Higher-order Orography

[tommbendall]

PR Summary

Sci/Tech Reviewer: @atb1995
Code Reviewer:

This PR implements the capability to represent orography with higher-order finite elements. This allows the heights of cell centres to be match the values defined in the orography ancillary files, and avoids loss of power in the orography from the process of averaging from W3 to W0 points. This has shown a significant improvement in NWP scores.

Please See

This branch is built on the changes in #277 and #179, and until those PRs are merged, the diff on this PR will also include the changes from those branches. I have created PRs in my own fork to show useful diffs for reviewing:

• Diff for code changes in this PR
• Diff for test branch to show action of upgrade macro, and KGO changes

Linked-To

• there will need to be a linked JEDI-LFRic PR

Blocked-By

This branch includes the changes from #277 and #179, which are necessary to use the increased coordinate order efficiently.

• LFRic Core #284 and its linked ticket, LFRic Apps #277
• LFRic Core #284 and its linked ticket, LFRic Apps #179

Details

The changes in this PR can be summarised as:

1. Ensure that the surface_altitude field has a degree that is specified through a new namelist option (and is not inherited from element_order)
2. Reorganise orography namelist, to make this more coherent by:

• moving n_orog_smooth into the orography namelist from initialization
• moving w0_orography_mapping into the orography namelist and renaming it as w0_multigrid_mapping
• introducing the orography_order option

3. Set coord_order=2, orography_order=2 and w0_multigrid_mapping=.true. as default for the gungho_model, lfric_atm, lfric_coupled, linear_model and jedi_lfric_tests apps (which updates KGOs)
4. science/gungho/source/orography/assign_orography_field_mod.F90 is directly passed surface_altitude_w0. Previously the W3 field was passed in here, which meant that the mapping from W3 to W0 and a deep halo exchange were duplicated for setting the orography for both the prime and shifted meshes
5. science/gungho/source/orography/setup_orography_alg_mod.x90: this is the most significant coding change, as this file has been reorganised to ensure that:

• the surface_altitude_w0 field has the appropriate element order
• the restriction/prolongation to form the surface_altitude fields on other meshes is handled appropriately with the new option

Results

Plots from the gungho_model and lfric_atm test suites for the changes in this PR are shown in the following PDFs. The only significant difference comes in the gungho_model DCMIP mountain test, which shows that the mountain is now being resolved properly.

• gungho_model results
• lfric_atm results

The use of quadratic coordinate order has shown considerable improvement in NWP scores. For results, see:

• Winter DA trials
• Standard NWP case studies
• C64 AMIP

Some timing results are shown in the following table. The change to use coord_order=2 will increase costs for the calculation of the runtime constants, and parts of the timestep that use chi: map_physics_fields and the conversions between the W2 wind field and Cartesian components for transport, but this table shows that the increase in runtime is small (1-3% of timestepping cost) and should be acceptable for the level of scientific improvement.

timestepping	vn3.1: coord_space='Wchi', coord_order=1	#179: coord_space='Wtheta', coord_order=1	#180: coord_space'Wtheta', coord_order=2
UKV	312.62	312.38	324.05
C48 climate	333.72	335.41	343.26
C224	221.83	220.18	222.62
C896	416.21	413.34	419.47

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)

trac.log

Test Suite Results - lfric_apps - test_high_order_orog/run10

Suite Information

Item	Value
Suite Name	test_high_order_orog/run10
Suite User	thomas.bendall
Workflow Start	2026-03-14T11:53:06
Groups Run	all

Dependency	Reference	Main Like
casim	MetOffice/[email protected]	True
jules	MetOffice/[email protected]	True
lfric_apps	tommbendall/lfric_apps@TBendall/TestHighOrderOrog	False
lfric_core	tommbendall/lfric_core@TBendall/CoordSpace	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 - 1511

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

[github-actions]

⚠️ Hello @tommbendall!

Your CLA signature was found on the base branch, but you appear to have modified the CONTRIBUTORS.md file in this PR.

Please do not edit the CONTRIBUTORS.md file. If you have already signed the CLA, revert changes to the file and your signature will be picked up.