[James Manners (mo-jmanners)]

PR Summary

Add scheme to set Rayleigh scattering coefficients per k-term

Sci/Tech Reviewer: Dr Stephan Havemann (@Petzi1)
Code Reviewer:

Rayleigh scattering has a strong dependence on wavelength but we currently only apply a single coefficient for each band in the spectral file. Rayleigh coefficients are provided per sub-band in block 17 (for use with varying solar spectra), so are used here to give different Rayleigh coefficients for each major gas k-term.

The original band values for the Rayleigh coefficients are maintained to calculate the band averaged asymmetry. The extinction and scattering coefficients used for each k-term are then adjusted based on the sub-band Rayleigh coefficients.

• closes Application of Rayleigh scattering coefficients per k-term rather than per band #41

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.)

• There are some failures in the LFRic Apps tests that are unrelated to this change.

Socrates testing

[~/git/socrates_admin/examples](41_rayleigh %=):$ ./quick_tests 
Testing code compiled in /home/users/james.manners/git/socrates_admin/bin
---
Testing simple calls to the runes interface:
Matched gfortran output
OK
---
Testing the runes_nc driver using LFRic diagnostic input:
Matched SW output
Matched LW output
OK
---
Testing raw_input to convert column data into input files:
OK
---
Testing Cl_run_cdl for ICRCCM case 27 (LW) on AER profiles:
OK
---
Testing Cl_run_cdf on multiple profiles:
OK
---
Test Cl_run_cdf for CIRC case 6
(HadGEM, GA7, SES and 300/260 band spectral files):
OK
---
Testing pseudo-spherical geometry code:
Calculating zenith angles:  75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
OK
---
Testing photolysis and non-LTE code:
Mapping sub-bands to channels.
Matched gfortran output
OK
---
Test McICA code (create mcica_data file and run on CRM profile):
OK
---
Testing creation of aerosol properties for a spectral file:
Running scatter_90...
Running scatter_average_90...
Running prep_spec...
Matched gfortran12 output
OK
---
Testing generating and running with prescribed optical properties:
Running raw_input...
Running Cscatter... please wait...
Running Cscatter... please wait...
Running Cscatter_average...
Running Cscatter_average...
Running prep_opt_profile...
Running Cl_run_cdl...
All done.
OK
---
Testing Crun_mono to calculate radiances:
Matched ref output
OK
---
Testing Ccorr_k to generate correlated-k coefficients:
Matched gfortran12 output
OK
---
Testing flexchem chemistry:
Matched KGO output
OK
---
Testing CDL scripts:
OK
---
All passed.

UM trac.log

Test Suite Results - um - um_socrates41_rayleigh/run4

Suite Information

Item	Value
Suite Name	um_socrates41_rayleigh/run4
Suite User	james.manners
Workflow Start	2026-11-05T13:23:59
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@4a94869	True
jules	MetOffice/jules@1fbe60f	True
moci	MetOffice/moci@2026.07.1	True
mule	MetOffice/mule@2026.07.1	True
shumlib	MetOffice/shumlib@2026.07.1	True
socrates	mo-jmanners/socrates@41_rayleigh	True
SimSys_Scripts	MetOffice/SimSys_Scripts@393eddb	True
ukca	MetOffice/ukca@7be5459	True
um	mo-jmanners/um@451fa60	True
um_aux	MetOffice/um_aux@2026.07.1	True
um_meta	MetOffice/um_meta@2026.07.1	True

Approvals

Code Owners

• No UM Code Owners Required

Config Owners

No UM Config Owners Required

Task Information

✅ succeeded tasks - 895

LFRic trac.log

Test Suite Results - lfric_apps - lfric_apps_socrates41_rayleigh/run2

Suite Information

Item	Value
Suite Name	lfric_apps_socrates41_rayleigh/run2
Suite User	james.manners
Workflow Start	2026-10-07T10:46:34
Groups Run	developer

Dependency	Reference	Main Like
casim	MetOffice/casim@2026.07.1	True
jules	MetOffice/jules@2026.07.1	True
lfric_apps	mo-jmanners/lfric_apps@33c73a5	True
lfric_core	MetOffice/lfric_core@2026.07.2	True
moci	MetOffice/moci@2026.07.1	True
SimSys_Scripts	MetOffice/SimSys_Scripts@2026.07.1	True
socrates	mo-jmanners/socrates@41_rayleigh	True
socrates-spectral	MetOffice/socrates-spectral@2026.07.1	True
ukca	MetOffice/ukca@2026.07.1	True

Task Information

❌ failed tasks - 5

Task	State
run_coupled_interface_unit_tests_ex1a_gnu_64bit	failed
run_gungho_integration_tests_ex1a_gnu_64bit	failed
run_gungho_unit_tests_ex1a_gnu_64bit	failed
run_jedi_lfric_interface_integration_tests_ex1a_gnu_64bit	failed
run_jedi_lfric_tests_integration_tests_ex1a_cce_fast-debug-64bit	failed

✅ succeeded tasks - 1204

⌛ waiting tasks - 1

Task	State
housekeep_ex1a	waiting

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