Hello Jonathon,
The use of the word "preformed" in "Preformed Salinity" is the same use as in "preformed nitrate", NO, and "preformed phosphate" PO. The idea is to recover the conservative variable that would be present if there were no biogeochemistry. The methods that we use probably subtract off some effects of geochemistry as well as of biogeochemistry, at least in the open ocean. The aim in forming Preformed Salinity has been to subtract off from Absolute Salinity those contributions that have arisen from all types of prior non-conservative source terms. These source terms are primarily biogeochemical, not geochemical, but it is possible that some contributions to seawater composition from geochemistry have been mixed up in our methods with those caused by biogeochemistry. But really, this is an area of research in which there is presently only one world expert (Rich Pawlowicz), and the research area needs boosting so we can better answer such questions. I'm sure this paragraph is more information than anyone
wanted to know!
Preformed Salinity is a relatively new concept, first appearing in the following two papers, and in the TEOS-10 Manual.
(1) Pawlowicz, R., D. G. Wright and F. J. Millero, 2011: The effects of biogeochemical processes on oceanic conductivity/salinity/density relationships and the characterization of real seawater. Ocean Science, 7, 363-387.
http://www.ocean-sci.net/7/363/2011/os-7-363-2011.pdf
(2) Wright, D. G., R. Pawlowicz, T. J. McDougall, R. Feistel and G. M. Marion, 2011: Absolute Salinity, "Density Salinity" and the Reference-Composition Salinity Scale: present and future use in the seawater standard TEOS-10. Ocean Sci., 7, 1-26.
http://www.ocean-sci.net/7/1/2011/os-7-1-2011.pdf
(3) IOC, SCOR and IAPSO, 2010: The international thermodynamic equation of seawater - 2010: Calculation and use of thermodynamic properties. Intergovernmental Oceanographic Commission, Manuals and Guides No. 56, UNESCO (English), 196 pp.
Available from
http://www.TEOS-10.org/TEOS-10_Manual.pdf
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I don't disagree with your suggestion of adding the descriptor "specific" to indicate that these things are "per unit mass".
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As for what salinity is carried in existing ocean models, I think there is a clear definitive answer, namely Practical Salinity. Why? Because ocean models are initialized with Practical Salinity data and the equation of state has, for 30 years, been written in terms of Practical Salinity. The fact that it is model output and not observed data should be clear from the metadata, yes?
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To add to a previous comment from me, I should point out that the software to calculate both Absolute Salinity and Preformed Salinity from Practical Salinity is available from www.TEOS-10.org in Matlab, Fortran (and C), and soon, Python. All these are the same version 3.0 of the software.
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Note that TEOS-10 uses upper case letters for
Conservative Temperature
Absolute Salinity
Preformed Salinity
to indicate specifically defined quantities. Note also that Practical Salinity has always had upper case letters, while potential temperature has always been lower case, as has in-situ temperature.
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This is the end of this post today.
Trevor J McDougall
-----Original Message-----
From: Jonathan Gregory [mailto:j.m.gregory at reading.ac.uk]
Sent: Tuesday, 26 July 2011 6:49 PM
To: Lowry, Roy K.
Cc: McDougall, Trevor (CMAR, Hobart); ngalbraith at whoi.edu; CF-metadata at cgd.ucar.edu; Durack, Paul (CMAR, Hobart); Barker, Paul (CMAR, Hobart); rainer.feistel at io-warnemuende.de; rich at eos.ubc.ca; King, Brian A.
Subject: Re: [CF-metadata] new TEOS-10 standard names
Dear all
I agree with Roy in his remark that "the existing salinity Standard Name is a
much broader term than the TEOS-10 recommendations".
In some datasets, it may not be well-defined precisely which "kind" of salinity
we have. This is particularly the case for model datasets, since most ocean
models used for climate are not capable of distinguishing owing to the
approximations they make. (I note that CF and the standard name table began
as a convention for GCMs, and later expanded to accommodate observations.) We
cannot redefine the existing standard name because of the existing datasets and
because it is useful to have a "generic" name anyway.
However it is fine both to keep this existing generic name and to define some
new ones to make the distinction in new obs and model datasets where it is
appropriate, as proposed by Paul and Trevor. It is usual in CF to have a choice
of precision for different applications.
On Paul's proposals, I have a couple of comments:
sea_water_preformed_salinity
Definition: Preformed Salinity is a salinity variable that is designed to be as
conservative as possible, by removing the estimated biogeochemical influences
on the seawater composition from other forms of salinity.
I assume this is a newly introduced term. I would say that it would be good
to be more informative. "Preformed" does not tell me what it is - it doesn't
suggest anything in particular to me as a non-expert. CF standard names do not
have to be the term in common use if we could be more self-explanatory.
Perhaps we could be more self-explanatory in this term with a phrase such as
assuming_no_biogeochemical_influence. But actually, I am unsure what that
means - could you explain a bit further? How can salinity not be influenced
by geochemistry, in particular? Please excuse my ignorance.
sea_water_potential_enthalpy
Since this quantity is in J kg-1, I suggest that it should contain the word
"specific". Omitting this might imply that it was an extensive quantity e.g.
an ocean integral. By analogy with the existing standard name
specific_kinetic_energy_of_sea_water
it might be best phrased as
specific_potential_enthalpy_of_sea_water
The salinity quantities are by definition intensive and so "specific" is
not required.
Best wishes
Jonathan
Received on Tue Jul 26 2011 - 05:49:58 BST
