Recent Updates to the NASA/GEWEX SRB Longwave Flux Algorithm

The NASA/GEWEX (Global Energy and Water Exchanges project) Surface Radiation Budget (SRB) project produces longwave and shortwave radiative fluxes for the surface and top-of-atmosphere (TOA). The primary inputs of cloud and meteorology data have been undergoing improvements in quality and spatial and temporal resolution. In anticipation of the release of these data, the SRB longwave flux algorithm has been updated both to accommodate these data and to improve the algorithm used in deriving radiative fluxes.

This presentation reports on numerous improvements made to the longwave algorithm. Major among them are the inclusion of time-dependent aerosol profiles from the Max Planck Institute. Updated meteorological and ancillary data include the new ISCCP cloud data, satellite-derived meteorology from HIRS, diurnally varying sea surface and land surface temperatures, new topography and surface type maps and snow/ice maps. Many of these inputs are being developed improved in collaboration with other GEWEX projects to improve inconsistency between GEWEX radiation and other GEWEX energy and water cycle data products (i.e., ISCCP, SeaFlux, LandFlux, NVAP, etc.)

With aerosols included in the algorithm, the fluxes available to the user will now include pristine-sky conditions, in addition to all-sky and clear-sky conditions. The capability to produce fluxes at levels other than TOA and surface has also been added. Currently, these new levels are produced at 70, 200 and 500 hPa to compare to CERES SYN 1 degree flux products.

In early results using these new inputs in the algorithm, the monthly average global outgoing longwave (OLR) flux has been reduced by 2-3 Wm-2 from the previous release, while the downward surface flux has been increased by 3-4 Wm-2. Much of these differences can be attributed to the addition of aerosols to the input.

This GLW version will be released as part of the SRB Release 4.0 Integrated Product recognizing the collaboration of other GEWEX teams. The current schedule of this new data set is discussed.