mom6_bathy.grid module

class mom6_bathy.grid.Grid(lenx: float, leny: float, nx: int = None, ny: int = None, resolution: float | None = None, xstart: float = 0.0, ystart: float | None = None, cyclic_x: bool = False, name: str | None = None, type: str = 'uniform_spherical')

Bases: object

Horizontal MOM6 grid. The first step of constructing a MOM6 grid within the CESM simpler models framework is to create a Grid instance.

tlon

array of t-grid longitudes

Type:

xr.DataArray

tlat

array of t-grid latitudes

Type:

xr.DataArray

ulon

array of u-grid longitudes

Type:

xr.DataArray

ulat

array of u-grid latitudes

Type:

xr.DataArray

vlon

array of v-grid longitudes

Type:

xr.DataArray

vlat

array of v-grid latitudes

Type:

xr.DataArray

qlon

array of corner longitudes

Type:

xr.DataArray

qlat

array of corner latitudes

Type:

xr.DataArray

dxt

x-distance between U points, centered at t

Type:

xr.DataArray

dyt

y-distance between V points, centered at t

Type:

xr.DataArray

dxCv

x-distance between q points, centered at v

Type:

xr.DataArray

dyCu

y-distance between q points, centered at u

Type:

xr.DataArray

dxCu

x-distance between y points, centered at u

Type:

xr.DataArray

dyCv

y-distance between t points, centered at v

Type:

xr.DataArray

angle

angle grid makes with latitude line

Type:

xr.DataArray

angle_q

angle q-grid makes with latitude line

Type:

xr.DataArray

tarea

T-cell area

Type:

xr.DataArray

Grid instance constructor.

Parameters:

  • lenx (float) – grid length in x direction, e.g., 360.0 (degrees)

  • leny (float) – grid length in y direction, e.g., 160.0 (degrees)

  • nx (int, optional) – Number of grid points in x direction

  • ny (int, optional) – Number of grid points in y direction

  • resolution (float, optional) – grid resolution in degrees. If provided, the grid dimensions are computed based on the resolution: nx = int(lenx / resolution) and ny = int(leny / resolution)

  • xstart (float, optional) – starting x coordinate. 0.0 by default.

  • ystart (float, optional) – starting y coordinate. -0.5*leny by default.

  • cyclic_x (bool, optional) – flag to make the grid cyclic in x direction. False by default.

  • name (str, optional) – name of the grid. None by default.

  • type (str, optional) – If not specified, creates an uniform_degree grid. Options are uniform_degree or rectilinear_cartesian

static check_supergrid(supergrid: Dataset) → None

Check if a given supergrid contains the necessary attributes and has consistent units.

Parameters:

supergrid (xarray.Dataset) – MOM6 Supergrid dataset

classmethod from_center(center_lat: float, center_lon: float, width_m: float, height_m: float, resolution_m: float, angle_deg: float = 0.0, name: str | None = None) → Grid

Create a rotated rectangular grid centred at a geographic point.

Uses an azimuthal equidistant projection centred at (center_lat, center_lon) and rotates the domain by angle_deg clockwise from north. Useful for aligning a regional domain with a coastline feature — for example, placing one grid boundary perpendicular to an estuary mouth.

Parameters:

  • center_lat (float) – Geographic centre of the domain in degrees.

  • center_lon (float) – Geographic centre of the domain in degrees.

  • width_m (float) – Domain width (x) and height (y) in metres.

  • height_m (float) – Domain width (x) and height (y) in metres.

  • resolution_m (float) – Grid resolution in metres.

  • angle_deg (float, optional) – Clockwise rotation from north in degrees. Default 0 (north-up). Example: angle_deg=45 places the x-axis along a NE–SW estuary mouth.

  • name (str, optional) – Name of the grid.

Return type:

Grid

classmethod from_projection(crs, x_min: float, x_max: float, y_min: float, y_max: float, resolution_m: float, name: str | None = None) → Grid

Create a Grid from projected coordinate extents.

Builds a uniform grid in the given pyproj CRS (e.g., polar stereographic, Lambert conformal) and reprojects to geographic coordinates. Grid metrics are computed using exact great-circle geometry, making this accurate at high latitudes where RectilinearCartesianSupergrid degrades.

Parameters:

  • crs (pyproj.CRS, int, or str) –

    Map projection. Examples:

    ”EPSG:3995” — Arctic Polar Stereographic “EPSG:3031” — Antarctic Polar Stereographic

  • x_min (float) – Projected x extent in metres.

  • x_max (float) – Projected x extent in metres.

  • y_min (float) – Projected y extent in metres.

  • y_max (float) – Projected y extent in metres.

  • resolution_m (float) – Grid resolution in metres.

  • name (str, optional) – Name of the grid.

Return type:

Grid

classmethod from_supergrid(path: str, name: str | None = None) → Grid

Create a Grid instance from a supergrid file.

Parameters:

  • path (str) – Path to the supergrid file to be written

  • name (str, optional) – Name of the new grid. If provided, it will be used as the name of the grid. If not provided, the name will be derived from the file name.

Returns:

The Grid instance created from the supergrid file.

Return type:

Grid

classmethod from_supergrid_ds(ds: Dataset, name: str | None = None) → Grid

Create a Grid instance from a supergrid file.

Parameters:

  • ds (xr.Dataset) – xarray Dataset of the supergrid file to be written

  • name (str, optional) – Name of the new grid. If provided, it will be used as the name of the grid.

Returns:

The Grid instance created from the supergrid file.

Return type:

Grid

classmethod get_bounding_boxes_of_rectangular_grid(hgrid)

Extract lat/lon bounding boxes for each edge of a rectangular regional MOM6 grid. This function is used when subsetting global datasets (e.g. GLORYS) down to the lat/lon ranges required for efficient regridding:

  • north, south, east, west boundaries

  • Entire domain initial condition files

Parameters:

hgrid (Grid or xarray.Dataset in the supergrid format)

Returns:

A dictionary containing bounding boxes for:

  • ”east”

  • ”west”

  • ”north”

  • ”south”

  • ”ic” (full domain for initial conditions)

Return type:

dict

get_indices(tlat: float, tlon: float) → tuple[int, int]

Get the i, j indices of a given tlat and tlon pair.

Parameters:

  • tlat (float) – The latitude value.

  • tlon (float) – The longitude value.

Returns:

The j, i indices of the given tlat and tlon pair.

Return type:

Tuple[int, int]

static is_cyclic_x(supergrid) → bool

Check if a given supergrid x coordinate array is cyclic along the x-axis.

Parameters:

supergrid (xr.DataArray or np.array or SupergridBase) – Supergrid to check for cyclic x.

is_rectangular(rtol=0.001) → bool

Check if the grid is a rectangular lat-lon grid by comparing the first and last rows and columns of the tlon and tlat arrays.

static is_tripolar(supergrid) → bool

Check if the given supergrid x coordinates form a tripolar grid.

Parameters:

supergrid (xr.DataArray or np.array or SupergridBase) – Supergrid to check if tripolar.

property kdtree: cKDTree

KDTree for fast nearest neighbor search.

property lenx: float

Length of the grid in the x-direction.

property leny: float

Length of the grid in the y-direction.

property name: str

Name of the grid.

property nx

Number of cells in x-direction.

property ny

Number of cells in y-direction.

plot(property_name)

Plot a given grid property using cartopy. Warning: cartopy module must be installed seperately

Parameters:

property_name (str) – The name of the grid property to plot, e.g., ‘tlat’.

plot_cross_section(property_name, iy=None, ix=None)

Plot the cross-section of a given grid metric.

Parameters:

  • property_name (str) – The name of the grid property to plot, e.g., ‘tlat’.

  • iy (int) – y-index of the cross section

  • ix (int) – x-inted of the cross section

classmethod subgrid_from_supergrid(path: str, llc: tuple[float, float], urc: tuple[float, float], name: str) → Grid

Create a Grid instance from a subset of a supergrid file.

Parameters:

  • path (str) – Path to the full supergrid file to be carved out.

  • llc (tuple[float, float]) – Lower left corner coordinates (lat, lon) of the subdomain to extract

  • urc (tuple[float, float]) – Upper right corner coordinates (lat, lon) of the subset to extract

  • name (str) – Name of the subgrid

Returns:

The Grid instance created from the supergrid file.

Return type:

Grid

property supergrid: SupergridBase

MOM6 supergrid contains the grid metrics and the areas at twice the nominal resolution (by default) of the actual computational grid.

update_supergrid(xdat: array, ydat: array) → None

Update the supergrid x and y coordinates. Running this method also updates the nominal grid coordinates and metrics.

Parameters:

  • xdat (np.array) – 2-dimensional array of the new x coordinates.

  • ydat (np.array) – 2-dimensional array of the new y coordinates.

write_supergrid(path: str | None = None, author: str | None = None) → None

Write supergrid to a netcdf file. The supergrid file is to be read in by MOM6 during runtime.

Parameters:

  • path (str, optional) – Path to the supergrid file to be written.

  • author (str, optional) – Name of the author. If provided, the name will appear in files as metadata.