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For the time being and until further notice, ERA-Interim (1st January 1979 to 31st August 2019) shall continue to be accessible through the ECMWF Web API. Keeping in mind that ERA-Interim is published with an offset of about three months from the dataset's reference date, ERA-Interim August 2019 data will be made available towards the end of October 2019. ERA5 is now available from the Climate Data Store (CDS) (What are the changes from ERA-Interim to ERA5?) and users are strongly advised to migrate to ERA5 (How to migrate from ECMWF Web API to CDS API). |
Through systematic increases of computing power, 4-dimensional variational assimilation (4D-Var) became feasible and part of ECMWF operations since 1997, paving the way to base ERA-Interim on 4D-Var (rather than 3D-Var as in ERA-40).
Enhanced computing power also allowed horizontal resolution to be increased from T159 (N80) to T255 (N128), and the latest cycle of the atmospheric model (IFS CY31r1 and CY31r2) to be used, taking advantage of improved model physics.
ERA-interim retains the same 60 model levels used for ERA-40 with the highest level being 0.1 hectopascal.
In addition, data assimilation of ERA-Interim also benefits from quality control that draws on experience from ERA-40, variational bias correction of satellite radiance data, and more extensive use of radiances with an improved fast radiative transfer model.
See ECMWF publication on ERA-40 for further details. An open-access journal article describing the ERA-Interim reanalysis is available from the Quarterly Journal of the Royal Meteorological Society
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