swTheta {oce} | R Documentation

## Seawater potential temperature

### Description

Compute theta, the potential temperature of seawater.

### Usage

    swTheta(salinity, temperature=NULL, pressure=NULL, referencePressure=0,
        longitude=300, latitude=30, 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

The potential temperature is defined to be the temperature that a water parcel of salinity `S`, in-situ temperature `t` and pressure `p` would have if were to be moved adiabatically to a location with pressure `referencePressure`. This quantity is commonly denoted theta in the oceanographic literature.

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.

For `eos="unesco"` the method of Fofonoff et al. (1983), is used [1,2]. For `eos="gsw"`, `gsw_pt_from_t` is used [3,4].

### Value

Potential temperature [degC] of seawater.

### 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

The corresponding potential density anomaly sigma-theta can be calculated with `swSigmaTheta`.

### Examples

    library(oce)

    print(swTheta(40, T90fromT68(40), 10000, 0, eos="unesco")) # 36.89073 (Fofonoff et al., 1983)

    # Demonstrate that the UNESCO and GSW methods agree to a about 0.1C over a
    # typical span of values.
    S <- c(30,35,30,35)
    T <- c(-2,-2,30,30)
    p <- 1000 * runif(n=4)
    print(max(abs(swTheta(S,T90fromT68(T),p) - swTheta(S,T,p,0,eos="gsw"))))

    # 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("topleft", lty=1:2,
           legend=c("potential", "in-situ"),
           bg='white', title="Station 70")

[Package oce version 0.9-18 Index]