Hi Rich,
I should clarify that my comment was following on from Nan's and referred only to practical salinity, otherwise known as PSS-78. Absolute salinity has dimensions mass/mass and so is not dimensionless.
Cheers, Roy.
________________________________________
From: Signell, Richard [rsignell at usgs.gov]
Sent: 22 May 2015 20:01
To: Lowry, Roy K.
Cc: Reyna Jenkyns; cf-metadata at cgd.ucar.edu; OceanSITES Data Management Team; Nan Galbraith; Richard Pawlowicz
Subject: Re: [CF-metadata] Salinity units
Roy,
For sure dimensionless. But "1.0", "0.001" or "g/kg"?
The latest version (27) of the CF Standard Name list
(
http://cfconventions.org/Data/cf-standard-names/27/build/cf-standard-name-table.html)
states:
sea_water_salinity: "0.001"
sea_water_absolute_salinity: "g kg-1"
sea_water_practical_salinity: "0.001"
sea_water_preformed_salinity: "g kg-1"
sea_water_cox_salinity: "0.001"
and units packages, of course, would treat "g kg-1" the same as "0.001".
Yet in the IOC manual on equation of seawater:
http://www.teos-10.org/pubs/TEOS-10_Manual.pdf
it states (PDF page 176, printed page 166) that Practical Salinity
should have units of "1", while "Absolute Salinity" (the argument used
in the toolbox functions) and "Preformed Salinity" (used in numerical
ocean models) should have units "g kg-1".
So it appears that TEOS agrees with CF on units for Absolute Salinity
and Preformed Salinity, but not on Practical Salinity.
And OceanSites (as least here:
http://www.oceansites.org/docs/OS_PAP-3_201205_P_deepTS.txt)
is using "sea_water_practical_salinity" with units of "1", so they are
consistent with the TEOS publication, but not the current CF
convention (v27).
On the TEOS site, there is software to calculate Absolute Salinity
from Practical Salinity. So it would seem that the technically
correct thing to do would be to use the "gsw_SA_from_SP" routine to
convert OceanSites Practical Salinity (in units of "1") to Absolute
Salinity (in units of "g/kg") before comparing with the "Preformed
Salinity" output "g/kg" from ocean models.
I'm pretty confused though, so I'm cc'ing Rich Pawlowicz on this,
hoping for his input.
Thanks,
-Rich
On Fri, May 22, 2015 at 1:49 PM, Lowry, Roy K. <rkl at bodc.ac.uk> wrote:
> Dimensionless. Please????
>
> This is the view of physical oceanographers for whom I have the greatest respect.
>
> Cheers, Roy.
> ________________________________________
> From: Reyna Jenkyns [reyna at uvic.ca]
> Sent: 22 May 2015 18:06
> To: cf-metadata at cgd.ucar.edu; OceanSITES Data Management Team; Nan Galbraith
> Subject: Re: [CF-metadata] Salinity units
>
> I'm interested in this topic since I didn't realize what had been discussed previously, and now I think we must be non-compliant as well. Is this documented formally in the CF documentation?
>
> Reyna Jenkyns | Data Stewardship Team Lead - Digital Infrastructure
> Ocean Networks Canada | T 250 853 3908 | oceannetworks.ca
> University of Victoria PO Box 1700 STN CSC 2300 McKenzie Avenue Victoria, BC V8W 2Y2
>
> ________________________________________
> From: CF-metadata <cf-metadata-bounces at cgd.ucar.edu> on behalf of Nan Galbraith <ngalbraith at whoi.edu>
> Sent: Friday, May 22, 2015 10:03 AM
> To: cf-metadata at cgd.ucar.edu; OceanSITES Data Management Team
> Subject: Re: [CF-metadata] Salinity units
>
> Hello all -
>
> It's been a long time, but is anyone interested in re-visiting the subject
> of units for practical salinity in CF?
>
> I was recently notified that my salinity data was likely to be
> overlooked by
> some users, because I'd used '1' as the units, not '.001'. Somehow, I'd
> forgotten the (long-ago) discussion on the CF list about salinity units.
>
> Some members of the OceanSITES project are interested in revising our
> format spec to encourage the use of '1' as an indication that salinity does
> not have units - but, of course, we'd mostly rather remain CF-compliant.
>
> Thanks for any feedback on this.
>
> Cheers - Nan
>
>
> On 6/17/09 2:48 AM, Lowry, Roy K wrote:
>
> > Dear All,
> >
> > During an exercise with Alison mapping the CF Standard Names to a
> > units vocabulary in the BODC vocabulary server I noticed that the
> > units for salinity were '1.00E-03', i.e. parts per thousand. My
> > understanding in that since the introduction of the Practical
> > Salinity Scale that salinity is dimensionless with units of '1'. Is
> > there agreement for our changing the units in the Standard Name
> > table?
> >
> > Cheers, Roy.
>
> --
> *******************************************************
> * Nan Galbraith Information Systems Specialist *
> * Upper Ocean Processes Group Mail Stop 29 *
> * Woods Hole Oceanographic Institution *
> * Woods Hole, MA 02543 (508) 289-2444 *
> *******************************************************
>
>
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Received on Fri May 22 2015 - 14:37:29 BST
