Compute \(\sigma_\theta\), the potential density of seawater (minus 1000 kg/m\(^3\)), referenced to 4000db pressures.
swSigma4(salinity, temperature = NULL, pressure = NULL,
longitude = NULL, latitude = NULL, eos = getOption("oceEOS",
default = "gsw"))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.
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 [dbar]
longitude of observation (only used if eos="gsw";
see ‘Details’).
latitude of observation (only used if eos="gsw"; see
‘Details’).
equation of state, either "unesco" [1,2] or "gsw"
[3,4].
Potential density anomaly [kg/m\(^3\)].
Definition: \(\sigma_1=\sigma_\theta=\rho(S,\theta(S,t,p),4000\) - 1000 kg/m\(^3\).
See citations provided in the swRho documentation.
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