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.

Usage

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swSigma4(salinity, temperature = NULL, pressure = NULL, longitude = 300,
  latitude = 30, 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.

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

Details

Definition: sigma_1=sigma_theta=rho(S,theta(S,t,p),4000) - 1000 kg/m^3.

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, swAbsoluteSalinity, swAlphaOverBeta, swAlpha, swBeta, swCSTp, swConservativeTemperature, swDepth, swDynamicHeight, swLapseRate, swN2, swPressure, swRho, swRrho, swSCTp, swSTrho, swSigma0, swSigma1, swSigma2, swSigma3, swSigmaTheta, swSigmaT, swSigma, swSoundAbsorption, swSoundSpeed, swSpecificHeat, swSpice, swTFreeze, swTSrho, swThermalConductivity, swTheta, swViscosity, swZ

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