Pycnocline depth and maximum N^2 of one CTD cast — ctd

Rasmus Swalethorp's definition (email 2026-09-24, R draft "Boyancy frequency and pycnocline.r"; the legacy bottle script F_PycnoclineDepth.m after Fiedler et al. 2013, J. Climate): "The pycnocline is defined physically as the depth of maximum static stability": the pressure at which the smoothed N^2 of ctd_n2() is greatest within the search window p_min-p_max dbar (the draft's 10-200 m), and n2_max that value. The legacy script's conditions are kept: the cast must start no deeper than surface_max_m (15 m) and reach at least depth_min_m (50 m), with at least min_points (5) good values inside the window; an exact tie goes to the centre of the tied run.

Usage

ctd_pycnocline(
  pressure,
  n2,
  p_min = 10,
  p_max = 200,
  min_points = 5,
  surface_max_m = 15,
  depth_min_m = 50
)

Arguments

pressure: sea pressure (dbar), one cast.
n2: the smoothed N^2 at those pressures, from ctd_n2() (NA where flagged).
p_min, p_max: the search window (dbar), default 10-200.
min_points: fewest good values inside the window, default 5.
surface_max_m: deepest acceptable first good sample (m), default 15.
depth_min_m: shallowest acceptable deepest good sample (m), default 50.

Value

one-row tibble: pycnocline_depth_m, n2_max, status (ok, no_surface, too_shallow, too_few, no_data), n (good values inside the window).

Examples

p <- 1:300
n2 <- ctd_n2(ifelse(p < 60, 16, 10), 33.5, p, -120, 33)
ctd_pycnocline(p, n2)   # about 60 dbar
#> # A tibble: 1 × 4
#>   pycnocline_depth_m  n2_max status     n
#>                <dbl>   <dbl> <chr>  <int>
#> 1                 59 0.00206 ok       191