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.
(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 attached 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.
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 just there as a supporting thermodynamic framework.
Trevor
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
>>
>
--
*******************************************************
* Nan Galbraith (508) 289-2444 *
* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
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