ERA5 monthly averaged data on single levels from 1940 to present

ERA5 is highly suitable for climate and meteorological research, as it offers high-resolution, globally consistent, hourly time-resolved reanalysis data. Its comprehensive coverage and assimilation of various observations make it suitable for applications ranging from climate monitoring to model validation and impact studies.

Key Strengths

• Comprehensive Dataset: A wide range of atmospheric, land, and oceanic variables are available, making this dataset versatile for various applications, with data at higher spatial, vertical and temporal resolution compared to other reanalysis systems and covering more than eight decades;
• Advanced Data Assimilation: It incorporates data assimilation techniques that integrate observations from satellites, ground stations, and other sources; the Ensemble of Data Assimilations (EDA), is designed to provide information about the uncertainty in the analysis of atmospheric observations;
• High quality and consistency: Studies evaluating ERA5 have highlighted its accuracy in representing patterns of main variables, globally and regionally, compared to peer datasets (e.g. near-surface air temperature over Arctic, tropical and temperate region, Antarctic Peninsula and over ocean, near-surface wind, precipitation, water vapour content), as well as its good performance in representing extreme weather events such as heatwaves, heavy precipitation, and cyclones. An overall evaluation of the dataset in its extension back to 1940 until 2022 by Soci et al. and references inside are also available.

Improvements with respect to ERA-Interim:

• Higher Spatial and Temporal Resolution: ERA5 has a finer spatial resolution of 31 km (0.25° x 0.25° grid) compared to the 79 km of ERA-Interim (0.75° x 0.75° grid). It provides hourly data, whereas those of ERA-Interim are available at 6-hour intervals. This higher temporal resolution allows for more detailed temporal analyses and better capture of short-term weather events;
• Extended Temporal Coverage: Extends further back in time to January 1940, while ERA-Interim starts in 1979. This extended period provides a longer climate record, which is useful for studying climate trends and variability over a longer period;
• Advanced Data Assimilation System: Uses a more advanced 4D-Var data assimilation system than the 3D-Var system used in ERA-Interim. This improvement enables better integration of observational data into the model, leading to more accurate and consistent reanalyses:
• Increased Number of Atmospheric Levels: Resolves the atmosphere with 137 vertical levels above 0.01 hPa, compared to 60 levels up to 10 hPa in ERA-Interim. This improvement provides better vertical resolution of atmospheric processes;
• Better Handling of Observational Data: Incorporates more satellite observations and uses improved quality control and bias correction techniques. This leads to a better representation of observed climatic conditions, especially in regions with poor observational coverage;
• Improved Physical Parameterizations:
  • ERA5 benefits from improved physical parameterisation of atmospheric processes, such as radiation, cloud microphysics and interactions with the Earth's surface. These improvements contribute to a more accurate representation of radiative forcing, including total solar radiation, ozone, greenhouse gases and aerosols. It also takes into account stratospheric sulphate aerosols from major volcanic eruptions, which ERA-Interim does not consider;
  • Uses up-to-date sea surface temperature and sea ice datasets, providing a more accurate and consistent representation over time;
  • Shows significant improvements in the conservation of potential temperature in the stratosphere, indicating a more consistent forecasting model and better alignment with observations;
  • The dataset is also better able to capture convective updrafts, gravitational waves and other atmospheric features on a meso-synoptic scale due to its higher resolution and improved model capabilities.

Key Limitations

• Large Data Volume: High resolution and wide time coverage entail large volumes of data, which can be difficult to handle and can require considerable storage and computing resources;
• Complexity: The complexity of the dataset and the wide range of variables can make it difficult for non-experts to use without sufficient training or guidance. Training resources and data quality assessments available through the Climate Data Store should be consulted for guidance on use.;
• Observational data Gaps: Larger uncertainty in the early years and in data-poor regions may be due to the lack of satellite data.

Example Applications

• Agriculture: ERA5 data provide a comprehensive resource for improving agricultural productivity, sustainability and resilience by assessing the impact of weather and climate conditions on crop yields and enabling improved decision-making and agricultural practices, as well as optimised resource use through tools such as AgERA5;
• Biodiversity: Bioclimatic indicators at global and regional scales relevant for applications within the biodiversity and ecosystem services community have been produced with ERA5. Also, risk assessments for the environment can be performed, monitoring e.g. fires and high-impact weather events, or through a biased-adjusted dataset ERA5-based specially made for impact studies, the WATCH Forcing Data;
• Hydrology: Thanks to its good performance in the representation of hydrological processes, this dataset has been used in different projects related to water management, such as GLoFAS in the context of Copernicus activities. ERA5 is also used to compute climate indicators for analysis over coastal regions;
• Energy: ERA5 is widely used in evaluating wind, solar and wave energy potential and derive energy indicators; for the European Union, an operational data service providing supply and demand for electricity from wind, solar photovoltaic and hydroelectric sources has been developed under the name C3S Energy;
• Health: ERA5 supports the development of proactive strategies to mitigate health risks and improve overall public health outcomes, e.g. through the specially created dataset ERA5-HEAT (Human thErmAl comforT) or through the monitoring of air pollution;
• Tourism: Weather and snow indicators are calculated on the basis of ERA5 reanalyses supporting the mountain tourism sector;
• Climate Research: The high quality and consistency of this dataset and its long extension in time make it suitable for climate monitoring, an example of which is the Climate Pulse application developed in the context of the outreach activities of the Copernicus Climate Change Service. The dataset is also widely used in studies of trends reconstruction, climate variability and climatology studies;
• Data-driven Weather Forecasting: The large amount of data provided by the ERA5 reanalysis is a key component for the development and training of innovative machine learning models such as AIFS by the European Centre for Medium-Range Weather Forecasts.

Recommendations for Users

• Using ERA5 for long-term climate trend analysis requires caution (see e.g. convective environments, land surface wind speed or snow cover over Alps) due to potential inhomogeneities introduced by changes in observation systems over time, differences in scale, the quality of the atmospheric model, data assimilation methods, and the availability of observations;
• For applications that require high-resolution and accurate land surface data, particularly in fields such as hydrology, agriculture, urban planning, disaster risk reduction, and ecological studies. ERA5-Land may be preferable. Its enhanced spatial resolution and more detailed representation of land surface variables make it a valuable resource for these.fields.
• ERA5 pressure levels are essential for applications that require a comprehensive understanding of the vertical structure and dynamics of the atmosphere. Such applications include weather forecasting, climate research, aviation, atmospheric chemistry, severe weather analysis, mountain meteorology, and stratospheric studies.