Gibbs Energy of Seawater, and its Derivatives
Gibbs Energy of Seawater, and its Derivatives
gsw_gibbs(ns, nt, np, SA, t, p = 0)
ns |
An integer, the order of the |
nt |
An integer, the order of the |
np |
An integer, the order of the |
SA |
Absolute Salinity [ g/kg ] |
t |
in-situ temperature (ITS-90) [ degC ] |
p |
sea pressure [dbar], i.e. absolute pressure [dbar] minus 10.1325 dbar |
The present R function works with a wrapper to a C function contained within the GSW-C system (Version 3.05-4 dated 2017-08-07, available at https://github.com/TEOS-10/GSW-C, as git commit '5b4d959e54031f9e972f3e863f63e67fa4f5bfec'), which stems from the GSW-Fortran system (https://github.com/TEOS-10/GSW-Fortran) which in turn stems from the GSW-Matlab system (https://github.com/TEOS-10/GSW-Matlab). Consult http://www.teos-10.org to learn more about these software systems, their authorships, and the science behind it all.
Gibbs energy [ J/kg ] if ns=nt=np=0. Derivative of energy
with respect to SA [ J/kg/(g/kg)^ns ] if ns is nonzero and nt=np=0,
etc. Note that derivatives with respect to pressure are in units with Pa, not dbar.
The TEOS-10 webpage for gsw_gibbs does not provide test values, so
the present R version should be considered untested.
library(gsw) p <- seq(0, 100, 1) SA <- rep(35, length(p)) t <- rep(-5, length(p)) ## Check the derivative wrt pressure. Note the unit change E <- gsw_gibbs(0, 0, 0, SA, t, p) # Estimate derivative from linear fit (try plotting: it is very linear) m <- lm(E ~ p) print(summary(m)) plot(p, E) abline(m) dEdp1 <- coef(m)[2] # Calculate derivative ... note we multiply by 1e4 to get from 1/Pa to 1/dbar dEdp2 <- 1e4 * gsw_gibbs(0, 0, 1, SA[1], t[1], p[1]) ## Ratio dEdp1 / dEdp2
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