The Clouds and the Earth's Radiant Energy System (CERES) Experiment is the latest and most accurate satellite-based instrument designed to measure the Earth's global energy budget. With improvements in instrument calibration accuracy and stability, coupled with the development of new angular directional models, temporal sampling is the largest remaining error source for CERES regional monthly mean fluxes. CERES addresses the time sampling issue in two ways. First, CERES was designed to sample the diurnal cycle using a 3-satellite constellation with instruments aboard the sun-synchronous Terra and Aqua satellites and the temporally precessing TRMM spacecraft. Second, improved modeling of unsampled time periods is provided by the incorporation of 3-hourly radiance and cloud property data from narrowband instruments aboard geostationary satellites. The failure of the CERES TRMM instrument in April 2000, and launch delays for Terra and Aqua have resulted in single-satellite coverage for most of the mission to date. Therefore the use of geostationary data has become crucial for the accurate modeling of diurnal variations of clouds during these time periods when the full complement of CERES instruments is not available.

The techniques used to calculate monthly mean fluxes for CERES will be reviewed and the first results of this new interpolation process will be presented. Particular attention will be paid to the differences in these new monthly mean fluxes with CERES ERBE-like products. The ERBE-like processing was designed to provide a climate data record consistent with the ERBE experiment. The new CERES monthly means will remove angular and sampling biases found in the ERBE-like data and also provide extensive additional information on the effects of clouds on the radiation budget.