Remove unnecessary netcdf variable attributes in favor of cf-compliant ones

[cbegeman]

As noted in E3SM-Project/polaris#727, Omega currently writes both Units and units as attributes but only the latter should be retained as it is the cf-compliant case.

e.g., ncinfo -v "time" output.nc:

<class 'netCDF4.Variable'>
float64 time(time)
    Description: time
    Name: time
    StdName: time
    Units: seconds since 0001-01-01 00:00:00
    ValidMax: 1e+20
    ValidMin: 0.0
    _FillValue: 9.969209968386869e+36
    calendar: noleap
    long_name: time
    name: time
    standard_name: time
    units: seconds since 0001-01-01 00:00:00
    valid_max: 1e+20
    valid_min: 0.0
unlimited dimensions: time
current shape = (3,)
filling on

[xylar]

I wonder if the redundant capitalized attributes in general are ones we should remove. _FillValues is definitely the exception.

[cbegeman]

Yes, I now see that many attributes are duplicated. The shorter list could be:

<class 'netCDF4.Variable'>
float64 time(time)
-    Description: time
-    Name: time
-    StdName: time
-    Units: seconds since 0001-01-01 00:00:00
-    ValidMax: 1e+20
-    ValidMin: 0.0
    _FillValue: 9.969209968386869e+36
    calendar: noleap
    long_name: time
    name: time
    standard_name: time
    units: seconds since 0001-01-01 00:00:00
    valid_max: 1e+20
    valid_min: 0.0
unlimited dimensions: time
current shape = (3,)
filling on

[xylar]

I think long_name and description are the same thing.

[cbegeman]

I was just looking into that. It looks like if additional description is needed, the attribute should be called comment. In this case, we wouldn't need it and description would be removed and not replaced by anything.