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The error

You try to retrieve data from the ECMWF data archive in NetCDF format but the retrieval fails with this message:

ECCODES ERROR : Wrong number of fields
ECCODES ERROR : File contains 806 GRIBs, 806 left in internal description, 745 in request
ECCODES ERROR : The fields are not considered distinct!
ECCODES ERROR : Hint: This may be due to several fields having the same validity time.
ECCODES ERROR : Try using the -T option (Do not use time of validity)

Cause

This is known issue when downloading forecast data in the NetCDF format:

For example, from the ERA-Interim archive one can download data from four daily forecasts (00:00, 06:00, 12:00, 18:00) and for steps 0 to 120 (in 3-hour steps)

In this case you will get data for:

2016-12-01, 00:00 (time 00:00 + step 0)
2016-12-01, 03:00 (time 00:00 + step 3)
2016-12-01, 06:00 (time 00:00 + step 6)
2016-12-01, 06:00 (time 06:00 + step 0)
2016-12-01, 09:00 (time 06:00 + step 3)

... and so on.

So in this example you get two values at validity time 2016-12-01, 06:00.

The NetCDF format only supports a single, one-dimensional time dimension, so a specific time can not have two values.

This is why trying to retrieve this data in NetCDF format results in an error.

Possible workarounds

Download the data in its native GRIB format, then convert the GRIB files to NetCDF following these guidelines. The GRIB format supports multiple data values at any one validity time.
If you are only interested in the analysis, but not forecasts, download data only for step 0
If you need overlapping forecast, download for each time option separately, for example:
- first with time = 00:00 and all required steps
- then with time = 06:00 and all required steps
- then with time = 12:00 and all required steps
- then with time = 18:00 and all required steps

The error

Cause

Possible workarounds

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