The original daily tar files are available on NCAR's MSS only.
The original daily tar files are from NCEP. Both "a" and "b" files are included. The main file (the "a" file, though there is no "a" in the file name) contains the complete archive of all analysis variables valid at the time indicated in the filename. In addition, the "b" file has 3-hr accumulations (e.g. precipitation) and averages (e.g. sensible and latent heat fluxes).