[CF-metadata] Is "psu" a valid cf unit?

Sean Arms sarms at ucar.edu
Tue Jul 18 07:34:17 MDT 2017


There was a github issue opened on UDUNITS2 a few years back (still
open, btw) regarding the support for PSU in the package:

https://github.com/Unidata/UDUNITS-2/issues/27

An interesting point is made regarding units and physical quantities.

Sean


On Tue, Jul 18, 2017 at 7:12 AM, V. Balaji - NOAA Affiliate
<v.balaji at noaa.gov> wrote:
> The ocean modeling community is adamant that they will continue to use PSUs
> for salinity: it's this unit, rather than its SI or dimensionless
> equivalent, that gives the maximum digits of precision in a floating-point
> representation of salinity.
>
> It's a valid concern, and CF should perhaps reconsider, with a new
> discussion giving weight to the views of modelers as well as physical
> oceanographers.
>
> Thanks,
>
> Lowry, Roy K. writes:
>
>> Hello Martin,
>>
>>
>> This topic has been debated at length in CF. To cut a long story short,
>> the term 'Practical Salinity Unit' was coined when the 1978 Practical
>> Salinity scale was devised. However, the term fell out of favour with the
>> physical oceanographic community whose current recommended practice is that
>> Practical Salinity - a ratio - should be a dimensionless number.  CF
>> followed this recommendation and so PSU is not a part of CF.
>>
>>
>> Have a dig around in the mailing list archive if you want to find out
>> more.
>>
>>
>> Cheers, Roy.
>>
>>
>> Please note that I partially retired on 01/11/2015. I am now only working
>> 7.5 hours a week and can only guarantee e-mail response on Wednesdays, my
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>>
>>
>> ________________________________
>> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of
>> martin.juckes at stfc.ac.uk <martin.juckes at stfc.ac.uk>
>> Sent: 18 July 2017 13:43
>> To: cf-metadata at cgd.ucar.edu; d.c.hassell at reading.ac.uk;
>> r.s.hatcher at reading.ac.uk
>> Subject: [CF-metadata] Is "psu" a valid cf unit?
>>
>> Hello David, all,
>>
>> Is "psu" a valus CF unit? It is not in Udunits, but it is added in
>> cf-python as a unit alias and also appears to be accpeted by the cf-checker.
>> I can't see any mention of it in the CF Convention document: the latter only
>> lists level, layer, and sigma_level permitted departures from Udunits,
>>
>> regards,
>> Martin
>>
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>
> --
> V. Balaji                               Office:  +1-609-452-6516
> Head, Modeling Systems Group, GFDL      Mobile:  +1-917-273-9824
> Princeton University                    Email: v.balaji at noaa.gov
> https://www.gfdl.noaa.gov/v-balaji-homepage
>
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