The first depth below ref_depth where the profile departs from its value at ref_depth by
threshold, linearly interpolated between the two bracketing samples (CalCOFI/workflows#101).
The criterion is an argument because the choice is Rasmus Swalethorp's to confirm; the defaults
are de Boyer Montegut et al. (2004, JGR 109, C12003): reference 10 m, sigma-theta increase of
0.03 kg m^-3. The classic alternative is 0.125 kg m^-3 (Levitus 1982; Monterey & Levitus 1997);
the temperature criterion (|Delta T| >= 0.2 deg C) needs no salinity, so it is the only one a
preliminary_without_bottle cast can have.
Usage
ctd_mld(
depth,
value,
qual = NA,
criterion = c("sigma_theta", "temperature"),
threshold = NULL,
ref_depth = 10
)Arguments
- depth
depth (m), positive down; one cast.
- value
sigma-theta (kg m^-3) or temperature (deg C), per
criterion.- qual
quality codes of
value(NA= good).- criterion
"sigma_theta"(value must increase bythreshold) or"temperature"(absolute departure ofthreshold).- threshold
the departure that ends the mixed layer; default 0.03 for sigma-theta, 0.2 for temperature.
- ref_depth
reference depth (m), default 10.
Value
one-row tibble: mld_m, ref_value, depth_max_m (deepest good sample), status
(ok, mixed_to_bottom, no_reference, no_data), criterion, threshold, ref_depth.
Details
The value at ref_depth is interpolated from the samples either side of it (it is NA, status
no_reference, when the cast does not bracket it); a cast that never crosses the threshold has
mld_m = NA and status mixed_to_bottom (its deepest sample is reported, so a consumer can say
"deeper than"). Flagged samples (8/9) are dropped first.
Examples
z <- 0:100
ctd_mld(z, ifelse(z < 40, 25, 25.5)) # step at 40 m
#> # A tibble: 1 × 7
#> mld_m ref_value depth_max_m status criterion threshold ref_depth
#> <dbl> <dbl> <dbl> <chr> <chr> <dbl> <dbl>
#> 1 39.1 25 100 ok sigma_theta 0.03 10
ctd_mld(z, ifelse(z < 40, 25, 25.5), threshold = 0.125)
#> # A tibble: 1 × 7
#> mld_m ref_value depth_max_m status criterion threshold ref_depth
#> <dbl> <dbl> <dbl> <chr> <chr> <dbl> <dbl>
#> 1 39.2 25 100 ok sigma_theta 0.125 10