Triggered Lightning: Implement Layer Mean Temperature Plugins by Anzerkhan27 · Pull Request #2321 · metoppv/improver

Anzerkhan27 · 2026-03-03T15:10:30Z

This PR implements the mean layer temperature calculation step as part of the ongoing migration of the Helicopter-Triggered Lightning (GPP → EPP) workflow (eppuk_triggered_lightning).

The GPP implementation contained a single monolithic function calculate_layer_mean_temperature() which handled both the vertical layer extraction and the weighted mean calculation in one function. This PR introduces two IMPROVER-style plugins to replace this, following EPP conventions.

Two new plugins have been implemented:

1. `LayerExtractionAndInterpolation`

Extracts all UKV temperature model levels falling strictly between 2000 ft and 3000 ft (converted to metres).
Interpolates temperature at the exact 2000 ft and 3000 ft boundaries using iris.analysis.Linear().
Concatenates the interpolated boundaries with the extracted interior levels into a single cube.

2. `CalculateLayerMeanTemperature`

Takes the output of LayerExtractionAndInterpolation as input.
Computes the altitude-weighted mean temperature across the layer using a trapezoidal weighting scheme (thickness between levels as weights).
Returns a 2D Iris cube (projection_y_coordinate, projection_x_coordinate) with scalar coordinates forecast_period, forecast_reference_time, and time preserved from the input.
Output metadata uses standard_name="air_temperature" (CF convention) with units="K".

…-lightning-layer-mean-temperature-plugin

robertplatt-mo

@Anzerkhan27 I've requested a few changes the main comments being in layer_mean_temperature and probably the most time consuming being type hints which I understand improver style guide expects.

Generally it all looks pretty sensible though.

improver/temperature/layer_mean_temperature.py

robertplatt-mo · 2026-03-06T13:18:07Z

improver/temperature/layer_mean_temperature.py

+                            (base, interior, and top).
+        """
+        if bottom >= top:
+            raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")


Suggested change

raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")

raise ValueError(f"Bottom ({bottom} ft) must be less than top ({top} ft).")

change added

robertplatt-mo · 2026-03-06T13:20:09Z

improver/temperature/layer_mean_temperature.py

+from improver import BasePlugin
+
+
+class LayerExtractionAndInterpolation(BasePlugin):


I'm not keen on the name of this plugin. Firstly extract and interpolate feels like it does two things. Generally it's good if functionality can be explained as doing one thing. Extraction seems to me to be something we do in service of the more important interpolation. The name also doesn't communicate that the method is primarily a tool for temperature interpolation at layer boundaries. This makes the tool seem like it's generic when it surely is not.

How about BoundaryTemperatureInterpolation?

Or LayerTemperatureInterpolation or TemperatureInterpolationAtLayers?

I think you are correct, the main overarching thing the function does here is Interpolate temperature at given heights. The extraction depends upon the boundary arguments that we provide. So it make sense to rename the plugin to LayerTemperatureInterpolation

robertplatt-mo · 2026-03-06T13:27:00Z

improver/temperature/layer_mean_temperature.py

+        Extract and interpolate temperature values at layer boundaries.
+
+        Args:
+            temp_cube (iris.cube.Cube): Input temperature cube with a height coordinate.


Ryan has previously informed me that the way improver docs are generated we don't need type hints in the args as these can be dynamically generated for the types (for more info on this though probably best to ask him).

I noticed this and then subsequently noticed we haven't got any type hints. My understanding is the improver style guide has these as a requirement. Please consider this comment to apply to all docstrings and all methods (sorry I know it's a pain).

Type hints added to method signature

robertplatt-mo · 2026-03-06T13:28:05Z

improver/temperature/layer_mean_temperature.py

+            iris.Constraint(
+                height=lambda point: bottom / self.metres_to_ft
+                < point
+                < top / self.metres_to_ft


As noted above I don't think we should be passing this in (but please correct me if I'm mistaken and there is a good reason I am not aware of). I'd set it at the top of the file as a constant.

I have change it to a constant added at the top of file

robertplatt-mo · 2026-03-06T13:30:29Z

improver/temperature/layer_mean_temperature.py

+        if verbosity:
+            print("Layer mean temperature array:", lmt_array)
+
+        # Wrap result in a cube (add metadata as needed)


Suggested change

# Wrap result in a cube (add metadata as needed)

# Wrap result in a cube and add required metadata

As needed rather implies the user will choose what metadata is added imv

Thank you pointing this out. I have made the change

Anzerkhan27 · 2026-03-09T10:33:46Z

@Anzerkhan27 I've requested a few changes the main comments being in layer_mean_temperature and probably the most time consuming being type hints which I understand improver style guide expects.

Generally it all looks pretty sensible though.

Thank you @robertplatt-mo . I have added the METRES_TO_FT as a constant at top of the file rather than as an argument, changed the plugin name to reflect its main function. I have also added type hints in the method signature and removed it from the docstrings. Also added the small changes to the comments and Docstrings

improver/temperature/layer_mean_temperature.py

mo-DavidJohnJohnston · 2026-03-09T13:49:18Z

improver_tests/temperature/layer_mean_temperature/test_calculate_layer_mean_temperature.py

+    """
+    height_points = np.array([100, 200, 300], dtype=np.float32)
+    y_points = np.array([0, 1], dtype=np.float32)
+    x_points = np.array([0, 1], dtype=np.float32)


If lines 22-24 were customised to the shape of the input data, then
make_layer_cube would be more general. I think make_layer_cube
could be used in more places in the unit tests.

improver_tests/temperature/layer_mean_temperature/test_layer_temperature_interpolation.py

correct a docstring comment

mo-DavidJohnJohnston

Added an extra test after discussions with Anzer to check the mean layer temperature
when there is a varying temperature field. The existing check of the output value is for a
constant value fields.

to combat different versions of ruff

…yer-mean-temperature-plugin' into EPPT-2747-triggered-lightning-layer-mean-temperature-plugin

mo-DavidJohnJohnston

Changes discussed with Anzer have been made.

One extra unit test was needed to cover the case
when the temperature field is not constant.

I approve the PR.

gavinevans · 2026-03-11T08:03:08Z

improver/temperature/layer_mean_temperature.py

+
+from improver import BasePlugin
+
+METRES_TO_FT = 3.28084


Just a comment, to avoid this hardcoded conversion factor, you could use the cf_units package i.e. https://cf-units.readthedocs.io/en/latest/unit.html#cf_units.Unit.convert to handle the unit conversion, which we use elsewhere in IMPROVER.

Thank you for the comment @gavinevans. I added cf_units to handle unit conversion, it looks cleaner.

Anzerkhan27 · 2026-03-11T12:09:35Z

Changes discussed with Anzer have been made.

One extra unit test was needed to cover the case when the temperature field is not constant.

I approve the PR.

Thank your adding in the missing test and fixing docstrings

Resolved the requested changes

mo-DavidJohnJohnston

The latest change to use cf_units for conversion is an improvement.
I have not checked the unit tests this time, but I am assuming this is a
formality, and I approve the PR.

…emperature-plugin

Add layer extraction and interpolation plugin

bb0a3e1

Anzerkhan27 changed the title ~~Add layer extraction and interpolation plugin~~ Add Improver plugins to calculate Layer Mean temperature for Triggered Lightning Mar 3, 2026

Anzerkhan27 added 6 commits March 4, 2026 12:27

Add calculate layer mean temperature plugin

c4579b6

Add doctsrtings

67925e4

Add unit tests for layer extraction and interpolation

38b9321

Add unit test for CalculateLayerMeanTemperature plugin

8b2d3ce

Add unit tests for edge cases

3d198f7

Merge remote-tracking branch 'origin/master' into EPPT-2747-triggered…

0ca3d0c

…-lightning-layer-mean-temperature-plugin

Anzerkhan27 changed the title ~~Add Improver plugins to calculate Layer Mean temperature for Triggered Lightning~~ Triggered Lightning: Implement Layer Mean Temperature Plugins Mar 5, 2026

refactor: Test file renamed

9725faf

robertplatt-mo previously requested changes Mar 6, 2026

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refac: robert changes

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Anzerkhan27 requested a review from robertplatt-mo March 9, 2026 10:39

mo-DavidJohnJohnston reviewed Mar 9, 2026

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mo-DavidJohnJohnston added 2 commits March 10, 2026 08:42

added a missing unit test

aa8ea48

correct a docstring comment

corrected misalignment in docstring

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mo-DavidJohnJohnston previously approved these changes Mar 10, 2026

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change for ruff

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mo-DavidJohnJohnston dismissed their stale review via 2999b0b March 10, 2026 09:53

mo-DavidJohnJohnston added 6 commits March 10, 2026 10:14

change for ruff

4a882a7

change for ruff

b887204

change for ruff - bring back to original

8c0c4db

to combat different versions of ruff

add a noqa

96b63be

resolving ruff issue

a0dbfc4

revert to 6 out of 7 passes

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Anzerkhan27 and others added 4 commits March 10, 2026 16:23

add david in Contributing

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test to see if permissions are correct

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nominal chnage to test permissions

a4a93d3

Merge remote-tracking branch 'origin/EPPT-2747-triggered-lightning-la…

c24ac75

…yer-mean-temperature-plugin' into EPPT-2747-triggered-lightning-layer-mean-temperature-plugin

mo-DavidJohnJohnston previously approved these changes Mar 10, 2026

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gavinevans reviewed Mar 11, 2026

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cf_units used instead of hardcorded constant

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Anzerkhan27 dismissed mo-DavidJohnJohnston’s stale review via 35e8a8d March 11, 2026 12:28

mo-DavidJohnJohnston approved these changes Mar 11, 2026

View reviewed changes

Merge branch 'master' into EPPT-2747-triggered-lightning-layer-mean-t…

0e30978

…emperature-plugin

Anzerkhan27 merged commit 9a6e346 into master Mar 12, 2026
7 checks passed

gavinevans deleted the EPPT-2747-triggered-lightning-layer-mean-temperature-plugin branch March 13, 2026 10:52

gavinevans mentioned this pull request Mar 13, 2026

Remove David's name due to git merging behaviour #2330

Merged

2 tasks

	raise ValueError(f"bottom ({bottom} ft) must be less than top ({top} ft).")
	raise ValueError(f"Bottom ({bottom} ft) must be less than top ({top} ft).")

		from improver import BasePlugin


		class LayerExtractionAndInterpolation(BasePlugin):

	# Wrap result in a cube (add metadata as needed)
	# Wrap result in a cube and add required metadata

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Anzerkhan27 commented Mar 3, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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1. LayerExtractionAndInterpolation

2. CalculateLayerMeanTemperature

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Anzerkhan27 commented Mar 3, 2026 •

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1. `LayerExtractionAndInterpolation`

2. `CalculateLayerMeanTemperature`

robertplatt-mo Mar 6, 2026 •

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Anzerkhan27 Mar 9, 2026 •

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Anzerkhan27 commented Mar 9, 2026 •

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