ERA-20C¶

ECMWF Atmospheric Reanalysis of the 20th Century

Discontinued

At a glance¶

Note on period: January 1900 to December 2010. Production ran as 22 parallel streams, and the first year of each stream was used only for spin-up and discarded. Some forecast products in the NCAR copy extend to 2011-01-01 06 UTC.

Overview¶

ERA-20C is ECMWF's first atmospheric reanalysis of the 20th century, from 1900 to 2010, produced in the ERA-CLIM project with a single, fixed system. Upper-air and satellite observations are deliberately excluded: it assimilates only surface and mean sea level pressure (ISPD, ICOADS) and surface marine winds (ICOADS) with a 24-hour 4D-Var, to limit discontinuities from changes in the observing system. Sea surface temperature and sea ice come from HadISST2.1, and other forcings follow CMIP5, as in ERA-20CM.

Available variables¶

Main parameters confirmed from the NCAR GDEX ERA-20C (d626000) THREDDS metadata and the ECMWF parameter database. Names are ECMWF GRIB short names; in NCAR THREDDS/NetCDF they appear as long names such as Temperature_isobaric. Accumulated fields (precipitation, radiation, heat fluxes) are accumulated from the 06 UTC forecast start.

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 levels¶

Accumulated forecast fields¶

Pressure levels (37 levels)¶

Land surface¶

The full variable list is in the official documentation.

How to get the data¶

• NSF NCAR GDEX — ERA-20C Project (d626000) — Web download (HTTPS) / Globus / THREDDS and OPeNDAP / subsetting and NetCDF conversion
  • Model-level, pressure-level, potential-temperature-level, 2 PVU and surface analyses and forecasts, plus invariant fields, organised as per-variable time-series files (GRIB1/GRIB2, about 80 TB in total). Subsetting and format conversion require an NCAR login, so select only the variables and periods you need.
• NCAR GDEX THREDDS catalogue (d626000) — OPeNDAP / NetCDF Subset Service
  • Yearly aggregations allow remote subsetting and can be opened directly in xarray and similar tools.

Practical tips¶

• With only surface pressure and marine winds assimilated, ERA-20C is less accurate than ERA5 or ERA-Interim in well-observed periods such as after 1979. Use it for long-term variability in the early and mid-20th century.
• Poli et al. (2016) report a spurious mean sea level pressure trend over 60–90°S, a drop of more than 5 hPa over the century, and a dry bias in total column water vapour compared with satellite observations. Treat long-term trends over Antarctica and the Southern Hemisphere with caution.
• Some surface analysis fields, including 2 m temperature, sea surface temperature and the soil fields, exist only every 6 hours, not every 3 hours.
• Forecasts start daily at 06 UTC (steps 3–27), so check the start time when building daily totals from accumulated fields. Monthly means of forecast fields are cut and spliced at month boundaries.

Notices and change history¶

References for your paper¶

Dataset citation¶

NCAR GDEX copy (d626000) — DOI 10.5065/D6VQ30QG

@misc{era20c_d626000,
  author    = {{European Centre for Medium-Range Weather Forecasts}},
  title     = {{ERA-20C} Project ({ECMWF} Atmospheric Reanalysis of the 20th Century)},
  year      = {2014},
  publisher = {NSF National Center for Atmospheric Research},
  doi       = {10.5065/D6VQ30QG},
  note      = {Accessed DD MMM YYYY}
}

Reference papers¶

ERA-20C reference paper — DOI 10.1175/JCLI-D-15-0556.1

@article{poli2016era20c,
  author  = {Poli, Paul and Hersbach, Hans and Dee, Dick P. and Berrisford, Paul and Simmons, Adrian J. and Vitart, Fr{\'e}d{\'e}ric and Laloyaux, Patrick and Tan, David G. H. and Peubey, Carole and Th{\'e}paut, Jean-No{\"e}l and Tr{\'e}molet, Yannick and H{\'o}lm, El{\'i}as V. and Bonavita, Massimo and Isaksen, Lars and Fisher, Michael},
  title   = {{ERA-20C}: An Atmospheric Reanalysis of the Twentieth Century},
  journal = {Journal of Climate},
  volume  = {29},
  number  = {11},
  pages   = {4083--4097},
  year    = {2016},
  doi     = {10.1175/JCLI-D-15-0556.1}
}

Acknowledgements¶

Credit ECMWF (ERA-CLIM project) as the producer; if you obtained the data from NCAR GDEX, also give the GDEX DOI and your access date. GDEX provides the data on condition that users accept the ECMWF Terms of Use.

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¶

• ECMWF — ERA-20C
• ECMWF — Decommissioning of ECMWF Public Datasets Service
• NCAR Climate Data Guide — ERA-20C (with comparisons to NOAA's 20CR)