[paulfield2024]

PR Summary

** Fix a bug in the hail diagnostic **

Sci/Tech Reviewer: Paul Barrett (@paul-barrett)
Code Reviewer: James Bruten (@james-bruten-mo)

Added 2 limiters to the hail diagnostic. One to set the change of particle size to 0 if the size goes negative. The second is in the melting equation which just limits the delta temperature to positive values in the profile. This fixed the failure from PS48 that i was given.

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

Testing

• 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 - um - casim_hail_diagnostic/run4

Suite Information

Item	Value
Suite Name	casim_hail_diagnostic/run4
Suite User	paul.field
Workflow Start	2026-10-29T18:01:32
Groups Run	developer,casim

Dependency	Reference	Main Like
casim	paulfield2024/casim@casim_hail_diagnostic	True
jules	MetOffice/jules@main	True
moci	MetOffice/moci@main	True
mule	MetOffice/mule@main	True
shumlib	MetOffice/shumlib@main	True
socrates	MetOffice/socrates@main	True
SimSys_Scripts	MetOffice/SimSys_Scripts@main	True
ukca	MetOffice/ukca@main	True
um	paulfield2024/um@d7019a7	True
um_aux	MetOffice/um_aux@main	True
um_meta	MetOffice/um_meta@main	True

Approvals

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Task Information

✅ succeeded tasks - 979

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

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

[paulfield2024]

added trac.log now - all passed

[paulfield2024]

Hello James - thanks for picking this up.
I think i was able to make the casim branch and do the rose-stem off the latest main for um and casim from about an hour ago. Let me know if anything wrong!

[Paul Barrett (paul-barrett)]

not sure why Re could be negative - is this just sign convention for particles terminal velocity vs updraughts? Every other parameter must be postive?

[Paul Barrett (paul-barrett)]

why would Reynolds number be negative - is this just fixing some numerical errors, or is it when "fall"speed is upwards?

[Paul Barrett (paul-barrett)]

could just have an a .gt. 0. check before calling the mason_melt routine?

[paulfield2024]

yep - done that now in the elf4299 change. Moved the if out of mason_melting and into the loop that calls mason_melting.

The ensemble test still passes.

[paulfield2024]

updated the rose-stem trac.log with new branch. All passes still.

[Paul Barrett (paul-barrett)]

great, looks good to me

[Paul Barrett (paul-barrett)]

looks good to me, ready for CR James Bruten (@james-bruten-mo)

[Paul Barrett (paul-barrett)]

maintains style of the hail check (a .gt. 0.0), happy with that

[James Bruten (james-bruten-mo)]

The changes look sensible to me. I'll rerun the testing suites then get it on