Grid: Vertical Pressure Grid

The oceanarray grid command linearly interpolates the stacked (N_LEVELS, time) dataset onto a regular pressure grid, producing (time, pressure) output suitable for T-S section plots and density diagnostics.

Command

oceanarray grid {mooring} --basedir /path/to/data [--p-start 200] [--p-end 1000] [--dp 20] [--force]

Python API

from oceanarray.mooring_level import MooringGridder

MooringGridder(base_dir).grid(mooring_name, p_start=200.0, p_end=1000.0, dp=20.0, force=False)

Purpose

Grid reads the stacked {mooring}_stack.nc file and interpolates each variable from the sparse instrument levels onto a uniform pressure axis. The result is a (time, pressure) dataset convenient for section plots, density cross-sections, and further analysis.

Run oceanarray stack first; the grid step requires a {mooring}_stack.nc file containing a pressure variable.

Input files

proc/{mooring}/{mooring}_stack.nc

Algorithm

At each time step, the N_LEVELS pressure values and each variable are gathered. Only levels with both a finite pressure value and a finite variable value contribute to the interpolation. The available points are sorted by pressure and passed to numpy.interp onto the target pressure grid. Values at pressures outside the range of finite instruments at that time step are set to NaN; there is no extrapolation.

Note on QC flags

The stack step applies QC masking before gridding: when a companion *_qc variable exists, samples flagged suspect (3), bad (4), or missing (9) are replaced with NaN so they do not contribute to the vertical interpolation. QC flag variables themselves are not gridded.

Pressure grid axis

p_grid = numpy.arange(p_start, p_end + dp / 2, dp)   # dbar

Default: 200 to 1000 dbar in 20 dbar steps.

Output

Dimensions

(time, pressure) — OceanSITES convention with TIME as the first dimension.

Variables gridded

All (N_LEVELS, time) variables present in the stack file, except pressure itself, are interpolated onto the pressure axis. This includes derived quantities such as sigma0 or sigma2 computed at the stack step.

Output file

proc/{mooring}/{mooring}_grid.nc

Global attributes are inherited from the stack file. The following attributes are added: p_start_dbar, p_end_dbar, dp_dbar. The history attribute is extended. Each gridded variable carries a vertical_interpolation note in its attributes.

Grid report

The command oceanarray report {mooring} --grid generates {mooring}_grid_report.html containing:

Variable coverage table (name, long name, units, percentage non-NaN).
Temperature pcolormesh and contourf (colormap RdYlBu_r, 20 discrete levels).
Practical salinity pcolormesh and contourf (colormap YlGnBu_r, reversed so that low salinity maps to blue).
Potential density (sigma0 or sigma2) pcolormesh and contourf (colormap BuPu) with iso-density contour lines overlaid (default 27.7 and 27.8 kg m^-3, configurable via parameters.SIGMA_CONTOUR_LEVELS).

All figures use 20 human-readable discrete colorbar levels computed by utilities._nice_colorbar_bounds(vmin, vmax, n=20), which rounds the step to one significant figure and centres the range on the data midpoint.