sw.N2 {oce}R Documentation

Seawater square of buoyancy frequency

Description

Compute N^2, the square of the buoyancy frequency for a seawater profile.

Usage

N2 <- sw.N2(ctd, ...)
N2 <- sw.N2(p, sigma.theta=NULL, ...)

Arguments

ctd an object of class "ctd".
p pressure [dbar]
sigma.theta Surface-referenced potential density minus 1000 [kg/m^3]
... Extra arguments that will be passed to smooth.spline if supplied. A common example is to set df, the degrees of freedom for the spline fit; if not set, this will be set to the value length(p)/5.

Details

In the first form, the argument is a ctd object, from which the salinity, temperature and pressure values are extracted, used to calculate sigma.theta, and then used for the calculation of the square of the buoyancy frequency.

The result is calculated from the derivative of a smoothing cubic spline fitted to the density profile using smooth.spline. Optional arguments in ... are passed to this routine, and this gives the user a great deal of control over the smoothing technique; see the documentation on smooth.spline for details. For example, plot.profile uses df=length(x$p)/5 as an optional argument to N2 to do some smoothing of the density profile.

Value

Square of buoyancy frequency [radian/s].

Author(s)

Dan Kelley

Examples

library(oce)
data(ctd)
# Illustrate effect of changing df
plot(sw.N2(ctd), ctd$data$pressure,
        ylim=rev(range(ctd$data$pressure)), xlab="N2",ylab="p", type='l')
lines(sw.N2(ctd, df=10), ctd$data$pressure, col="blue")
grid()

[Package oce version 0.1.72 Index]