Thank you, Roy, especially for reminding us of the recommendation
that data centers store practical salinity. We are following that
recommendation in the oceansites project, as is every other
project that keeps observational data - as far as I know.
S_P is closer to the measured variables (C,T, P) than absolute
salinity is; TEOS relies on the global Absolute Salinity Anomaly
Ratio data set to convert from S_P to S_A. I have to ask what will
happen when that table is revised; I think some standards for
auxiliary metadata to go along with S_A are in order.
I support adding absolute and practical salinity standard names,
with sea_water_practical_salinity being an equivalent to
sea_water_salinity. But I also hope there will be some
discussion on important metadata that needs to be logged
along with any absolute salinity values.
(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".
Please remember that CF is not just used for models. When
we deploy thermistors on a mooring, we record temperature,
and we use it, as-is, quite a lot. The label 'sea_water_temperature'
seems quite clear and appropriate.
Cheers - Nan
On Jul/21/2011 10:05 PM, trevor.mcdoug...@csiro.au wrote:
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:r...@bodc.ac.uk]
Sent: Friday, 22 July 2011 7:10 AM
To: McDougall, Trevor (CMAR,
Hobart);ngalbra...@whoi.edu;CF-metadata@cgd.ucar.edu; Durack, Paul (CMAR,
Hobart); Barker, Paul (CMAR,
Hobart);rainer.feis...@io-warnemuende.de;r...@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-boun...@cgd.ucar.edu [cf-metadata-boun...@cgd.ucar.edu] On
Behalf Of Karl Taylor [taylo...@llnl.gov]
Sent: Friday, 22 July 2011 3:12 AM
To:cf-metadata@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: 'ngalbra...@whoi.edu'; 'CF-metadata@cgd.ucar.edu'; Durack, Paul (CMAR,
Hobart); Barker, Paul (CMAR, Hobart); 'Rainer Feistel'; Richard Pawlowicz;
'b...@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 [ngalbra...@whoi.edu]
Sent: Friday, 8 July 2011 12:53 AM
To: Durack, Paul (CMAR, Hobart)
Cc:CF-metadata@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.dur...@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-boun...@cgd.ucar.edu
[mailto:cf-metadata-boun...@cgd.ucar.edu] On Behalf Of Nan Galbraith
Sent: Thursday, July 07, 2011 3:40 AM
To:cf-metadata@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.dur...@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
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*******************************************************
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* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
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* Upper Ocean Processes Group Mail Stop 29 *
* Woods Hole Oceanographic Institution *
* Woods Hole, MA 02543 *
*******************************************************
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