Jonathan et al.,
An aside, perhaps...
I have been told by a physical oceanographer that "PSU" is no longer
accepted as a valid unit by most in physical oceanography circles. The
argument being that, because salinity is measured as "grams per grams",
many oceanographers prefer a "unitless" description: "35" rather than
"35 PSU" or "35?".
The anti-PSU comment was part of the feedback I got when asking folks
around here to do QC checks of our CMORized model output for IPCC AR4. I
can not judge if it is truly representative (i.e., the physical
oceanographer that sent me the strong anti-PSU comment may be an
outlier). Is the physical oceanography community represented on this
email list? If so, perhaps they could help clear up the matter of
salinity units.
-Keith D.
=======================
Jonathan Gregory wrote:
> Dear all
>
> I don't think it's right to use the units to indicate the quantity, which is
> what kg N would do. COARDS uses special dimensionless units to indicate
> vertical levels in a similar way, but early on in CF we decided to distinguish
> the identification of a quantity from the units it is measured in. The
> quantity being discussed is (for instance) a mass of nitrogen. The units of
> mass are the same for nitrogen, chalk and cheese.
>
> PSU (practical salinity units) is an interesting case in Alison's list.
> This is really a dimensionless number (a mass fraction), so we could survive
> without a unit for it, but it seems less clear to say the salinity is 35 1e-3
> than to say it is 35 PSU.
>
>> Clearly with CF1.0 we are stuck with udunits.
>>
>> However, it's worth thinking about the future. I wasn't involved when
>> the decision to be udunit compatible was made. Can anyone summarise the
>> benefits that requiring udunit conformance confer on the CF community?
>
> The choice of udunits was made by COARDS. We carry on with it for COARDS
> compatibility. Are there any other similarly comprehensive and flexible
> standards for interpreting units strings? I think the main benefit is to
> provide a general syntax, and secondarily some associated software for parsing
> and converting units.
>
> Cheers
>
> Jonathan
> _______________________________________________
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> CF-metadata at cgd.ucar.edu
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Received on Tue Oct 10 2006 - 06:49:38 BST
