Assessing Uncertainties and Variability in Global and Regional Radiative Budgets from the NASA/GEWEX Surface Radiation Budget (SRB) Release-3.0 Dataset

The surface radiation budget (SRB), consisting of downward and upward components of shortwave (SW) and longwave (LW) radiation is a major component of the energy exchanges between the atmosphere and land/ocean surfaces and thus affects surface temperature fields, fluxes of sensible and latent heat, and every aspect of energy and hydrological cycles. The NASA Global Energy and Water-cycle Experiment (GEWEX) SRB project has now updated and improved a global dataset of surface radiative fluxes on a 1-degree grid for a 24-year period (July 1983 to December 2007). Both SW and LW fluxes were derived with two sets of algorithms: one designated as primary and the other as quality-check. The primary algorithms use a more explicit treatment of surface and atmospheric processes while quality-check algorithms use a more parameterized approach. Cloud and surface properties for input to the algorithms were derived from ISCCP pixel level (DX) data, temperature and humidity profiles from GEOS-4 reanalysis products, and column ozone from a composite of TOMS, TOVS, and assimilated SBUV-2 datasets. Several top-of-atmosphere (TOA) radiation budget parameters were also derived with the primary algorithms. Surface fluxes from all algorithms are extensively validated with ground-based measurements obtained from the Baseline Surface Radiation Network (BSRN), the Global Energy Balance Archive (GEBA), and the World Radiation Data Center (WRDC) archives. This dataset is a major contributor to the GEWEX Radiative Flux Assessment (RFA) activity.

Recently, articles have been published analyzing ISCCP for artifacts in long-term cloud properties (Evan et al. 2007; Raschke et al. 2008). This presentation provides a summary of the assessment of the radiative fluxes on global and regional scales due to uncertainties in the ISCCP radiance and cloud inputs and summarizes the implications for interpreting long-term changes. The assessment includes comparisons with other global TOA and surface flux datasets such as the ISCCP FD, CERES SRBAVG and AVG will also be presented during relevant periods and against validation against surface measurements. The global and zonal statistics of fluxes, inferred cloud radiative forcing, and results of the validation activities will be presented along with analysis of flux anomalies related to El Nino/La Nina episodes, phases of North Atlantic Oscillation (NAO), and other interannual phenomena of the period. Spatial and temporal variability of model-derived fluxes will be examined relative to that observed in surface-based measurements and that arising from corresponding variability in various input parameters based on sensitivity studies with the models. We intend to include an estimate of the uncertainty of total (net SW + net LW) radiative budget implied by the respective SW and LW uncertainties. The entire dataset is being made available to the worldwide science community by NASA/LaRC Atmospheric Sciences Data Center (see http://gewex-srb.larc.nasa.gov for more information).