Is it possible to retrieve the individual ensemble members of the forecasts from the ECMWF system for the dataset "Seasonal forecast daily data on single levels"?

I only ever receive a single value per startdate, location and lead time. Either I am missing something or the individual ensemble members are not available throught the CDS API?

3 Comments

  1. Felix Froehlich

    To add to my question above, when using the web interface to make a request, I don't see any option regarding ensemble members for "Seasonal forecast daily data on single levels".

    For the dataset "Seasonal forecast monthly statistics on single levels", there are some options regarding ensembles (see image below), but still it does not seem possible to retrieve individual ensemble members, only statistical values.

  2. Felix Froehlich

    I found out that I was getting the ensemble members after all. The reason why I didn't realize this is that the GRIB file contains multiple entries per timestamp for each ensemble member and the ensemble number is not a separate dimension. When looking into the file e.g. with Panoply, you don't see the individual members. CDO showed me that timestamps occur multiple times per location and lead time. This format seems hard to process, though (see also ECMWF seasonal forecasts - GRIB/NETCDF and ensemble format).

    Luckily, I found out by chance that if I specify "format:netcdf" in the CDS-API request, I get a netCDF file, which contains ensemble member numbers as a separate dimension (albeit labelled as "vertical coordinates" but that doesn't really matter to me).

    Maybe someone should edit this page Climate Data Store (CDS) API Keywords#Seasonalforecastsdatasets to include the "format" keyword for the seasonal forecasts.


  3. Kevin Marsh

    Hi Felix,

    These C3S Seasonal Forecast data CDS API requests do indeed provide all the ensemble members by default (GRIB or netCDF). The current netCDF conversion for Seasonal forecast data does have a number of issues e.g. when dealing with multiple forecasts start time/multiple forecast step GRIB data, so for this reason, the netCDF option is not activated on the form, and should be used with caution in CDS API requests.

    A new GRIB to netCDF converter is currently under development which will address these issues.

    Hope that helps,

    Kevin

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