lfric2lfric: Allow multiple meshes to be created and reorganise configs

[cjohnson-pi]

PR Summary

App tasks (e.g. lfric_atm) specify which mesh to run with (in the resolution setting). A mesh task is then created to create that mesh. But this only allows for one mesh to be created per app task. lfric2lfric requires 2 meshes, and so this PR allows for more multiple meshes to be created per task.

The lfric2lfric tasks are also reorganised so that there will be 3 main types of configuration file:

• rose-app-src_mesh_levels.conf (the source data e.g. data filename, mesh, vertical levels - all this info is kept together as the data will always be for a particular mesh and levels )
• rose-app-dst_mesh.conf (the destination mesh)
• rose-app-dst_levels.conf (the destination vertical levels - this is separate to the mesh as they are not necessarily together)

At the moment only horizontal regridding is applied, so there are no dst_levels configurations on this PR.

The reorganisation of the configs means that some of the fail-ifs in the rose-meta have needed to be removed so that the validate rose-meta task suceeds.

Sci/Tech Reviewer: Mike Hobson (@mike-hobson)
Code Reviewer: James Bruten (@james-bruten-mo)

This makes it a little easier to add new tasks, and avoids assumed dependencies on other tasks e.g. at the moment some lfric2lfric tasks are using meshes created by other tasks. This might cause failures if those meshes are not created in time or if the associated tasks are removed.

Single mesh (including multigrid) tasks (as current implementation):

{% do task_dict.update({
    "resolution": "C224_MG",

Multiple-mesh (double or more) tasks (new):

{% do task_dict.update({	
    "resolution": ["melbourne","C224"],

To enable this, the following files are changed.

rose-stem/templates/graph/populate_gen_weights_graph.cylc
• Lfric2lfric weight generation needs to use 2 meshes rather than 1.
• This is setup as:
build_mesh => run_mesh1 => run_mesh2 => generate_weights

rose-stem/templates/graph/populate_graph_sections.cylc
• Lfric2lfric regridding needs to use 2 meshes rather than 1.
• This is set up as:

build_mesh => run_mesh1
build_mesh => run_mesh2
build_application => run_application

(This assumes that building the application takes longer than building and creating the meshes, as also assumed currently).

rose-stem/templates/runtime/generate_runtime_application.cylc
• Remove adding the mesh .conf file to the lfric2lfric task options (its only needed to generate the meshes)

blocks #660
This is a small part split from #530

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• I have tested this change locally, using the LFRic Apps rose-stem suite
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
• I have added tests to cover new functionality as appropriate (e.g. system tests, unit tests, etc.)
• Any new tests have been assigned an appropriate amount of compute resource and have been allocated to an appropriate testing group (i.e. the developer tests are for jobs which use a small amount of compute resource and complete in a matter of minutes)

trac.log

Test Suite Results - lfric_apps - multiple_meshes/run5

Suite Information

Item	Value
Suite Name	multiple_meshes/run5
Suite User	christine.johnson
Workflow Start	2026-07-23T10:03:58
Groups Run	all

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.07.1	True
jules	MetOffice/jules@2026.07.1	True
lfric_apps	cjohnson-pi/lfric_apps@multiple_meshes	False
lfric_core	MetOffice/lfric_core@2026.07.1	True
moci	MetOffice/moci@2026.07.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True
socrates	MetOffice/socrates@2026.07.1	True
socrates-spectral	MetOffice/socrates-spectral@2026.07.1	True
ukca	MetOffice/ukca@2026.07.1	True

Task Information

✅ succeeded tasks - 1592

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Performance Impact

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AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

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• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

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Sci/Tech Review

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Code Review

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[github-actions]

⚠️ Hello cjohnson-pi!

Your CLA signature was found on the base branch, but you appear to have modified the CONTRIBUTORS.md file in this PR.

Please do not edit the CONTRIBUTORS.md file. If you have already signed the CLA, revert changes to the file and your signature will be picked up.

[Mike Hobson (mike-hobson)]

The ability to support providing multiple meshes to a task is definitely something we need. I'm no expert on how this should be done in the suites. James knows far more about this than I do and is the code reviewer, so I'll leave it to him to make any technical judgements.

When I added a coupling test to the Core test suite, this needed to use two meshes and James set this up for me. We should make sure that whatever the method used to specify two meshes is, it is consistent across all tasks that need it in Apps and Core repository test suites.

Over to James Bruten (@james-bruten-mo) for a proper review

[James Bruten (james-bruten-mo)]

Hi Christine,
This looks reasonable. For the populate_graph_sections file, could you have a look at doing it in the same way as we've done in core to help with maintainability. I've linked to the relevant changeset below.

For populate_gen_weights_graph, I think it does what you've described in the PR description. But I'm unclear why we need to wait for the first mesh to be built before building the 2nd one?

[James Bruten (james-bruten-mo)]

Suggested change

	{% if task_values["resolution"] is iterable and task_values["resolution"] is not string %}
	{% set resolutions = task_values["resolution"] %}
	{% else %}
	{% set resolutions = [task_values["resolution"]] %}
	{% endif %}
	{% if task_values["resolution"] is string %}
	{% set resolutions = [task_values["resolution"]] %}
	{% endif %}

I think you can simplify this by just checking whether it's a string

[cjohnson-pi]

Yes I could just check for a string. But I'll still need to have both parts, because sometimes its a string (for cases with 2 meshes) and sometimes its not (for cases with 1 mesh).

[James Bruten (james-bruten-mo)]

For this file, Mike and I did something very similar in lfric core a while ago. Could you look to do it in the same way here (I think they're functionally identical), so that the 2 files remain as similar as possible. The changeset for lfric_core is at MetOffice/lfric_core@03f9e4d#diff-239288cf861d4d3cf49db1b9cb5fb35fb70a23d90e4c7d9679df64e7c9b0df39

[cjohnson-pi]

Thanks for pointing me to that change. I will have a go at trying to align my changes with that.

[cjohnson-pi]

Hi Christine, This looks reasonable. For the populate_graph_sections file, could you have a look at doing it in the same way as we've done in core to help with maintainability. I've linked to the relevant changeset below.

For populate_gen_weights_graph, I think it does what you've described in the PR description. But I'm unclear why we need to wait for the first mesh to be built before building the 2nd one?

Many thanks for the review.

Ah you're right, we don't need to wait for the first mesh to be built before the second one. But the reason I did it like this is that both meshes need to have completed before the lfric2lfric task. And the logic for ( mesh1 and mesh2 and lfric2lfric build) => lfric2lfric seemed too complicated. So I decided the mesh1 => mesh2 => lfric2lfric would solve this requirement.