Parser is too strict with meta data.

[WillyChap]

I propose we switch to a convention like this, because the values are what is importnat and not the file metadata:

(ds_upper_air['latitude'] == ds_static.coords['latitude']).all()

the current system

ds_upper_air['latitude'].equals(ds_static.coords['latitude'])

throws an error if meta data is not preserved.

[yingkaisha]

@WillyChap I think if you merge two xr.datasets, their coordinates must be strictly equal, otherwise xarray will duplicate coordinate dims.