gsw (version 1.2-0)

gsw_Nsquared: Calculate Brunt Vaisala Frequency squared

Description

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).

Usage

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

Value

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

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.)

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.

References

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

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)))