ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-7165-2012 The direct effect of aerosols on solar radiation over the broader Mediterranean basin Papadimas C. D. 1 Hatzianastassiou N. 1 Matsoukas C. 2 Kanakidou M. 3 4 Mihalopoulos N. 3 4 Vardavas I. 5 Laboratory of Meteorology, Department of Physics, University of Ioannina, 45110 Ioannina, Greece Department of Environment, University of the Aegean, 81100 Mytilene, Greece Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, P.O. Box 2208, 71003 Heraklion, Crete, Greece Institute of Chemical Engineering and High Temperature Chemical Processes (ICE-HT), Foundation for Research and Technology Hellas (FORTH), Patras, 26504, Greece Department of Physics, University of Crete, 71110 Heraklion, Crete, Greece 07 08 2012 12 15 7165 7185 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/7165/2012/acp-12-7165-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/7165/2012/acp-12-7165-2012.pdf

For the first time, the direct radiative effect (DRE) of aerosols on solar radiation is computed over the entire Mediterranean basin, one of the most climatically sensitive world regions, using a deterministic spectral radiation transfer model (RTM). The DRE effects on the outgoing shortwave radiation at the top of atmosphere (TOA), DRE<sub>TOA</sub>, on the absorption of solar radiation in the atmospheric column, DRE<sub>atm</sub>, and on the downward and absorbed surface solar radiation (SSR), DRE<sub>surf</sub> and DRE<sub>netsurf</sub>, respectively, are computed separately. The model uses input data for the period 2000–2007 for various surface and atmospheric parameters, taken from satellite (International Satellite Cloud Climatology Project, ISCCP-D2), Global Reanalysis projects (National Centers for Environmental Prediction – National Center for Atmospheric Research, NCEP/NCAR), and other global databases. The spectral aerosol optical properties (aerosol optical depth, AOD, asymmetry parameter, <i>g</i><sub>aer</sub> and single scattering albedo, &omega;<sub>aer</sub>), are taken from the MODerate resolution Imaging Spectroradiometer (MODIS) of NASA (National Aeronautics and Space Administration) and they are supplemented by the Global Aerosol Data Set (GADS). The model SSR fluxes have been successfully validated against measurements from 80 surface stations of the Global Energy Balance Archive (GEBA) covering the period 2000–2007. <br><br> A planetary cooling is found above the Mediterranean on an annual basis (regional mean DRE<sub>TOA</sub> = &minus;2.4 W m<sup>−2</sup>). Although a planetary cooling is found over most of the region, of up to −7 W m<sup>−2</sup>, large positive DRE<sub>TOA</sub> values (up to +25 W m<sup>−2</sup>) are found over North Africa, indicating a strong planetary warming, and a weaker warming over the Alps (+0.5 W m<sup>−2</sup>). Aerosols are found to increase the absorption of solar radiation in the atmospheric column over the region (DRE<sub>atm</sub> = +11.1 W m<sup>−2</sup>) and to decrease SSR (DRE<sub>surf</sub> = &minus;16.5 W m<sup>−2</sup> and DRE<sub>netsurf</sub>&minus;13.5 W m<sup>−2</sup>) inducing thus significant atmospheric warming and surface radiative cooling. The calculated seasonal and monthly DREs are even larger, reaching −25.4 W m<sup>−2</sup> (for DRE<sub>surf</sub>). Within the range of observed natural or anthropogenic variability of aerosol optical properties, AOD seems to be the main responsible parameter for modifications of regional aerosol radiative effects, which are found to be quasi-linearly dependent on AOD, &omega;<sub>aer</sub> and <i>g</i><sub>aer</sub>.

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