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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