NCEP-DOE Reanalysis II (R2) is an improved version of the NCEP-NCAR Reanalysis I (R1). The improvements include an updated model with better physical parameterizations, assorted data assimilation errors were fixed and additional data were included. Still, it is still a 'first generation' product.
Better than NCEP-NCAR (R1) but still a first generation reanalysis. It is best to use 3rd generation reanalyses, specifically, ERA-Interim and MERRA. The CFSR has not yet been analyzed by many researchers.
NCEP_Reanalysis 2 data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/
National Center for Atmospheric Research Staff (Eds). Last modified 06 Oct 2016. "The Climate Data Guide: NCEP Reanalysis (R2)." Retrieved from https://climatedataguide.ucar.edu/climate-data/ncep-reanalysis-r2.