Gridded Data Template

Grid.ipynb

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   "source": [
    "Grab the usual imports:"
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   "source": [
    "    import netCDF4\n",
    "    import numpy as np"
   ]
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   "source": [
    "Let's first create our netCDF file:"
   ]
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    "    try:\n",
    "        ncfile.close()  # just to be safe, make sure dataset is not already open.\n",
    "    except:\n",
    "        pass\n",
    "    ncfile = netCDF4.Dataset('grid.nc',\n",
    "                             mode='w',\n",
    "                             format='NETCDF4_CLASSIC')"
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   "source": [
    "Let's define the size of our data:"
   ]
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   "source": [
    "    lat_size = 361\n",
    "    lon_size = 720\n",
    "    z_size = 1\n",
    "    time_size = 1"
   ]
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   "source": [
    "Create latitude, longitude, and time netCDF dimensions:"
   ]
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   "source": [
    "    lat_dim = ncfile.createDimension('lat_dim', lat_size)\n",
    "    lon_dim = ncfile.createDimension('lon_dim', lon_size)\n",
    "    z_dim = ncfile.createDimension('z_dim', z_size)\n",
    "    time_dim = ncfile.createDimension('time_dim', time_size)"
   ]
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   "source": [
    "Create the time dimension. Make sure [to follow UDUNITS guidance described in the CF convention](http://cfconventions.org/cf-conventions/v1.6.0/cf-conventions.html#time-coordinate) for the `time` and all variables. For example:"
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   "source": [
    "    time = ncfile.createVariable('time', np.float64, ('time_dim', ))\n",
    "    time.standard_name = 'time'\n",
    "    time.units = 'hours since 2016-01-15 00:00:00'\n",
    "    time.long_name = 'time'\n",
    "    time[:] = np.array([0])"
   ]
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   "source": [
    "Define the mesh:"
   ]
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   "source": [
    "    latitudes = np.linspace(-90.0, 90.0, num=lat_size)\n",
    "    longitudes = np.linspace(-180.0, 180.0, num=lon_size)\n",
    "    lons, lats = np.meshgrid(longitudes, latitudes)"
   ]
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   "source": [
    "Create `latitude` variable:"
   ]
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   "source": [
    "    latitude = ncfile.createVariable('latitude', np.float32, ('lat_dim',\n",
    "                                                              'lon_dim', ))\n",
    "    latitude.standard_name = 'latitude'\n",
    "    latitude.units = 'degrees_north'\n",
    "    latitude.long_name = 'latitude'\n",
    "    latitude[:] = lats"
   ]
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   "source": [
    "Create `longitude` variable:"
   ]
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   "source": [
    "    longitude = ncfile.createVariable('longitude', np.float32, ('lat_dim',\n",
    "                                                                'lon_dim', ))\n",
    "    longitude.standard_name = 'longitude'\n",
    "    longitude.units = 'degrees_east'\n",
    "    longitude.long_name = 'longitude'\n",
    "    longitude[:] = lons"
   ]
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   "source": [
    "Create `z` variable:"
   ]
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   "source": [
    "    z = ncfile.createVariable('z', np.float32, ('z_dim'))\n",
    "    z.standard_name = 'air_pressure_at_sea_level'\n",
    "    z.units = 'hPa'\n",
    "    z.long_name = 'mean sea level pressure'\n",
    "    z[:] = np.array([850])"
   ]
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   "source": [
    "Create a variable, say temperature:"
   ]
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   "source": [
    "    temperature = ncfile.createVariable('temperature', np.float64, (\n",
    "        'time_dim', 'z_dim', 'lat_dim', 'lon_dim'))\n",
    "    temperature.units = 'Celsius'\n",
    "    temperature.standard_name = 'air_temperature'\n",
    "    temperature.coordinates = 'time z latitude longitude'\n",
    "    temperature[:] = np.zeros((time_size, z_size, lat_size, lon_size))\n",
    "    ncfile.Conventions = \"CF-1.6\""
   ]
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   "source": [
    "Finally close the datasets we've been working with."
   ]
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   "source": [
    "    ncfile.close();"
   ]
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   "source": [
    "You can load this netCDF file into the IDV."
   ]
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     "text": [
      "netcdf grid {\r\n",
      "dimensions:\r\n",
      "\tlat_dim = 361 ;\r\n",
      "\tlon_dim = 720 ;\r\n",
      "\tz_dim = 1 ;\r\n",
      "\ttime_dim = 1 ;\r\n",
      "variables:\r\n",
      "\tdouble time(time_dim) ;\r\n",
      "\t\ttime:standard_name = \"time\" ;\r\n",
      "\t\ttime:units = \"hours since 2016-01-15 00:00:00\" ;\r\n",
      "\t\ttime:long_name = \"time\" ;\r\n",
      "\tfloat latitude(lat_dim, lon_dim) ;\r\n",
      "\t\tlatitude:standard_name = \"latitude\" ;\r\n",
      "\t\tlatitude:units = \"degrees_north\" ;\r\n",
      "\t\tlatitude:long_name = \"latitude\" ;\r\n",
      "\tfloat longitude(lat_dim, lon_dim) ;\r\n",
      "\t\tlongitude:standard_name = \"longitude\" ;\r\n",
      "\t\tlongitude:units = \"degrees_east\" ;\r\n",
      "\t\tlongitude:long_name = \"longitude\" ;\r\n",
      "\tfloat z(z_dim) ;\r\n",
      "\t\tz:standard_name = \"air_pressure_at_sea_level\" ;\r\n",
      "\t\tz:units = \"hPa\" ;\r\n",
      "\t\tz:long_name = \"mean sea level pressure\" ;\r\n",
      "\tdouble temperature(time_dim, z_dim, lat_dim, lon_dim) ;\r\n",
      "\t\ttemperature:units = \"Celsius\" ;\r\n",
      "\t\ttemperature:standard_name = \"air_temperature\" ;\r\n",
      "\t\ttemperature:coordinates = \"time z latitude longitude\" ;\r\n",
      "\r\n",
      "// global attributes:\r\n",
      "\t\t:Conventions = \"CF-1.6\" ;\r\n",
      "}\r\n"
     ]
    }
   ],
   "source": [
    "    !ncdump -h grid.nc"
   ]
  }
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