Hi Jonathan, Martin, et al.,
Although Mass-Moles and frequency-period are examples of pairs of physically
different units that are trivially convertible, DU is subtly different because
it is defined in two physically different but equivalent ways.
My preference is to add an additional comment to the notes for both std_names
that recommends using the new std_name for consistency with other std_names,
but would also happily live with the other two options (ie, either deprecating
the old std_name, or expressing no preference).
Best wishes,
Philip
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Dr Philip Cameron-Smith, [email protected], Lawrence Livermore National Lab.
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-----Original Message-----
From: CF-metadata [mailto:[email protected]] On Behalf Of
Jonathan Gregory
Sent: Friday, December 07, 2012 5:31 AM
To: [email protected]
Subject: Re: [CF-metadata] new standard name proposal for total ozone in DU
Dear Martin
> Philip also raises a good point with respect to alias names: has it been
> stated clearly that they must refer to "exactly the same quantity"? I believe
> they should, because if we allow "trivial" unit conversions to count as
> aliases, then even "wavelength" and "frequency" could be considered of
> aliases, which surely no one would want.
It does not say explicitly in your terms, but the convention (Appendix B)
implies that the alias has the same definition as the quantity of which it is
an alias, which I would say means it is exactly the same quantity. As Philip
says, these quantities cannot be the same because they have different physical
dimensions, even though the values may be numerically equal.
I tend to think it should be sufficient to point out the alternative in the
definition of each of these quantities (the one in mm and the one in mol m-2).
Deprecation of a quantity would be a step further than CF usually takes. CF
provides metadata for things people want to describe, rather than prescribing
which things they ought to describe.
Best wishes
Jonathan
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