ECMWF’s ERA5 reanalysis extends back to 1979

Hans Hersbach

 

In January 2019, ECMWF released a further 21 years of its new global atmospheric reanalysis, ERA5, which now extends back to 1979. The data is available from the Copernicus Climate Change Service (C3S) implemented by ECMWF on behalf of the EU (https://climate.copernicus.eu/). This innovative dataset will eventually go back all the way to 1950.

Atmospheric reanalysis combines a weather model with observations to create a complete and consistent picture of meteorological conditions typically over several decades in the recent past. Reanalysis datasets are used for climate monitoring, climate studies and meteorological research, and they underpin an increasing variety of sectoral applications. They also support operational numerical weather prediction, for example by providing a reference against which the quality of forecasts from successive model versions can be compared.

ERA5 is by far the most popular dataset in the openly accessible C3S Climate Data Store. It contains estimates of atmospheric variables such as air temperature, pressure and wind at different altitudes, as well as surface variables such as rainfall, soil moisture content and ocean wave height. ERA5 replaces ECMWF’s previous atmospheric reanalysis, ERA-Interim, which also covers the period from 1979 to the present. The main differences to ERA-Interim are that ERA5:

  • benefits from 10 years of improvements in numerical weather prediction (it uses Cycle 41r2 of ECMWF’s Integrated Forecasting System, implemented in March 2016)
  • uses improved historical observations, boundary conditions and external forcing
  • provides hourly information at a grid spacing of around 31 km globally and 137 levels in the vertical, up from six-hourly fields at a grid spacing of 79 km and 60 levels in ERA-Interim
  • includes uncertainty information by providing an ensemble of 10 reanalyses.

The production of data back to 1950 will be complete near the end of this year. Continuous improvement of climate reanalysis (centennial, coupled, regional) features prominently in plans for the development of C3S.

Hurricane Florence in ERA5 and ERA-Interim. The ERA5 reanalysis provides a detailed picture of the track, intensity (contours, in hPa) and accumulated rainfall (shading, in mm) associated with Hurricane Florence, which struck the east coast of the US in September 2018. The plots show the situation at 09 UTC on 15 September 2018 as reconstructed by ERA5 (left) and ERA-Interim (right).