Global reanalysis: goodbye ERA-Interim, hello ERA5
Hersbach, Hans ; Bell, Bill ; Berrisford, Paul ; Horányi, András ; Muñoz Sabater, Joaquín ; Nicolas, Julien ; Radu, Raluca ; Schepers, Dinand ; Simmons, Adrian ; Soci, Cornel ; Dee, Dick
As part of implementing the EU-funded Copernicus Climate Change Service (C3S), ECMWF is producing the ERA5 reanalysis of the global weather and climate. Production is complete for the period 1979 to the present, and by the first quarter of 2020 ERA5 will provide a detailed record of the global atmosphere, land surface and ocean waves from 1950 onwards. This new reanalysis replaces the highly successful ERA-Interim reanalysis that was started in 2006 and spans the period from 1979 to the present. ERA5 is based on 4D-Var data assimilation using Cycle 41r2 of the Integrated Forecasting System (IFS), which was operational at ECMWF in 2016. ERA5 thus benefits from a decade of developments in model physics, core dynamics and data assimilation relative to ERA-Interim. In addition to a significantly enhanced horizontal resolution (31 km grid spacing compared to 79 km for ERA-Interim), ERA5 has a number of innovative features. These include hourly output throughout and an uncertainty estimate. The uncertainty information is obtained from a 10-member ensemble of data assimilations with 3-hourly output at half the horizontal resolution (63 km grid spacing). Compared to ERA-Interim, ERA5 also provides an enhanced number of output parameters, including for example a 100 m wind product. The move from ERA-Interim to ERA5 represents a step change in overall quality and level of detail. An overview of the main characteristics of ERA5 and a comparison with ERA-Interim is presented in Table 1. A more detailed description of the ERA5 configuration, how it was produced and how it fits into the framework of other reanalysis activities at ECMWF can be found in Hersbach et al. (2018).
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