Seawater Quasi-Potential Density Anomaly

Compute \(\sigma_t\), a rough estimate of potential density of seawater, minus 1000 kg/m\(^3\).

Usage

swSigmaT(
  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 (\(^\circ\)C), 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

Quasi-potential density anomaly (kg/m\(^3\)), defined as the density calculated with pressure set to zero.

Details

If the first argument is an oce object, then salinity, etc., are extracted from it, and used for the calculation.

References

See citations provided in the swRho() documentation.

Other functions that calculate seawater properties: T68fromT90(), T90fromT48(), T90fromT68(), computableWaterProperties(), locationForGsw(), swAbsoluteSalinity(), swAlpha(), swAlphaOverBeta(), swBeta(), swCSTp(), swConservativeTemperature(), swDepth(), swDynamicHeight(), swLapseRate(), swN2(), swPressure(), swRho(), swRrho(), swSCTp(), swSR(), swSTrho(), swSigma(), swSigma0(), swSigma1(), swSigma2(), swSigma3(), swSigma4(), swSigmaTheta(), swSoundAbsorption(), swSoundSpeed(), swSpecificHeat(), swSpice(), swSpiciness0(), swSpiciness1(), swSpiciness2(), swSstar(), swTFreeze(), swTSrho(), swThermalConductivity(), swTheta(), swViscosity(), swZ()

Author

Dan Kelley

Examples

swSigmaT(35, 13, 1000, longitude = 300, latitude = 30, eos = "gsw") # 26.39623
#> [1] 26.39623
swSigmaT(35, T90fromT68(13), 1000, eos = "unesco") # 26.39354
#> [1] 26.39354