The Surface Radiation Budget: An evaluation of climate data records for the downwelling surface radiation

The surface energy budget is driven by the incoming short- and longwave radiation. While the energy of the downwelling longwave (thermal) radiation exceeds the shortwave (solar) radiation (~342 W m^-2 compared to ~187 W m^-2 for the global climatological average), the incoming shortwave radiation represents an external energy source for the Earth-Atmosphere system. Accurate monitoring of the downwelling radiative energy fluxes is of high importance for the understanding and the detection of changes in the climate system.

Here, we present an evaluation of available monthly-mean surface short- and longwave downwelling radiation data sets focussing on their suitability for climate monitoring. These data sets include the ISCCP FD data set, the NASA/GEWEX Surface Radiation Budget (SRB), and the ECMWF ERA-Interim Reanalysis. Surface observations from the Baseline Surface Radiation Network (BSRN) serve as the reference data set. For the longwave radiation, the ERA-Interim data set fulfils the GCOS requirements for climate monitoring (bias below 10 W m^-2) . For the shortwave radiation, none of the available data sets has sufficient accuracy for climate monitoring based on the GCOS requirement.

The goal of the EUMETSAT Satellite Application Facility on Climate Monitoring (CM-SAF) is to produce and to distribute high-quality climate data records derived from satellite data. In 2010/2011 two new data sets for the surface solar downwelling radiation will become available from CM-SAF. Based on the MVIRI / SEVIRI instruments onboard the geostationary Meteosat satellites a high-resolution climate data record from 1986 to present will be derived using the Heliosat-algorithm. The Global Area Coverage (GAC) AVHRR data set (available from 1982 to present) will be used to derive a global data set for the surface solar radiation. An overview and a first assessment of these new data sets will be presented.