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")
)

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)

referencePressure

The reference pressure, in 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

Potential density anomaly (kg/m\(^3\)), defined as \(\sigma_\theta=\rho(S,\theta(S,t,p),0\)

  • 1000 kg/m\(^3\).

Details

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.

References

See citations provided in the swRho() documentation.

Author

Dan Kelley

Examples

stopifnot(abs(26.4212790994 - swSigmaTheta(35, 13, 1000, eos="unesco")) < 1e-7)