CAMS radiation service v4.6 for solar energy: Evaluation of Himawari based surface solar irradiance products

The Copernicus Atmospheric Monitoring Service (CAMS) offers solar radiation service (CRS) which provides time series of surface solar irradiance (SSI) as its primary product. As a first step towards the global evolution of the service for solar energy applications, the Himawari measurements by Japan Meteorological Agency (JMA) are integrated since version 4.6. This study introduces a hierarchical evaluation framework and evaluates CRS for 32 stations distributed in different climates inside the Himawari field of view (FOV). Besides standard all-sky validation the framework includes APOLLO_NG cloud-type specific evaluation as well as seasonal, diurnal and interannual variability. The assessment is further deepened with the establishment of an irradiance variability based classification as a diagnostic tool for SSI validation allowing quantitative evaluation of various error sources due to different cloud conditions on the retrieval performance. The rMBE and rRMSE in all-sky conditions are in the ranges −7.4 to 4.9% and 8 to 30% for hourly Global Horizontal Irradiance (GHI), and − 26.6 to 15.3% and 18 to 64.1% for Beam Normal Irradiance (BNI), respectively. The evaluations show very good performance of CRS schemes under clear-sky and nearly clear-sky conditions and good handlings of thin clouds in most stations. However, broken cloud fields are observed to introduce notable overestimation. While a direct comparison with other validation studies for the Himawari FOV is limited due to differences in temporal and spatial coverage, CRS v4.6 achieved overall performance levels comparable to or better than other published approaches.