oce (version 0.9-14)

swDynamicHeight: Dynamic height of seawater profile

Description

Compute the dynamic height of a column of seawater.

Usage

swDynamicHeight(x, referencePressure=2000)

Arguments

x

a section object, or a ctd object.

referencePressure

reference pressure [dbar]

Value

• In the first form, a list containing distance, the distance [km] from the first station in the section and height, the dynamic height [m].

  In the second form, a single value, containing the dynamic height [m].

Details

If the first argument is a section, then dynamic height is calculated for each station within a section, and returns a list containing distance along the section along with dynamic height.

If the first argument is a ctd, then this returns just a single value, the dynamic height.

Stations are analysed in steps. First, a piecewise-linear model of the density variation with pressure is developed using approxfun. (The option rule=2 is used to extrapolate the uppermost density up to the surface, preventing a possible a bias for bottle data, in which the first depth may be a few metres below the surface.) A second function is constructed as the density of water with salinity 35PSU, temperature of 0$^\circ$C, and pressure as in the ctd. The reciprocal difference of these densities is then integrated using integrate with pressure limits 0 to referencePressure, and divided by the acceleration due to gravity, to calculate the dynamic height.

If the water column is too short to have bottom pressure exceeding referencePressure, a missing value is reported.

References

Gill, A.E., 1982. Atmosphere-ocean Dynamics, Academic Press, New York, 662 pp.

Examples

library(oce)

# Dynamic height and geostrophy
par(mfcol=c(2,2))
par(mar=c(4.5,4.5,2,1))

# Left-hand column: whole section
# (The smoothing lowers Gulf Stream speed greatly)
westToEast <- subset(section, 1<=stationId&stationId<=123)
dh <- swDynamicHeight(westToEast)
plot(dh$distance, dh$height, type='p', xlab="", ylab="dyn. height [m]")
ok <- !is.na(dh$height)
smu <- supsmu(dh$distance, dh$height)
lines(smu, col="blue")
f <- coriolis(section[["station", 1]][["latitude"]])
g <- gravity(section[["station", 1]][["latitude"]])
v <- diff(smu$y)/diff(smu$x) * g / f / 1e3 # 1e3 converts to m
plot(smu$x[-1], v, type='l', col="blue", xlab="distance [km]", ylab="velocity [m/s]")

# right-hand column: gulf stream region, unsmoothed
gs <- subset(section, 102<=stationId&stationId<=124)
dh.gs <- swDynamicHeight(gs)
plot(dh.gs$distance, dh.gs$height, type='b', xlab="", ylab="dyn. height [m]")
v <- diff(dh.gs$height)/diff(dh.gs$distance) * g / f / 1e3
plot(dh.gs$distance[-1], v, type='l', col="blue",
  xlab="distance [km]", ylab="velocity [m/s]")