gsw_Nsquared function

Calculate Brunt Vaisala Frequency squared

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 list("oce") package).

gsw_Nsquared(SA, CT, p, latitude = 0)

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 lat in the TEOS-10 Matlab code.)

Returns

list containing N2 [ 1/s^2 ] and mid-point pressure p_mid [ dbar ]

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)))

References

http://www.teos-10.org/pubs/gsw/html/gsw_Nsquared.html