Hygroscopicity MS11 ratio option

[Joe Carton-Kelly (JoeCartonKelly-MO)]

PR Summary

Sci/Tech Reviewer: mo-dangrosvenor
Code Reviewer: Pierre Siddall (@Pierre-siddall)

This change impacts Glomap mode setup 11 (SOL/INSOL). In this PR we make it so that users can, via a rose namelist (there is an attached UM PR below), redistribute the sulphate aerosol into its 4 actual species (sulphate, sea salt, black carbon and organic carbon) within the hygroscopicity calculations. We found that when treating everything as sulphate, in environments when sulphate is not the dominant aerosol, we saw too much hygroscopic growth from our aerosols and by having this option we allow users to get a better reflection of the growth of the area they are modelling. I am going to attach some figures showing the impact that this change can have on aerosol optical depth further down - linked MetOffice/um#70 and MetOffice/um_doc#16 - closes #29

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

• I have tested this change locally, using the UKCA 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.)

I have run Mohit's um14.1 rigorous test (a copy of suite dx-502) with the trac.log printed below. I have run umdp3_checker on UKCA and ran the fixer to make it all okay. I will show a full UM solinsol rose-stem-test where I have changed the value to show that kgo fails in this case and one where I haven't to show that it doesn't when given default values.

trac.log

|| Suite Name: || '''u-dy599/run4''' ||
|| Suite Owner: || joseph.cartonkelly ||
|| Report Generated: || 2026/04/15 11:06:23 ||
|| Cylc-Review: || https://cylchub/services/cylc-review/taskjobs/joseph.cartonkelly/?suite=u-dy599/run4 ||
|| ''ROSE_ORIG_HOST:'' || cazldf0000F3.spice.sc.metoffice.gov.uk ||

|| '''Task''' || '''State''' ||
|| atmos_cristrat_16x8 || succeeded ||
|| atmos_cristrat_16x8_2omp || succeeded ||
|| atmos_cristrat_col_16x8 || succeeded ||
|| atmos_cristrat_col_8x12 || succeeded ||
|| atmos_cristrat_crun || succeeded ||
|| atmos_cristrat_nrun || succeeded ||
|| atmos_cristrat_rigorous_16x8 || succeeded ||
|| atmos_offl_16x8 || succeeded ||
|| atmos_offl_8x12 || succeeded ||
|| atmos_strat_16x8 || succeeded ||
|| atmos_strat_16x8_2omp || succeeded ||
|| atmos_strat_col_16x8 || succeeded ||
|| atmos_strat_col_8x12 || succeeded ||
|| atmos_strat_crun || succeeded ||
|| atmos_strat_nrun || succeeded ||
|| atmos_strat_rigorous_16x8 || succeeded ||
|| extract || succeeded ||
|| fcm_make || succeeded ||
|| fcm_make_rigorous || succeeded ||
|| housekeep_cririgor || succeeded ||
|| housekeep_cristrat || succeeded ||
|| housekeep_offl || succeeded ||
|| housekeep_rigor || succeeded ||
|| housekeep_strat || succeeded ||
|| recon_cristrat || succeeded ||
|| recon_cristrat_rigorous || succeeded ||
|| recon_offl || succeeded ||
|| recon_strat || succeeded ||
|| recon_strat_rigorous || succeeded ||
|| rose_ana_cristrat_atmos_kgo || succeeded ||
|| rose_ana_cristrat_atmos_nruncrun || succeeded ||
|| rose_ana_cristrat_atmos_omp || succeeded ||
|| rose_ana_cristrat_col_atmos_proc || succeeded ||
|| rose_ana_offl_atmos_kgo || succeeded ||
|| rose_ana_offl_atmos_proc || succeeded ||
|| rose_ana_strat_atmos_kgo || succeeded ||
|| rose_ana_strat_atmos_nruncrun || succeeded ||
|| rose_ana_strat_atmos_omp || succeeded ||
|| rose_ana_strat_atmos_rigorous || succeeded ||
|| rose_ana_strat_col_atmos_kgo || succeeded ||
|| rose_ana_strat_col_atmos_proc || succeeded ||

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

[Joe Carton-Kelly (JoeCartonKelly-MO)]

For evidence of the science changes, I ran one version with the ratio as (1.0,0.0,0.0,0.0) which is the default and automatically passes kgo for any solinsol tests. I also ran a version with values set to (0.075,0.492,0.050,0.383). The images on the left are the default values and on the right are new values
Aitken soluble AOD 550nm:

Accumulation soluble AOD 550nm:

Coarse soluble AOD 550nm:

Accumulation insoluble AOD 550nm:

Coarse insoluble AOD 550nm:

You can see a large reduction in AOD for the soluble species when we don't treat everything as Sulphate (a more physically realistic set up) so this change allows us better control over hygroscopic growth in mode setup 11 (SOL/INSOL)

[mo-dangrosvenor]

Is this correct? Since mdcopy(:,imode,cp_su) will have been changed by the line above? Shouldn't you use the original md(:,imode,cp_su) arrays to calculate mdcopy, instead of using mdcopy itself?

[Joe Carton-Kelly (JoeCartonKelly-MO)]

Yes this is a very good point. You are correct that by using mdcopy throughout we are making everything much smaller as we are compounding the changes. I am addressing this in the next commit and will rerun tests after I have addressed all your comments

[mo-dangrosvenor]

It looks like there is no equivalent to this for cp_bc? If not, then there doesn't seem much point in adding in cp_bc since it is never used? Also, why do you only use the new md values for the concentration (cl) calculations and not in the rest of the routine that also uses md?

[Joe Carton-Kelly (JoeCartonKelly-MO)]

You are correct that cp_bc is never used. I think its important to have an input for black carbon so that we are taking percentages across the 4 species (sulphate, sea salt, organic carbon and black carbon) however there is no need to actually include it in this script. My logic was to keep everything in, even if it isn't used to show consistency but I will remove the bc stuff as you are correct it doesn't need to actually be in this script.

[mo-dangrosvenor]

My above point was also asking why you don't use the updated md values in the rest of the routine. Here for example. Shouldn't you be using mdcopy here and throughout the rest of the routine? You could just replace md with mdcopy? Or preserve mdcopy as the original values and then only update md perhaps?

[Joe Carton-Kelly (JoeCartonKelly-MO)]

Hi Dan,

I did this change with Anthony Jones so I'm going to speak to him soon to verify the reasoning but I believe the reason why we created mdcopy is that we only wanted to affect cl (ion concentration) as this would only affect the hygroscopic growth of particles and make them grow more slowly (we saw particles grow too fast in environments where there wouldn't normally be much sulphate - in solinsol every soluble aerosol is treated as sulphate). This means that after line 426 (call for ukca_water_content...) we want to use the original all sulphate values.

Further, I only change md to mdcopy for variables that had one of cp_su,cp_oc or cp_cl to minimise the changes but I could easily change line 402 for example (one of the cp_nitrate ones) to include mdcopy as this wouldn't have an impact as nitrate isn't being factored into this