The Twentieth Century Reanalysis (20CR) provides a comprehensive global atmospheric circulation data set spanning 1870-2010. Its chief motivation is to provide an observational validation data set, with quantified uncertainties, for assessing climate model simulations of the 20th century, with emphasis on the statistics of daily weather. The analyses are generated by assimilating only surface pressures and using monthly SST and sea ice distributions as boundary conditions within a 'deterministic' Ensemble Kalman Filter (EKF). A unique feature of the 20CR is that estimates of uncertainty are derived using a 56 member ensemble. Overall, the quality is approximately that of current three-day NWP forecasts.
National Center for Atmospheric Research Staff (Eds). Last modified 06 Nov 2013. "The Climate Data Guide: NOAA 20th-Century Reanalysis, Version 2." Retrieved from https://climatedataguide.ucar.edu/climate-data/noaa-20th-century-reanalysis-version-2.