The Twentieth Century Reanalysis Project, produced by the Earth System Research Laboratory Physical Sciences Division from NOAA and the University of Colorado Cooperative Institute for Research in Environmental Sciences, is an effort to produce a global reanalysis dataset spanning a portion of the nineteenth century and the entire twentieth century (1851 - near present), assimilating only surface observations of synoptic pressure. Boundary conditions of pentad sea surface temperature and monthly sea ice concentration and time-varying solar, volcanic, and carbon dioxide radiative forcings are prescribed. Products include 6-hourly ensemble mean and spread analysis fields on a 2 by 2 degree global latitude-longitude grid, and 3 and 6-hourly ensemble mean and spread forecast (first guess) fields on a global Gaussian T62 grid. Fields are accessible in yearly time series (1 file per parameter) and monthly synoptic time (all parameters per synoptic hour) files. This dataset provides the first estimates of global tropospheric variability spanning 1851 to 2012 at six-hourly resolution. Fields from 1851 to 1860 are a first attempt at this period and will be improved in future versions. Fields from 1861 to 2011 are most relevant for climate and weather studies.

20th Century Reanalysis Version 2c uses the same model as version 2 with new sea ice boundary conditions from the COBE-SST2 (Hirahara et al. 2014), new pentad Simple Ocean Data Assimilation with sparse input (SODAsi.2, Giese et al. 2015) sea surface temperature fields from through 2012, Daily High-Resolution-Blended Analyses for Sea Surface Temperature starting with 2013, and additional observations from ISPD version 3.2.9.

A low pressure bias in marine pressures from the US Maury Collection (Woodruff et al. 2005, Wallbrink et al. 2009, ) appears to have affected the resultant 20CR version 2c mass-related fields (e.g., pressure, geopotential height) from 1851 to about 1865. Please see opportunities for improvement for additional information.

The Twentieth Century Reanalysis Project version 2c used resources of the National Energy Research Scientific Computing Center managed by Lawrence Berkeley National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Version 2c is a contribution to the international Atmospheric Circulation Reconstructions over the Earth initiative. Support for the Twentieth Century Reanalysis Project is provided by the U.S. Department of Energy Office of Science (BER) and the NOAA Climate Program Office MAPP program.

RELEASE POLICY: Please use the citations listed below (See Publications section below) in any submitted publications using this dataset.

Additionally, papers using the Twentieth Century Reanalysis Project dataset are requested to include the following text in their acknowledgements:

Support for the Twentieth Century Reanalysis Project dataset is provided by the U.S. Department of Energy, Office of Science Innovative and Novel Computational Impact on Theory and Experiment (DOE INCITE) program, and Office of Biological and Environmental Research (BER), and by the National Oceanic and Atmospheric Administration Climate Program Office.