A 1-year remote sensing study of radiative effects of aerosol and clouds over the NE Mediterranean

Direct aerosol radiative forcing ARF and cloud radiative forcing CRF over the Aegean Sea are investigated using 1 year of almost continuous observations of aerosol optical properties, cloud data and Clouds and the Earth's Radiant Energy System CERES satellite short-wave SW and long-wave LW fluxes during 2005–2006. Aerosol optical depth AOD values from moderate resolution imaging spectroradiometer MODIS over the Aegean Sea are found to be high during summer and spring months. This period of the year, the air masses come predominantly from the eastern and northeastern part of Europe. The monthly mean ARF at the top of the atmosphere TOA over the Aegean Sea resulted in net cooling and ranged from −6.0 to −15.8 W m−2, within the range of results from previous studies. The presence of fine particles greatly influenced the ARF. The CRF was also characterized by net cooling and ranged from −23 to −84 W m−2 and appeared to be driven primarily by changes in cloud fraction. An apparent aerosol weekly cycle with lower values during the weekend as well as a cloud fraction weekly cycle with lower values during the weekend is observed over the Aegean Sea, which, if confirmed, could result in net TOA forcing of around −20 W m−2.