Handle vertical levels generically

[jfrost-mo]

What problem does your feature request solve?

There are multiple kinds of vertical levels, such as pressure or model level. This is exacerbated in LFRic world, where we also have half_levels and full_levels, and the names are different. This prevents recipes that handle vertical levels from being model agnostic.

Describe the solution you'd like

We should have a lookup for the vertical coordinate in a cube, similar to the get_cube_yxcoordnames utility function. This will allow operators to correctly handle any cube without regard to the vertical levels. Then a single recipe and rose-edit entry can be added.

Describe alternatives you've considered

Pressure should probably be handled separately, at least in rose edit, as it would be more meaningful to select specific pressure values than for other levels.

[jwarner8]

I think there are only finite combinations of coordinate name for vertical levels. We also want to ensure operators understand 'pressure' coordinates, 'model level' coordinates, and 'height' coordinates appropriately as the way they interact with each will differ. I am going to create a fix for the LFRic 'pressure_levels' as a callback for now.

[jfrost-mo]

Do we know if there is a reason that LFRic outputs pressure_levels here, rather than the CF compliant pressure?

[jwarner8]

Do we know if there is a reason that LFRic outputs pressure_levels here, rather than the CF compliant pressure?

Possibly to make the distinction between a variable pressure and the coordinate itself. Though usually a variable would be more descriptive and be called 'air_pressure or surface_pressure

[jwarner8]

Anne comment on why 'pressure_levels' is used: "It was just what was used in the rose-stem lfric output file and is also consistent with the global lfric suite. So not particularly chosen by us. If you can work with pressure_levels, then I'd be in favour of going with that, as I'm keen to be as consistent with other practices as possible."