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, pjc at llnl.gov, Lawrence Livermore National Lab.
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-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Gregory
Sent: Friday, December 07, 2012 5:31 AM
To: cf-metadata at cgd.ucar.edu
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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Received on Fri Dec 07 2012 - 13:06:11 GMT
