Key Improvements in ERA6

ERA6, the successor to ERA5, will incorporate several years of R&D by the European Centre for Medium-Range Weather Forecasts (ECMWF) and benefit from enhanced computational capabilities. This new reanalysis will address limitations of ERA5 and set a new standard for high-resolution climate data.

• Higher Resolution: ERA6 will feature a horizontal resolution of 18 km, significantly finer than ERA5's 27 km (0.25 degrees of latitude and longitude). This will allow for better representation of mesoscale phenomena and ocean-atmosphere coupling.

Horizontal grid of ERA5 and ERA6 most likely configuration. Credit: Copernicus Climate Change Service/ECMWF




• Improved Bias Reduction: Enhanced 4D-Var data assimilation methods and reprocessed observations will minimize known biases, such as cold temperature biases in the lower stratosphere (above 10 hPa). Snow assimilation and representation will also be improved.
• Expanded Observational Dataset: ERA6 will integrate rescued early satellite data (pre-1979) and reprocessed historical observations (C3S2_310, EUMETSAT, and C3S2_314). Efforts include decoding original archives, correcting geolocation and timing errors, and ensuring high-quality data storage.

Example of correction for geolocation at the poles in early Nimbus sensors THIR. Credit: Copernicus Climate Change Service/ECMWF




• Enhanced Near-Surface and Radiative Forcing Parameters: Improvements include dynamic vegetation cover and type, lake properties, urban tiles, and new aerosol species, enhancing near-surface realism and radiative forcing accuracy.
• Ocean Waves Physics: One-way model coupled with the ocean, providing a consistent representation of ocean-atmosphere processes. ERA6 will be forced by ORAS6 and OCEAN6 fields.

Example of hourly surface Eastward/Northward sea water velocity. Credit: Copernicus Climate Change Service/ECMWF

References:

• Hersbach, H. et al. (2024). ERA6 update. https://climate.copernicus.eu/sites/default/files/custom-uploads/7th%20GA%20C3S/Presentations/Day%202/S3/02-18062024_Reanalysis_Hersbach_v1.pdf
• Hersbach, H. et al. (2023). ERA5, the story so far & plans for ERA6. https://climate.copernicus.eu/sites/default/files/2023-09/C3S_GA_2023-Hersbach.pdf
• Hersbach, H. et al. (2022). Characteristics of ERA5 and innovations for ERA6. https://climate.copernicus.eu/sites/default/files/2022-09/S3_Hans_Hersbach_v1.pdf
• Hersbach, H. et al. (2020). The ERA5 Global Reanalysis. Quarterly Journal of the Royal Meteorological Society, 146, 1999-2049. https://doi.org/10.1002/qj.3803
• Deryng, D., Poli, P., Buontempo, C., et al. (2024). Position Paper - ERA6 User Community Needs. ECMWF COPERNICUS REPORT.