The error
You try to retrieve data from the ECMWF data archive in NetCDF format but the retrieval fails with this message:
| 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
Cause of the error:This is known issue when downloading forecast data in the NetCDF format:
For example, you select all times from the ERA-Interim archive one can download data from four daily forecasts (00:00, 06:00, 12:00, 18:00) and you select all 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
- Use Download the data 's in its native GRIB format i.e. download the data in GRIB format and , then convert the data file yourself following 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
...