Add a grib to netcdf conversion scirpt

[alexamici]

This can be done easily with xarray and netcdf4.

[alexamici]

A simple conversion script has been added in 80ade61

[alexamici]

The usage is:

$ cfgrib to_netcdf --help
Usage: cfgrib to_netcdf [OPTIONS] [INPATHS]...

Options:
  -o, --outpath TEXT
  -c, --cdm TEXT
  -e, --engine TEXT
  --help              Show this message and exit.

For example:

$ cfgrib to_netcdf -c CDS tests/sample-data/era5-levels-members.grib
$ ncdump -h tests/sample-data/era5-levels-members.nc 
netcdf era5-levels-members {
dimensions:
	realization = 10 ;
	forecast_reference_time = 4 ;
	plev = 2 ;
	lat = 61 ;
	lon = 120 ;
variables:
	double lon(lon) ;
		lon:units = "degrees_east" ;
		lon:standard_name = "longitude" ;
		lon:long_name = "longitude" ;
		lon:_FillValue = NaN ;
	double lat(lat) ;
		lat:units = "degrees_north" ;
		lat:standard_name = "latitude" ;
		lat:long_name = "latitude" ;
		lat:stored_direction = "decreasing" ;
		lat:_FillValue = NaN ;
	float z(realization, forecast_reference_time, plev, lat, lon) ;
		z:GRIB_paramId = 129 ;
		z:GRIB_shortName = "z" ;
		z:GRIB_units = "m**2 s**-2" ;
		z:GRIB_name = "Geopotential" ;
		z:GRIB_cfName = "geopotential" ;
		z:GRIB_cfVarName = "z" ;
		z:GRIB_dataType = "an" ;
		z:GRIB_missingValue = 9999 ;
		z:GRIB_numberOfPoints = 7320 ;
		z:GRIB_totalNumber = 10 ;
		z:GRIB_typeOfLevel = "isobaricInhPa" ;
		z:GRIB_NV = 0 ;
		z:GRIB_stepUnits = 1 ;
		z:GRIB_stepType = "instant" ;
		z:GRIB_gridType = "regular_ll" ;
		z:GRIB_gridDefinitionDescription = "Latitude/Longitude Grid" ;
		z:GRIB_Nx = 120 ;
		z:GRIB_iDirectionIncrementInDegrees = 3. ;
		z:GRIB_iScansNegatively = 0 ;
		z:GRIB_longitudeOfFirstGridPointInDegrees = 0. ;
		z:GRIB_longitudeOfLastGridPointInDegrees = 357. ;
		z:GRIB_Ny = 61 ;
		z:GRIB_jDirectionIncrementInDegrees = 3. ;
		z:GRIB_jPointsAreConsecutive = 0 ;
		z:GRIB_jScansPositively = 0 ;
		z:GRIB_latitudeOfFirstGridPointInDegrees = 90. ;
		z:GRIB_latitudeOfLastGridPointInDegrees = -90. ;
		z:long_name = "Geopotential" ;
		z:units = "m**2 s**-2" ;
		z:standard_name = "geopotential" ;
		z:coordinates = "leadtime time" ;
		z:_FillValue = NaNf ;
	float t(realization, forecast_reference_time, plev, lat, lon) ;
		t:GRIB_paramId = 130 ;
		t:GRIB_shortName = "t" ;
		t:GRIB_units = "K" ;
		t:GRIB_name = "Temperature" ;
		t:GRIB_cfName = "air_temperature" ;
		t:GRIB_cfVarName = "t" ;
		t:GRIB_dataType = "an" ;
		t:GRIB_missingValue = 9999 ;
		t:GRIB_numberOfPoints = 7320 ;
		t:GRIB_totalNumber = 10 ;
		t:GRIB_typeOfLevel = "isobaricInhPa" ;
		t:GRIB_NV = 0 ;
		t:GRIB_stepUnits = 1 ;
		t:GRIB_stepType = "instant" ;
		t:GRIB_gridType = "regular_ll" ;
		t:GRIB_gridDefinitionDescription = "Latitude/Longitude Grid" ;
		t:GRIB_Nx = 120 ;
		t:GRIB_iDirectionIncrementInDegrees = 3. ;
		t:GRIB_iScansNegatively = 0 ;
		t:GRIB_longitudeOfFirstGridPointInDegrees = 0. ;
		t:GRIB_longitudeOfLastGridPointInDegrees = 357. ;
		t:GRIB_Ny = 61 ;
		t:GRIB_jDirectionIncrementInDegrees = 3. ;
		t:GRIB_jPointsAreConsecutive = 0 ;
		t:GRIB_jScansPositively = 0 ;
		t:GRIB_latitudeOfFirstGridPointInDegrees = 90. ;
		t:GRIB_latitudeOfLastGridPointInDegrees = -90. ;
		t:long_name = "Temperature" ;
		t:units = "K" ;
		t:standard_name = "air_temperature" ;
		t:coordinates = "leadtime time" ;
		t:_FillValue = NaNf ;
	int realization(realization) ;
		realization:long_name = "ensemble member numerical id" ;
		realization:units = "1" ;
		realization:standard_name = "realization" ;
	int forecast_reference_time(forecast_reference_time) ;
		forecast_reference_time:long_name = "initial time of forecast" ;
		forecast_reference_time:standard_name = "forecast_reference_time" ;
		forecast_reference_time:units = "seconds since 1970-01-01T00:00:00+00:00" ;
		forecast_reference_time:calendar = "proleptic_gregorian" ;
	double time(forecast_reference_time) ;
		time:standard_name = "time" ;
		time:long_name = "time" ;
		time:units = "seconds since 1970-01-01T00:00:00+00:00" ;
		time:calendar = "proleptic_gregorian" ;
		time:_FillValue = NaN ;
	double plev(plev) ;
		plev:long_name = "pressure" ;
		plev:units = "Pa" ;
		plev:positive = "down" ;
		plev:stored_direction = "decreasing" ;
		plev:standard_name = "air_pressure" ;
		plev:_FillValue = NaN ;
	double leadtime ;
		leadtime:long_name = "time since forecast_reference_time" ;
		leadtime:standard_name = "forecast_period" ;
		leadtime:units = "hours" ;
		leadtime:_FillValue = NaN ;

// global attributes:
		:GRIB_edition = 1 ;
		:GRIB_centre = "ecmf" ;
		:GRIB_centreDescription = "European Centre for Medium-Range Weather Forecasts" ;
		:GRIB_subCentre = 0 ;
		:Conventions = "CF-1.7" ;
		:institution = "European Centre for Medium-Range Weather Forecasts" ;
		:history = "GRIB to CDM+CF via cfgrib-0.9.5.1.dev0/ecCodes-2.8.2 with source=\'/Users/amici/devel/MPY/cfgrib/tests/sample-data/era5-levels-members.grib\', filter_by_keys={}, encode_cf=(\'parameter\', \'time\', \'geography\', \'vertical\')" ;
}

[mstrahl]

I tested this cfgrib to_netcdf with C3S seasonal forecast data and it required dask and scipy to function. so the cfgrib install with conda would need some fixes in the requirements.