Vertical temperature gradient

The difference between surface and bottom temperature in each cell: a stratification index, large where a warm surface layer sits over cold deep water and near zero where the column is well mixed.

Usage

vertical_gradient(
  env_dat,
  surface = "SST",
  bottom = "BOTT",
  depth = NULL,
  name = NULL
)

Arguments

env_dat: an sf POINT object with one row per location and time step, as datamatch's access functions return
surface: name of the shallower temperature column
bottom: name of the deeper temperature column
depth: optional depth column name; when given, the difference is divided by depth to give a per-metre rate rather than a total difference. datamatch::attach_bathymetry() supplies a DEPTH column.
name: name for the new column

Value

env_dat with the vertical gradient column added

Details

Both defaults come from the same Copernicus physics dataset (SST and BOTT in the datamatch catalog, thetao and bottomT as Copernicus codes), so the usual case needs no extra fetch — it is a difference between two columns already present.

Other levels, and a better measure

The two columns are arguments, not fixed, so this is not restricted to the surface and the sea floor. datamatch::accessCopernicus() takes a depth argument and returns one level per call, so a second fetch at a chosen depth gives a temperature at that level, and the difference between any two levels can be taken the same way.

Where the two levels are known, buoyancy_frequency() is the better quantity. This is a temperature difference, which stands in for stratification only where salinity is uniform — and in the Gulf of Maine it is not, since Scotian Shelf inflow is fresh enough to stratify water barely warmer at the surface. \(N^2\) counts both contributions with the weights the equation of state gives them.

Examples

if (FALSE) { # \dontrun{
env <- datamatch::accessCopernicus(vars = c("SST", "BOTT"), ...)
env <- vertical_gradient(env)                 # SST and BOTT are the defaults

# As a per-metre rate, with depth from datamatch's bathymetry
bathy <- datamatch::fetch_bathymetry(bounding_box = bb)
env <- datamatch::attach_bathymetry(env, bathy, "DEPTH")
env <- vertical_gradient(env, depth = "DEPTH")

# Between two chosen levels rather than surface and sea floor
deep <- datamatch::accessCopernicus(vars = "SST", depth = c(90, 100), ...)
env$SST_90m <- deep$SST
env <- vertical_gradient(env, surface = "SST", bottom = "SST_90m")
} # }