Desert dust outbreaks at the Mediterranean Basin: Optical properties and impact on surface solar radiation

The Mediterranean Basin is one of the sunniest regions globally. Thus, aerosols, and especially dust, play a key role in radiative transfer processes in the atmosphere, which locally can be comparable to or even more significant than the role of clouds. The physical (i.e., size, shape) and chemical (e.g., composition) properties of dust that is transported across the Mediterranean Basin depend strongly on its origin, as well as on its ageing and mixing with other atmospheric constituents. For instance, the mixing of dust with anthropogenic particles can alter its chemical composition and hygroscopicity/ hygroscopic properties. Changing physical and/or chemical properties of dust also alter its optical properties and subsequently its radiative effects.By analyzing synergistically back-trajectories of the air masses at different altitudes from the HYSPLIT model, aerosol optical properties from Aerosol Robotic Network (AERONET), and dust optical depth from the ModIs Dust AeroSol (MIDAS) climatology, we identified three strong dust events in the period 2015 2022 where dust originated from different regions of Africa and the Middle East and travelled over many AERONET stations located in (and near) the Mediterranean Basin (in an area covering latitudes from 30 N to 45 N and longitudes from -10 E to 40 E. After identifying the origin of desert dust, we studied the changes in its optical (Optical Depth, Angstrom Exponent, Single Scattering Albedo) and microphysical (size distribution) properties as derived from different AERONET stations, using quality assured, AERONET level 2 (version 3), products. Finally, Radiative Transfer (RT) simulations for clear sky (cloudless) conditions were performed, employing the UVSPEC model from the libRadtran package in order to estimate the impact of dust, as well as the effect of its changing optical properties, on downwelling surface solar radiation in terms of Global Horizontal Irradiance (GHI) and Direct Normal Irradiance (DNI).Acknowledgements: Authors would like to acknowledge the Action Harmonia CA21119 supported by COST (European Cooperation in Science and Technology).