Evaluation and Applications of the satellite-based CM SAF Solar Surface Radiation Climate Data Set

Abstract:

The incoming surface solar radiation has been defined as an essential climate variable by GCOS. It is mandatory to monitor this part of the earth’s energy balance, and thus gain insights on the state and variability of the climate system. In addition, data sets of surface solar radiation have received increased attention over the recent years as an important source of information for solar energy applications.

The EUMETSAT Satellite Application Facility on Climate Monitoring (CM SAF) is deriving surface solar radiation from geostationary and polar-orbiting satellite instruments. While CM SAF is focusing on high-quality long-term climate data records, operational data is also provided with a short time latency within about 2 weeks.

Here we present the SARAH data set (Solar Surface Radiation Dataset – Heliosat) based on Meteosat satellite observations. SARAH provides hourly, daily- and monthly-averaged data of the effective cloud albedo (CAL), the direct normalized solar radiation (DNI) and the solar irradiance (SIS) from 1983 to 2013 for the full view of the Meteosat satellite (i.e, Europe, Africa, parts of South America, and the Atlantic ocean). The data sets are generated with a high spatial resolution of 0.05 deg allowing for detailed regional studies, and are available in netcdf-format at no cost without restrictions at www.cmsaf.eu.

The mean absolute bias (i.e., the accuracy) of the SARAH data set as compared to surface reference observations has been determined to be 5.5 W/m² for SIS and 8.2 W/m² for DNI, i.e., within the accuracy of the ground-based measurements. The interannual and decadal variability of the SARAH SIS data are comparable to surface observations in Europe, although with a tendency to underestimate the mean increase in surface solar radiation (1.65 W/m²/dec compared to 3.3 W/m²/dec). Substantial temporal and spatial variability in the overall increase in surface solar radiation is found in the SARAH data set.

Temporal changes in the frequency of Großwetterlagen (GWL) can cause trends in surface solar radiation. A cluster analysis technique has been applied to identify 11 regions in Europe with similar day-to-day variability in solar radiation. This result can be used to assess the impact of changes in GWL frequency on regional trends in the surface solar radiation.