Abstract
Abstract. 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), DRETOA, on the absorption of solar radiation in the atmospheric column, DREatm, and on the downward and absorbed surface solar radiation (SSR), DREsurf and DREnetsurf, 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, gaer and single scattering albedo, ωaer), 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. A planetary cooling is found above the Mediterranean on an annual basis (regional mean DRETOA = −2.4 W m−2). Although a planetary cooling is found over most of the region, of up to −7 W m−2, large positive DRETOA values (up to +25 W m−2) are found over North Africa, indicating a strong planetary warming, and a weaker warming over the Alps (+0.5 W m−2). Aerosols are found to increase the absorption of solar radiation in the atmospheric column over the region (DREatm = +11.1 W m−2) and to decrease SSR (DREsurf = −16.5 W m−2 and DREnetsurf−13.5 W m−2) inducing thus significant atmospheric warming and surface radiative cooling. The calculated seasonal and monthly DREs are even larger, reaching −25.4 W m−2 (for DREsurf). 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, ωaer and gaer.
Highlights
Atmospheric aerosols influence the Earth’s climate by modifying its energy balance through the direct, indirect and semidirect effects
The aerosol direct effect on surface solar radiation, i.e. DREsurf, is very important because SSR plays a key role for many processes of the Earth-atmosphere system, for example surface heating or evaporation
Direct validation of the model computation of DREsurf is not feasible owing to the absence of measurements of surface solar radiation fluxes in the absence of aerosol particles, Fsurf,no-aerosol (Eq 2)
Summary
Atmospheric aerosols influence the Earth’s climate by modifying its energy balance through the direct, indirect and semidirect effects. The uncertainty of aerosol effects on the Earth’s radiation budget greatly exceeds that of any other climate forcing agent (Kaufman et al, 2002; Forster, 2007; Vardavas and Taylor, 2011). Improved assessments of aerosol radiative effects are essential for reducing the uncertainty of future climate changes (IPCC, 2007) and have to be performed on global and on regional scales. Such assessments are important in the context of changes in solar radiation at the Earth’s surface, commonly known as global dimming and brightening, which are of primary importance for the Earth’s climate and have received much attention lately (see Wild, 2009)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
