The ERA5 global reanalysis, produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a detailed record of the global atmosphere, land surface, and ocean waves from 1950 onwards. It replaces the ERA-Interim reanalysis, which was started in 2006 and spans from 1979 onwards. ERA5 is based on the Integrated Forecasting System (IFS) Cy41r2, which was operational from 2016. It benefits from a decade of model physics, core dynamics, and data assimilation improvements. ERA5 has a significantly enhanced horizontal resolution of 31 km compared to ERA-Interim's 80 km, and provides hourly output throughout, along with an uncertainty estimate from an ensemble (3-hourly at half the horizontal resolution). ERA5 has shown improved performance compared to ERA-Interim, with re-forecasts showing a gain of up to one day in skill. It has improved fits for temperature, wind, and humidity in the troposphere, but not the stratosphere. A comparison with independent buoy data shows a much improved fit for ocean wave height. The uncertainty estimate reflects the evolution of the observing systems used in ERA5. The enhanced temporal and spatial resolution allows for a detailed evolution of weather systems. For precipitation, global-mean correlation with monthly-mean GPCP data is increased from 67% to 77%. Low-frequency variability is well represented, and from 10 hPa downwards, general patterns of anomalies in temperature match those from ERA-Interim, MERRA-2, and JRA-55 reanalyses. ERA5 includes an ensemble component (EDA) of one control and nine perturbed members, which provide background-error estimates for the deterministic HRES DA system. The EDA system provides estimates of analysis and short-range forecast uncertainty, which are considered to represent the evolution of the errors in the HRES system. This allows for the estimation of uncertainties in the reanalysis products. ERA5 also includes a timely, preliminary product available within 5 days of real time, which is replaced by a more thoroughly quality-checked final product two months later. In practice, both products are expected to rarely differ, and in case they do, users will be notified. The step forward with ERA5 is illustrated by Figure 1, which shows a gain of up to one day in skill of re-forecasts started from ERA5 analyses using the ERA5 model, compared to the re-forecasts run using the ERA-Interim system. The distinct improvement originates from a better forecast model and in particular the improved analyses from which these forecasts are started. ERA5 provides an overview of its configuration and a basic description of its characteristics and performance. It includes a detailed description of the model improvements that took place between the ECMWF IFS cycle releases between ERA-Interim and ERA5. ItThe ERA5 global reanalysis, produced by the European Centre for Medium-Range Weather Forecasts (ECMWF), is a detailed record of the global atmosphere, land surface, and ocean waves from 1950 onwards. It replaces the ERA-Interim reanalysis, which was started in 2006 and spans from 1979 onwards. ERA5 is based on the Integrated Forecasting System (IFS) Cy41r2, which was operational from 2016. It benefits from a decade of model physics, core dynamics, and data assimilation improvements. ERA5 has a significantly enhanced horizontal resolution of 31 km compared to ERA-Interim's 80 km, and provides hourly output throughout, along with an uncertainty estimate from an ensemble (3-hourly at half the horizontal resolution). ERA5 has shown improved performance compared to ERA-Interim, with re-forecasts showing a gain of up to one day in skill. It has improved fits for temperature, wind, and humidity in the troposphere, but not the stratosphere. A comparison with independent buoy data shows a much improved fit for ocean wave height. The uncertainty estimate reflects the evolution of the observing systems used in ERA5. The enhanced temporal and spatial resolution allows for a detailed evolution of weather systems. For precipitation, global-mean correlation with monthly-mean GPCP data is increased from 67% to 77%. Low-frequency variability is well represented, and from 10 hPa downwards, general patterns of anomalies in temperature match those from ERA-Interim, MERRA-2, and JRA-55 reanalyses. ERA5 includes an ensemble component (EDA) of one control and nine perturbed members, which provide background-error estimates for the deterministic HRES DA system. The EDA system provides estimates of analysis and short-range forecast uncertainty, which are considered to represent the evolution of the errors in the HRES system. This allows for the estimation of uncertainties in the reanalysis products. ERA5 also includes a timely, preliminary product available within 5 days of real time, which is replaced by a more thoroughly quality-checked final product two months later. In practice, both products are expected to rarely differ, and in case they do, users will be notified. The step forward with ERA5 is illustrated by Figure 1, which shows a gain of up to one day in skill of re-forecasts started from ERA5 analyses using the ERA5 model, compared to the re-forecasts run using the ERA-Interim system. The distinct improvement originates from a better forecast model and in particular the improved analyses from which these forecasts are started. ERA5 provides an overview of its configuration and a basic description of its characteristics and performance. It includes a detailed description of the model improvements that took place between the ECMWF IFS cycle releases between ERA-Interim and ERA5. It