Grids for New Projections (Arctic & Antarctic)

Standard lat/lon grids degrade at high latitudes — cell aspect ratios become extreme, and the MOM6 timestep constraint can become prohibitively tight near the poles. For Arctic or Antarctic domains, mom6_forge can build a grid in a projected coordinate system (e.g. polar stereographic) and reproject it to the geographic coordinates MOM6 expects.

Two approaches are shown here:

Interactive — use the GridCreator widget and select From Projection mode.
Programmatic — call Grid.from_projection() directly.

Launch the widget, choose From Projection in the method dropdown, select Arctic Polar Stereographic (EPSG:3995) or Antarctic Polar Stereographic (EPSG:3031) from the CRS dropdown, set a resolution, then drag a rectangle on the polar map to define the domain. The widget calls Grid.from_projection() under the hood and saves the result to GridLibrary/.

from mom6_forge.grid_creator import GridCreator

gc = GridCreator()
gc

Approach 2: Programmatic — `Grid.from_projection()`¶

Pass a pyproj CRS (as an EPSG string or integer) along with the domain extents in metres in the native projection. The method reprojects to geographic coordinates and computes grid metrics using exact great-circle geometry.

CRS	Region
`"EPSG:3995"`	Arctic Polar Stereographic
`"EPSG:3031"`	Antarctic Polar Stereographic

Arctic domain (EPSG:3995)¶

EPSG:3995 is centred at the North Pole. Extents are in metres from the pole. The example below creates a 2000 km × 2000 km domain at 50 km resolution.

from mom6_forge.grid import Grid

arctic_grid = Grid.from_projection(
    crs="EPSG:3995",
    x_min=-1_000_000,  # metres from pole
    x_max= 1_000_000,
    y_min=-1_000_000,
    y_max= 1_000_000,
    resolution_m=50_000,  # 50 km
    name="arctic_50km",
)

print(f"Grid size: {arctic_grid.nx} x {arctic_grid.ny}")
print(f"Lat range: {arctic_grid.tlat.values.min():.1f}° to {arctic_grid.tlat.values.max():.1f}°")

import cartopy.crs as ccrs
import matplotlib.pyplot as plt

fig, ax = plt.subplots(subplot_kw={"projection": ccrs.NorthPolarStereo()}, figsize=(6, 6))
ax.set_extent([-180, 180, 45, 90], crs=ccrs.PlateCarree())
ax.coastlines()
ax.gridlines()
ax.pcolormesh(
    arctic_grid.tlon, arctic_grid.tlat,
    arctic_grid.tlat,   # colour by latitude as a sanity check
    transform=ccrs.PlateCarree(), cmap="Blues", alpha=0.6,
)
ax.set_title("Arctic domain — EPSG:3995")
plt.tight_layout()

Antarctic domain (EPSG:3031)¶

EPSG:3031 is centred at the South Pole. The example below creates a 3000 km × 3000 km domain (covering most of Antarctica) at 25 km resolution.

antarctic_grid = Grid.from_projection(
    crs="EPSG:3031",
    x_min=-1_500_000,
    x_max= 1_500_000,
    y_min=-1_500_000,
    y_max= 1_500_000,
    resolution_m=25_000,  # 25 km
    name="antarctic_25km",
)

print(f"Grid size: {antarctic_grid.nx} x {antarctic_grid.ny}")
print(f"Lat range: {antarctic_grid.tlat.values.min():.1f}° to {antarctic_grid.tlat.values.max():.1f}°")

fig, ax = plt.subplots(subplot_kw={"projection": ccrs.SouthPolarStereo()}, figsize=(6, 6))
ax.set_extent([-180, 180, -90, -45], crs=ccrs.PlateCarree())
ax.coastlines()
ax.gridlines()
ax.pcolormesh(
    antarctic_grid.tlon, antarctic_grid.tlat,
    antarctic_grid.tlat,
    transform=ccrs.PlateCarree(), cmap="Blues_r", alpha=0.6,
)
ax.set_title("Antarctic domain — EPSG:3031")
plt.tight_layout()

Next steps¶

Once you have a polar grid, pass it to Topo and then to Case exactly as you would any other Grid object — the rest of the CrocoDash workflow is unchanged. See Getting Started for the full case setup walkthrough.

Grids for New Projections (Arctic & Antarctic)

Approach 1: Interactive GridCreator widget¶

Approach 2: Programmatic — Grid.from_projection()¶

Arctic domain (EPSG:3995)¶

Antarctic domain (EPSG:3031)¶

Next steps¶

Approach 2: Programmatic — `Grid.from_projection()`¶