Evaluation of satellite-derived surface irradiance in Greece using reference surface measurements

Satellite-based climate data records of surface irradiance that offer spatio-temporal information have recently become available. These data can be very useful for many purposes, but their quality needs to be carefully assessed, e.g., by comparison to suitable surface reference measurements. Here we evaluate the quality of the CM SAF SARAH-3 climate data record in Greece through comparison with long-term reference measurements from Athens and Thessaloniki. The SARAH-3 data records realistically reproduce the climatological spatial distribution of surface irradiance in Greece as well as its monthly and inter-annual variability. The decadal trends estimated from the satellite-based data record underestimate the positive trends derived from the surface measurements, in particular during the summer months. The neglect of inter-annual changes of the aerosol optical depth in the satellite retrieval might contribute to the too low positive trend in surface irradiance from SARAH-3, which is likely caused by changes in cloudiness.