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ERA-Interim is a climate reanalysis dataset, covering the period from 1979 to 31st August 2019. ERA stands for 'ECMWF Re-Analysis' and refers to a series of research projects at ECMWF which produced various datasets (ERA-Interim, ERA-40, etcetera).

 ERA-Interim data is open access and free to download for all uses from the ECMWF data archive. Please see our guidelines on How to download ERA-Interim data from the ECMWF data archive.

ERA-Interim uses a fixed version of a numerical weather prediction (NWP) system (IFS - Cy31r2CY31r2) to produce reanalysed data. The fixed version ensures that no spurious trends are caused by an evolving NWP system, though the changing observing system can still create such trends. The NWP system blends, or assimilates observations with a previous forecast to obtain the best fit to both. The result of this blending is called an analysis and is the starting point for the next forecast. In this manner, data is produced at increasingly later times.

Analysed data is described as instantaneous, though it does represent an average over the model time step (30 minutes for ERA-Interim). Depending on the parameter, forecast data in ERA-Interim is either instantaneous or accumulated from the beginning of the forecast (twice daily forecasts starting at 00 and 12 UTC). Parameters such as precipitation and radiation are accumulated. The accumulated parameters in ERA-Interim are listed in Table 9 (and 13, 14 and 15) of the ERA-Interim archive document:

http://www.ecmwf.int/en/elibrary/8174-era-interim-archive-version-20

Analyses are available every 6 hours (0, 6, 12, 18 UTC) and the twice daily forecasts (from 00 and 12 UTC) provide output for surface and pressure level parameters, at forecast steps every 3 hours to 24 hours, then with decreasing frequency to 10 days.

Table 8 in the ERA-Interim archive document lists the non-accumulated surface parameters (but not the invariants, see Table 7) and indicates whether they are available from the analyses and/or forecasts.

Product description

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The ERA-Interim dataset contains atmospheric and surface parameters:

• 6-hourly atmospheric fields on model levels, pressure levels, potential temperature and potential vorticity
• 3-hourly surface fields and daily vertical integrals
• Monthly averages of daily means

• Synoptic monthly averages at

  0

  00 UTC,

  6

  06 UTC, 12 UTC, 18 UTC

• The temporal coverage is from 1 January 1979 to present
• The spatial coverage is global
• The spectral resolution is T255 (T255 spherical-harmonic representation of the basic dynamic fields)
• The native horizontal resolution is ~80 km  (reduced Gaussian grid N128); ~83km/0.75 deg  when interpolated to a regular lat/long grid
• There are 60 vertical levels from the surface up to 0.1 hPa.

• The data assimilation system used to produce ERA-Interim is based on a 2006 release of the Integrated Forecast System (IFS - Cy31r2). The system includes a 4-dimensional variational analysis (4D-Var) with a 12-hour analysis window.

Parameters and download

For a list of fields (parameters) in ERA-Interim and for downloading data see the ECMWF dataserver. Note that while ERA-Interim "runs" in near real time, data is published with a few months delay.

Note that we are aware of several quality issues with ERA-Interim data.

For download instructions please see  How to download ERA-Interim data from the ECMWF data archive

Please refer to the ERA-Interim daily retrieval efficiency documentation for best practices in retrieving ERA-Interim data.

Further documentation

See Berrisford et al. (2011) for detailed documentation of the parameters in this dataset.

ERA-Interim data is archived in the GRIB file format.

Please see ERA-Interim documentation for full details (including list of parameters).

For further details please see:An open-access journal article describing the ERA-Interim reanalysis is available from the Quarterly Journal of the Royal Meteorological Society. Additional details of the modelling and data assimilation system used to produce ERA-Interim can be found in the IFS documentation (choose Cy31r1) .

Berrisford, P., P. Kållberg, P  S. , Kobayashi, S D. , Dee, DS. , Uppala, S., Simmons, A. J. Simmons, P. Poli, P  and H. and Sato, H. ( 2011), : Atmospheric conservation properties in ERA-Interim. Q.J.R. Meteorol. Soc., 137: 1381–1399 1381–1399. doi: 10.1002/qj.864Further detailed documentation on ERA-Interim is available in the ECMWF eLibrary

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