The result is computed based on first-differencing a computed density with
respect pressure, and this can yield noisy results with CTD data that
have not been smoothed and decimated. It also yields infinite values,
for repeated adjacent pressure (e.g. this occurs twice with the ctd
dataset provided in the oce package).
Arguments
- SA
Absolute Salinity [ g/kg ]. The valid range for most `gsw` functions is 0 to 42 g/kg.
- CT
Conservative Temperature [ degC ].
- p
sea pressure [dbar], i.e. absolute pressure [dbar] minus 10.1325 dbar
- latitude
latitude in decimal degrees, positive to the north of the equator. (This is called
latin the TEOS-10 Matlab code.)
Implementation Note
This R function uses a wrapper to a C function contained within the GSW-C system as updated 2022-10-11 at https://github.com/TEOS-10/GSW-C with git commit `657216dd4f5ea079b5f0e021a4163e2d26893371`.
The C function uses data from the library/gsw_data_v3_0.mat
file provided in the GSW-Matlab source code, version 3.06-11.
Unfortunately, this version of the mat file is no longer displayed on the
TEOS-10.org website. Therefore, in the interests of making GSW-R be
self-contained, a copy was downloaded from
http://www.teos-10.org/software/gsw_matlab_v3_06_11.zip on 2022-05-25,
the .mat file was stored in the developer/create_data directory of
https://github.com/TEOS-10/GSW-R, and then the dataset used in GSW-R
was created based on that .mat file.
Please consult http://www.teos-10.org to learn more about the various TEOS-10 software systems.
Examples
SA <- c(34.7118, 34.8915, 35.0256, 34.8472, 34.7366, 34.7324)
CT <- c(28.8099, 28.4392, 22.7862, 10.2262, 6.8272, 4.3236)
p <- c( 10, 50, 125, 250, 600, 1000)
latitude <- 4
r <- gsw_Nsquared(SA, CT, p, latitude=4)
stopifnot(all.equal(r$N2*1e3, c(0.060843209693499, 0.235723066151305, 0.216599928330380,
0.012941204313372, 0.008434782795209)))
stopifnot(all.equal(r$p_mid, c(30, 87.5, 187.5, 425, 800)))