Adding fix for ORAS5

[jmalles]

Description

Fix for ORAS5. It includes the option to make the 'irregular' (2d) grid 'unstructured' (1d) and UGRID-compliant. To do so, one needs to add the extra facet 'make_unstructured: true' and/or 'ugrid: true' in the recipe.

The mesh description ('horizontal_grid' in the recipe) needs to be read from a file (oras5_mesh.zip), which is based on a file that can be downloaded here. Since ORAS5 data is on the ORCA025 (Arakawa-C grid), there are different mesh files for tracers (T), and zonal/meridional velocities (u/v).

An example recipe for ORAS5 can be found here.

Some already downloaded data are stored here:
/work/bd1083/b380216/extraobsraw/Tier2/ORAS5/single_level
/work/bd1083/b380216/extraobsraw/Tier2/ORAS5/all_levels
/work/bd1083/b382555/extraobsraw/Tier2/ORAS5/single_level
/work/bd1083/b382555/extraobsraw/Tier2/ORAS5/all_levels

(for 3D data in all_levels so far usually only short time periods are downloaded, due to their size)

The grid files are also stored on Levante:
/work/bd0854/b382555/extraobsraw/Tier2/ORAS5/grids

Link to documentation: https://esmvaltool--2422.org.readthedocs.build/projects/ESMValCore/en/2422/quickstart/find_data.html#oras5

---

Before you get started

• ☝ Create an issue to discuss what you are going to do

Checklist

It is the responsibility of the author to make sure the pull request is ready to review. The icons indicate whether the item will be subject to the 🛠 Technical or 🧪 Scientific review.

• 🧪 The new functionality is relevant and scientifically sound
• 🛠 This pull request has a descriptive title and labels
• 🛠 Code is written according to the code quality guidelines
• 🧪 and 🛠 Documentation is available
• 🛠 Unit tests have been added
• 🛠 Changes are backward compatible
• 🛠 Any changed dependencies have been added or removed correctly
• 🛠 The list of authors is up to date
• 🛠 All checks below this pull request were successful

---

To help with the number pull requests:

• 🙏 We kindly ask you to review two other open pull requests in this repository

[codecov]

Codecov Report

❌ Patch coverage is 93.25843% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 95.53%. Comparing base (f7d004d) to head (9f61cb4).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
esmvalcore/cmor/_fixes/native6/oras5.py	93.25%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2422      +/-   ##
==========================================
- Coverage   95.55%   95.53%   -0.03%     
==========================================
  Files         263      264       +1     
  Lines       15508    15686     +178     
==========================================
+ Hits        14819    14985     +166     
- Misses        689      701      +12     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[bettina-gier]

Tried with the example recipe and it looks good, output seems as expected. Fast look through the code looks good. I'll do a more detailed review when I have more time.

[schlunma]

Hi @jmalles, thanks for contributing!

To start the review process and finalize this, we need tests (see e.g., here) and some documentation (see e.g, here). Thanks!!

[schlunma]

Hello, this pull request has been marked with the v2.14.0 milestone. The release of version 2.14.0 is currently scheduled for February 2026. To get this into the new release, it would be great to get this merged by the end of January.

If you won't be able to finish this in time, don't worry - just unassign the milestone v2.14.0. If you need any support, ping myself (@schlunma; the release manager for v2.14.0) or the @ESMValGroup/technical-lead-development-team. Please note that I won't be available until the beginning of February, though.

[schlunma]

I am sorry, it looks like this pull request won't make it into v2.14.0. If there are strong objections, please let me know. Moving this to v2.15.0.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 3 committers have signed the CLA.

✅ katjaweigel
❌ Jan-Hendrik Malles
❌ jmalles

---

Jan-Hendrik Malles seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[rbeucher]

Hi all, a quick note for the ESMValCore v2.15.0 release: the planned code freeze date is 19 June 2026.

This PR is currently included in the v2.15.0 milestone. Could you please confirm whether it is still intended for this release and what needs to happen before it can be merged?

@flicj191 tagging you for release planning visibility.