This dataset contains ECMWF ERA40 monthly mean model forecasts of geopotential, temperature, wind and moisture variables on 23 constant pressure surfaces for the period September, 1957 to August, 2002. The means, which are available for the 6 hour forecast only, have been computed for each analysis hour, with a diurnal mean also being ... available. All variables are archived at global T159 spectral resolution in spherical harmonics, except the moisture, ozone and potentical vorticity, which are archived on a reduced N80 gaussian grid with an approximate horizontal resolution of 125 kilometers. The monthly mean analysis fields have been archived in ds119.1 [http://dss.ucar.edu/datasets/ds119.1]. The ECMWF ERA40 project is a global atmospheric analysis of many conventional observations and satellite data streams for the period September,1957- August,2002. There are numerous data products that are separated into dataset series based on resolution, vertical coordinate reference, and possible research applications. Descriptions of the series organization and direct links to information about all ERA40 products are available [http://dss.ucar.edu/cgi-bin/joey/era40sum.pl?ds=ds121.1] The ERA-Interim data from ECMWF is an update to the ERA-40 project. The ERA-Interim data starts in 1989 and has a higher horizontal resolution (T255, N128 nominally 0.703125 degrees) than the ERA-40 data (T159, N80 nominally 1.125 degrees). ERA-Interim is based on a more current model than ERA-40 and uses 4-D VAR (as apposed to 3-D VAR in ERA-40). ECMWF will continue to run the ERA-Interim model in near real time thru at least 2010, and possibly longer. This data is available in ds627.0 [http://dss.ucar.edu/datasets/ds627.0].