R: Seawater potential density anomaly referenced to 4000db...

swSigma4 {oce} | R Documentation

## Seawater potential density anomaly referenced to 4000db pressure

### Description

Compute sigma, the potential density of seawater (minus 1000 kg/m^3), referenced to 4000db pressures. This is defined as sigma_1=sigma_theta=rho(S,theta(S,t,p),4000)

- 1000 kg/m^3.

### Usage

    swSigma4(
      salinity,
      temperature = NULL,
      pressure = NULL,
      longitude = NULL,
      latitude = NULL,
      eos = getOption("oceEOS", default = "gsw")
    )

### Arguments

`salinity` | either practical salinity (in which case `temperature` and `pressure` must be provided) or an `oce` object, in which case `salinity`, `temperature` (in the ITS-90 scale; see next item), etc. are inferred from the object, ignoring the other parameters, if they are supplied.
`temperature` | in-situ temperature (degC), defined on the ITS-90 scale. This scale is used by GSW-style calculation (as requested by setting `eos="gsw"`), and is the value contained within `ctd` objects (and probably most other objects created with data acquired in the past decade or two). Since the UNESCO-style calculation is based on IPTS-68, the temperature is converted within the present function, using `T68fromT90()`.
`pressure` | 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).

### Value

Potential density anomaly (kg/m^3).

### Author(s)

Dan Kelley

### References

See citations provided in the `swRho()` documentation.

### 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()`, `swSigmaTheta()`, `swSigmaT()`, `swSigma()`, `swSoundAbsorption()`, `swSoundSpeed()`, `swSpecificHeat()`, `swSpice()`, `swSstar()`, `swTFreeze()`, `swTSrho()`, `swThermalConductivity()`, `swTheta()`, `swViscosity()`, `swZ()`

[Package oce version 1.7-2 Index]