Adds reading of omega HorzMesh from mesh iostream

[philipwjones]

Uses an input IOStream to read the input horizontal mesh variables. Mesh metadata have been added to the mesh class and are also read from this file. The same filename is used by Decomp. If the Decomp optional argument for a mesh file is supplied (eg in some unit test drivers), that value overrides the mesh stream filename. All physical mesh fields are defined for IO and are added to a field group HorzMeshIn. Some cleanup of the HorzMesh test driver is included to reduce test output and conform to omega code conventions. User and developer docs have been updated with these changes.

Checklist

• Documentation:
  • Design document has been generated and added to the docs
  • User's Guide has been updated
  • Developer's Guide has been updated
  • Documentation has been built locally and changes look as expected
• Linting
  • Pre-commit run locally
• Building
  • CMake build does not produce any new warnings from changes in this PR
• Testing
  • Add a comment to the PR titled Testing with the following:
    • Which machines CTest unit tests
      have been run on and indicate that are all passing.
    • The Polaris omega_pr test suite
      has passed, using the Polaris e3sm_submodules/Omega baseline
    • Document machine(s), compiler(s), and the build path(s) used for -p for both the baseline (Polaris e3sm_submodules/Omega) and the PR build
    • Indicate "All tests passed" or document failing tests
    • Document testing used to verify the changes including any tests that are added/modified/impacted.
    • Performance related PRs: Please include a relevant PACE experiment link documenting performance before and after.

Fixes #311
Fixes #395

[philipwjones]

Passes ctests on Perlmutter (CPU)

[xylar]

Thanks @philipwjones! I'll take a look ASAP.

[xylar]

I'm working on the Polaris side of supporting these changes in E3SM-Project/polaris#527. That's going to need some fixes in Polaris for the horizontal pressure gradient before it can be tested.

[xylar]

@philipwjones, this is excellent work! I've been able to make use of it in Polaris in E3SM-Project/polaris#544. It allows a major refactor where we split out the mesh and initial conditions into entirely separate files.

I did run into an issue that I'll comment on below.

[xylar]

@philipwjones and @brian-oneill, in the merry-go-round test, which may be the only current omega_pr test that has multiple vertical layers, I'm seeing:

[info] Omega using calendar type: No Leap
[info] Successfully read stream HorzMeshIn from file mesh.nc
[info] VertCoord: vertical dimension not found in mesh file, using NVertLayers = 1
[critical] [IOStream.cpp:682] Inconsistent length for dimension NVertLayers in stream InitialVertCoord
[critical] [Error.cpp:43] Omega aborting

This is on Frontier at:

/lustre/orion/cli115/scratch/xylar/polaris_0.7/frontier/test_20260418/omega-pr-split-mesh2/ocean/planar/merry_go_round/default/forward/5m_90s_limiter

in case it's helpful.

Looking at the code, it seems that VertCoord is mistakenly still trying to get its vertical dimension (and maybe all of its fields?) from the mesh file:

https://github.com/philipwjones/E3SM/blob/omega/add-mesh-stream/components/omega/src/ocn/VertCoord.cpp#L90-L119

not from the separate InitialVertCoord stream:
https://github.com/philipwjones/E3SM/blob/omega/add-mesh-stream/components/omega/configs/Default.yml#L95-L104

I don't know if this is something we want to address in this branch or leave for a follow-up PR. But I won't be able to fully test E3SM-Project/polaris#544 until it gets addressed.

[brian-oneill]

@xylar It's a minor change, but probably makes more sense to do it separately. I can code it up and create the PR today.

[xylar]

@brian-oneill, does is make sense to fold that into a broader fix for #391?