GFDL Atmospheric Circulation Analyses by Bram Oort, monthly May 1958 to April 1973

The "classic" derived by Bram Oort from MIT, GTS, ETAC, NCDC and NCAR data. See also DS431.0 [rda.ucar.edu/datasets/ds431.0/]. Unless you have a special interest in this dataset, DSS recommends that you use one of our reanalysis datasets, such as ds090.2 [rda.ucar.edu/datasets/ds090.2/].

That's because those are based on a more complete collection of observations, improved analysis methods, and are provided in a common modern format (GRIB).