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"` [1,2] or `"gsw"` [3,4].

### Details

Different formulae are used depending on the equation of state. If `eos` is `"unesco"`, the method of Fofonoff et al. (1983) is used [1,2]. Otherwise, `swTheta` uses `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 1.1-1 Index]