Add code for cloud-top height diagnostic

[Adrian Lock (Adrian-Lock)]

Add code for cloud-top height diagnostic, mirroring existing cloud-base height

PR Summary

Sci/Tech Reviewer: Paul Barrett (@paul-barrett) -->
Code Reviewer: Pierre Siddall (@Pierre-siddall)

Only difference in how this new cloud-top height diagnostic is treated compared to cloud-base height, is in setting cloud-free columns to missing data
cld_top_altitude(map_2d(1)) = rmdi
rather than "to beyond top of model" as is done for cloud base:
cld_base_altitude(map_2d(1)) = 1.1_r_def * &
z_asl_centre_of_levels(nlayers) * &
m_to_kfeet

As an example that the new diagnostic works, I've added it to the rose stem seukv job:

which can be compared with the cloud-base height diagnostic:

These are plotted using ngview which means the colour scale is unhelpful, because it doesn’t recognise missing data, but at least the cloud is in the right place (compared to the CBH) and the max of 32.3 kfeet is plausible.

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 - main905c_cth_diagnostic/run3

Suite Information

Item	Value
Suite Name	main905c_cth_diagnostic/run3
Suite User	adrian.lock
Workflow Start	2026-05-06T17:31:13
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.03.2	True
jules	MetOffice/jules@2026.03.2	True
lfric_apps	Adrian-Lock/lfric_apps@main905c_cth_diagnostic	False
lfric_core	MetOffice/lfric_core@3c8ccc6	True
moci	MetOffice/moci@2026.03.2	True
SimSys_Scripts	MetOffice/SimSys_Scripts@cab3315	True
socrates	MetOffice/socrates@2026.03.2	True
socrates-spectral	MetOffice/socrates-spectral@2026.03.2	True
ukca	MetOffice/ukca@1cdb9c2	True

Task Information

✅ succeeded tasks - 1185

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Performance Impact

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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)

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PSyclone Approval

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Sci/Tech Review

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• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

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• Security considerations have been addressed
• Performance impact is acceptable

[Paul Barrett (paul-barrett)]

seems fine, from the perspective of this one DIAG, but should we expand use of rmdi to other DIAGS in this (and other?) routine>

[Paul Barrett (paul-barrett)]

surprised to see this is the first instance of rmdi in this set of diags. Should we be extending this to be used in other output in a separate PR?

[Paul Barrett (paul-barrett)]

should this setting of data to missing be replicated elsewhere in this routine?
iboutle

[iboutle]

Yeah, possibly something to revisit in a separate PR - I can't remember what Cyril's reasoning was for doing it how he did originally!

[Pierre Siddall (Pierre-siddall)]

Thanks Adrian Lock (@Adrian-Lock), as this is a small change and the code of the added do loop looks fine , I'm happy to put this through testing.