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Distance to the nearest eddy

Source: R/eddies.R
distance_to_eddy.Rd

The sibling of distance_to_front() and distance_to_isobath(). Being outside an eddy but close to one is a different place from being far from any, and a binary inside/outside flag cannot express it: a station 5 km from a rotating core and one 300 km away both score zero.

Usage

distance_to_eddy(
  env_dat,
  u = "UO",
  v = "VO",
  threshold = 0.2,
  min_cells = 4L,
  polarity = c("any", "cyclonic", "anticyclonic"),
  per = c("km", "m"),
  name = NULL
)

Arguments

env_dat

an sf POINT object with one row per location and time step, as datamatch's access functions return

u

name of the eastward velocity column, in m/s

v

name of the northward velocity column, in m/s

threshold

multiple of the standard deviation of Okubo-Weiss below which a cell counts as rotational. Positive; 0.2 follows the literature

min_cells

smallest connected region kept, in cells

polarity

"any", "cyclonic", or "anticyclonic"

per

distance unit for the radius, "km" or "m"

name

name for the new column

Value

env_dat with a distance column, in per units. A cell inside a qualifying eddy has a distance of 0. A step containing no qualifying eddy returns NA rather than a distance to nothing

Details

polarity narrows it to one kind. Because cyclonic and anticyclonic eddies do opposite things to the water column, distance to the nearest cyclonic eddy is often the covariate that carries a signal where distance to the nearest eddy of any sort does not.

See also

detect_eddies(), distance_to_front()

Examples

if (FALSE) { # \dontrun{
env <- distance_to_eddy(env, polarity = "cyclonic")
} # }