Hi.
I checked the operation of udunits2, and I found that it is fine with
converting between parts per thousand, fraction of whole, and g/kg. From
a simple dimensional analysis perspective they sure look like they are
all dimensionless and differ from each other only by a factor of 1000 at
the most. Is that too simplistic?
Grace and peace,
Jim
On 5/22/15 4:37 PM, Lowry, Roy K. wrote:
> 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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>
> --
> Dr. Richard P. Signell (508) 457-2229
> USGS, 384 Woods Hole Rd.
> Woods Hole, MA 02543-1598
>
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