[NOT FOR CHANGELOG; PR NOT IN MAIN] Add mappings for ocean variables

[jmalles]

Mappings for ICON-XPP ocean variables.

The sea ice variables (sithick/sic) will need adjustments in the fix, since they have an extra "lev" dimension that is not expected by CMOR. I posted one possible generic solution in the comments of #2699. Otherwise, the variables would need to fixed be individually.

Moreover, variables like mixed layer depth (mlotst) or sea surface height (zos) might have different names/definitions in different output files. I added mappings of what I considered to be reasonable defaults.

Does not close but helps to close #2694

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.13%. Comparing base (14d36a7) to head (73cd5e7).
Report is 8 commits behind head on icon-xpp.

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@@            Coverage Diff            @@
##           icon-xpp    #2702   +/-   ##
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  Coverage     95.13%   95.13%           
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  Files           257      257           
  Lines         15057    15057           
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  Hits          14324    14324           
  Misses          733      733           

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[schlunma]

I can't find sic in the CMOR tables, do you mean siconc? In this case, we can remove it from above and put it here (siconca, the sea ice concentration on the atm grid should stay above).

[jmalles]

I think sic was the short_name in CMIP5, hence it still worked in the recipe. If you think it should be the one from the atmosphere output anyways, the entry from the ocean variables could be deleted I suppose. Otherwise, it could be changed to siconc to accomodate for both ocean and atmosphere output.

[schlunma]

Since ICON uses the CMIP6 tables, I think siconc would be better here.

[schlunma]

The sea ice variables (sithick/sic) will need adjustments in the fix, since they have an extra "lev" dimension that is not expected by CMOR. I posted one possible generic solution in the comments of #2699. Otherwise, the variables would need to fixed be individually.

I thought about this more, and I guess there's a more or less safe way to do this in general. You could check if a dimensional coordinate lev with the exact format is in the cube and then remove it if necessary:

lev_coord = DimCoord(0.0, var_name="lev")
if cube.coords(lev_coord, dim_coords=True):
    slices = [slice(None)] * cube.ndim
    slices[cube.coord_dims(lev_coord)[0]] = 0
    cube = cube[tuple(slices)]
    cube.remove_coord(lev_coord)    

[jmalles]

duplication of key "siconc" in mapping: I remove the ocean mapping?

[schlunma]

Remove the siconc entry in the atmosphere part above. siconc is supposed to be the "Sea-Ice Area Percentage (Ocean Grid)", so I guess this should be derived from the ocean files.