From 9c98423a85aa7b82bdb8918baaf8045a4c20495b Mon Sep 17 00:00:00 2001
From: Matthew Mizielinski <matthew.mizielinski@metoffice.gov.uk>
Date: Fri, 10 Apr 2026 16:50:45 +0000
Subject: [PATCH 01/16] #886: First draft of how to add cell measures

---
 .../mip_convert/requested_variables.py        | 10 ++++++
 .../mip_convert/save/cmor/cmor_wrapper.py     | 31 +++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index 31c07e6c4..9483c6f90 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -125,6 +125,16 @@ def produce_mip_requested_variable(
     if frequency:
         saver.cmor.set_frequency(frequency)
 
+    # Apply cell_measures if a <mip_era>_cell_measures.json file exists
+    saver.cmor.apply_cell_measures(
+        user_config.mip_era,
+        user_config.inpath,
+        mip_table.id,
+        variable_name,
+        frequency,
+        user_config.global_attributes['region'],
+        saver.varid)
+
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
     period = user_config.slicing.get(stream_id, 'year')
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index 56c5a6463..a1dbb372c 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -1,6 +1,8 @@
 # (C) British Crown Copyright 2009-2025, Met Office.
 # Please see LICENSE.md for license details.
 from collections import OrderedDict
+import os
+import json
 
 import cmor
 
@@ -115,3 +117,32 @@ def zfactor(self, *args, **kwargs):
     def set_frequency(self, frequency, **kwargs):
         self._debug_on_args('frequency', [frequency], kwargs)
         cmor.cmor.set_cur_dataset_attribute('frequency', frequency)
+
+    def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
+        # self._debug_on_args('apply_cell_measures', [mip_table_dir])
+        """
+        Add cell measures read from json file in with mip tables
+        """
+
+        cell_measures_file = os.path.join(mip_table_dir, f'{mip_era}_cell_measures.json')
+
+        if os.path.exists(cell_measures_file):
+            with open(cell_measures_file) as fh:
+                cell_measures = json.load(fh)
+            if 'cell_measures' not in cell_measures:
+                self.logger.debug(f'"cell_measures" key not found in {cell_measures_file}')
+                return
+            cell_measures = cell_measures['cell_measures']
+
+            root_label, branding = variable.split('_')
+            key = f'{realm}.{root_label}.{branding}.{frequency}.{region}'
+            if key in cell_measures:
+                retval = cmor.cmor.set_variable_attribute(
+                    variable_id,
+                    'cell_measures',
+                    'c',
+                    cell_measures[key])
+                if retval != 0:
+                    self.logger.debug('cell_measures assignment failed. Check cmor log file for details')
+        else:
+            self.logger.debug(f'Cell_measures file "{cell_measures_file}" not found. Continuing')

From 22530bb7d99c12bb04b4e31e220eb2542e551bba Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Fri, 5 Jun 2026 10:36:37 +0000
Subject: [PATCH 02/16] #886: Fix keyerror.

---
 mip_convert/mip_convert/requested_variables.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index 9483c6f90..c6c7b52c9 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -132,7 +132,7 @@ def produce_mip_requested_variable(
         mip_table.id,
         variable_name,
         frequency,
-        user_config.global_attributes['region'],
+        user_config.global_attributes.get('region', ''),
         saver.varid)
 
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'

From 3a54a40c1cf018b5e8a48c29749471e0717551d8 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Mon, 8 Jun 2026 09:53:02 +0100
Subject: [PATCH 03/16] #886: Further iteration, fix varid=None bug.

---
 .../mip_convert/requested_variables.py        | 34 ++++++++++++-------
 .../mip_convert/save/cmor/cmor_wrapper.py     |  2 +-
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index c6c7b52c9..2f3996080 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -14,7 +14,7 @@
 from mip_convert.configuration.json_config import MIPConfig
 from mip_convert.configuration.python_config import ModelToMIPMappingConfig
 
-from mip_convert.save import save
+from mip_convert.save import create_cmor_variable
 from mip_convert.save.cmor import cmor_lite
 from mip_convert.mip_table import get_variable_model_to_mip_mapping, get_variable_mip_metadata
 
@@ -125,23 +125,33 @@ def produce_mip_requested_variable(
     if frequency:
         saver.cmor.set_frequency(frequency)
 
-    # Apply cell_measures if a <mip_era>_cell_measures.json file exists
-    saver.cmor.apply_cell_measures(
-        user_config.mip_era,
-        user_config.inpath,
-        mip_table.id,
-        variable_name,
-        frequency,
-        user_config.global_attributes.get('region', ''),
-        saver.varid)
-
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
     period = user_config.slicing.get(stream_id, 'year')
+    cell_measures_applied = False
     for time_slice in variable.slices_over(period):
         time_slice.process()
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
-        save(time_slice, saver)
+
+        # Build the CMOR variable first so the CMOR varid can be created
+        # before any write, allowing variable attributes to be set safely.
+        cmor_variable = create_cmor_variable(time_slice)
+        if not cell_measures_applied:
+            if saver.varid is None:
+                saver._getVarId(cmor_variable)
+            # Apply cell_measures if a <mip_era>_cell_measures.json file exists.
+            # Must be called before the first write to satisfy CMOR.
+            saver.cmor.apply_cell_measures(
+                user_config.mip_era,
+                user_config.inpath,
+                mip_table.id,
+                variable_name,
+                frequency,
+                user_config.global_attributes.get('region', ''),
+                saver.varid)
+            cell_measures_applied = True
+
+        saver(cmor_variable)
 
     # Close the 'output netCDF file'.
     cmor_lite.close(saver.varid)
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index a1dbb372c..1e437d760 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -119,10 +119,10 @@ def set_frequency(self, frequency, **kwargs):
         cmor.cmor.set_cur_dataset_attribute('frequency', frequency)
 
     def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
-        # self._debug_on_args('apply_cell_measures', [mip_table_dir])
         """
         Add cell measures read from json file in with mip tables
         """
+        self._debug_on_args('apply_cell_measures', [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {})
 
         cell_measures_file = os.path.join(mip_table_dir, f'{mip_era}_cell_measures.json')
 

From d8b5977f3cda4a9ce4c2405d35b8341b034861ae Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Mon, 8 Jun 2026 09:53:32 +0000
Subject: [PATCH 04/16] #886: Refine comments.

---
 mip_convert/mip_convert/requested_variables.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index 2f3996080..f836a25a0 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -134,13 +134,14 @@ def produce_mip_requested_variable(
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
 
         # Build the CMOR variable first so the CMOR varid can be created
-        # before any write, allowing variable attributes to be set safely.
+        # before any write, allowing variable attributes to be set safely
+        # (a valid varid is required by apply_cell_measures to set the
+        # cell_measures attribute via cmor.set_variable_attribute).
         cmor_variable = create_cmor_variable(time_slice)
         if not cell_measures_applied:
             if saver.varid is None:
                 saver._getVarId(cmor_variable)
             # Apply cell_measures if a <mip_era>_cell_measures.json file exists.
-            # Must be called before the first write to satisfy CMOR.
             saver.cmor.apply_cell_measures(
                 user_config.mip_era,
                 user_config.inpath,

From 099d59d5e19c1957f237dcf03e7924865294331d Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Mon, 8 Jun 2026 10:43:18 +0000
Subject: [PATCH 05/16] #886: Clarify behaviour in docstring.

---
 mip_convert/mip_convert/requested_variables.py    | 3 +--
 mip_convert/mip_convert/save/cmor/cmor_wrapper.py | 8 +++++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index f836a25a0..c334e0eb8 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -139,8 +139,7 @@ def produce_mip_requested_variable(
         # cell_measures attribute via cmor.set_variable_attribute).
         cmor_variable = create_cmor_variable(time_slice)
         if not cell_measures_applied:
-            if saver.varid is None:
-                saver._getVarId(cmor_variable)
+            saver._getVarId(cmor_variable)
             # Apply cell_measures if a <mip_era>_cell_measures.json file exists.
             saver.cmor.apply_cell_measures(
                 user_config.mip_era,
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index 1e437d760..5640f8ded 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -120,7 +120,13 @@ def set_frequency(self, frequency, **kwargs):
 
     def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
         """
-        Add cell measures read from json file in with mip tables
+        Set the cell_measures attribute on a CMOR variable using a lookup in
+        ``{mip_era}_cell_measures.json`` from the MIP tables directory. Returns
+        silently if the file does not exist.
+
+        The lookup key has the form ``{realm}.{root_label}.{branding}.{frequency}.{region}``
+        (variable name split on ``_``), so entries in the JSON must follow the
+        convention used for CMIP7.
         """
         self._debug_on_args('apply_cell_measures', [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {})
 

From fb6e14b7baa6c2e86754f86a999daaa98303a7c1 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Tue, 9 Jun 2026 09:02:23 +0000
Subject: [PATCH 06/16] #886: Move code into time_slice.process.

---
 mip_convert/mip_convert/new_variable.py       | 15 +++++++-
 .../mip_convert/requested_variables.py        | 35 +++++++------------
 .../mip_convert/save/cmor/cmor_outputter.py   | 12 +++++++
 3 files changed, 38 insertions(+), 24 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index 32d116603..e6fa2682a 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -337,7 +337,7 @@ def ordered_coords(self):
 
         return self._ordered_coords
 
-    def process(self):
+    def process(self, saver=None, cell_measures_config=None):
         """Process the data.
 
         The units of the data of the |MIP requested variable| are the
@@ -367,6 +367,19 @@ def process(self):
             self._update_time_units()
         if hasattr(self.model_to_mip_mapping, 'valid_min'):
             self._apply_valid_min_correction()
+        if saver is not None and cell_measures_config is not None:
+            self.apply_cell_measures(saver, cell_measures_config)
+
+    def apply_cell_measures(self, saver, cell_measures_config):
+        """Apply cell measures to the CMOR variable if not already applied.        Parameters
+        ----------
+        saver:
+            The CMOR outputter for this variable.
+        cell_measures_config: tuple
+            Arguments forwarded to cmor_wrapper.apply_cell_measures,
+            in the form (mip_era, mip_table_dir, realm, variable, frequency, region).
+        """
+        saver.apply_cell_measures(self, *cell_measures_config)
 
     def _remove_alevhalf_bounds(self):
         """
diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index c334e0eb8..96889d997 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -14,7 +14,7 @@
 from mip_convert.configuration.json_config import MIPConfig
 from mip_convert.configuration.python_config import ModelToMIPMappingConfig
 
-from mip_convert.save import create_cmor_variable
+from mip_convert.save import save
 from mip_convert.save.cmor import cmor_lite
 from mip_convert.mip_table import get_variable_model_to_mip_mapping, get_variable_mip_metadata
 
@@ -128,30 +128,19 @@ def produce_mip_requested_variable(
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
     period = user_config.slicing.get(stream_id, 'year')
-    cell_measures_applied = False
+
+    cell_measures_config = (
+        user_config.mip_era,
+        user_config.inpath,
+        mip_table.id,
+        variable_name,
+        frequency,
+        user_config.global_attributes.get('region', ''))
+
     for time_slice in variable.slices_over(period):
-        time_slice.process()
+        time_slice.process(saver, cell_measures_config)
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
-
-        # Build the CMOR variable first so the CMOR varid can be created
-        # before any write, allowing variable attributes to be set safely
-        # (a valid varid is required by apply_cell_measures to set the
-        # cell_measures attribute via cmor.set_variable_attribute).
-        cmor_variable = create_cmor_variable(time_slice)
-        if not cell_measures_applied:
-            saver._getVarId(cmor_variable)
-            # Apply cell_measures if a <mip_era>_cell_measures.json file exists.
-            saver.cmor.apply_cell_measures(
-                user_config.mip_era,
-                user_config.inpath,
-                mip_table.id,
-                variable_name,
-                frequency,
-                user_config.global_attributes.get('region', ''),
-                saver.varid)
-            cell_measures_applied = True
-
-        saver(cmor_variable)
+        save(time_slice, saver)
 
     # Close the 'output netCDF file'.
     cmor_lite.close(saver.varid)
diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index b9007455c..795442860 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -38,6 +38,7 @@
 from mip_convert import mip_parser
 import mip_convert.common
 from mip_convert.common import RelativePathChecker
+from mip_convert.save import create_cmor_variable
 from mip_convert.save.mip_config import MipTableFactory
 
 
@@ -301,6 +302,17 @@ def _optional_kwargs(self, variable):
             kwargs['comment'] = self._name_space.namespace_stamp(variable.comment)
         return kwargs
 
+    def apply_cell_measures(self, mip_output_variable, *cell_measures_config):
+        """Apply cell measures to this CMOR variable.
+
+        Ensures the CMOR variable ID exists (creating it if needed), then
+        sets the cell_measures attribute via the CMOR wrapper.
+        """
+        if self.varid is None:
+            cmor_variable = create_cmor_variable(mip_output_variable)
+            self._getVarId(cmor_variable)
+        self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
+
     def _close_file(self):
         self.cmor.close(self.varid, preserve=True)
 

From 23a411c9e609456374f216fd67894e9e56e23e8a Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Tue, 9 Jun 2026 09:26:24 +0000
Subject: [PATCH 07/16] #886: Correct indentation.

---
 mip_convert/mip_convert/save/cmor/cmor_outputter.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index 795442860..312ecd009 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -311,7 +311,7 @@ def apply_cell_measures(self, mip_output_variable, *cell_measures_config):
         if self.varid is None:
             cmor_variable = create_cmor_variable(mip_output_variable)
             self._getVarId(cmor_variable)
-        self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
+            self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
 
     def _close_file(self):
         self.cmor.close(self.varid, preserve=True)

From 30a912a9c435d6f75d11fc68474329d417343316 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Tue, 9 Jun 2026 10:23:19 +0000
Subject: [PATCH 08/16] #886: Switch to using lazy import.

---
 mip_convert/mip_convert/new_variable.py             |  9 +++++++--
 mip_convert/mip_convert/save/cmor/cmor_outputter.py | 12 ------------
 2 files changed, 7 insertions(+), 14 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index e6fa2682a..27053d299 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -371,7 +371,8 @@ def process(self, saver=None, cell_measures_config=None):
             self.apply_cell_measures(saver, cell_measures_config)
 
     def apply_cell_measures(self, saver, cell_measures_config):
-        """Apply cell measures to the CMOR variable if not already applied.        Parameters
+        """Apply cell measures to the CMOR variable if not already applied.
+        Parameters
         ----------
         saver:
             The CMOR outputter for this variable.
@@ -379,7 +380,11 @@ def apply_cell_measures(self, saver, cell_measures_config):
             Arguments forwarded to cmor_wrapper.apply_cell_measures,
             in the form (mip_era, mip_table_dir, realm, variable, frequency, region).
         """
-        saver.apply_cell_measures(self, *cell_measures_config)
+        if saver.varid is None:
+            from mip_convert.save import create_cmor_variable  # deferred to avoid circular import
+            cmor_variable = create_cmor_variable(self)
+            saver._getVarId(cmor_variable)
+            saver.cmor.apply_cell_measures(*cell_measures_config, saver.varid)
 
     def _remove_alevhalf_bounds(self):
         """
diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index 312ecd009..b9007455c 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -38,7 +38,6 @@
 from mip_convert import mip_parser
 import mip_convert.common
 from mip_convert.common import RelativePathChecker
-from mip_convert.save import create_cmor_variable
 from mip_convert.save.mip_config import MipTableFactory
 
 
@@ -302,17 +301,6 @@ def _optional_kwargs(self, variable):
             kwargs['comment'] = self._name_space.namespace_stamp(variable.comment)
         return kwargs
 
-    def apply_cell_measures(self, mip_output_variable, *cell_measures_config):
-        """Apply cell measures to this CMOR variable.
-
-        Ensures the CMOR variable ID exists (creating it if needed), then
-        sets the cell_measures attribute via the CMOR wrapper.
-        """
-        if self.varid is None:
-            cmor_variable = create_cmor_variable(mip_output_variable)
-            self._getVarId(cmor_variable)
-            self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
-
     def _close_file(self):
         self.cmor.close(self.varid, preserve=True)
 

From 19af1b0b25125443324cacc7e635400b2ecb05f5 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Wed, 10 Jun 2026 10:44:48 +0000
Subject: [PATCH 09/16] #886: Move cell_measures_config into Process.

---
 mip_convert/mip_convert/new_variable.py       | 35 +++++++++++--------
 .../mip_convert/requested_variables.py        | 18 ++++------
 2 files changed, 27 insertions(+), 26 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index 33c640d63..2cb536556 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -38,7 +38,8 @@ class VariableMetadata(object):
     def __init__(self, variable_name, stream_id, substream, mip_table_name, mip_metadata, site_information,
                  hybrid_height_information, replacement_coordinates, model_to_mip_mapping, timestep, run_bounds,
                  calendar, base_date, deflate_level, shuffle, ancil_variables, force_coordinate_rotation=False,
-                 reference_time=None, masking=None, removal=None):
+                 reference_time=None, masking=None, removal=None,
+                 mip_era=None, mip_table_dir=None, mip_table_id=None, frequency=None, region=''):
         """
         Parameters
         ----------
@@ -104,6 +105,11 @@ def __init__(self, variable_name, stream_id, substream, mip_table_name, mip_meta
         if ancil_variables:
             self.ancil_variables.extend(ancil_variables)
         self.force_coordinate_rotation = force_coordinate_rotation
+        self.mip_era = mip_era
+        self.mip_table_dir = mip_table_dir
+        self.mip_table_id = mip_table_id
+        self.frequency = frequency
+        self.region = region
         self._validate_timestep()
 
     def _validate_timestep(self):
@@ -337,7 +343,7 @@ def ordered_coords(self):
 
         return self._ordered_coords
 
-    def process(self, saver=None, cell_measures_config=None):
+    def process(self, saver=None):
         """Process the data.
 
         The units of the data of the |MIP requested variable| are the
@@ -367,24 +373,23 @@ def process(self, saver=None, cell_measures_config=None):
             self._update_time_units()
         if hasattr(self.model_to_mip_mapping, 'valid_min'):
             self._apply_valid_min_correction()
-        if saver is not None and cell_measures_config is not None:
-            self.apply_cell_measures(saver, cell_measures_config)
+        if saver is not None:
+            self.apply_cell_measures(saver)
 
-    def apply_cell_measures(self, saver, cell_measures_config):
-        """Apply cell measures to the CMOR variable if not already applied.
-        Parameters
-        ----------
-        saver:
-            The CMOR outputter for this variable.
-        cell_measures_config: tuple
-            Arguments forwarded to cmor_wrapper.apply_cell_measures,
-            in the form (mip_era, mip_table_dir, realm, variable, frequency, region).
-        """
+    def apply_cell_measures(self, saver):
+        """Apply cell measures to the CMOR variable if not already applied."""
         if saver.varid is None:
             from mip_convert.save import create_cmor_variable  # deferred to avoid circular import
             cmor_variable = create_cmor_variable(self)
             saver._getVarId(cmor_variable)
-            saver.cmor.apply_cell_measures(*cell_measures_config, saver.varid)
+            saver.cmor.apply_cell_measures(
+                self._variable_metadata.mip_era,
+                self._variable_metadata.mip_table_dir,
+                self._variable_metadata.mip_table_id,
+                self.variable_name,
+                self._variable_metadata.frequency,
+                self._variable_metadata.region,
+                saver.varid)
 
     def _remove_alevhalf_bounds(self):
         """
diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index 96889d997..ee54fc05a 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -111,7 +111,12 @@ def produce_mip_requested_variable(
         user_config.atmos_timestep, user_config.run_bounds, user_config.calendar, user_config.base_date,
         user_config.deflate_level, user_config.shuffle, user_config.ancil_variables,
         user_config.force_coordinate_rotation, user_config.reference_time, user_config.masking,
-        user_config.halo_removals
+        user_config.halo_removals,
+        mip_era=user_config.mip_era,
+        mip_table_dir=user_config.inpath,
+        mip_table_id=mip_table.id,
+        frequency=frequency,
+        region=user_config.global_attributes.get('region', '')
     )
 
     # Load the data from the 'model output files' and store each 'input variable' in the 'Variable' object
@@ -128,17 +133,8 @@ def produce_mip_requested_variable(
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
     period = user_config.slicing.get(stream_id, 'year')
-
-    cell_measures_config = (
-        user_config.mip_era,
-        user_config.inpath,
-        mip_table.id,
-        variable_name,
-        frequency,
-        user_config.global_attributes.get('region', ''))
-
     for time_slice in variable.slices_over(period):
-        time_slice.process(saver, cell_measures_config)
+        time_slice.process(saver)
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
         save(time_slice, saver)
 

From abe53d9b4b166141067bec308de29045131f4368 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Wed, 10 Jun 2026 13:00:02 +0000
Subject: [PATCH 10/16] #886: Restore files to state in commit 22530bb .

---
 mip_convert/mip_convert/new_variable.py       | 45 ++++---------------
 .../mip_convert/requested_variables.py        | 19 +++++---
 .../mip_convert/save/cmor/cmor_wrapper.py     | 10 +----
 3 files changed, 22 insertions(+), 52 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index 2cb536556..32d116603 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015-2026, Met Office.
+# (C) British Crown Copyright 2015-2025, Met Office.
 # Please see LICENSE.md for license details.
 # pylint: disable=no-member, eval-used, wildcard-import
 # pylint: disable=unused-wildcard-import
@@ -38,8 +38,7 @@ class VariableMetadata(object):
     def __init__(self, variable_name, stream_id, substream, mip_table_name, mip_metadata, site_information,
                  hybrid_height_information, replacement_coordinates, model_to_mip_mapping, timestep, run_bounds,
                  calendar, base_date, deflate_level, shuffle, ancil_variables, force_coordinate_rotation=False,
-                 reference_time=None, masking=None, removal=None,
-                 mip_era=None, mip_table_dir=None, mip_table_id=None, frequency=None, region=''):
+                 reference_time=None, masking=None, removal=None):
         """
         Parameters
         ----------
@@ -105,11 +104,6 @@ def __init__(self, variable_name, stream_id, substream, mip_table_name, mip_meta
         if ancil_variables:
             self.ancil_variables.extend(ancil_variables)
         self.force_coordinate_rotation = force_coordinate_rotation
-        self.mip_era = mip_era
-        self.mip_table_dir = mip_table_dir
-        self.mip_table_id = mip_table_id
-        self.frequency = frequency
-        self.region = region
         self._validate_timestep()
 
     def _validate_timestep(self):
@@ -237,7 +231,7 @@ def slices_over(self, period):
                 # Slice the 'input variable(s)', since they have not yet been processed.
                 message = '-'.join([str(items) for items in date_time])
                 self.logger.debug('Creating data for "{}"'.format(message))
-                sliced_input_variables = self._slice_input_variables(date_time, date_times)
+                sliced_input_variables = self._slice_input_variables(date_time)
                 yield Variable(sliced_input_variables, self._variable_metadata)
             else:
                 # Slice the 'MIP output variable'.
@@ -343,7 +337,7 @@ def ordered_coords(self):
 
         return self._ordered_coords
 
-    def process(self, saver=None):
+    def process(self):
         """Process the data.
 
         The units of the data of the |MIP requested variable| are the
@@ -373,23 +367,6 @@ def process(self, saver=None):
             self._update_time_units()
         if hasattr(self.model_to_mip_mapping, 'valid_min'):
             self._apply_valid_min_correction()
-        if saver is not None:
-            self.apply_cell_measures(saver)
-
-    def apply_cell_measures(self, saver):
-        """Apply cell measures to the CMOR variable if not already applied."""
-        if saver.varid is None:
-            from mip_convert.save import create_cmor_variable  # deferred to avoid circular import
-            cmor_variable = create_cmor_variable(self)
-            saver._getVarId(cmor_variable)
-            saver.cmor.apply_cell_measures(
-                self._variable_metadata.mip_era,
-                self._variable_metadata.mip_table_dir,
-                self._variable_metadata.mip_table_id,
-                self.variable_name,
-                self._variable_metadata.frequency,
-                self._variable_metadata.region,
-                saver.varid)
 
     def _remove_alevhalf_bounds(self):
         """
@@ -867,10 +844,10 @@ def _data_dimension(self, coord, axis_direction):
             raise ValueError(message)
         return data_dimension
 
-    def _slice_input_variables(self, date_time, date_times):
+    def _slice_input_variables(self, date_time):
         input_variables = {}
-        if (len(date_time) > 1 and date_time[1] != 12) and date_time != date_times[-1]:
-            # don't attach New Year midnight to months that are not december or the final chunk in the slice,
+        if len(date_time) > 1 and date_time[1] != 12:
+            # don't attach New Year midnight to other months
             new_year_midnight = False
         else:
             new_year_midnight = True
@@ -1251,16 +1228,10 @@ def _mip_table_requested_bounds(bounds):
 
 def _setup_time_constraint(date_time, with_new_year_midnight=True):
     def time_constraint(cell):
-        """Runs only if with_new_year_midnight evaluates to True. Checks the current cell point and confirms if it
-        signifies a new year (e.g. 1980-01-01) or a new month (e.g. 1980-04-01). If so, it returns that value and
-        ensures that the data point is kept, hence maintaining time contiguity between slices."""
-        new_month = PartialDateTime(date_time[0], date_time[1] + 1, 1, 0, 0, 0, 0) if len(date_time) > 1 else ""
         return (PartialDateTime(*date_time) == cell.point or
-                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point or
-                new_month == cell.point)
+                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point)
 
     def time_constraint2(cell):
-        # Returns the original input cell point if with_new_year_midnight evaluates to false.
         return PartialDateTime(*date_time) == cell.point
 
     return time_constraint if with_new_year_midnight else time_constraint2
diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index ee54fc05a..c6c7b52c9 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -111,12 +111,7 @@ def produce_mip_requested_variable(
         user_config.atmos_timestep, user_config.run_bounds, user_config.calendar, user_config.base_date,
         user_config.deflate_level, user_config.shuffle, user_config.ancil_variables,
         user_config.force_coordinate_rotation, user_config.reference_time, user_config.masking,
-        user_config.halo_removals,
-        mip_era=user_config.mip_era,
-        mip_table_dir=user_config.inpath,
-        mip_table_id=mip_table.id,
-        frequency=frequency,
-        region=user_config.global_attributes.get('region', '')
+        user_config.halo_removals
     )
 
     # Load the data from the 'model output files' and store each 'input variable' in the 'Variable' object
@@ -130,11 +125,21 @@ def produce_mip_requested_variable(
     if frequency:
         saver.cmor.set_frequency(frequency)
 
+    # Apply cell_measures if a <mip_era>_cell_measures.json file exists
+    saver.cmor.apply_cell_measures(
+        user_config.mip_era,
+        user_config.inpath,
+        mip_table.id,
+        variable_name,
+        frequency,
+        user_config.global_attributes.get('region', ''),
+        saver.varid)
+
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
     period = user_config.slicing.get(stream_id, 'year')
     for time_slice in variable.slices_over(period):
-        time_slice.process(saver)
+        time_slice.process()
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
         save(time_slice, saver)
 
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index 5640f8ded..a1dbb372c 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -119,16 +119,10 @@ def set_frequency(self, frequency, **kwargs):
         cmor.cmor.set_cur_dataset_attribute('frequency', frequency)
 
     def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
+        # self._debug_on_args('apply_cell_measures', [mip_table_dir])
         """
-        Set the cell_measures attribute on a CMOR variable using a lookup in
-        ``{mip_era}_cell_measures.json`` from the MIP tables directory. Returns
-        silently if the file does not exist.
-
-        The lookup key has the form ``{realm}.{root_label}.{branding}.{frequency}.{region}``
-        (variable name split on ``_``), so entries in the JSON must follow the
-        convention used for CMIP7.
+        Add cell measures read from json file in with mip tables
         """
-        self._debug_on_args('apply_cell_measures', [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {})
 
         cell_measures_file = os.path.join(mip_table_dir, f'{mip_era}_cell_measures.json')
 

From e57005b48dbebb96e2b4c9c545851de5e9a1790b Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Wed, 10 Jun 2026 13:18:39 +0000
Subject: [PATCH 11/16] #886: Match state of main.

---
 mip_convert/mip_convert/new_variable.py | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index 32d116603..d82e385e2 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015-2025, Met Office.
+# (C) British Crown Copyright 2015-2026, Met Office.
 # Please see LICENSE.md for license details.
 # pylint: disable=no-member, eval-used, wildcard-import
 # pylint: disable=unused-wildcard-import
@@ -231,7 +231,7 @@ def slices_over(self, period):
                 # Slice the 'input variable(s)', since they have not yet been processed.
                 message = '-'.join([str(items) for items in date_time])
                 self.logger.debug('Creating data for "{}"'.format(message))
-                sliced_input_variables = self._slice_input_variables(date_time)
+                sliced_input_variables = self._slice_input_variables(date_time, date_times)
                 yield Variable(sliced_input_variables, self._variable_metadata)
             else:
                 # Slice the 'MIP output variable'.
@@ -844,10 +844,10 @@ def _data_dimension(self, coord, axis_direction):
             raise ValueError(message)
         return data_dimension
 
-    def _slice_input_variables(self, date_time):
+    def _slice_input_variables(self, date_time, date_times):
         input_variables = {}
-        if len(date_time) > 1 and date_time[1] != 12:
-            # don't attach New Year midnight to other months
+        if (len(date_time) > 1 and date_time[1] != 12) and date_time != date_times[-1]:
+            # don't attach New Year midnight to months that are not december or the final chunk in the slice,
             new_year_midnight = False
         else:
             new_year_midnight = True
@@ -1228,10 +1228,16 @@ def _mip_table_requested_bounds(bounds):
 
 def _setup_time_constraint(date_time, with_new_year_midnight=True):
     def time_constraint(cell):
+        """Runs only if with_new_year_midnight evaluates to True. Checks the current cell point and confirms if it
+        signifies a new year (e.g. 1980-01-01) or a new month (e.g. 1980-04-01). If so, it returns that value and
+        ensures that the data point is kept, hence maintaining time contiguity between slices."""
+        new_month = PartialDateTime(date_time[0], date_time[1] + 1, 1, 0, 0, 0, 0) if len(date_time) > 1 else ""
         return (PartialDateTime(*date_time) == cell.point or
-                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point)
+                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point or
+                new_month == cell.point)
 
     def time_constraint2(cell):
+        # Returns the original input cell point if with_new_year_midnight evaluates to false.
         return PartialDateTime(*date_time) == cell.point
 
     return time_constraint if with_new_year_midnight else time_constraint2

From 8993a3e43b44ad79ce5baddfc104a4c72fc60e3c Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Wed, 10 Jun 2026 13:26:06 +0000
Subject: [PATCH 12/16] 886: Apply Matts original draft of implementation
 again.

---
 mip_convert/mip_convert/new_variable.py       | 33 +++++++++++--------
 .../mip_convert/save/cmor/cmor_outputter.py   | 12 +++++++
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index d82e385e2..e6fa2682a 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015-2026, Met Office.
+# (C) British Crown Copyright 2015-2025, Met Office.
 # Please see LICENSE.md for license details.
 # pylint: disable=no-member, eval-used, wildcard-import
 # pylint: disable=unused-wildcard-import
@@ -231,7 +231,7 @@ def slices_over(self, period):
                 # Slice the 'input variable(s)', since they have not yet been processed.
                 message = '-'.join([str(items) for items in date_time])
                 self.logger.debug('Creating data for "{}"'.format(message))
-                sliced_input_variables = self._slice_input_variables(date_time, date_times)
+                sliced_input_variables = self._slice_input_variables(date_time)
                 yield Variable(sliced_input_variables, self._variable_metadata)
             else:
                 # Slice the 'MIP output variable'.
@@ -337,7 +337,7 @@ def ordered_coords(self):
 
         return self._ordered_coords
 
-    def process(self):
+    def process(self, saver=None, cell_measures_config=None):
         """Process the data.
 
         The units of the data of the |MIP requested variable| are the
@@ -367,6 +367,19 @@ def process(self):
             self._update_time_units()
         if hasattr(self.model_to_mip_mapping, 'valid_min'):
             self._apply_valid_min_correction()
+        if saver is not None and cell_measures_config is not None:
+            self.apply_cell_measures(saver, cell_measures_config)
+
+    def apply_cell_measures(self, saver, cell_measures_config):
+        """Apply cell measures to the CMOR variable if not already applied.        Parameters
+        ----------
+        saver:
+            The CMOR outputter for this variable.
+        cell_measures_config: tuple
+            Arguments forwarded to cmor_wrapper.apply_cell_measures,
+            in the form (mip_era, mip_table_dir, realm, variable, frequency, region).
+        """
+        saver.apply_cell_measures(self, *cell_measures_config)
 
     def _remove_alevhalf_bounds(self):
         """
@@ -844,10 +857,10 @@ def _data_dimension(self, coord, axis_direction):
             raise ValueError(message)
         return data_dimension
 
-    def _slice_input_variables(self, date_time, date_times):
+    def _slice_input_variables(self, date_time):
         input_variables = {}
-        if (len(date_time) > 1 and date_time[1] != 12) and date_time != date_times[-1]:
-            # don't attach New Year midnight to months that are not december or the final chunk in the slice,
+        if len(date_time) > 1 and date_time[1] != 12:
+            # don't attach New Year midnight to other months
             new_year_midnight = False
         else:
             new_year_midnight = True
@@ -1228,16 +1241,10 @@ def _mip_table_requested_bounds(bounds):
 
 def _setup_time_constraint(date_time, with_new_year_midnight=True):
     def time_constraint(cell):
-        """Runs only if with_new_year_midnight evaluates to True. Checks the current cell point and confirms if it
-        signifies a new year (e.g. 1980-01-01) or a new month (e.g. 1980-04-01). If so, it returns that value and
-        ensures that the data point is kept, hence maintaining time contiguity between slices."""
-        new_month = PartialDateTime(date_time[0], date_time[1] + 1, 1, 0, 0, 0, 0) if len(date_time) > 1 else ""
         return (PartialDateTime(*date_time) == cell.point or
-                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point or
-                new_month == cell.point)
+                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point)
 
     def time_constraint2(cell):
-        # Returns the original input cell point if with_new_year_midnight evaluates to false.
         return PartialDateTime(*date_time) == cell.point
 
     return time_constraint if with_new_year_midnight else time_constraint2
diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index b9007455c..312ecd009 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -38,6 +38,7 @@
 from mip_convert import mip_parser
 import mip_convert.common
 from mip_convert.common import RelativePathChecker
+from mip_convert.save import create_cmor_variable
 from mip_convert.save.mip_config import MipTableFactory
 
 
@@ -301,6 +302,17 @@ def _optional_kwargs(self, variable):
             kwargs['comment'] = self._name_space.namespace_stamp(variable.comment)
         return kwargs
 
+    def apply_cell_measures(self, mip_output_variable, *cell_measures_config):
+        """Apply cell measures to this CMOR variable.
+
+        Ensures the CMOR variable ID exists (creating it if needed), then
+        sets the cell_measures attribute via the CMOR wrapper.
+        """
+        if self.varid is None:
+            cmor_variable = create_cmor_variable(mip_output_variable)
+            self._getVarId(cmor_variable)
+            self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
+
     def _close_file(self):
         self.cmor.close(self.varid, preserve=True)
 

From 34cb06211649ad7606b692d28fcf5e282c00188b Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Wed, 10 Jun 2026 13:29:25 +0000
Subject: [PATCH 13/16] #886: Revert changes brought in by mistake.

---
 mip_convert/mip_convert/new_variable.py       | 33 ++++++++-----------
 .../mip_convert/save/cmor/cmor_outputter.py   | 12 -------
 2 files changed, 13 insertions(+), 32 deletions(-)

diff --git a/mip_convert/mip_convert/new_variable.py b/mip_convert/mip_convert/new_variable.py
index e6fa2682a..d82e385e2 100644
--- a/mip_convert/mip_convert/new_variable.py
+++ b/mip_convert/mip_convert/new_variable.py
@@ -1,4 +1,4 @@
-# (C) British Crown Copyright 2015-2025, Met Office.
+# (C) British Crown Copyright 2015-2026, Met Office.
 # Please see LICENSE.md for license details.
 # pylint: disable=no-member, eval-used, wildcard-import
 # pylint: disable=unused-wildcard-import
@@ -231,7 +231,7 @@ def slices_over(self, period):
                 # Slice the 'input variable(s)', since they have not yet been processed.
                 message = '-'.join([str(items) for items in date_time])
                 self.logger.debug('Creating data for "{}"'.format(message))
-                sliced_input_variables = self._slice_input_variables(date_time)
+                sliced_input_variables = self._slice_input_variables(date_time, date_times)
                 yield Variable(sliced_input_variables, self._variable_metadata)
             else:
                 # Slice the 'MIP output variable'.
@@ -337,7 +337,7 @@ def ordered_coords(self):
 
         return self._ordered_coords
 
-    def process(self, saver=None, cell_measures_config=None):
+    def process(self):
         """Process the data.
 
         The units of the data of the |MIP requested variable| are the
@@ -367,19 +367,6 @@ def process(self, saver=None, cell_measures_config=None):
             self._update_time_units()
         if hasattr(self.model_to_mip_mapping, 'valid_min'):
             self._apply_valid_min_correction()
-        if saver is not None and cell_measures_config is not None:
-            self.apply_cell_measures(saver, cell_measures_config)
-
-    def apply_cell_measures(self, saver, cell_measures_config):
-        """Apply cell measures to the CMOR variable if not already applied.        Parameters
-        ----------
-        saver:
-            The CMOR outputter for this variable.
-        cell_measures_config: tuple
-            Arguments forwarded to cmor_wrapper.apply_cell_measures,
-            in the form (mip_era, mip_table_dir, realm, variable, frequency, region).
-        """
-        saver.apply_cell_measures(self, *cell_measures_config)
 
     def _remove_alevhalf_bounds(self):
         """
@@ -857,10 +844,10 @@ def _data_dimension(self, coord, axis_direction):
             raise ValueError(message)
         return data_dimension
 
-    def _slice_input_variables(self, date_time):
+    def _slice_input_variables(self, date_time, date_times):
         input_variables = {}
-        if len(date_time) > 1 and date_time[1] != 12:
-            # don't attach New Year midnight to other months
+        if (len(date_time) > 1 and date_time[1] != 12) and date_time != date_times[-1]:
+            # don't attach New Year midnight to months that are not december or the final chunk in the slice,
             new_year_midnight = False
         else:
             new_year_midnight = True
@@ -1241,10 +1228,16 @@ def _mip_table_requested_bounds(bounds):
 
 def _setup_time_constraint(date_time, with_new_year_midnight=True):
     def time_constraint(cell):
+        """Runs only if with_new_year_midnight evaluates to True. Checks the current cell point and confirms if it
+        signifies a new year (e.g. 1980-01-01) or a new month (e.g. 1980-04-01). If so, it returns that value and
+        ensures that the data point is kept, hence maintaining time contiguity between slices."""
+        new_month = PartialDateTime(date_time[0], date_time[1] + 1, 1, 0, 0, 0, 0) if len(date_time) > 1 else ""
         return (PartialDateTime(*date_time) == cell.point or
-                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point)
+                PartialDateTime(date_time[0] + 1, 1, 1, 0, 0, 0, 0) == cell.point or
+                new_month == cell.point)
 
     def time_constraint2(cell):
+        # Returns the original input cell point if with_new_year_midnight evaluates to false.
         return PartialDateTime(*date_time) == cell.point
 
     return time_constraint if with_new_year_midnight else time_constraint2
diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index 312ecd009..b9007455c 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -38,7 +38,6 @@
 from mip_convert import mip_parser
 import mip_convert.common
 from mip_convert.common import RelativePathChecker
-from mip_convert.save import create_cmor_variable
 from mip_convert.save.mip_config import MipTableFactory
 
 
@@ -302,17 +301,6 @@ def _optional_kwargs(self, variable):
             kwargs['comment'] = self._name_space.namespace_stamp(variable.comment)
         return kwargs
 
-    def apply_cell_measures(self, mip_output_variable, *cell_measures_config):
-        """Apply cell measures to this CMOR variable.
-
-        Ensures the CMOR variable ID exists (creating it if needed), then
-        sets the cell_measures attribute via the CMOR wrapper.
-        """
-        if self.varid is None:
-            cmor_variable = create_cmor_variable(mip_output_variable)
-            self._getVarId(cmor_variable)
-            self.cmor.apply_cell_measures(*cell_measures_config, self.varid)
-
     def _close_file(self):
         self.cmor.close(self.varid, preserve=True)
 

From fed70745080c27e6aa2a4ebc51191a80e83cf248 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Thu, 11 Jun 2026 08:54:17 +0000
Subject: [PATCH 14/16] #886: Implementation using save.

---
 mip_convert/mip_convert/requested_variables.py    | 8 +++-----
 mip_convert/mip_convert/save/__init__.py          | 9 ++++++++-
 mip_convert/mip_convert/save/cmor/cmor_wrapper.py | 2 +-
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index c6c7b52c9..0781a7b10 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -125,15 +125,13 @@ def produce_mip_requested_variable(
     if frequency:
         saver.cmor.set_frequency(frequency)
 
-    # Apply cell_measures if a <mip_era>_cell_measures.json file exists
-    saver.cmor.apply_cell_measures(
+    cell_measures_config = (
         user_config.mip_era,
         user_config.inpath,
         mip_table.id,
         variable_name,
         frequency,
-        user_config.global_attributes.get('region', ''),
-        saver.varid)
+        user_config.global_attributes.get('region', ''))
 
     # Process the data by performing the appropriate 'model to MIP mapping', then save the 'MIP output variable'
     # to an 'output netCDF file'.
@@ -141,7 +139,7 @@ def produce_mip_requested_variable(
     for time_slice in variable.slices_over(period):
         time_slice.process()
         logger.debug('MIP output variable contains: {}'.format(time_slice.info))
-        save(time_slice, saver)
+        save(time_slice, saver, cell_measures_config=cell_measures_config)
 
     # Close the 'output netCDF file'.
     cmor_lite.close(saver.varid)
diff --git a/mip_convert/mip_convert/save/__init__.py b/mip_convert/mip_convert/save/__init__.py
index e5127823a..6aa56d34c 100644
--- a/mip_convert/mip_convert/save/__init__.py
+++ b/mip_convert/mip_convert/save/__init__.py
@@ -19,7 +19,7 @@
                                   make_masked)
 
 
-def save(mip_output_variable, saver):
+def save(mip_output_variable, saver, cell_measures_config=None):
     """Save the |MIP output variable| to an |output netCDF file|
     using |CMOR|.
 
@@ -41,10 +41,17 @@ def save(mip_output_variable, saver):
         The |MIP output variable|.
     saver: callable
         A function with the signature ``function(object)``
+    cell_measures_config: tuple, optional
+        Arguments for :meth:`cmor_wrapper.apply_cell_measures` (excluding
+        ``variable_id``).  When provided, cell measures are applied once,
+        after the CMOR variable is registered but before data is written.
     """
     logger = logging.getLogger(__name__)
     logger.debug('Saving MIP output variable to an output netCDF file')
     cmor_variable = create_cmor_variable(mip_output_variable)
+    if cell_measures_config is not None and saver.varid is None:
+        saver._getVarId(cmor_variable)
+        saver.cmor.apply_cell_measures(*cell_measures_config, saver.varid)
     saver(cmor_variable)
 
 
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index a1dbb372c..1e437d760 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -119,10 +119,10 @@ def set_frequency(self, frequency, **kwargs):
         cmor.cmor.set_cur_dataset_attribute('frequency', frequency)
 
     def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
-        # self._debug_on_args('apply_cell_measures', [mip_table_dir])
         """
         Add cell measures read from json file in with mip tables
         """
+        self._debug_on_args('apply_cell_measures', [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {})
 
         cell_measures_file = os.path.join(mip_table_dir, f'{mip_era}_cell_measures.json')
 

From a01acf21288851573598299f635da4d2a784ff1a Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Thu, 11 Jun 2026 11:34:07 +0000
Subject: [PATCH 15/16] #886: Update functional tests and KGO data to new
 versions.

---
 .../test_functional_cmip7/test_cmip7_fx_rootd_ti_u_hxy_lnd.py   | 2 +-
 .../test_cmip7_fx_slthick_ti_sl_hxy_lnd.py                      | 2 +-
 .../test_functional_cmip7/test_cmip7_mon_mcd_tavg-alh-hxy-u.py  | 2 +-
 .../test_functional_cmip7/test_cmip7_mon_uas_tavg_h10m_hxy_u.py | 2 +-
 .../test_cmip7_rlucs4co2_tavg-alh-hxy-u.py                      | 2 +-
 5 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_rootd_ti_u_hxy_lnd.py b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_rootd_ti_u_hxy_lnd.py
index 83c556a28..b77ba29cd 100644
--- a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_rootd_ti_u_hxy_lnd.py
+++ b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_rootd_ti_u_hxy_lnd.py
@@ -44,7 +44,7 @@ def get_test_data(self):
                     'ancil': {'CMIP7_land@fx': 'rootd_ti-u-hxy-lnd'}
                 },
                 other={
-                    'reference_version': 'v5',
+                    'reference_version': 'v6',
                     'filenames': ['rootd_ti-u-hxy-lnd_fx_glb_g100_UKESM1-3-LL_1pctCO2_r1i1p1f3.nc'],
                     'ignore_history': True,
                 }
diff --git a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_slthick_ti_sl_hxy_lnd.py b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_slthick_ti_sl_hxy_lnd.py
index 2d2a69443..5d8d774ba 100644
--- a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_slthick_ti_sl_hxy_lnd.py
+++ b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_fx_slthick_ti_sl_hxy_lnd.py
@@ -44,7 +44,7 @@ def get_test_data(self):
                     'ancil': {'CMIP7_land@fx': 'slthick_ti-sl-hxy-lnd'}
                 },
                 other={
-                    'reference_version': 'v5',
+                    'reference_version': 'v6',
                     'filenames': ['slthick_ti-sl-hxy-lnd_fx_glb_g100_UKESM1-3-LL_1pctCO2_r1i1p1f3.nc'],
                     'ignore_history': True,
                 }
diff --git a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_mcd_tavg-alh-hxy-u.py b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_mcd_tavg-alh-hxy-u.py
index 25e6d279e..b1210d7fa 100644
--- a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_mcd_tavg-alh-hxy-u.py
+++ b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_mcd_tavg-alh-hxy-u.py
@@ -41,7 +41,7 @@ def get_test_data(self):
                     'ap5': {'CMIP7_atmos@mon': 'mcd_tavg-alh-hxy-u'}
                 },
                 other={
-                    'reference_version': 'v3',
+                    'reference_version': 'v4',
                     'filenames': ['mcd_tavg-alh-hxy-u_mon_glb_g100_UKESM1-3-LL_1pctCO2_r1i1p1f3_200001-200002.nc'],
                     'ignore_history': True,
                 }
diff --git a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_uas_tavg_h10m_hxy_u.py b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_uas_tavg_h10m_hxy_u.py
index b28c9ec8a..95b4bcec4 100644
--- a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_uas_tavg_h10m_hxy_u.py
+++ b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_mon_uas_tavg_h10m_hxy_u.py
@@ -41,7 +41,7 @@ def get_test_data(self):
                     'ap5': {'CMIP7_atmos@mon': 'uas_tavg-h10m-hxy-u'}
                 },
                 other={
-                    'reference_version': 'v7',
+                    'reference_version': 'v8',
                     'filenames': ['uas_tavg-h10m-hxy-u_mon_glb_g100_UKESM1-3-LL_1pctCO2_r1i1p1f3_196002-196003.nc'],
                     'ignore_history': True,
                 }
diff --git a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_rlucs4co2_tavg-alh-hxy-u.py b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_rlucs4co2_tavg-alh-hxy-u.py
index e298cbebf..c957f02cf 100644
--- a/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_rlucs4co2_tavg-alh-hxy-u.py
+++ b/mip_convert/mip_convert/tests/test_functional/test_functional_cmip7/test_cmip7_rlucs4co2_tavg-alh-hxy-u.py
@@ -47,7 +47,7 @@ def get_test_data(self):
                 },
                 streams={"ap5": {"CMIP7_atmos@mon": "rlucs4co2_tavg-alh-hxy-u"}},
                 other={
-                    "reference_version": "v3",
+                    "reference_version": "v4",
                     "filenames": [
                         "rlucs4co2_tavg-alh-hxy-u_mon_glb_g100_UKESM1-3-LL_esm-piControl_r1i1p1f1_190001-190002.nc"
                     ],

From 190545bd8b93cb2f37b3cd8b3daf7b9b73dea274 Mon Sep 17 00:00:00 2001
From: mo-gill <edward.gillett@metoffice.gov.uk>
Date: Thu, 11 Jun 2026 12:26:19 +0000
Subject: [PATCH 16/16] #886: Enhance docstrings, typing and formatting.

---
 .../mip_convert/requested_variables.py        |  1 +
 mip_convert/mip_convert/save/__init__.py      |  8 ++++-
 .../mip_convert/save/cmor/cmor_outputter.py   |  3 +-
 .../mip_convert/save/cmor/cmor_wrapper.py     | 34 +++++++++++++++++--
 4 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/mip_convert/mip_convert/requested_variables.py b/mip_convert/mip_convert/requested_variables.py
index 0781a7b10..18f8fe3f7 100644
--- a/mip_convert/mip_convert/requested_variables.py
+++ b/mip_convert/mip_convert/requested_variables.py
@@ -125,6 +125,7 @@ def produce_mip_requested_variable(
     if frequency:
         saver.cmor.set_frequency(frequency)
 
+    # Assemble the arguments needed to apply cell measures when saving.
     cell_measures_config = (
         user_config.mip_era,
         user_config.inpath,
diff --git a/mip_convert/mip_convert/save/__init__.py b/mip_convert/mip_convert/save/__init__.py
index 6aa56d34c..08bcee2bb 100644
--- a/mip_convert/mip_convert/save/__init__.py
+++ b/mip_convert/mip_convert/save/__init__.py
@@ -6,6 +6,7 @@
 import copy
 import logging
 from operator import attrgetter
+from typing import Optional, Tuple
 
 import iris
 import numpy as np
@@ -14,12 +15,17 @@
     DEFAULT_FILL_VALUE, has_auxiliary_latitude_longitude, check_values_equal)
 from mip_convert.load.pp.pp_axis import (BoundedAxis, AxisHybridHeight,
                                          TimeSeriesSiteAxis, ReferenceTimeAxis)
+from mip_convert.save.cmor.cmor_outputter import AbstractCmorOutputter
 from mip_convert.variable import Variable as CMORVariable
 from mip_convert.variable import (CoordinateDomain, PolePoint, TripolarGrid,
                                   make_masked)
 
 
-def save(mip_output_variable, saver, cell_measures_config=None):
+def save(
+    mip_output_variable,
+    saver: AbstractCmorOutputter,
+    cell_measures_config: Optional[Tuple[str, str, str, str, Optional[str], str]] = None,
+):
     """Save the |MIP output variable| to an |output netCDF file|
     using |CMOR|.
 
diff --git a/mip_convert/mip_convert/save/cmor/cmor_outputter.py b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
index b9007455c..797267184 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_outputter.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_outputter.py
@@ -38,6 +38,7 @@
 from mip_convert import mip_parser
 import mip_convert.common
 from mip_convert.common import RelativePathChecker
+from mip_convert.save.cmor.cmor_wrapper import CmorWrapper
 from mip_convert.save.mip_config import MipTableFactory
 
 
@@ -219,7 +220,7 @@ class AbstractCmorOutputter(object):
     """
 
     def __init__(self, entry, cmor_wrapper):
-        self.cmor = cmor_wrapper
+        self.cmor: CmorWrapper = cmor_wrapper
         self.entry = entry
         self._name_space = MoNameSpace()
         self.varid = None
diff --git a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
index 1e437d760..32c2ae4c6 100644
--- a/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
+++ b/mip_convert/mip_convert/save/cmor/cmor_wrapper.py
@@ -119,10 +119,38 @@ def set_frequency(self, frequency, **kwargs):
         cmor.cmor.set_cur_dataset_attribute('frequency', frequency)
 
     def apply_cell_measures(self, mip_era, mip_table_dir, realm, variable, frequency, region, variable_id):
+        """Set the ``cell_measures`` attribute on a registered CMOR variable.
+
+        Looks up ``{mip_table_dir}/{mip_era}_cell_measures.json`` and, if a
+        matching entry is found, calls ``cmor.set_variable_attribute`` to
+        attach the cell-measures string to the variable before any data are
+        written.  If the file does not exist, or no matching key is found,
+        the method returns silently.
+
+        This method must be called after ``cmor.variable()`` has registered
+        the variable (so that ``variable_id`` is valid) and before
+        ``cmor.write()`` is called.
+
+        Parameters
+        ----------
+        mip_era: str
+            The MIP era (e.g. ``"CMIP7"``).
+        mip_table_dir: str
+            Directory containing the MIP tables and the cell-measures JSON.
+        realm: str
+            The MIP table identifier (e.g. ``"Amon"``).
+        variable: str
+            The variable name in ``{root_label}_{branding}`` form.
+        frequency: str or None
+            The output frequency (e.g. ``"mon"``).
+        region: str
+            The region string (e.g. ``""`` for global).
+        variable_id: int
+            The integer handle returned by ``cmor.variable()``.
         """
-        Add cell measures read from json file in with mip tables
-        """
-        self._debug_on_args('apply_cell_measures', [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {})
+        self._debug_on_args(
+            "apply_cell_measures", [mip_era, mip_table_dir, realm, variable, frequency, region, variable_id], {}
+        )
 
         cell_measures_file = os.path.join(mip_table_dir, f'{mip_era}_cell_measures.json')