Modelled-based Photosynthetically Active Radiation climatology for Cyprus: Validation with measurements and trends

The visible part of the surface downward solar radiation (400 – 700 nm) known as Photosynthetically Active Radiation (PAR) is a key parameter for many land process models and terrestrial applications. More specifically, it is a critical ecological factor affecting agriculture productivity, ecosystem-atmosphere energy, CO2 fluxes, canopy architecture in forest ecosystems, and the growth of phytoplankton, among others. Despite its high importance, PAR measurements are rather scarce and no relevant worldwide radiometric networks for this quantity, in contrast with other actinometric quantities (e.g., global horizontal irradiance), exist. For these reasons, PAR levels are mostly estimated by satellite observations and modeling techniques.   In the current study, we present a 16-year PAR climatology over Cyprus, based on the combined use of radiative transfer (RT) models and satellite imagery. Copernicus Atmospheric Monitoring Service (CAMS) AOD and PWV, aerosol climatology of SSA and AE based on the MACv3 aerosol climatology, Ozone – OMI data for the period 2005 – 2021, are used as input to the RT model LibRadtran to obtain the clear sky PAR levels. Consequently, the CAMS Cloud Modification Factor based on MSG images will be used to derive the PAR under all sky conditions. The derived climatology has a spatial resolution of 0.05x0.05 degrees and a temporal variation of 15 minutes, as constrained by the availability of Seviri/MSG images. Finally, the quality of the retrieved climatology is assessed by comparison with ground-based PAR measurements and PAR retrievals from measurements of GHI through relevant conversion algorithms, from quantum sensors and pyranometers that are installed in selected stations of the Meteorological Service of Cyprus. Acknowledgments: The authors acknowledge the ‘EXCELSIOR’: ERATOSTHENES: EΧcellence Research Centre for Earth Surveillance and Space-Based Monitoring of the Environment H2020 Widespread Teaming project (www.excelsior2020.eu). The ‘EXCELSIOR’ project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 857510, from the Government of the Republic of Cyprus through the Directorate General for the European Programmes, Coordination and Development and the Cyprus University of Technology. The Department of Meteorology of the Republic of Cyprus is acknowledged for providing ground-based data for validating the modelled quantities.