[CF-metadata] cellmethods="lat: lon: mean over land"

[Jonathan Gregory]

Dear Karl

> I don't have time to think about this right now, but are your 
> conclusions consistent with what we decided to do for the AR4?  In 
> particular, we should check the definitions given in:
> http://www-pcmdi.llnl.gov/ipcc/standard_output.html

Yes, I believe so. You and I agreed on this, in order to be consistent with
the AR4. The point was to recognise that we had been vague about what
the "mean" method means. That's why you had to be prescriptive in the AR4
diagnostic specification. Your spec amounts to deciding whether it is
"mean over land/sea" or "mean". In future, the cell_methods should specify
this correctly. Does CMOR generate cell_methods?

Possibly some standard_names with _where_ in them don't actually need it.
That's not a problem as we can alias them to new names without _where_.

Best wishes

Jonathan