oce (version 0.9-18)

swTheta: Seawater potential temperature

Description

Compute $\theta$, the potential temperature of seawater.

Usage

swTheta(salinity, temperature=NULL, pressure=NULL, referencePressure=0,
    longitude=300, latitude=30, eos=getOption("oceEOS", default="gsw"))

Arguments

salinity

either salinity [PSU] (in which case temperature and pressure must be provided) or an oce object (in which case salinity, etc. are inferred from the object).

temperature

in-situ temperature [$^\circ$C], defined on the ITS-90 scale; see Temperature units in the documentation for swRho, and the examples below.

pressure

pressure [dbar]

referencePressure

reference 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" [1,2] or "gsw" [3,4].

Value

• Potential temperature [$^\circ$C] of seawater.

Details

The potential temperature is defined to be the temperature that a water parcel of salinity S, in-situ temperature t and pressure p would have if were to be moved adiabatically to a location with pressure referencePressure. This quantity is commonly denoted $\theta$ in the oceanographic literature.

If the first argument is a ctd or section object, then values for salinity, etc., are extracted from it, and used for the calculation, and the corresponding arguments to the present function are ignored.

For eos="unesco" the method of Fofonoff et al. (1983), is used [1,2]. For eos="gsw", gsw_pt_from_t is used [3,4].

References

[1] Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for computation of fundamental properties of seawater. Unesco Technical Papers in Marine Science, 44, 53 pp

[2] Gill, A.E., 1982. Atmosphere-ocean Dynamics, Academic Press, New York, 662 pp.

[3] IOC, SCOR, and IAPSO (2010). The international thermodynamic equation of seawater-2010: Calculation and use of thermodynamic properties. Technical Report 56, Intergovernmental Oceanographic Commission, Manuals and Guide.

[4] McDougall, T.J. and P.M. Barker, 2011: Getting started with TEOS-10 and the Gibbs Seawater (GSW) Oceanographic Toolbox, 28pp., SCOR/IAPSO WG127, ISBN 978-0-646-55621-5.

See Also

The corresponding potential density anomaly $\sigma_\theta$ can be calculated with swSigmaTheta.

Examples

library(oce)

print(swTheta(40, T90fromT68(40), 10000, 0, eos="unesco")) # 36.89073 (Fofonoff et al., 1983)
	
# Demonstrate that the UNESCO and GSW methods agree to a about 0.1C over a
# typical span of values.
S <- c(30,35,30,35)
T <- c(-2,-2,30,30)
p <- 1000 * runif(n=4)
print(max(abs(swTheta(S,T90fromT68(T),p) - swTheta(S,T,p,0,eos="gsw"))))

# Example from a cross-Atlantic section
data(section)
stn <- section[['station', 70]]
plotProfile(stn, 'theta', ylim=c(6000, 1000))
lines(stn[['temperature']], stn[['pressure']], lty=2)
legend("topleft", lty=1:2,
       legend=c("potential", "in-situ"),
       bg='white', title="Station 70")