Paul, regarding the unit of an implemented quantity, in the SIA library we have added unit tags to any of them, such as sea_density_si where "_si" indicates that the value is given in SI basic units, kg/m3 in this case. If non-basic SI units or non-SI units are used, this is explicitly indicated in the tag, such as absolute_salinity_gkg if the unit associated with salinity is g/kg. Such tags permit some flexibility in the units to be used and help to avoid confusion. absolute_salinity_si would then mean kg/kg.
Regarding PSS-78, I think "_psu" may be best understood by any user. I know that even "mpsu" (milli-psu) is used by some authors, so practical_salinity alone may not be enough to avoid ambiguity. Rainer > Thanks for all your work getting this fairly scattered discussion into a > submittable shape Alison! > > I've supplemented your comments with some additional descriptive text > below. I have additionally added a "References:" attribute for each of > these proposed variables if applicable, I am not sure whether the format > of the current standard_names table can deal with this suggestion? > > The new proposed name sea_water_cox_salinity has also been added (this is > a new one). > > I am also wondering if while we're trying to tidy up this all, if we > propose the "units": "PSS-78", "ppt" and "psu" to become part of an update > to the udunits codebase? I am not sure how we would go about this > however.. It seems arbitrary that we continue to use the canonical units > of 1e-3 for salinity, as you note we currently scale this. A nice thing > with TEOS-10 is that we get back units, so g kg-1 rather than the ratio of > the past, however I would note that regardless of the notation it's still > 1e-3.. I apologise below my units are a little all over the place.. > > I have also rearranged the name of "specific_enthalpy" to > sea_water_specific.. I think it is better to maintain the convention of > sea_water_X, as this then lists together when viewing the entire table > alphabetically.. > > As noted below I believe that 5 of the 8 proposed new names would benefit > from a change_over_time_in_X name too, and the notation you have proposed > with the ..."change_over_time_in_X" means change in a quantity X... Seems > reasonable to me. > > I have appended my suggested edits below.. If anyone notes any issues > below, please fix and resubmit this.. > > Cheers, > > P > > *** > Add PSS-78, ppt & psu to udunits provide request info to Unidata? > > sea_water_salinity > Definition: The standard name sea_water_salinity is the salt content of > sea water normally on the Practical Salinity Scale of 1978 (PSS-78), and > is usually based on the electrical conductivity of sea water in > observations since the 1960s. There are standard names for the more > precisely defined salinity quantities sea_water_knudsen_salinity > (1901-1966), sea_water_cox_salinity (1967-1977), > sea_water_practical_salinity (1978-present day), > sea_water_absolute_salinity and sea_water_preformed_salinity. The more > precise standard names should be used where appropriate for both modelled > and observed salinities. In particular, the use of sea_water_salinity to > describe salinity observations made from 1978 onwards is now deprecated in > favour of the term sea_water_practical_salinity which is the salinity > quantity stored by national data centres for post-1978 observations. The > only exception to this is where the observed salinities are definitely > known not to be recorded on the Practical Salinity Scale. > Canonical units: 1e-3; practical salinity units, which is dimensionless. > The use of parts per thousand (ppt) was expressed for > sea_water_knudsen_salinity and sea_water_cox_salinity. > > 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 sea water (as well as temperature and pressure). This name should be > used to describe salinity observations made from 1978 onwards; practical > salinity is the salinity quantity stored by national data centres for > post-1978 observations. The only exception to this is where the observed > salinities are definitely known not to be recorded on the Practical > Salinity Scale. More recently remote salinity measurements from satellites > (SMOS/AQUARIUS) also provide surface estimates of salinity presented in > S_P, however these are not obtained from conductivity measurements. In > these cases information about calibration and validation techniques to > convert remotely sensed salinity to S_P should be documented within the > variable "comment" attribute. There are also standard names for the > precisely defined salinity quantities sea_water_absolute_salinity and > sea_water_preformed_salinity. Salinity quantities that do not match any of > the precise definitions should be given the more general standard name of > sea_water_salinity. > Canonical units: Officially S_P is unitless, so that, while convenient, > and while it is common practice, it is not officially sanctioned to say > S_P = 35 psu. Often authors use PSS-78, as in S_P = 35 PSS-78. If salinity > was measured using remote satellite techniques, then it is recommended > that additional metadata (calibration/validation information) be described > in the variable comment attribute. > Reference: www.teos-10.org > > sea_water_cox_salinity > Definition: Cox Salinity, S_C, is defined unitless as a fraction per mil > (0/00). S_C was the standard salinity measure until S_P (Practical > Salinity) was established with PSS-78 (1978). Chlorinity Cl is calculated > from the conductivity of a seawater sample, and since the work of the > Joint Panel for Oceanographic Tables (1966) is converted into Cox Salinity > using S_C = 1.80655 Cl. This type of salinity was called simply ³salinity² > from 1967 to 1978 and had the ³units² of 0/00, or ³parts per thousand² or > ppt. Practical Salinity replaced Cox Salinity in 1978. > Canonical units: (0/00) or ³parts per thousand². > Reference: Cox et al., 1967 doi: 10.1016/0011-7471(67)90006-X > > sea_water_knudsen_salinity > Definition: Knudsen Salinity, S_K, is defined unitless as a fraction per > mil (0/00) and was calculated from the titration of inorganic salts from a > sample of sea water after a commission to study the problem of determining > salinity and density was initiated by the International Council for the > Exploration of the Sea (ICES) in 1899. S_K was the standard salinity > measure until S_C (Cox Salinity) was established in 1967. Chlorinity Cl is > calculated by titration from a sample of seawater, and since the work of > Knudsen (1901) is converted into Knudsen Salinity using S_K = 0.030 + > 1.805 Cl. This type of salinity was called simply ³salinity² from 1901 to > 1966 and had the ³units² of 0/00, or ³parts per thousand² or ppt. From > 1950 onwards electrical conductivity was used to estimate the Knudsen > Salinity rather than chemical titration, which was the standard before > this time. Cox Salinity replaced Knudsen Salinity in 1967. > Canonical units: (0/00) or ³parts per thousand². > Reference: Knudsen, 1901; Thomas et al., 1934 doi: 10.1093/icesjms/9.1.28; > Lyman, 1969 doi: 10.4319/lo.1969.14.6.0928; Wooster et al., 1969 doi: > 10.4319/lo.1969.14.3.0437; Lewis, 1980 doi: 10.1109/JOE.1980.1145448; > Millero et al., 2008 doi: 10.1016/j.dsr.2007.10.001; > > sea_water_reference_salinity > Definition: If a seawater sample has the Reference Composition (dissolved > solutes, additional to Cl), then its Reference Salinity is the best > available estimate of its Absolute Salinity. For general purposes, > Reference Salinity is (35.16504 g kg-1)/35 times Practical Salinity. > Canonical units: g kg-1 > Reference: www.teos-10.org; Millero et al., 2008 doi: > 10.1016/j.dsr.2007.10.001 > > sea_water_absolute_salinity > Definition: Absolute salinity, S_A, is defined as a term in the > Thermodynamic Equation of Seawater 2010 (TEOS-10) which was adopted in > 2010 by the Intergovernmental Oceanographic Commission (IOC). It is the > mass fraction of dissolved material in sea water and TEOS-10 prescribes > units of g kg-1. Absolute Salinity incorporates the spatial variations in > the composition of seawater. This type of absolute salinity is also called > "Density Salinity". 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 > Reference Composition. In practice, Absolute Salinity is often calculated > from Practical Salinity using a pre-defined value for the Absolute > Salinity Anomaly, which is provided in the form of a global climatology. > It is recommended that the version of (TEOS-10) software and the > associated Absolute Salinity Anomaly climatology be specified within > metadata within the variable "comment" attribute. Standard names exist > for the related quantity, S_*, Preformed Salinity. Salinity observations > made using measurements of the conductivity of sea water after 1978 should > be given the standard name of sea_water_practical_salinity. > Canonical units: g kg-1 > Reference: www.teos-10.org; Millero et al., 2008 doi: > 10.1016/j.dsr.2007.10.001 > > sea_water_preformed_salinity > Definition: Preformed Salinity, S*, is defined as a term in the > Thermodynamic Equation of Seawater 2010 (TEOS-10) which was adopted in > 2010 by the Intergovernmental Oceanographic Commission (IOC). Preformed > Salinity is a salinity variable that is designed to be as conservative as > possible, by removing the estimated biogeochemical influences on the sea > water composition. Preformed Salinity is Absolute Salinity, S_A (which has > the standard name sea_water_absolute_salinity), minus all contributions to > sea water composition from biogeochemical processes. Preformed Salinity > incorporates the spatial variations in the composition of sea water > because of its relationship to Absolute Salinity. It is a mass fraction of > dissolved material in sea water and TEOS-10 prescribes units of g kg-1. > Salinity observations made using measurements of the conductivity of sea > water after 1978 should be given the standard name of > sea_water_practical_salinity. > Canonical units: g kg-1 > Reference: www.teos-10.org; Pawlowicz et al., 2011 doi: > 10.5194/os-7-363-2011; Wright et al., 2011 doi: 10.5194/os-7-1-2011 > > sea_water_conservative_temperature > Definition: Conservative Temperature is defined as a term in the > Thermodynamic Equation of Seawater 2010 (TEOS-10) which was adopted in > 2010 by the Intergovernmental Oceanographic Commission (IOC). Conservative > Temperature is specific potential enthalpy (which has the standard name > specific_potential_enthalpy_of_sea_water) divided by a fixed value of the > specific heat capacity of sea water, namely cp_0 = 3991.86795711963 J kg-1 > K-1. Conservative Temperature is a more accurate measure of the "heat > content" of sea water, by a factor of one hundred, than is potential > temperature. Because of this, it can be regarded as being proportional to > the heat content of sea water per unit mass. Enthalpy can be written > either as (1) CpT, where Cp is heat capacity at constant pressure, T is > absolute temperature, or (2) U+pV, where U is internal energy, p is > pressure and V is volume. > Canonical units: K (or usually, degrees Celsius) > Reference: www.teos-10.org; McDougall, 2003 doi: > 10.1175/1520-0485(2003)033<0945:PEACOV>2.0.CO;2 > > sea_water_specific_potential_enthalpy > Definition: The potential enthalpy of a sea water parcel is the enthalpy > after an adiabatic and isohaline change in pressure from its in situ > pressure to the sea water pressure p = 0 dbar. "specific" means per unit > mass. Enthalpy can be written either as (1) CpT, where Cp is heat capacity > at constant pressure, T is absolute temperature, or (2) U+pV, where U is > internal energy, p is pressure and V is volume. > Canonical units: J kg-1 > Reference: www.teos-10.org; McDougall, 2003 doi: > 10.1175/1520-0485(2003)033<0945:PEACOV>2.0.CO;2 > > > change_over_time_in_X: append text "change_over_time_in_X" means change in > a quantity X over a time-interval, which should be defined by the bounds > of the time coordinate. > Canonical units: unit of X + s-1 > > > So for clarity, the new proposed names are: > sea_water_practical_salinity > sea_water_cox_salinity > sea_water_knudsen_salinity > sea_water_reference_salinity > sea_water_absolute_salinity > sea_water_preformed_salinity > sea_water_conservative_temperature > sea_water_potential_enthalpy > change_over_time_in_sea_water_practical_salinity > change_over_time_in_sea_water_absolute_salinity > change_over_time_in_sea_water_preformed_salinity > change_over_time_in_sea_water_conservative_temperature > change_over_time_in_sea_water_potential_enthalpy > *** > > > > > > -----Original Message----- > From: "[email protected]" <[email protected]> > Date: Mon, 28 Nov 2011 09:12:14 -0800 > To: "Durack, Paul J." <[email protected]> > Subject: Re: [CF-metadata] new TEOS-10 standard names > >> >>________________________________________ >>From: [email protected] [[email protected]] >>On Behalf Of Jonathan Gregory [[email protected]] >>Sent: Tuesday, 29 November 2011 1:05 AM >>To: [email protected] >>Subject: Re: [CF-metadata] new TEOS-10 standard names >> >>Dear Alison >> >>This is great. Thanks for going through it so thoroughly. >> >>> (b) sea_water_temperature >>> There is agreement to retain the standard name sea_water_temperature as >>>this is useful particularly for observations. It currently has no >>>explanatory text. In response to the discussion I propose to add the >>>following sentence: 'Sea temperature is the in situ (bulk) temperature >>>of the sea water, not the surface or skin temperature.' >> >>It is important for models too; although the prognostic is often >> potential >>temperature, in-situ temperature is considered sometimes. Since this is a >>very general term, maybe we can leave it vague (and thus sidestep the >> need >>to define surfaces). It is the in-situ temperature of sea water. SST is a >>species of sea_water_temperature. It is analogous to air_temperature. >> >>> (d) Do we need to modify the explanations of all the existing salinity >>>quantities? >>> As I mentioned, there are twelve salinity names already in the standard >>>name table. >> >>I think these terms can remain vague too. In their vagueness, they are >>parallel to sea_water_salinity, which we are retaining, though >>deprecating for >>future obs quantities, and models where applicable. If salinity is >>generic, >>these generic quantities can also be used for specific purposes. When it >>becomes necessary to be specific about *which* salinity is meant by e.g. >> product_of_northward_sea_water_velocity_and_salinity >>then a new specific standard name can be defined. We could modify the >>definitions to say that they can be used with any definition of salinity >>(but specific ones could be proposed if required to make distinctions). >> >>> (b) sea_water_knudsen_salinity >> >>Yes, I believe this should be in units of 1e-3. >> >>> (c) sea_water_reference_salinity >>> There has been a suggestion that this quantity should also be >>>introduced as a standard name. No comments have so far been received on >>>this proposal. >> >>Please could you remind us of the context? >> >>Best wishes >> >>Jonathan >>_______________________________________________ >>CF-metadata mailing list >>[email protected] >>http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata > _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
