[James Bruten (james-bruten-mo)]

PR Summary

Sci/Tech Reviewer:
Code Reviewer: Jenny Hickson (@jennyhickson)

#161 changed imogen kgo unexpectedly. The nightly testing has failed the kgo testing again, with the kgo consistently changing.
Switching to a noomp build fixes this issue, and matches the original kgo from before the update. I've run this a few times to be sure it isn't intermittent. This suggests some sort of race condition in the imogen code which will be investigated in slower time. Switching to noomp will not have a performance impact as only 1 thread was used previously.

Code Quality Checklist

(Some checks are automatically carried out via the CI pipeline)

• 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
• If editing rose-meta/jules-shared then have you supplied a linked UM and LFRic Apps PR?

Testing

• I have tested this change locally, using the JULES rose-stem suite
• If shared files have been modified, I have run the UM and LFRic Apps rose stem suites
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (eg. kgo changes)
• I have added tests to cover new functionality as appropriate (eg. system tests, unit tests, etc.)

trac.log

Test Suite Results - jules - imogen_noomp/run1

Suite Information

Item	Value
Suite Name	imogen_noomp/run1
Suite User	james.bruten
Workflow Start	2026-10-23T09:52:08
Groups Run	all

Dependency	Reference	Main Like
jules	james-bruten-mo/jules@imogen_kgo	False
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True

Task Information

✅ succeeded tasks - 676

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

Approvals

Please request all relevant approvals. See the CodeOwners.txt file for section owners.

Technical

• JULES Code Owner
• OpenMP
• River Routing
• Rose Stem
• Rose Metadata
• Upgrade Macros

Scientific

• Surface
• Hydrology
• Vegetation
• Veg3 RED Demography
• Biogeochemistry
• Biogenic fluxes
• Fire
• Lakes
• Evaluation
• Imogen

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

[Copilot]

🟢 Approval recommended

The runtime and workflow changes are consistent, no blocking issues remain, and the supplied full-suite results report 676 successful tasks.

No open issues 🎉

What changed in this PR

Switches IMOGEN rose-stem tests to the non-OpenMP build to address inconsistent known-good output comparisons observed after #161.

Changes:

• Aligns the IMOGEN runtime build selection and all four workflow dependencies to noomp.
• Restores the known-good output baseline to vn8.2.

File	Description
rose-stem/​include/​variables.cylc	Restores the vn8.2 comparison baseline.
rose-stem/​include/​meto/​runtime-ex1a-gfortran.cylc	Selects the non-OpenMP build for IMOGEN.
rose-stem/​include/​meto/​graph-ex1a-gfortran.cylc	Updates all four IMOGEN workflows to depend on the non-OpenMP build.

_{Review effort: Balanced}

[Jenny Hickson (jennyhickson)]

Tests also passed for me. Happy for this to go on.

[Jenny Hickson (jennyhickson)]

Thanks for opening #185 to further track this issue.