sw.theta {oce} | R Documentation |
Compute theta, the potential temperature of seawater.
t.potential <- sw.theta(S, t, p, pref=0, method=c("Bryden1973","UNESCO1983"));
S |
in-situ salinity [PSU] |
t |
in-situ temperature [degC] |
p |
in-situ pressure [dbar] |
pref |
reference pressure [dbar] |
method |
algorithm to be used (see 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 pref
. This quantity is commonly denoted
theta(S,t,p,pref) in the oceanographic
literature.
The "Bryden1973"
method does not use the reference pressure, since
it is set up to approximate potential temperature referenced to the
surface.
For general use, the "UNESCO1983"
method is preferable, since it
permits calculation for arbitrary reference pressure. The UNESCO formula
is derived from Bryden's earlier method, as Fofonoff et al.
(1983) explain.
This is not the place to discuss the two methods in detail, but users may note from the example that the two typically yield values that agree to a few millidegrees.
Potential temperature [degC] of seawater.
Dan Kelley Dan.Kelley@Dal.Ca
Bryden, H. L., 1973. New polynomials for thermal expansion, adiabatic temperature gradient and potential temperature of seawater, Deep-Sea Res., 20, 401-408.
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.
N/A.
library(oce) print(sw.theta(35, 13, 1000)) # 12.858 print(sw.theta(40,40,10000,0,"UNESCO1983")) # 36.89073 (Fofonoff et al., 1983) # Demonstrate that the methods agree to a couple of # millidegrees over a typical span of values S <- c(30,30,38,38) T <- c(-2,-2,30,30) p <- rep(1000,4) print(max(abs(sw.theta(S,T,p) - sw.theta(S,T,p,0,"UNESCO1983"))))