Enable variable precision checkpoint-restart files

[iboutle]

PR Summary

Sci/Tech Reviewer: Harry Shepherd (@harry-shepherd)
Code Reviewer: Ricky Wong (@mo-rickywong)

Currently, checkpoint-restart files are forced to be double-precision, by the setting of prec="8" in various xml files. Typically, we run the model at single-precision, and therefore are writing checkpoint-restart files which are double the size they need to be.

These PRs fix this, by removing the precision from the xml file specification, and setting it instead via the model-xios interface depending on the precision of the model.

They also provide some preparatory work required for packing of diagnostics, namely removing the precision specification from diagnostic files, instead specifying the precision in the diagnostics definition. In future this will allow packed prec="2" diagnostics to be added, without their precision being over-ridden by the prec specification of the diagnostic files.

• linked Enable variable precision checkpoint-restart files lfric_core#456

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 - spdump/run1

Suite Information

Item	Value
Suite Name	spdump/run1
Suite User	ian.boutle
Workflow Start	2026-08-27T13:10:13
Groups Run	developer', 'lfric_atm_extra', 'lfric_atm_weekly

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.07.1	True
jules	MetOffice/jules@2026.07.1	True
lfric_apps	iboutle/lfric_apps@spdump	False
lfric_core	iboutle/lfric_core@spdump_core	True
moci	MetOffice/moci@2026.07.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@77a5166	True
socrates	MetOffice/socrates@2026.07.1	True
socrates-spectral	MetOffice/socrates-spectral@2026.07.1	True
ukca	MetOffice/ukca@9fc2b6d	True

Task Information

✅ succeeded tasks - 1431

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 HPC Optimisation Team

Sci/Tech Review

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• 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
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• Tests are adequate and have passed
• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable