Compute the potential density (minus 1000 kg/m^3) that seawater would have if raised
adiabatically to the surface. In the UNESCO system, this quantity is
is denoted \(\sigma_\theta\) (hence the function name), but in
the GSW system, a somewhat related quantity is denoted sigma0. (In a
deep-water CTD cast, the RMS deviation between sigma-theta and sigma0 is
typically of order 0.0003 kg/m^3, corresponding to a temperature shift of
about 0.002C, so the distinction between the quantities is not large.)
swSigmaTheta(
salinity,
temperature = NULL,
pressure = NULL,
referencePressure = 0,
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, ignoring the
other parameters, if they are supplied.
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)
The reference pressure, in 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" (references 1 and 2)
or "gsw" (references 3 and 4).
Potential density anomaly (kg/m\(^3\)), defined as \(\sigma_\theta=\rho(S,\theta(S,t,p),0\)
1000 kg/m\(^3\).
If the first argument is an oce object, then salinity, etc., are
extracted from it, and used for the calculation instead of any values
provided in the other arguments.
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(),
swSigmaT(),
swSoundAbsorption(),
swSoundSpeed(),
swSpecificHeat(),
swSpice(),
swSpiciness0(),
swSpiciness1(),
swSpiciness2(),
swSstar(),
swTFreeze(),
swTSrho(),
swThermalConductivity(),
swTheta(),
swViscosity(),
swZ()