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.

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 and orography_order=2 as default for the gungho_model, lfric_atm, linear_model and jedi_lfric_tests apps (which updates KGOs)

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

Important Links:
This branch is built on top of two other PRs. To see the changes just for this PR, please see here: https://github.com/tommbendall/lfric_apps/pull/2/changes

There is also a test branch which shows the KGO changes and action of the upgrade macro. To see the changes in that test branch, please see here: https://github.com/tommbendall/lfric_apps/pull/3/changes

Blocked By:

• Allow different meshes to have different maximum halo depths #174
• New function space options for coordinate fields #179

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

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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)

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
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• Security considerations have been addressed
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