Applying an existing land fraction

In this notebook, we create a spherical grid with uniform resolution. We then implement a flat-bottom bathymetry. Finally, we apply a land fraction obtained from an already generated land dataset.

1. Import Modules

%%capture
import numpy as np
from mom6_forge.grid import Grid
from mom6_forge.topo import Topo

2. Create a horizontal MOM6 grid

Spherical grid. x coordinates interval= [0, 360] degrees. y coordinates interval = [-80,+80] degrees

# Instantiate a MOM6 grid instance
grid = Grid(
    nx         = 360,         # Number of grid points in x direction
    ny         = 160,          # Number of grid points in y direction
    lenx       = 360.0,       # grid length in x direction, e.g., 360.0 (degrees)
    leny       = 160,         # grid length in y direction
    cyclic_x   = True,      # reentrant, spherical domain
    ystart     = -80          # start/end 10 degrees above/below poles to avoid singularity
)

3. Configure the bathymetry

# Instantiate a Topo object associated with the horizontal grid object (grid).
topo = Topo(grid, min_depth=10.0)

flat bottom bathymetry

# Set the bathymetry to be a flat bottom with a depth of 2000m
topo.set_flat(D=2000.0)

topo.tmask.plot()

locate an existing land fraction

import xarray as xr
ds_land = xr.open_dataset("/glade/work/altuntas/cesm.input/vcg/fill_indianocean.nc")
ds_land.landfrac.plot(size=7)

apply the existing land frac – bilinear (default)

topo.generate_mask_from_landfrac_file(
    landfrac_filepath = "/glade/work/altuntas/cesm.input/vcg/fill_indianocean.nc",
    landfrac_name = "landfrac",
    xcoord_name = "lon",
    ycoord_name = "lat"
)

topo.tmask.plot(size=7)

Try out a different cutoff fraction (default is 0.5)

# reset bathymetry
topo.set_flat(D=2000.0)

# re-apply land frac with a different cutoff
topo.generate_mask_from_landfrac_file(
    landfrac_filepath = "/glade/work/altuntas/cesm.input/vcg/fill_indianocean.nc",
    landfrac_name = "landfrac",
    xcoord_name = "lon",
    ycoord_name = "lat",
    cutoff_frac = 0.3 ### reduce the cutoff from 0.5 to 0.3
)

topo.tmask.plot(size=7)

4. Save the grid and bathymetry files

# MOM6 supergrid file:
grid.write_supergrid("./ocean_hgrid_4.nc")

# MOM6 topography file:
topo.write_topo("./ocean_topog_4.nc")

# CICE grid file:
topo.write_cice_grid("./cice_grid_4.nc")

# SCRIP grid file (for runoff remapping, if needed):
topo.write_scrip_grid("./scrip_grid_4.nc")

# ESMF mesh file:
topo.write_esmf_mesh("./ESMF_mesh_4.nc")