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, for the ERA-Interim dataset there are two daily forecasts (00:00, 12:00), with 3-hourly forecast steps. So one could specify in a data retrieval script:

"date":"2016-12-01"
"type":"fc"
"time": "00:00/12:00",
"step": "0/3/6/9/12",

With the above specification you get data for the following validity times:

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

The NetCDF format (generated by MARS) 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

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