Deprecate copy field halo kernel

[Alistair Pirrie (mo-alistairp)]

PR Summary

Sci/Tech Reviewer: Mike Hobson (@mike-hobson)
Code Reviewer: Benjamin Went (@MetBenjaminWent)

This PR replaces copy_field_halo_kernel_mod.f90 with a temporary PSyKAl-lite script. This is documented in issue #334. The PSyKAl-lite script will search for the last clean halo and copy the field up to that point in a DoF-wise manner.

linked MetOffice/lfric_apps#471

is related to #334

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 Core rose-stem suite
• If required (e.g. API changes) I have also run the LFRic Apps test suite using this branch
• 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_core - deprecate_copy_field_halo_core/run1

Suite Information

Item	Value
Suite Name	deprecate_copy_field_halo_core/run1
Suite User	alistair.pirrie
Workflow Start	2026-04-30T12:54:16
Groups Run	developer

Dependency	Reference	Main Like
lfric_core	mo-alistairp/lfric_core@deprecate_copy_field_halo_kernel	False
SimSys_Scripts	MetOffice/SimSys_Scripts@cab3315	True

Task Information

✅ succeeded tasks - 390

Security Considerations

• I have reviewed my changes for potential security issues
• Sensitive data is properly handled (if applicable)
• Authentication and authorisation are properly implemented (if applicable)

Performance Impact

• Performance of the code has been considered and, if applicable, suitable performance measurements have been conducted

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)

Documentation

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

PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the TCD Team

Sci/Tech Review

• I understand this area of code and the changes being added
• The proposed changes correspond to the pull request description
• Documentation is sufficient (do documentation papers need updating)
• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
• Related Issues have been properly linked and addressed
• CLA compliance has been confirmed
• Code quality standards have been met
• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable

[Mike Hobson (mike-hobson)]

This all looks very straightforward. I just have one very minor query.

[Mike Hobson (mike-hobson)]

Apart from these lines and the declarations on line 760, 761, max_halo_depth_mesh and mesh don't appear to be used. Can they just be removed?

[Alistair Pirrie (mo-alistairp)]

Good spot, yes I think you're right. I'll remove it and check it hasn't affected anything

[Alistair Pirrie (mo-alistairp)]

I've re-run with the removal and it's still passing fine

[Mike Hobson (mike-hobson)]

I'm happy - onto BenW for code review...