Sea-surface salinity and potential temperature restoring

Regrid surface salinity and potential temperature from land filled WOA dataset to the ocean model grid.

import xarray as xr
import numpy as np
import datetime 
import os, subprocess
import xesmf
import warnings
warnings.filterwarnings("ignore")

today = datetime.date.today().strftime("%y%m%d")
print(today)

260305

Read grid

ds_out = xr.open_dataset('../mesh/tx2_3v3_grid.nc').rename({'tlon': 'lon','tlat': 'lat', 'qlon': 'lon_b','qlat': 'lat_b',})

Read WOA file with land fill

# WOA sfc state file with land fill, created using create_filled_sfc.py
fname = '/glade/campaign/cgd/oce/datasets/cesm/WOA_MOM6/woa18_sfc_state_filled.nc'
woa = xr.open_dataset(fname, decode_times=False)

# average between two-layers (depth = 0 and depth = 10, depth indices 0 and 2)
woa_s_an_surface_ave = woa.s_an.isel(depth=[0,2]).mean('depth')
woa_theta0_surface_ave = woa.theta0.isel(depth=[0,2]).mean('depth')

def regrid_tracer(fld, ds_in, ds_out, method='bilinear'):

    regrid = xesmf.Regridder(
        ds_in,
        ds_out,
        method=method,
        periodic=True,
    )
    fld_out = regrid(fld)
    return fld_out

ds_out_s_an = regrid_tracer(woa_s_an_surface_ave, woa_s_an_surface_ave, ds_out)

ds_out_theta0 = regrid_tracer(woa_theta0_surface_ave, woa_theta0_surface_ave, ds_out)

Create state file for MOM6

We opted to create this file via ncgen to avoid issues with FMS reading the netCDF file.

!ncgen -o state_restore_tx2_3.nc state_restore_tx2_3.cdl

state = xr.open_dataset('state_restore_tx2_3.nc', decode_times=False)

ds_out

<xarray.Dataset> Size: 42MB
Dimensions:  (ny: 480, nx: 540, nxp: 541, nyp: 481)
Dimensions without coordinates: ny, nx, nxp, nyp
Data variables: (12/20)
    lon      (ny, nx) float64 2MB -286.7 -286.0 -285.3 ... 72.97 72.98 73.0
    lat      (ny, nx) float64 2MB -81.56 -81.56 -81.56 ... 50.27 50.11 49.99
    ulon     (ny, nxp) float64 2MB ...
    ulat     (ny, nxp) float64 2MB ...
    vlon     (nyp, nx) float64 2MB ...
    vlat     (nyp, nx) float64 2MB ...
    ...       ...
    tarea    (ny, nx) float64 2MB ...
    tmask    (ny, nx) float64 2MB ...
    angle    (ny, nx) float64 2MB ...
    depth    (ny, nx) float64 2MB ...
    ar       (ny, nx) float64 2MB ...
    egs      (ny, nx) float64 2MB ...
Attributes:
    Description:  CESM MOM6 2/3 degree grid
    Author:       Frank, Fred, Gustavo (gmarques@ucar.edu)
    Created:      2026-03-05T14:49:28.971877
    type:         Glogal 2/3 degree grid file

xarray.Dataset

• Dimensions:
  • ny: 480
  • nx: 540
  • nxp: 541
  • nyp: 481
• Data variables: (20)
  • lon
    (ny, nx)
    float64
    -286.7 -286.0 -285.3 ... 72.98 73.0

    long_name :

    array of t-grid longitudes

    units :

    degrees_east

    array([[-286.666667, -286.      , -285.333333, ...,   71.333333,   72.      ,
              72.666667],
           [-286.666667, -286.      , -285.333333, ...,   71.333333,   72.      ,
              72.666667],
           [-286.666667, -286.      , -285.333333, ...,   71.333333,   72.      ,
              72.666667],
           ...,
           [-286.970638, -286.909025, -286.86341 , ...,   72.86341 ,   72.909025,
              72.970638],
           [-286.987224, -286.947478, -286.919655, ...,   72.919655,   72.947478,
              72.987224],
           [-286.999825, -286.983349, -286.973852, ...,   72.973852,   72.983349,
              72.999825]], shape=(480, 540))

  • lat
    (ny, nx)
    float64
    -81.56 -81.56 ... 50.11 49.99

    long_name :

    array of t-grid latitudes

    units :

    degrees_north

    array([[-81.558125, -81.558125, -81.558125, ..., -81.558125, -81.558125,
            -81.558125],
           [-81.459689, -81.459689, -81.459689, ..., -81.459689, -81.459689,
            -81.459689],
           [-81.360114, -81.360114, -81.360114, ..., -81.360114, -81.360114,
            -81.360114],
           ...,
           [ 49.981551,  50.10076 ,  50.266038, ...,  50.266038,  50.10076 ,
             49.981551],
           [ 49.988104,  50.105166,  50.270311, ...,  50.270311,  50.105166,
             49.988104],
           [ 49.993627,  50.107298,  50.272397, ...,  50.272397,  50.107298,
             49.993627]], shape=(480, 540))

  • ulon
    (ny, nxp)
    float64
    ...

    long_name :

    array of u-grid longitudes

    units :

    degrees_east

    [259680 values with dtype=float64]

  • ulat
    (ny, nxp)
    float64
    ...

    long_name :

    array of u-grid latitudes

    units :

    degrees_north

    [259680 values with dtype=float64]

  • vlon
    (nyp, nx)
    float64
    ...

    long_name :

    array of v-grid longitudes

    units :

    degrees_east

    [259740 values with dtype=float64]

  • vlat
    (nyp, nx)
    float64
    ...

    long_name :

    array of v-grid latitudes

    units :

    degrees_north

    [259740 values with dtype=float64]

  • lon_b
    (nyp, nxp)
    float64
    ...

    long_name :

    array of q-grid longitudes

    units :

    degrees_east

    [260221 values with dtype=float64]

  • lat_b
    (nyp, nxp)
    float64
    ...

    long_name :

    array of q-grid latitudes

    units :

    degrees_north

    [260221 values with dtype=float64]

  • dxt
    (ny, nx)
    float64
    ...

    long_name :

    x-distance between u-points, centered at t

    units :

    meters

    [259200 values with dtype=float64]

  • dyt
    (ny, nx)
    float64
    ...

    long_name :

    y-distance between v-points, centered at t

    units :

    meters

    [259200 values with dtype=float64]

  • dxCv
    (ny, nx)
    float64
    ...

    long_name :

    x-distance between q-points, centered at v

    units :

    meters

    [259200 values with dtype=float64]

  • dyCu
    (ny, nx)
    float64
    ...

    long_name :

    y-distance between q-points, centered at u

    units :

    meters

    [259200 values with dtype=float64]

  • dxCu
    (ny, nx)
    float64
    ...

    long_name :

    x-distance between t-points, centered at u

    units :

    meters

    [259200 values with dtype=float64]

  • dyCv
    (ny, nx)
    float64
    ...

    long_name :

    y-distance between t-points, centered at v

    units :

    meters

    [259200 values with dtype=float64]

  • tarea
    (ny, nx)
    float64
    ...

    long_name :

    area of t-cells

    units :

    meters^2

    [259200 values with dtype=float64]

  • tmask
    (ny, nx)
    float64
    ...

    long_name :

    ocean fraction at t-cell centers

    units :

    none

    [259200 values with dtype=float64]

  • angle
    (ny, nx)
    float64
    ...

    long_name :

    angle grid makes with latitude line

    units :

    degrees

    [259200 values with dtype=float64]

  • depth
    (ny, nx)
    float64
    ...

    long_name :

    depth at h points

    units :

    meters

    [259200 values with dtype=float64]

  • ar
    (ny, nx)
    float64
    ...

    long_name :

    grid aspect ratio (dyt/dxt)

    units :

    none

    [259200 values with dtype=float64]

  • egs
    (ny, nx)
    float64
    ...

    long_name :

    grid effective grid spacing

    units :

    degrees

    [259200 values with dtype=float64]

• Attributes: (4)

  Description :

  CESM MOM6 2/3 degree grid

  Author :

  Frank, Fred, Gustavo (gmarques@ucar.edu)

  Created :

  2026-03-05T14:49:28.971877

  type :

  Glogal 2/3 degree grid file

jm, im = ds_out.lat.shape
state['LAT'] = ds_out.lat[:,int(im/2)].values
state['LON'] = ds_out.lon[int(jm/2),:].values

Overwrite salt and thetao

state['salt'].values[:] = ds_out_s_an.values[:]

state['theta0'].values[:] = ds_out_theta0.values[:]

TODO: Compare original and remapped fields

# Global attrs
state.attrs['title'] = 'surface salinity and potential temperature from WOA filled over continents'
state.attrs['src_file'] = fname
state.attrs['dst_grid_name'] = 'tx2_3v3'
state.attrs['author'] = 'Gustavo Marques (gmarques@ucar.edu)'
state.attrs['date'] = today
state.attrs['created_using'] = 'https://github.com/NCAR/tx2_3/state_restoring/state_restoring.ipynb'
# save 
fname1 = 'state_restore_tx2_3v3_{}.nc'.format(today)
state.to_netcdf(fname1, engine="netcdf4", format="NETCDF3_64BIT_DATA")