Coupled checkpoint restart

[iboutle]

PR Summary

Sci/Tech Reviewer: Dan Copsey (@DanCopsey)
Code Reviewer: Lottie Turner (@mo-lottieturner)

• Switch the coupled model to use xios2 (instead of 2.5)
• Add a coupled climate configuration in addition to the current NWP configuration
• Fig bug in previous merge whereby coupled checkpointing only works when stochastic physics is on
• Turn on nrun-crun comparison for climate jobs, including rose-stem changes to allow this to work

• linked XIOS2 coupled model lfric_core#464

• blocks Migrate to XIOS 3 #805

• blocks Convert checkpoint files from legacy domains to layered CF #782

• blocks Enable variable precision checkpoint-restart files #740

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 - cpl_ckp/run1

Suite Information

Item	Value
Suite Name	cpl_ckp/run1
Suite User	ian.boutle
Workflow Start	2026-09-14T15:30:14
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.07.1	True
jules	MetOffice/jules@2026.07.1	True
lfric_apps	iboutle/lfric_apps@cpl_ckp	False
lfric_core	iboutle/lfric_core@cpl_xios2	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 - 1225

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

• 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

[Dan Copsey (DanCopsey)]

Hi Ian,
Is the intention for this PR to also turn on stochastic physics in the coupled model rose-stem and also turn on checkpointing. i.e. also include these changes from my branch? Or do we include these in a separate PR?
Dan.

[iboutle]

Hi Ian, Is the intention for this PR to also turn on stochastic physics in the coupled model rose-stem and also turn on checkpointing. i.e. also include these changes from my branch? Or do we include these in a separate PR? Dan.

Sorry Dan, I should have explained what's going on better - it does do all of that.

The new clim_gc6 rose-stem test is a full coupled-climate setup (so includes stochastic physics), and the addition of "crun":2 to both of the coupled task makes them each split into 2 segments with a checkpoint-restart in between. It also includes a longer nrun to compare to, ensuring that the 2 cruns bit-compare with the long nrun.

[Dan Copsey (DanCopsey)]

Thanks for clearing that up Ian. Now that I have looked at the coupled rose-stem setup I see it all now. I approve and move this into code review.

[Dan Copsey (DanCopsey)]

I approve.

[James Bruten (james-bruten-mo)]

I've added a new commit preventing the crun coupled tasks from running before the build has finished

[James Bruten (james-bruten-mo)]

I'm happy with the rose-stem changes here

[Lottie Turner (mo-lottieturner)]

Hi Ian. A couple of comments:

• please make note when files are added as these will need to be added to $BIG_DATA_DIR
• A note on where these files are living currently is also appreciated, along with some sort of provenance.
• These new files will need to be approved by someone who knows what they're looking at (ie not me) - we can discuss who when you're back from leave

[Lottie Turner (mo-lottieturner)]

Where are these files living? In future please flag on the PR summary that there are files that need to be added to $BIG_DATA_DIR

[iboutle]

There are no new files - this is just a namelist update to enable the new coupled climate task to run, the files already exist in big_data_dir

[iboutle]

Just adding a note that this needs to be on main before #805

[iboutle]

And #782

[iboutle]

And also blocks #740