API python script no longer working following netcdf era5 change

[Jim_Bungener]

HEllo,

Apparently there was a change mentioned in:

Limitation change on netCDF ERA5 requests

As many users will have already noticed, a change has recently been implemented in some ERA5 datasets with respect to the retrieval of data in NetCDF format versus GRIB format. The native ERA5 data is in GRIB format. When you download the data in NetCDF, additional processing is required which impacts the performance of the system. For this reason, a smaller amount of data in NetCDF can be retrieved rather than in GRIB format. You can check whether your request is within scope using the data d…

Which causes my script to no longer work
I used to download my data by envoking:
wave_variables = ['mean_direction_of_total_swell', 'significant_height_of_total_swell', 'mean_wave_period_of_first_swell_partition']

kwargs_wave_limits_1day = { 'variable': wave_variables, 'product_type': 'reanalysis', 'year': '2022', 'month': '1', 'day': ['01'], 'area': limits, 'time': '00:00', 'format': 'netcdf', }
cds_file_path_wave = os.path.join(os.getcwd(), 'tmp_working_dir', 'wave_limits_1day_download_lat%s.nc' % lat)

ct.retrieve(dataset, kwargs_wave_limits_1day, cds_file_path_wave)

Then I would access the data using
import xarray as xr
wave_variables_1day = xr.open_dataset(os.path.join(cds_file_path_wave))

But this no longer works.
I then tried using
from netCDF4 import Dataset
nc = Dataset(cds_file_path_wave 'r')

But this also doesn’t work.

for xr attempt I get the following error:
ValueError: did not find a match in any of xarray’s currently installed IO backends [‘netcdf4’, ‘h5netcdf’, ‘scipy’, ‘cfgrib’, ‘zarr’]. Consider explicitly selecting one of the installed engines via the engine parameter, or installing additional IO dependencies, see:.......
But this script works on old downloaded .nc files.
Any suggestions?

Thank you

[Kevin_Marsh]

Hi Jim,

I suspect this may be because the file provided by the CDS for download may be a zip archive. Can you try unzipping the file before using it?

[Jim_Bungener]

Thank you for that.

I was tricked by the fact that it is a zipped file with a .nc extension.

By implementing a “is this file zipped” test I am now able to get it to work.