Satellite-Based Versus Ground-Based Radiation Fluxes Under ALL-Sky and CLEAR-Sky Conditions: The GEWEX SRB GSW(Rel. 4.0-IP) Results Versus Their BSRN and RadFlux Counterparts

After making available its Rel. 3.0 shortwave flux products in 2011 for a 24.5‑year period from July 1983 to December 2007, the NASA Global Energy and Water Exchanges (GEWEX) Surface Radiation Budget (SRB) project is now making significant progress towards its Release 4.0 integrated products (Rel. 4.0-IP). The new products will first continue to be on a quasi-equal-area grid system consisting of 44,016 grid boxes whose sizes range from 1° longitude by 1° latitude around the Equator to 120° longitude by 1° latitude around the Poles and will be available as 3-hourly, daily and monthly means. The higher resolution of its new input data from the International Satellite Cloud Climatology Project (ISCCP), however, will enable the move to a 0.5° by 0.5° quasi-equal-area grid system with 165,018 grid boxes. Changes for the Rel. 4.0‑IP shortwave algorithm that have been made include: recalculated spectral atmospheric transmissivities and reflectivities for 18 bands using the Fu-Liou algorithm modified by the CERES group; liquid and ice clouds being treated separately; aerosol data from the Max-Planck Aerosol Climatology Version 1 (MAC-V1) that includes both asymmetry and single scattering albedo; the ocean surface spectral albedo as a function of wind speed, aerosol optical depth and chlorophyll concentration; the spectral albedo of snow and ice being differentiated. The inputs have been changed to the ISCCP HXS products of cloud and radiance properties, the ISCCP nnHIRS water vapor, the GISS ozone data, the MAC-V1/V2 data, and the solar irradiance from SORCE/TIM V17. As with our Rel. 3.0 products, we validate the Rel. 4.0-IP results against ground-based observations from the Baseline Surface Radiation Network (BSRN), the Pacific Marine Environmental Laboratory (PMEL) arrays of buoys in the tropical oceans, the World Radiation Data Centre (WRDC), and the Global Energy Balance Archive (GEBA). In addition, we now have the clear-sky shortwave/longwave downward fluxes at the majority of BSRN sites obtained through the Radiative Flux Analysis (RadFlux) Program at NOAA, and the data add up to over 7000 site-months spanning 1992 to late 2017, which makes it possible to validate our clear-sky fluxes extensively as well. Starting from 2007, the new results are expanding backward to 1998 and forward to 2015. The validation statistics show generally good agreement between the satellite-based and the ground-based data for both the all-sky and clear-sky conditions. Furthermore, if we raise the bar for completeness of the ground-based records of observation, and require that the input cloud amounts and their ground-based counterparts be equal to a given limit, the level of agreement can change dramatically for the better. The detected negative bias of the clear-sky surface shortwave downward fluxes can be at least partly attributed to the input aerosol and precipitable water that are systematically higher than their counterparts at the BSRN sites.