ERA-Interim¶

ECMWF Interim Reanalysis (ERA-Interim)

Discontinued

At a glance¶

Note on period: 1 January 1979 to 31 August 2019. The 1979–1988 segment was produced later, in 2011.

Overview¶

The ECMWF global atmospheric reanalysis that succeeded ERA-40, covering 1 January 1979 to 31 August 2019. It was the first ECMWF reanalysis to make full use of 12-hour 4D-Var data assimilation and variational bias correction of satellite radiances (VarBC), and was among the most widely cited reanalyses in climate research of the 2010s. It has been superseded by ERA5.

What changes with the successor¶

ERA-Interim → ERA5¶

Transition: 2019-08

Much higher resolution (79 km→31 km, 60→137 levels) and output frequency (6-hourly→hourly), plus ensemble-based uncertainty estimates and climate-oriented forcing; distribution moved to the CDS.

Sources: ECMWF — What are the changes from ERA-Interim to ERA5 and ERA5-Land? · Hersbach et al. (2020), The ERA5 global reanalysis, QJRMS · Dee et al. (2011), The ERA-Interim reanalysis, QJRMS · ECMWF Technical Memo — Global stratospheric temperature bias and other stratospheric aspects of ERA5 and ERA5.1 · NCAR GDEX — ERA5.1 Corrections to ERA5 Stratospheric Temperature 2000-2006

Compare the two side by side

Available variables¶

Main parameters from the parameter tables of the official ECMWF ERA-Interim documentation and the ERA-Interim archive report. Names are ECMWF GRIB short names. The data are GRIB1, and accumulated fields (precipitation, radiation, heat fluxes) are accumulated from the start of the forecast.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Surface and single level¶

Accumulated forecast fields¶

Pressure levels (37 levels)¶

Ocean waves (1.0° grid)¶

Land surface and invariants¶

The full variable list is in the official documentation.

How to get the data¶

• Copernicus Climate Data Store (CDS) — ERA-Interim — CDS API (cdsapi) scripts only
  • Requires an ECMWF account, and you must first accept the ERA-Interim Product licence on the dataset page. There is no web-form download; data can be retrieved only with scripts as described on the ECMWF help page. Format is GRIB1.
• ECMWF help — How to download ERA-Interim data from the ECMWF data archive — Documentation (example CDS API requests)
• NSF NCAR GDEX — ERA-Interim Project (d627000) — Web download / subsetting / NCAR HPC (GLADE)
  • NCAR account required (for subsetting, etc.). GRIB1, about 39 TB in total. GDEX flags this dataset as recommended for ancillary use only and superseded by a newer dataset.

Practical tips¶

• ECMWF known issue: CAPE is zero at forecast step 3 (03 and 15 UTC) because of an error in how ERA-Interim calculated CAPE at that step. Do not use CAPE at those times.
• At forecast steps 3/6/9/15/18/21, SST over land is 0 °C rather than missing. Always mask out land with the land-sea mask (lsm).
• The NCAR Climate Data Guide lists as main limitations an overly strong hydrological cycle over the oceans (precipitation and evaporation) and a warm, moist bias below 850 hPa in the Arctic relative to radiosondes.
• Old Web API scripts (ecmwfapi, class=ei) have not worked since June 2023. To reproduce earlier work, rewrite them for the CDS API or use the NCAR copy.

Notices and change history¶

References for your paper¶

Dataset citation¶

CDS dataset — DOI 10.24381/cds.f2f5241d

@misc{era_interim_cds,
  author    = {{Copernicus Climate Change Service}},
  title     = {{ERA-Interim} atmospheric reanalysis},
  year      = {2023},
  publisher = {ECMWF},
  doi       = {10.24381/cds.f2f5241d},
  note      = {Accessed on DD-MMM-YYYY}
}

NCAR GDEX copy (d627000) — DOI 10.5065/D6CR5RD9

@misc{era_interim_d627000,
  author    = {{European Centre for Medium-Range Weather Forecasts}},
  title     = {{ERA-Interim} Project},
  year      = {2009},
  publisher = {NSF National Center for Atmospheric Research},
  doi       = {10.5065/D6CR5RD9},
  note      = {Accessed DD MMM YYYY}
}

Reference papers¶

ERA-Interim reference paper — DOI 10.1002/qj.828

@article{dee2011erainterim,
  author  = {Dee, D. P. and Uppala, S. M. and Simmons, A. J. and Berrisford, P. and Poli, P. and Kobayashi, S. and others},
  title   = {The {ERA-Interim} reanalysis: configuration and performance of the data assimilation system},
  journal = {Quarterly Journal of the Royal Meteorological Society},
  volume  = {137},
  number  = {656},
  pages   = {553--597},
  year    = {2011},
  doi     = {10.1002/qj.828}
}

Archive (data organisation) report (optional)

Acknowledgements¶

If you obtained the data from the CDS, give the CDS DOI above and the access date, and attribute the Copernicus programme/C3S. If you used the NCAR copy, also give the GDEX DOI and, under the ECMWF terms of use, acknowledge ECMWF as the source of the data.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• ERA-Interim documentation (Copernicus Knowledge Base)
• ERA-Interim known issues
• What are the changes from ERA-Interim to ERA5 and ERA5-Land?
• Decommissioning of ECMWF Public Datasets service
• NCAR Climate Data Guide — ERA-Interim