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No Format
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 a known issue when downloading forecast data in NetCDF format, with multiple data values at the same validity time.

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:

No Format
"date":"2016-12-01"
"type":"fc"
"time": "00:00/12:00",
"step": "3/6/9/12/15",
"format": "netcdf"

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

  • time 00:00 + step 3 → validity time 2016-12-01, 03:00
  • time 00:00 + step 6 → validity time 2016-12-01, 06:00
  • time 00:00 + step 9 → validity time 2016-12-01, 09:00
  • time 00:00 + step 12 → validity time 2016-12-01, 12:00
  • time 00:00 + step 15 → validity time 2016-12-01, 15:00
  • time 12:00 + step 3 → validity time 2016-12-01, 15:00
  • time 12:00 + step 6 → validity time 2016-12-01, 18:00
  • time 12:00 + step 9 → validity time 2016-12-01, 21:00
  • time 12:00 + step 12 → validity time 2016-12-02, 00:00
  • time 12:00 + step 15 → validity time 2016-12-02, 03:00

In this example you get two data values at the same validity time 2016-12-01, 15:00.  The NetCDF format does not support multiple data values at a single time, hence the creation of the output NetCDF file fails, triggering the error message.

Workarounds

  • Retrieve 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, retrieve data only for step 0
  • If you need overlapping forecast, retrieve for each time option separately, for example for ERA-Interim:
    • first with time = 00:00 and all required steps
    • then with time = 12:00 and all required steps

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