CDS API code to download ERA5 windspeed data

gistfile1.txt

# load venv_cdsapi, which is a standard python venv plus `pip install cdsapi`
# and also needs ~/.cdsapirc with lines:
#   url: https://cds.climate.copernicus.eu/api
#   key: <CDS API KEY>

import os
import numpy as np
import cdsapi
import xarray as xr

for year in range(2000,2021):
  for month in ["01", "02", "03", "04", "05", "06", 
                "07", "08", "09", "10", "11", "12"]:
    # year = 2000
    # month = "01"
    #
    nc_file = f"era5_uv850_6hourly_global1deg_{year}{month}.nc"
    if os.path.exists(nc_file):
      print(f"skip existing {nc_file}")
      continue
    #
    print(f"requesting year {year} month {month} from CDS")
    dataset = 'reanalysis-era5-pressure-levels'
    request = {
        "product_type": ["reanalysis"],
        "variable": ["u_component_of_wind", "v_component_of_wind"],
        "year": [year],
        "month": [month],
        "day": ["01", "02", "03", "04", "05", "06", "07", "08", "09",
                "10", "11", "12", "13", "14", "15", "16", "17", "18",
                "19", "20", "21", "22", "23", "24", "25", "26", "27",
                "28", "29", "30", "31"],
        "time": ["00:00", "06:00", "12:00", "18:00"],
        "pressure_level": ["850"],
        "data_format": "grib",
        "download_format": "unarchived"
    }
    target = 'tmp_download.grib' # about 500Mb, won't be stored
    client = cdsapi.Client()
    client.retrieve(dataset, request, target)
    #
    # coarsen to 1 degree resolution by averaging over 4x4 patches
    uv850 = xr.load_dataset(target)
    uv850_1deg = uv850.coarsen(longitude=4, latitude=4, boundary="trim").mean()
    #
    # store as 0.1 m/s in int32, reduces file size 
    uv850_1deg_int = np.round(10 * uv850_1deg)
    # TODO: update uv850_1deg['u'].attrs (GRIB_NX/NY/units)
    #
    # save integer data to netcdf with compression
    uv850_1deg_int = uv850_1deg_int.astype("int32")
    encoding = {
        "u": {"dtype": "int32", "zlib": True, "complevel": 4},
        "v": {"dtype": "int32", "zlib": True, "complevel": 4}
    }
    uv850_1deg_int.to_netcdf(nc_file, encoding=encoding)
    # clean up
    if os.path.exists(target):
      os.remove(target)