NCEP/NCAR Reanalysis (1948-present)
The NCEP/NCAR Reanalysis 1 project is using a state-of-the-art analysis/forecast system to perform data assimilation using past data from 1948 to the present.  Data is from NMC initialized reanalysis (4x/day).  See the PROBLEMS LIST at https://www.esrl.noaa.gov/psd/data/reanalysis/problems.shtml