Absolute Salinity Anomaly Ratio

Usage

gsw_SAAR(p, longitude, latitude)

Arguments

p: sea pressure [dbar], i.e. absolute pressure [dbar] minus 10.1325 dbar
longitude: longitude in decimal degrees, positive to the east of Greenwich. (This is called long in the TEOS-10 Matlab code.)
latitude: latitude in decimal degrees, positive to the north of the equator. (This is called lat in the TEOS-10 Matlab code.)

Value

a list containing SAAR, which is the (unitless) Absolute Salinity Anomaly Ratio, and in_ocean is set to 1 if SAAR is nonzero, or to 0 otherwise.

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.

Bugs

The definition of in_ocean is incorrect, because the C function named gsw_saar, which is called by the present R function, does not calculate in_ocean, as the base Matlab function named gsw_SAAR does. However, examination of the Matlab code shows that in_ocean is set to 0 along with SAAR, whenever the original estimate of the latter is nonfinite. Thus, points that would be signalled as being on the land by the Matlab code are indicated in the same way with the present R function. However, other points may also be indicated as being on land, if SAAR is simply zero in the first calculation. Whether this poses a problem in practice is an open question, since it seems likely that this function would only be called with oceanic locations, anyway. If problems arise for users, a patch can be written to improve things.

References

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

Examples

p <- c(10, 50, 125, 250, 600, 1000)
longitude <- c(188, 188, 188, 188, 188, 188)
latitude <- c(4, 4, 4, 4, 4, 4)
SAAR <- gsw_SAAR(p, longitude, latitude)
stopifnot(all.equal(1e3*SAAR$SAAR, c(0.004794295602143, 0.007668755837570, 0.018919828449091,
                                     0.077293264028981, 0.161974583039298, 0.270652408428964)))
stopifnot(all.equal(SAAR$in_ocean, rep(1, 6)))