swTheta {oce} | R Documentation |
Compute theta, the potential temperature of seawater.
swTheta(salinity, temperature=NULL, pressure=NULL, referencePressure=0, longitude=300, latitude=30, eos=getOption("oceEOS", default="gsw"))
salinity |
either salinity [PSU] (in which case |
temperature |
in-situ temperature [degC], defined
on the ITS-90 scale; see “Temperature units” in the documentation for
|
pressure |
pressure [dbar] |
referencePressure |
reference pressure [dbar] |
longitude |
longitude of observation (only used if |
latitude |
latitude of observation (only used if |
eos |
equation of state, either |
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].
Potential temperature [degC] of seawater.
Dan Kelley
[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.
The corresponding potential density anomaly
sigma-theta can be calculated with
swSigmaTheta
.
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")