This is analogous to swSigma0(), but referenced to 4000db pressure.
swSigma4(
salinity,
temperature = NULL,
pressure = NULL,
longitude = NULL,
latitude = NULL,
eos = getOption("oceEOS", default = "gsw")
)Potential density anomaly (kg/m\(^3\)).
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)
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).
Dan Kelley
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(),
swSigmaT(),
swSigmaTheta(),
swSoundAbsorption(),
swSoundSpeed(),
swSpecificHeat(),
swSpice(),
swSpiciness0(),
swSpiciness1(),
swSpiciness2(),
swSstar(),
swTFreeze(),
swTSrho(),
swThermalConductivity(),
swTheta(),
swViscosity(),
swZ()