GEWEX Radiative Flux Assessment: Surface radiation budget data results

The GEWEX Radiative Flux Assessment (GEWEX-RFA) is an international scientific project commissioned by the GEWEX Radiation Panel to examine the current state of both the top of atmosphere (TOA) and surface Earth Radiation Budget (ERB) data sets and to give recommendations for future improvements of these climate data records. Earth radiation budget data producers from various institutions around the globe have responded to the GEWEX-RFA data request and submitted their scientific data sets into the GEWEX-RFA archive. This presentation will focus on comparisons of the surface data sets in this archive.

Satellite data products are evaluated over their entire record length and for the ERBE (1985-1989) and CERES (2000-2003) time periods. All radiation budget components (shortwave down, shortwave up, etc.) are evaluated individually. Analysis results for global and tropical (20°S-20°N) climatological means, regional variability, and annual cycle variability will be presented. In addition, comparisons to measurements from the Baseline Surface Radiometer Network (BSRN) will be shown. During the CERES period, global mean surface fluxes vary between 2 and 8 Wm^-2 (standard deviation) among the submitted data sets, while the tropical means agree to 1-11 Wm^-2. Satellite estimates of the downwelling radiative fluxes compare well to the in situ observations with monthly averaged root-mean-square differences of 15-24 Wm^-2 for the shortwave (SW) and 13–20 Wm^-2 for the longwave (LW) components. Ensemble mean anomaly time series are created for each satellite data set using data from those BSRN measurement locations having nearly continuous measurements over the period 1997-2004. The standard deviation of the differences between the BSRN and satellite matched SW (LW) ensemble time series fell in the range of 5.2–5.6 Wm^-2 (2–2.5 Wm^-2) for most of the satellite algorithms. This is taken as a measure of the precision of these data sets. The slope of the shortwave ensemble bias over time is observed to be negative and the reasons for this are explored. Such a change is not seen in the longwave.