Satellite based short wave irradiance validation over Africa

Downward short wave incoming irradiances play a key role in the radiation budget at the earth surface. The monitoring of this parameter is essential for the understanding of the basic mechanisms involved in climate change, such as the greenhouse effect, the global dimming, the change in cloud cover and precipitations, etc. The use of geostationary satellite observations becomes crucial, since they allow the retrieval of irradiance at the surface, with the best spatial and temporal coverage. Two of umetsat decentralized Satellite Application Facilities (SAFs) are retrieving on an operational basis the surface solar radiation from Meteosat images. This study presents a common validation of these SAFs radiation products against ground data from 19 stations covering up to one year of measurements over Europe and Africa. The overall conclusion is that the products of the different facilities are comparable in terms of bias and standard deviation. The surface solar irradiance is retrieved over the African continent with a standard deviation of 12% to 37% (21% average) and a -1% to 11% bias (5% average). If the atmospheric aerosol load becomes a better known input parameter, it remains sparlsy acquired over the African continent. On the other hand, the present validation shows that the atmospheric water vapor, retrieved from ground temperature and relative humidity, has a non-negligible effect on the results and should be better evaluated