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(3) How do I obtain the uncertainty estimate data based on the ERA5 EDA system?
The uncertainty data is archived, as all ERA5 data, in ECMWF's data archive MARS. Uncertainty data is archived in stream 'Ensemble data assimilation' (enda), as Ensemble mean (type=em), Ensemble standard deviation (type=es) and Scaled ensemble standard deviation (type=ses).
Public catalogue entry point: : uncertainty estimate data is not publicly available (stream=enda, with type=em and type=es; http://apps.ecmwf.int/data-catalogues/era5/?class=ea&stream=enda&expver=1)
MARS catalogue entry point (restricted): http://apps.ecmwf.int/mars-catalogue/?class=ea&stream=enda&expver=1
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In general we recommend using the raw ensemble standard deviation (spread) values ("es" fields in MARS) instead of the scaled ensemble standard deviation ("ses" fields in MARS). In fact, the Climate Data Store (CDS) only contains the raw ensemble standard deviation fields. The scaled ensemble standard deviation is used to compute background error statistics for the higher resolution ERA5 model and contains much fewer variables and levels. The scaled ensemble standard deviation is only available at step=3h from the forecasts starting at 06 and 18 UTC on model levels (and at the "surface" for brightness temperature), while the ensemble standard deviation is available every 3h to step=18h, on model, pressure, potential temperature and potential vorticity levels and also at the surface. Users are encouraged to compute additional (beside ensemble mean and standard deviation) uncertainty parameters based on the raw ensemble members.
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