الفهرس 
Surface solar irradianceOnly 14 pages are availabe for public view
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Abstract
In this study, we use the level-2 AERONET inversion products of 19 stations of North Africa, the Middle East, or downwind of them, to characterize the degree of enthronization of the corresponding sub-regions. For this, we define a new dust-index (Idust) based on the statistical analysis of the frequency distributions of the aerosol optical depth at 440nm and its Fine Mode Fraction (FMF440). Idust is found to be more than one order of magnitude larger at the remote Saharan site of Tamanrasset (Idust=6.3) and at the 4 Sahelian stations (2.1<Idust<5.8) than along the Mediterranean coast (Idust=0.06, 0.08, and 0.09, in Blida, Tunis, and Lampedusa, respectively) or in the Middle East (Idust=0.11 in Sede Boker and 0.05 in Cairo). In spite of the different degrees of anthropization of the 19 stations, the Aeronet inversions do not reveal any differentiation of the real (n) and imaginary (k) parts of the refractive index, asymmetry parameter (g), and single scattering albedo (SSA) of the coarse mineral dust component of the aerosol. As a result of these commonalities, the inter-site variability of the instantaneous dust radiative forcing efficiencies at TOA and BOA (relative to the AOD440, and for solar zenith angles in the range 60±5°) is found to be entirely explainable by the differences of albedo () of the underlying surfaces: FEBOA=161-145 (R2=0.91, n=19), and FETOA=192-103 W m-2 AOD440-1 (R2=0.93, n=19). Conversely, the characteristics of the fine anthropogenic aerosols are found to be more variable. In particular, the large k (0.010, 0.012, 0.013, and 0.017 at Banizoumbou, Dakar, Cinzana, and Cabo Verde, respectively) and low SSA of the pollution aerosols of the Sahelian region denote a strong absorbing character to be linked to their most probable bio-mass burning origin. Generally, under pollution episodes, the forcing efficiency is found to be more negative (cooling) at BOA than during dust episodes, but less negative at TOA, or even close to 0 over the brightest surfaces. These results stress the importance of accounting for the surface albedo in the quantification of the climate impact of the aerosols.