Dear Maarten
A mole is also a udunit, so mol m-3 and m-3 are different units, and quantities
with those canonical units also have to have different standard_names. The
standard_name indicates whether the quantity refers to number concentration or
molar concentration. I am not sure if I've understood you correctly.
Cheers
Jonathan
----- Forwarded message from Maarten Sneep <maarten.sneep at knmi.nl> -----
> Date: Tue, 6 Jan 2015 18:10:22 +0100
> From: Maarten Sneep <maarten.sneep at knmi.nl>
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] New UDUnits units for information: "byte" and
> "octet"
> User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101
> Thunderbird/31.2.0
>
> Sorry for the delayed reply,
>
> On 28-11-14 11:29, Jonathan Gregory wrote:
> >Dear all
> >
> >I agree with Steve and Roy about this:
> >
> >>>Now UDUnits has "molecule" and "byte". They (Steve)
> >>>are receptive to well-justified proposals, so do not feel daunted
> >>>in transmitting to them the suggestion for "photon".
> >>
> >>Adding such units is the wrong way to go about solving the problem of
> >>adding quantity-semantics to data values. It would be much better to have
> >>the names of the variables be things like
> >>
> >> "number_of_tents"
> >> "number_of_clouds"
> >etc.
> >>
> >>and whose units were "1" than to try to incorporate such semantic
> >>information into a unit
> >
> >That is exactly what the CF standard says. From Sect 3.1 on "Units":
> >
> >"Descriptive information about dimensionless quantities, such as sea-ice
> >concentration, cloud fraction, probability, etc., should be given in the
> >long_name or standard_name attributes rather than the units."
>
> I don't agree completely. A concentration or column amount in mol/m3
> or mol/m2 respectively can be converted to/from number
> concentrations or column densities expressed in molecules/cm3 or
> molecules/cm2. However, the explicit "molecules" is essential here,
> otherwise UDUnits will not be of help at all. 1/m3 is not equivalent
> to mol/m3.
>
> And yes, I agree that you should not try to do this for 'tents',
> 'moles' (the furry kind, [1]) or even aerosol particles. Molecules
> and photons are an exception in my view because there are large
> datasets out there that use explicit molecules and photons for these
> 'things'.
>
> Best,
>
> Maarten Sneep
>
> [1] https://what-if.xkcd.com/4/
> --
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> E: maarten.sneep at knmi.nl
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----- End forwarded message -----
Received on Wed Jan 07 2015 - 08:15:03 GMT
