ -4,9 +4,9 @@
 """
 import logging
 
-from cf_units import Unit
 import iris
 import numpy as np
+from cf_units import Unit
 
 logger = logging.getLogger(__name__)
 
@@ -21,6 +21,10 @@
         ('precipitation_flux', 'kg m-2 s-1'),
         ('lwe_precipitation_rate', 'mm s-1'),
     ],
+    [
+        ('equivalent_thickness_at_stp_of_atmosphere_ozone_content', 'm'),
+        ('equivalent_thickness_at_stp_of_atmosphere_ozone_content', '1e5 DU'),
+    ],
 ]
 
 
@@ -41,7 +45,7 @@ def _try_special_conversions(cube, units):
             if (cube.standard_name == std_name and
                     cube.units.is_convertible(special_units)):
                 for (target_std_name, target_units) in special_case:
-                    if target_std_name == std_name:
+                    if target_units == special_units:
                         continue
 
                     # Step 2: find suitable target name and units
@@ -79,8 +83,10 @@ def convert_units(cube, units):
 
     Currently, the following special conversions are supported:
 
-        * ``precipitation_flux`` (``kg m-2 s-1``) --
-          ``lwe_precipitation_rate`` (``mm day-1``)
+    * ``precipitation_flux`` (``kg m-2 s-1``) --
+      ``lwe_precipitation_rate`` (``mm day-1``)
+    * ``equivalent_thickness_at_stp_of_atmosphere_ozone_content`` (``m``) --
+      ``equivalent_thickness_at_stp_of_atmosphere_ozone_content`` (``DU``)
 
     Names in the list correspond to ``standard_names`` of the input data.
     Conversions are allowed from each quantity to any other quantity given in a
diff --git a/tests/unit/preprocessor/_units/test_convert_units.py b/tests/unit/preprocessor/_units/test_convert_units.py
index 02e67143f2..c1a2a2453b 100644
--- a/tests/unit/preprocessor/_units/test_convert_units.py
+++ b/tests/unit/preprocessor/_units/test_convert_units.py
@@ -44,6 +44,40 @@ def test_convert_compatible_units(self):
         self.assertEqual(result.units, expected_units)
         self.assert_array_equal(result.data, expected_data)
 
+    def test_convert_ozone_content_m_to_du(self):
+        """Test special conversion of ozone_content."""
+        self.arr.standard_name = (
+            'equivalent_thickness_at_stp_of_atmosphere_ozone_content'
+        )
+        self.arr.units = 'm'
+        result = convert_units(self.arr, 'DU')
+        self.assertEqual(
+            result.standard_name,
+            'equivalent_thickness_at_stp_of_atmosphere_ozone_content',
+        )
+        self.assertEqual(result.units, 'DU')
+        np.testing.assert_allclose(
+            result.data,
+            [[0.0, 1e5], [2e5, 3e5]],
+        )
+
+    def test_convert_ozone_content_du_to_m(self):
+        """Test special conversion of ozone_content."""
+        self.arr.standard_name = (
+            'equivalent_thickness_at_stp_of_atmosphere_ozone_content'
+        )
+        self.arr.units = 'DU'
+        result = convert_units(self.arr, 'mm')
+        self.assertEqual(
+            result.standard_name,
+            'equivalent_thickness_at_stp_of_atmosphere_ozone_content',
+        )
+        self.assertEqual(result.units, 'mm')
+        np.testing.assert_allclose(
+            result.data,
+            [[0.0, 1e-2], [2e-2, 3e-2]],
+        )
+
     def test_convert_precipitation_flux(self):
         """Test special conversion of precipitation_flux."""
         self.arr.standard_name = 'precipitation_flux'