Optical Properties and Direct Radiative Effects of Aerosol Species at Global Scale Based on the Synergistic Use of MERRA-2 Optical Properties and the Forth Radiative Transfer Model

The overarching goal of the current study is to quantify the aerosol induced clear-sky direct radiative effects (DREs) within the Earth-Atmosphere system at global scale and for the 40-year period 1979-2019. To this aim, the MERRA-2 aerosol radiative properties, along with meteorological fields and surface albedo, are utilized as inputs to the FORTH radiative transfer model (RTM). Our preliminary results, representative for the year 2015, reveal strong surface radiative cooling (down to -45 Wm^-2) over areas where high aerosol loadings and absorbing particles (i.e., dust and biomass burning) dominate. This reduction of the incoming solar radiation, in the aforementionned regions, is largely attributed to its absorption by the overlying suspended particles resulting in an atmospheric warming reaching up to 40 Wm^-2. At the top-of-atmosphere (TOA) negative DREs (planetary cooling) are computed worldwide (down to -20 Wm^-2) with few exceptions over bright surfaces (warming up to 5 Wm^-2). Finally, the strong variations between the obtained DREs of different aerosol species (dust, sea-salt, sulphate, organic/black carbon) as well as between hemispheres and surface types (i.e., land vs ocean) are also discussed.