R: Seawater potential temperature

swTheta {oce} | R Documentation

## Seawater potential temperature

### Description

Compute the potential temperature of seawater, denoted theta in the UNESCO system, and `pt` in the GSW system.

### Usage

    swTheta(
      salinity,
      temperature = NULL,
      pressure = NULL,
      referencePressure = 0,
      longitude = NULL,
      latitude = NULL,
      eos = getOption("oceEOS", default = "gsw")
    )

### Arguments

`salinity` | either salinity (PSU) (in which case `temperature` and `pressure` must be provided) or an `oce` object (in which case `salinity`, etc. are inferred from the object).
`temperature` | in-situ temperature (degC), defined on the ITS-90 scale; see “Temperature units” in the documentation for `swRho()`, and the examples below.
`pressure` | pressure (dbar)
`referencePressure` | reference pressure (dbar)
`longitude` | longitude of observation (only used if `eos="gsw"`; see ‘Details’).
`latitude` | latitude of observation (only used if `eos="gsw"`; see ‘Details’).
`eos` | equation of state, either `"unesco"` (references 1 and 2) or `"gsw"` (references 3 and 4).

### Details

Different formulae are used depending on the equation of state. If `eos` is `"unesco"`, the method of Fofonoff et al. (1983) is used (see references 1 and 2). Otherwise, `swTheta` uses `gsw::gsw_pt_from_t()` from the gsw package.

If the first argument is a `ctd` or `section` object, then values for salinity, etc., are extracted from it, and used for the calculation, and the corresponding arguments to the present function are ignored.

### Value

Potential temperature (degC) of seawater, referenced to pressure `referencePressure`.

### Author(s)

Dan Kelley

### References

1. Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for computation of fundamental properties of seawater. Unesco Technical Papers in Marine Science, 44, 53 pp

2. Gill, A.E., 1982. Atmosphere-ocean Dynamics, Academic Press, New York, 662 pp.

3. 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.

4. McDougall, T.J. and P.M. Barker, 2011: Getting started with TEOS-10 and the Gibbs Seawater (GSW) Oceanographic Toolbox, 28pp., SCOR/IAPSO WG127, ISBN 978-0-646-55621-5.

### 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()`, `swTFreeze()`, `swTSrho()`, `swThermalConductivity()`, `swViscosity()`, `swZ()`

### Examples

    library(oce)
    ## test value from Fofonoff et al., 1983
    expect_equal(36.8818748026, swTheta(40, T90fromT68(40), 10000, 0, eos="unesco"))

    # Example from a cross-Atlantic section
    data(section)
    stn <- section[['station', 70]]
    plotProfile(stn, 'theta', ylim=c(6000, 1000))
    lines(stn[['temperature']], stn[['pressure']], lty=2)
    legend("bottomright", lty=1:2,
           legend=c("potential", "in-situ"),
           bg='white', title="Station 70")

[Package oce version 1.2-0 Index]