Compute in-situ freezing temperature of seawater, using either the UNESCO
formulation (computed as in Section 5 of Fofonoff and Millard, 1983) or the
GSW formulation (computed by using gsw::gsw_SA_from_SP() to get Absolute
Salinity, and then gsw::gsw_t_freezing() to get the freezing temperature).
swTFreeze(
salinity,
pressure = NULL,
longitude = NULL,
latitude = NULL,
saturation_fraction = 1,
eos = getOption("oceEOS", default = "gsw")
)Arguments
- salinity
Either practical salinity (PSU) or a
ctdobject from which practical salinity and pressure (plus in theeos="gsw"case, longitude and latitude) are inferred.- pressure
Seawater pressure (dbar).
- longitude
Longitude of observation (only used if
eos="gsw"; see “Details”).- latitude
Latitude of observation (only used if
eos="gsw"; see “Details”).- saturation_fraction
The saturation fraction of dissolved air in seawater, ignored if
eos="unesco").- eos
The equation of state, either
"unesco"(Fofonoff and Millard, 1983; Gill 1982) or"gsw"(IOC, SCOR and IAPSO 2010; McDougall and Barker 2011).
Value
Temperature (degC), defined on the ITS-90 scale.
Details
If the first argument is an oce object, and if the pressure argument is
NULL, then the pressure is sought within the first argument. In the case of
eos="gsw", then a similar procedure also applies to the longitude and
latitude arguments.
References
Fofonoff, N. P., and R. C. Millard. Algorithms for Computation of Fundamental Properties of Seawater. UNESCO Technical Papers in Marine Research. SCOR working group on Evaluation of CTD data; UNESCO/ICES/SCOR/IAPSO Joint Panel on Oceanographic Tables and Standards, 1983.
Gill, A E. Atmosphere-Ocean Dynamics. New York, NY, USA: Academic Press, 1982.
IOC, SCOR, and IAPSO (2010). The international thermodynamic equation of seawater-2010: Calculation and use of thermodynamic properties. Technical Report 56, Intergovernmental Oceanographic Commission, Manuals and Guide, 2010.
McDougall, Trevor J., and Paul M. Barker. Getting Started with TEOS-10 and the Gibbs Seawater (GSW) Oceanographic Toolbox. SCOR/IAPSO WG127, 2011.
See also
Other functions that calculate seawater properties:
T68fromT90(),
T90fromT48(),
T90fromT68(),
computableWaterProperties(),
locationForGsw(),
swAbsoluteSalinity(),
swAlphaOverBeta(),
swAlpha(),
swBeta(),
swCSTp(),
swConservativeTemperature(),
swDepth(),
swDynamicHeight(),
swLapseRate(),
swN2(),
swPressure(),
swRho(),
swRrho(),
swSCTp(),
swSR(),
swSTrho(),
swSigma0(),
swSigma1(),
swSigma2(),
swSigma3(),
swSigma4(),
swSigmaTheta(),
swSigmaT(),
swSigma(),
swSoundAbsorption(),
swSoundSpeed(),
swSpecificHeat(),
swSpice(),
swSstar(),
swTSrho(),
swThermalConductivity(),
swTheta(),
swViscosity(),
swZ()
Examples
# 1. Test for a check-value given in reference 1. This value, -2.588567 degC,
# is in the 1968 temperature scale (IPTS-68), but swTFreeze reports
# in the newer ITS-90 scale, so we must convert before checking.
Tcheck <- -2.588567 # IPTS-68
T <- swTFreeze(salinity=40, pressure=500, eos="unesco")
stopifnot(abs(Tcheck - T68fromT90(T)) < 1e-6)
# 2. Compare unesco and gsw formulations.
data(ctd)
p <- ctd[["pressure"]]
par(mfrow=c(1, 2), mar=c(3, 3, 1, 2), mgp=c(2, 0.7, 0))
plot(swTFreeze(ctd, eos="unesco"),
p, xlab="unesco", ylim=rev(range(p)))
plot(swTFreeze(ctd, eos="unesco") - swTFreeze(ctd, eos="gsw"),
p, xlab="unesco-gsw", ylim=rev(range(p)))
