Toward improving the CERES derivation of SW broadband fluxes from GEO narrowband radiances

The Clouds and the Earth's Radiant Energy System (CERES) project provides top of atmosphere (TOA) broadband fluxes for the modeling community for climate studies and model validation. CERES fluxes observed by Aqua and Terra platforms need to be diurnally averaged to be meaningful. CERES provides daily averaged fluxes that assume constant meteorology between CERES measurements on the SSF1deg product, as well as using geostationary (GEO) 3-hourly derived broadband fluxes to resolve the regional diurnal cycle in between CERES measurements on the SYN1deg product. The GEO derived fluxes are based on theoretical and empirical narrowband to broadband radiance models. After which the GEO derived broadband radiances are converted to broadband fluxes using the same Angular Directional Models (ADM) that CERES uses. To ensure that the CERES instrument calibration is preserved the GEO SW derived fluxes are normalized to the CERES observed fluxes. Incorporating GEO visible channel radiances has its challenges. The GEO satellites do not have any onboard calibration and must be inter-calibrated against MODIS radiances. Each GEO satellite visible channel has its unique spectral response function. Due to the lack of coincident, collocated, and co-angled GEO and CERES radiance pairs to construct empirical models, radiative transfer computations must be deployed. The SW narrowband to broadband approach can be validated with coincident CERES and Moderate Resolution Imaging Spectroradiometer (MODIS) radiances. The SW narrowband to broadband process is being reexamined and improved for CERES Edition 4 products and will be presented at the meeting.