Aerosol shortwave daily radiative effect and forcing based on MODIS Level 2 data in the Eastern Mediterranean (Crete)
1Department of Physics, University of Crete, Greece
2Department of Physics, University of Ioannina, Greece
3Department of Environment, University of the Aegean, Greece
4Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, Greece
Abstract. The mean daily shortwave (SW) radiation budget was computed on a 10 km × 10 km resolution above FORTH-CRETE AERONET station in Crete, Greece, for the 9-yr period from 2000 to 2008. The area is representative of the Eastern Mediterranean region, where air pollution and diminishing water resources are exacerbated by high aerosol loads and climate change. The present study aims to quantify the aerosol direct effect and forcing on the local energy budget. A radiative transfer model was used, with daily climatological data from the Moderate Resolution Imaging Spectroradiometer (MODIS), on board NASA's Terra and Aqua satellites. The radiative fluxes were computed at the surface, within the atmosphere and at the top of atmosphere (TOA). Downward surface fluxes and aerosol optical thickness (AOT) were validated against ground measurements. Daily fluxes reveal the direct radiative effects of dust events, with mean daily values reaching up to −100, 55 and −30 W m−2 at the surface (cooling), within the atmosphere (warming) and at TOA (cooling), respectively. Mean monthly values show a decreasing trend of the aerosol direct radiative effect, in agreement with a similar trend in AOT. The analysis of the contribution of anthropogenic and natural aerosol show major peaks of natural aerosol direct effect occurring mainly in spring, while a summer maximum is attributed to anthropogenic aerosol. During their peaks, anthropogenic aerosol forcing can reach values of −15 W m−2 at the surface, 8 W m−2 in the atmosphere and over −4 W m−2 at TOA (monthly mean values). The corresponding daily peak values for natural aerosol are over −10 W m−2, 6 W m−2 and −3 W m−2. Annual mean values and standard deviations (interannual variability) of anthropogenic aerosol forcing are −10 ± 3 W m−2 at the surface, 5 ± 1 W m−2 in the atmosphere and −3 ± 1 W m−2 at TOA, while the corresponding values for natural aerosol are −6 ± 2 W m−2, 3 ± 1 W m−2 and −3 ± 1 W m−2.