Hi Jim -
Not too simplistic, but that 'factor of 1000' is the exact problem.
If I'm using '1' as the unit for practical salinity, and the canonical
unit is
'.001', the user (maybe via udunits) will assume the data values should be
divided by 1000 before using. That wasn't my intention, and will probably
mean my data is discarded.
And yes, I think we'd meant this to only be about practical salinity.
Cheers -
Nan
On 5/26/15 9:56 AM, Jim Biard wrote:
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 [rsign...@usgs.gov]
Sent: 22 May 2015 20:01
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.<r...@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 [re...@uvic.ca]
Sent: 22 May 2015 18:06
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
________________________________________
From: CF-metadata<cf-metadata-boun...@cgd.ucar.edu> on behalf of Nan
Galbraith<ngalbra...@whoi.edu>
Sent: Friday, May 22, 2015 10:03 AM
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 *
*******************************************************
_______________________________________________
CF-metadata mailing list
CF-metadata@cgd.ucar.edu
http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
