R: Seawater freezing temperature

swTFreeze {oce} | R Documentation

## Seawater freezing temperature

### Description

Compute in-situ freezing temperature of seawater, using either the UNESCO formulation (computed as in Section 5 of reference 1) 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).

### Usage

    swTFreeze(
      salinity,
      pressure = NULL,
      longitude = NULL,
      latitude = NULL,
      saturation_fraction = 1,
      eos = getOption("oceEOS", default = "gsw")
    )

### Arguments

`salinity` | Either practical salinity (PSU) or a `ctd` object from which practical salinity and pressure (plus in the `eos="gsw"` case, longitude and latitude) are inferred, using `lookWithin()`.
`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"` (references 1 and 2) or `"gsw"`. (references 3 and 4).

### 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.

### Value

Temperature (degC), defined on the ITS-90 scale.

### Author(s)

Dan Kelley

### References

1. 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. https://unesdoc.unesco.org/ark:/48223/pf0000059832.

2. Gill, A E. Atmosphere-Ocean Dynamics. New York, NY, USA: Academic Press,

4. 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.

5. 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()`, `swAbsoluteSalinity()`, `swAlphaOverBeta()`, `swAlpha()`, `swBeta()`, `swCSTp()`, `swConservativeTemperature()`, `swDepth()`, `swDynamicHeight()`, `swLapseRate()`, `swN2()`, `swPressure()`, `swRho()`, `swRrho()`, `swSCTp()`, `swSTrho()`, `swSigma0()`, `swSigma1()`, `swSigma2()`, `swSigma3()`, `swSigma4()`, `swSigmaTheta()`, `swSigmaT()`, `swSigma()`, `swSoundAbsorption()`, `swSoundSpeed()`, `swSpecificHeat()`, `swSpice()`, `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")
    expect_equal(Tcheck, T68fromT90(T), tolerance=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)))

[Package oce version 1.2-0 Index]