Add support for monsoon 3

[t00sa]

PR Summary

Sci/Tech Reviewer: @james-bruten-mo
Code Reviewer: @r-sharp

This is based on the changes in trac ticket #779. It also enables github personal access tokens by default on monsoon and defines an additional EX1A_WEIGHTS group to prevent undefined parent errors when running the ex1a group on monsoon.

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)

Test suite also run on the monsoon 3 partition. Build tasks passed as expected, as did a number of model runs. Some test runs failed due to known problems with missing files in $BIG_DATA_DIR.

trac.log

Test Suite Results - lfric_apps - monsoon-branch/run1

Suite Information

Item	Value
Suite Name	monsoon-branch/run1
Suite User	sam.clarke
Workflow Start	2026-01-20T14:32:41
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/[email protected]	True
jules	MetOffice/[email protected]	True
lfric_apps	t00sa/lfric_apps@monsoon3-support	False
lfric_core	MetOffice/[email protected]	True
moci	MetOffice/[email protected]	True
SimSys_Scripts	MetOffice/[email protected]	True
socrates	MetOffice/[email protected]	True
socrates-spectral	MetOffice/[email protected]	True
ukca	MetOffice/[email protected]	True

Task Information

✅ succeeded tasks - 1106

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