CERA-20C¶

ECMWF Coupled Reanalysis of the 20th Century

Discontinued

At a glance¶

Note on period: 1 January 1901 to 31 December 2010. The year 1900 was used only for spin-up and is not provided.

Overview¶

CERA-20C is ECMWF's 10-member ensemble of coupled climate reanalyses of the 20th century (1901–2010), produced in the ERA-CLIM2 project. It reconstructs past weather and climate of the atmosphere, ocean, land, ocean waves and sea ice by coupling the IFS atmosphere, land and wave components with the NEMO ocean and LIM2 sea-ice models, using a variational method with a common 24-hour assimilation window so that atmosphere and ocean remain mutually consistent. As in ERA-20C, only surface pressure and marine wind observations are assimilated in the atmosphere; in the ocean, temperature and salinity profiles are assimilated, and the air–sea interface is relaxed towards HadISST2 monthly sea-surface temperature.

Available variables¶

Main atmospheric and surface parameters, checked against the ECMWF CERA-20C dataset page and the ECMWF Parameter Database (ECMWF GRIB short names). Ocean and sea-ice fields are reported to have been distributed as separate NetCDF files, but no official list of their variable names could be found, so they are not listed. All parameters are available for each of the 10 ensemble members.

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 (surface)¶

The full variable list is in the official documentation.

How to get the data¶

• ECMWF CERA-20C dataset page — Documentation only (no download)
  • For data access questions, the page points to the ECMWF/C3S user support channels. The former web download and Web API (ecmwfapi, dataset=cera20c) were closed on 1 June 2023.
• ECMWF Support Portal (data access requests) — Support request
  • The only route ECMWF offers since public downloads closed. The data remain in the MARS archive (class=ep), but MARS access for users outside ECMWF Member and Co-operating States may require a separate service agreement.

Practical tips¶

• The ensemble is under-dispersive. According to the ECMWF Newsletter (2017), the RMSE in 2005 was about twice the analysis ensemble spread, so do not read the spread directly as the uncertainty.
• Because of sea-ice coupling problems, Arctic summer melt is too weak and sea ice accumulates year after year (thicknesses above 5 m over most of the Arctic basin). Do not use it for Arctic sea-ice thickness or volume.
• Production was split into several streams, and ocean heat content can jump at stream boundaries because of model drift. Check the stream boundaries before interpreting long-term ocean heat content trends.
• Upper-air and satellite observations are not assimilated, so it is not the best estimate of the late-20th-century atmosphere (NCAR Climate Data Guide). Use ERA5 for atmospheric studies after 1979.

Notices and change history¶

References for your paper¶

Reference papers¶

CERA-20C description paper — DOI 10.1029/2018MS001273

@article{laloyaux2018cera20c,
  author  = {Laloyaux, Patrick and de Boisseson, Eric and Balmaseda, Magdalena and Bidlot, Jean-Raymond and Broennimann, Stefan and Buizza, Roberto and Dahlgren, Per and Dee, Dick and Haimberger, Leopold and Hersbach, Hans and Kosaka, Yuki and Martin, Matthew and Poli, Paul and Rayner, Nick and Rustemeier, Elke and Schepers, Dinand},
  title   = {{CERA-20C}: A Coupled Reanalysis of the Twentieth Century},
  journal = {Journal of Advances in Modeling Earth Systems},
  volume  = {10},
  number  = {5},
  pages   = {1172--1195},
  year    = {2018},
  doi     = {10.1029/2018MS001273}
}

Coupled data assimilation system paper (optional) — DOI 10.1002/qj.2629

ECMWF Newsletter article (optional) — DOI 10.21957/ffs36birj2

Acknowledgements¶

There is no official dataset DOI. Credit ECMWF (ERA-CLIM2 project) as the data producer and cite Laloyaux et al. (2018). It is good practice to state in the Data availability section how and when you obtained the data (e.g. supplied via ECMWF support).

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 CERA-20C dataset page
• ECMWF Newsletter No. 150 — CERA-20C: An Earth system approach to climate reanalysis
• Decommissioning of ECMWF Public Datasets Service
• NCAR Climate Data Guide — CERA-20C