Hi Trevor,
As one who has worked in a data centre for a long time I can tell you that the transition to Practical Salinity was nowhere near as clean as you imply. The 1978 Equations of State weren't published by UNESCO until 1982 or 1983 and it took some people a long while to latch on (I remember locating at least one bit of code in use in the 90s that hadn't been updated). There was also uncertainty resulting from the lack of information on the algorithms built into the STD systems of the 70s that were still in use well into the 80s.
Hopefully, the transition to TEOS-10 will be much cleaner.
Thanks for correcting my misunderstanding that models couldn't generate Practical Salinity. However, I still feel that aliasing the current salinity standard names to practical salinity is a little too risky.
Cheers, Roy.
-----Original Message-----
From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Trevor.Mcdougall at csiro.au
Sent: 22 July 2011 03:05
To: Trevor.Mcdougall at csiro.au; ngalbraith at whoi.edu; CF-metadata at cgd.ucar.edu; Paul.Durack at csiro.au; Paul.Barker at csiro.au; rainer.feistel at io-warnemuende.de; rich at eos.ubc.ca; King, Brian A.; Stephen.Griffies at noaa.gov
Subject: Re: [CF-metadata] new TEOS-10 standard names:- reply to two emails.
Two replies follow, first to Karl Taylor, then to Roy Lowrie.
Hello Karl,
(1) "potential temperature" is what it always was, namely the temperature of a seawater parcel after an adiabatic and isohaline change of pressure to p = 0 dbar.
(2) "Conservative Temperature" is proportional to potential enthalpy which is the enthalpy of a seawater parcel after the same adiabatic and isohaline change of pressure to p = 0 dbar. Conservative temperature is a more accurate measure of the "heat content" of seawater, by a factor of one hundred, than is potential temperature. See the figure on page 10 of "Getting _Started.." to see how different Conservative Temperature is to potential temperature.
(3) "in situ temperature" is a pretty useless variable. It corresponds to electrical conductivity in that both are measured variables, but we quickly move on from these measured variables to calculate variables that have the "potential" property, and that are as "conservative" as possible.
It is, and always has been, a little dangerous (although not illegal) to use the word "temperature" if in-situ temperature t is intended. Rather it is best described as "in-situ temperature".
I refer you to the brochure "Getting Started with TEOS-10 and the Gibbs SeaWater Oceanographic Toolbox" (nicknamed "TEOS-10 for dummies") where the new variables, Absolute Salinity and Conservative Temperature are explained, as is the way in which TEOS-10 should be included in ocean models. This document can be found here
http://www.teos-10.org/pubs/Getting_Started.pdf
TEOS-10 allows the calculation of heaps of thermodynamic properties of seawater, ice and humid air; properties that we never had beforehand (the mathematical beauty and self-consistency of having three Gibbs functions allows this, namely Gibbs functions for seawater, for ice and for humid air). For example we now have entropy, enthalpy, internal energy, latent heat of melting, latent heat of evaporation, all precisely defined and we have algorithms that are really accurate and that are 100% consistent with each other. But the things that are important for oceanographers are Absolute Salinity and Conservative Temperature. These variables are the axes for our "T-S" diagrams now. As far as the practicing ocean modeller and climate scientist is concerned, once Absolute Salinity and Conservative Temperature are adopted, all of the other beautiful thermodynamic machinery that underlies TEOS-10 does not need to be learnt; it is there as a supporting thermodynamic framework.
_________________________________________________________
Now I am replying to an email from Roy Lowrie.
Roy, First, thanks for drawing attention to the following, <<<Finally, can I draw peoples' attention to the statement on the TEOS-10 Web Site that data centres should continue to ingest and store salinity observations as Practical Salinity. It is abundantly clear from a number of conversations I have had recently that this is being overlooked.>>>
This is perhaps the MOST IMPORTANT point for people to grasp, especially data centres! This is one thing we cannot afford to get wrong; observational data must be stored as Practical Salinity.
Then you make the point that the existing data bases contain at least two different types of salinity. There is the Knudsen salinity (ppt) which is calculated from
S_K = 0.03 + 1.805 Cl
and I think I am correct in saying that any salinity data in national data centres with dates between 1901 and 1977 will be this Knudsen salinity. Then after 1978, the salinity in national data bases should be Practical Salinity S_P (sometimes called PSAL). The salinity output of numerical models to date is Practical Salinity as well, yes? Because these models have been initialized with Practical Salinity and their model equations of sate have been written in terms of Practical Salinity.
Going forward from now, it is important that the stored Practical Salinity be identified as Practical Salinity, not as just "salinity". From 1st January 2010 (when the reign of TEOS-10 began) there are too many salinities for us to just call one of them "salinity".
It is clear to me that the data that is stored as "Salinity (psu)" in national data bases to date should remain there as that. But it is also equally clear to me that any new observed data going into such data bases that is Practical Salinity, should not be called "Salinity" but must be called "Practical Salinity". This is the only safe way that we can avoid confusing ourselves with observed data taken after 1st January 2010.
Now Paul Durack has suggested that an alias be created so that the old "salinity" data also appears as "Practical Salinity". I do not have a strong view on that. If that were done, it should only be done with data collected since 1st January 1978, since before that date the salinity was calculated by a different formula (the Knudsen formula given above) and so was definitely not Practical Salinity.
With best wishes,
Trevor
-----Original Message-----
From: Lowry, Roy K. [mailto:rkl at bodc.ac.uk]
Sent: Friday, 22 July 2011 7:10 AM
To: 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 think the point we're missing here is that the existing salinity Standard Name is a much broader term than the TEOS-10 recommendations, covering true practical salinity from conductivity measurements, other types of salinity measurement and salinity computed by a whole host of numerical model algorithms. This has been connected with the PSU units of measure, which is sometimes right and sometimes wrong. However, it is widespread in legacy data stock. It is therefore something that should be recognised for what it is warts and all and left alone. Renaming it 'practical salinity' would be a bad move because it would change the semantic labelling of some datasets from imprecise to precise but wrong.
I think the way forward would be to generate additional Standard Names for Practical Salinity and Absolute Salinity supported by TEOS-10 definitions, which can be semantically mapped as narrowMatches to the existing salinity, to give us the ability to label things properly from now on. It would be down to those holding data in CF to replace 'salinity' with the appropriate more precise term from the TEOS-10 recommendations.
I would also support the creation of new Standard Names for the other TEOS-10 variables (temperature plus derived parameters) under the watchful eye of Trevor and TEOS-10. Again these can be mapped to existing less precise terms as appropriate. Now is our chance to get this right.
Finally, can I draw peoples' attention to the statement on the TEOS-10 Web Site that data centres should continue to ingest and store salinity observations as Practical Salinity. It is abundantly clear from a number of conversations I have had recently that this is being overlooked.
Cheers, Roy.
From: cf-metadata-bounces at cgd.ucar.edu [cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Karl Taylor [taylor13 at llnl.gov]
Sent: Friday, 22 July 2011 3:12 AM
To: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] new TEOS-10 standard names
Dear Trevor,
Could you please clarify: Are "potential temperature" and "conservative temperature" identical, or is "conservative temperature" what everyone else considers to be simply "temperature", or what?
thanks,
Karl
-----Original Message-----
From: McDougall, Trevor (CMAR, Hobart)
Sent: Thursday, 21 July 2011 8:30 PM
To: 'ngalbraith at whoi.edu'; 'CF-metadata at cgd.ucar.edu'; Durack, Paul (CMAR, Hobart); Barker, Paul (CMAR, Hobart); 'Rainer Feistel'; Richard Pawlowicz; 'bak at noc.soton.ac.uk'
Subject: [CF-metadata] new TEOS-10 standard names
Dear Nan et al.,
I want to weigh in to this discussion, as chair of SCOR/IAPSO Working Group 127.
In June 2009 the Intergovernmental Oceanographic Commission, which is comprised of 146 nations, adopted TEOS-10 as the formal definition of seawater properties (and of ice and of humid air).
Part of TEOS-10 is the adoption of Absolute Salinity as the salinity variable which replaces Practical Salinity as the salinity argument for the algorithms that calculate density etc.
Because of the proliferation of different types of salinity, it is particularly important that the single word "Salinity" not be used henceforth. Rather, "Practical Salinity" should be used for Practical Salinity (not "Salinity"), and Absolute Salinity should be referred to as "Absolute Salinity" (not "Salinity"). The symbols S_P and S_A should be used, and the use of S should be discontinued immediately.
This is outlined in the attached Announcement which will shortly appear in 21 oceanographic journals. This Announcement specifically requests editors and authors to use S_P and S_A, not S. The aim of this recommendation is to minimize the potential for confusion.
We in WG127 have met with representatives of instrument manufacturers and they will be providing output from their software in the above manner. That is, they will discontinue the use of "Salinity" and of "S".
I note that a team of four people have recently installed TEOS-10 into MOM4, and so we now have Absolute Salinity S_A and Preformed Salinity, S_star, in MOM4. So this naming convention is actually already an issue in the ocean modelling world.
In the same vein, ocean models should not carry a variable called "temperature" but rather should carry either "potential temperature" or "Conservative Temperature" or both.
It is clear that we are now on the cusp of a transition in oceanography, with the potential for confusion unless we are all very careful in correctly labeling our variables.
I hope this discussion of the thinking of SCOR/IAPSO WG127 helps your community with the naming conventions for ocean and climate models,
With best wishes,
Trevor
PS. As for some definitions, I would suggest something along the lines of
sea_water_Practical_Salinity:
Definition: Salinity measured on the Practical Salinity Scale of 1978 (PSS-78),
which is based on measurements of the electrical conductivity of seawater.
sea_water_Absolute_Salinity:
Definition: The mass fraction of dissolved material in seawater as defined by the
Thermodynamic Equation Of Seawater - 2010 (TEOS-10). Absolute Salinity incorporates the
spatial variations in the composition of seawater. This type of absolute salinity
is also called "Density Salinity".
____________________________________
Note that I think the sea surface salinity estimated from satellite is output as Practical Salinity.
Note also that there are about 4 different types of absolute salinity (the subject is rather complicated
and involves carbon chemistry), and TEOS-10 has adopted the one that best estimates density, as
incorporated into the above definition.
________________________________________
From: Nan Galbraith [ngalbraith at whoi.edu]
Sent: Friday, 8 July 2011 12:53 AM
To: Durack, Paul (CMAR, Hobart)
Cc: CF-metadata at cgd.ucar.edu; McDougall, Trevor (CMAR, Hobart)
Subject: Re: [CF-metadata] new TEOS-10 standard names
Hi Paul -
I'm not sure if anyone else is ready to retire salinity as a
standard name meaning 'salinity on the practical salinity
scale'.
Also I still think your proposed definitions are a little too closely
tied to the teos-10 code and to the measurement/calculation
methods. For example, where does remotely sensed surface salinity
fit in? I'm really not sure, but I suspect it's reported on the PSS, but
without a conductivity observable in the "raw" data.
Which reminds me, do you want to add sea_surface_absolute_salinity
to your list?
Personally, I'd go with definitions closer to:
sea_water_salinity: Salt content of seawater on the Practical Salinity
Scale of 1978 (PSS-78), usually based on the electrical conductivity
of seawater.
sea_water_absolute_salinity
Definition: The mass fraction of salts in seawater as defined by the
Thermodynamic Equation Of Seawater - 2010 (TEOS-10), which
includes corrections for spatial variations in the composition of
seawater.
Cheers -
Nan
On 7/6/11 9:45 PM, Paul.Durack at csiro.au wrote:
> Fair point Nan..
>
> We should then do this..
>
> Convert the current "sea_water_salinity" (to be discontinued in its use) to be an alias of the new standard name "sea_water_practical_salinity".
>
> An updated definition for "sea_water_absolute_salinity" following your suggestion is included below, plus a new definition for "sea_water_practical_salinity".
>
> I would recommend each of the new standard names also has an additional copy created, with the prefix "change_over_time_in_*"
>
> ***
> sea_water_conservative_temperature
> Definition: Conservative Temperature is potential enthalpy divided by a fixed value of the specific heat of seawater, namely cp_0 = 3991.86795711963 J kg-1 K-1. Conservative temperature is designed to be as close as possible to potential temperature, but is two orders of magnitude more conservative in the ocean. Because of this, Conservative Temperature can be regarded as being proportional to the heat content of seawater per unit mass.
> Canonical units: K
> Reference: www.teos-10.org
>
> sea_water_absolute_salinity
> Definition: Absolute Salinity, S_A, is the mass fraction of dissolved material in seawater. In fact TEOS-10 estimates Absolute Salinity as the salinity variable that, when used with the TEOS-10 expression for density, yields the correct density of a seawater sample even when the sample is not of Standard Composition. In practice Absolute Salinity is often calculated from Practical Salinity and a value of Absolute Salinity Anomaly which is found using computer software via a global look-up table.
> Canonical units: g kg-1
> Reference: www.teos-10.org
>
> sea_water_practical_salinity
> Definition: Practical Salinity, S_P, is defined on the Practical Salinity Scale of 1978 (PSS-78) and is calculated from the electrical conductivity of seawater (as well as temperature and pressure).
> Canonical units: 1e-3, parts per thousand. Officially S_P is unitless, but often authors use psu, as in S_P = 35 psu.
> Reference: www.teos-10.org
>
> 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.
> Canonical units: g kg-1
> Reference: www.teos-10.org
>
> sea_water_potential_enthalpy
> Definition: Potential enthalpy is the enthalpy of a seawater parcel after an adiabatic and isohaline change in pressure from its in situ pressure to the sea pressure p = 0 dbar.
> Canonical units: J kg-1
> Reference: www.teos-10.org
> ***
>
> So for clarity, the new proposed names are:
>
> sea_water_conservative_temperature
> sea_water_absolute_salinity
> sea_water_practical_salinity
> sea_water_preformed_salinity
> sea_water_potential_enthalpy
> change_over_time_in_sea_water_conservative_temperature
> change_over_time_in_sea_water_absolute_salinity
> change_over_time_in_sea_water_practical_salinity
> change_over_time_in_sea_water_preformed_salinity
> change_over_time_in_sea_water_potential_enthalpy
>
> Cheers,
>
> P
>
> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Nan Galbraith
> Sent: Thursday, July 07, 2011 3:40 AM
> To: cf-metadata at cgd.ucar.edu
> Subject: Re: [CF-metadata] new TEOS-10 standard names
>
> I agree that we probably need these names now. I'd like to
> suggest, though, that the definition of absolute salinity should
> start with the phrase 'mass fraction of salt in seawater', or
> maybe 'concentration of salt in seawater'.
>
> And while we're at it, we should probably consider revising the
> definition of sea_water_salinity; currently all we have is: "The unit
> of salinity is PSU, which is dimensionless. The units attribute
> should be given as 1e-3 or 0.001 i.e. parts per thousand if
> salinity is in PSU."
>
> The units designation implies that we're using practical
> salinity, but the definition should probably be more explicit.
> We could add something like "Salinity ratio on the Practical Salinity
> Scale."
>
> Cheers - Nan
>
>
> On 7/6/11 3:35 AM, Paul.Durack at csiro.au wrote:
>> I'd like to propose a series of new standard names, these names are associated with the recent release of the Thermodynamic Equation Of Seawater 2010 (TEOS-10 - www.teos-10.org).
>>
>> Additional to these names, I would also like to propose the "change_over_time_in_*" prefixes are also created.
>>
>> The proposed new standard names, along with definition, units and reference details are below.
>>
>> ***
>> sea_water_conservative_temperature
>> Definition: Conservative Temperature is potential enthalpy divided by a fixed value of the specific heat of seawater, namely cp_0 = 3991.86795711963 J kg-1 K-1. Conservative temperature is designed to be as close as possible to potential temperature, but is two orders of magnitude more conservative in the ocean. Because of this, Conservative Temperature can be regarded as being proportional to the heat content of seawater per unit mass.
>> Canonical units: K
>> Reference: www.teos-10.org
>>
>> change_over_time_in_sea_water_conservative_temperature
>>
>> sea_water_absolute_salinity
>> Definition: Absolute Salinity is the salinity variable that when used with the TEOS-10 expression for density yields the correct density of a seawater sample even when the sample is not of Standard Composition. In practice Absolute Salinity is often calculated from Practical Salinity and a value of Absolute Salinity Anomaly which is found using computer software via a global look-up table.
>> Canonical units: g kg-1
>> Reference: www.teos-10.org
>>
>> change_over_time_in_sea_water_absolute_salinity
>>
>> 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.
>> Canonical units: g kg-1
>> Reference: www.teos-10.org
>>
>> change_over_time_in_sea_water_preformed_salinity
>>
>> sea_water_potential_enthalpy
>> Definition: Potential enthalpy is the enthalpy of a seawater parcel after an adiabatic and isohaline change in pressure from its in situ pressure to the sea pressure p = 0 dbar.
>> Canonical units: J kg-1
>> Reference: www.teos-10.org
>>
>> change_over_time_in_sea_water_potential_enthalpy
>> ***
>>
>> Cheers,
>>
>> P
>> _______________________________________________
>> CF-metadata mailing list
>> CF-metadata at cgd.ucar.edu
>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>>
>
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* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
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