🐛 Bug Report

I was trying to process LFRic output by loading several files into one CubeList. However, in the resulting dataset the cubes are not concatenated along the time coordinate, and are instead listed separately.

The time dimension is also not recognised as dimensional, which might be a related issue. Promoting it to the DimCoord class sometimes helps and sometimes does not, so it seems to be a bug (?).

I have tried comparing the cubes' metadata and the metadata of their coordinates - they are all identical. ncdump also shows no differences in the coordinate metadata.

When I force concatenation by using the concatenate_cube() method, I get this error:

ConcatenateError: failed to concatenate into a single cube.
  An unexpected problem prevented concatenation.

Note that this problem seems to occur for some LFRic runs but not others, and so far I cannot pinpoint the pattern. Could it be due to the number of files I try to load at once? (E.g. is 100 too many?)

How To Reproduce

Steps to reproduce the behaviour:

I have attached 2 files as an example concat_issue_lfric_diag.zip

For these two files, using concatenate(check_aux_coords=False) actually helps, but the issue with the time coordinate remains. I am happy to provide more LFRic data if needed.

Environment

• OS & Version: Ubuntu 22.04 LTS
• Iris Version: 3.7.0