The NCEP/NCAR Reanalysis Project is an effort to reanalyze historical data using state-of-the-art models. The reanalysis is done at NCEP (formerly NMC) using T62 (209 km) global spectral model of 28 vertical levels. This is the same model used in the assimilation system, as implemented in the NCEP operational system in December 1994. The model has 5 levels in the boundary layer and about 7 levels above 100 hPa. The lowest model level is about 5 hPa from the surface, and the top level is at about 3 hPa. This vertical structure was chosen so that the boundary layer is reasonably well resolved and the stratospheric analysis at 10 hPa isnot much affected by the top boundary conditions. The details of the model dynamics and physics are described in Development Division (1988), Kanamitsu (1989), and Kanamitsu et al(1991). The model includes parameterizations of all major physical processes, i.e., convection, large scale precipitation, shallow convection, gravity wave drag, radiation with diurnal cycle and interaction with clouds, boundary layer physics, an interactive surface hydrology, and vertical and horizontal diffusion processes. See http://dss.ucar.edu/pub/reanalyses.html for further documentation. The data sets consist of monthly means of surface fields.