Add Isopycnal Curves to a TS Plot

Adds isopycnal lines to an existing temperature-salinity plot. This is called by plotTS(), and may be called by the user also, e.g. if an image plot is used to show TS data density.

Usage

drawIsopycnals(
  nlevels = 6,
  levels,
  rotate = TRUE,
  rho1000 = FALSE,
  digits = 2,
  eos = getOption("oceEOS", default = "gsw"),
  longitude = NULL,
  latitude = NULL,
  trimIsopycnals = TRUE,
  gridIsopycnals = c(50, 50),
  cex = 0.75 * par("cex"),
  col = "darkgray",
  lwd = par("lwd"),
  lty = par("lty"),
  debug = getOption("oceDebug")
)

Arguments

nlevels: suggested number of density levels (i.e. isopycnal curves); ignored if levels is supplied. If this is set to 0, no isopycnal are drawn (see also levels, next).
levels: optional density levels to draw. If this is NULL, then no isopycnals are drawn.
rotate: boolean, set to TRUE to write all density labels horizontally.
rho1000: boolean, set to TRUE to write isopycnal labels as e.g. 1024 instead of 24.
digits: minimum number of decimal digits to use in label (supplied to round()). If the density range is very small, drawIsopycnals() will increase value of digits, to try to make labels be distinct.
eos: equation of state to be used, either "unesco" or "gsw". If it is "gsw" then latitude and longitude must be supplied, since these are needed to computer density in that formulation.
longitude, latitude: numerical values giving the location to be used in density calculations, if eos is "gsw".
trimIsopycnals: logical value (TRUE by default) that indicates whether to trim isopycnal curves (if drawn) to the region of temperature-salinity space for which density computations are considered to be valid in the context of the chosen eos; see the “Details” of the documentation for plotTS().
gridIsopycnals: a parameter that controls how the isopycnals are computed. This may be NULL, or an integer vector of length 2. Case 1: if gridIsopycnals is NULL, then the isopycnals are drawn by tracing density isopleths in salinity-temperature space. This method was used as the default prior to version 1.7-11, but it was found to yield staircase-like isopycnal curves for highly zoomed-in plots (e.g. with millidegree temperature ranges). Case 2 (the new default): If gridIsopycnals is a two-element integer vector, then a grid of density is constructed, with gridIsopycnals[1] salinity levels and gridIsopycnals[2] temperature levels, and then contourLines() is used to trace the isopycnals. The default value of gridIsopycnals yields a grid of millimeter-scale spacing for a typical plot.
cex: size for labels.
col: color for lines and labels.
lwd: line width for isopycnal curves
lty: line type for isopycnal curves
debug: an integer specifying whether debugging information is to be printed during the processing. This is a general parameter that is used by many oce functions. Generally, setting debug=0 turns off the printing, while higher values suggest that more information be printed. If one function calls another, it usually reduces the value of debug first, so that a user can often obtain deeper debugging by specifying higher debug values.

Value

None.

Details

The default method of drawing isopycnals was changed in February of 2023, so that even plots that are zoomed in to have millidegree temperature ranges will have smooth curves. See the discussion of gridIsopycnals for details.

References

Fofonoff, N. P., and R. C. Millard. "Algorithms for Computation of Fundamental Properties of Seawater." UNESCO Technical Papers in Marine Research. SCOR working group on Evaluation of CTD data; UNESCO/ICES/SCOR/IAPSO Joint Panel on Oceanographic Tables and Standards, 1983. https://unesdoc.unesco.org/ark:/48223/pf0000059832.
McDougall, Trevor J., David R. Jackett, Daniel G. Wright, and Rainer Feistel. "Accurate and Computationally Efficient Algorithms for Potential Temperature and Density of Seawater." Journal of Atmospheric and Oceanic Technology 20, no. 5 (May 1, 2003): 730-41. https://journals.ametsoc.org/jtech/article/20/5/730/2543/Accurate-and-Computationally-Efficient-Algorithms.

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