Desert Aerosol in the Mediterranean
Tropospheric aerosols may affect climate through different mechanisms. In particular, aerosols intervene in the water cycle, and may influence the hydrologic balance. In the Mediterranean a large role is played by desert dust originating in the Sahara. Mi
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Abstract Tropospheric aerosols may affect climate through different mechanisms. In particular, aerosols intervene in the water cycle, and may influence the hydrologic balance. In the Mediterranean a large role is played by desert dust originating in the Sahara. Mineral dust production depends on soil aridity, i.e., among other factors, on land use, and precipitationltemperature regimes. In the Mediterranean, desert dust is mostly transported northward during spring and summer, driven by low and high pressure systems over north Africa. In addition, depending on the synoptic situation, anthropogenic particles and marine aerosols are found over the Mediterranean. The Mediterranean basin is thus an excellent laboratory to study the complex interactions of different type of particles with the radiative field, the hydrological cycle, and clouds. Some results of measurements carried out at Lampedusa island (35SN, 12.6 E) in 1999, showing the presence of desert dust and its effects on the radiative field, are described.
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Introduction
Atmospheric aerosol produce a significant influence on the Earth radiative budget (e.g. Schwartz and Andreae, 1996), through scattering and absorption of radiation (direct forcing), and by influencing the cloud nucleation processes and the cloud microphysical properties (indirect forcing). Mineral or crustal (dust) particles are among the principal constituents of tropospheric aerosols. It is estimated that a fraction ranging between 30 and 50% of the total mineral aerosols are of anthropogenic origin such as produced in soils which have been disturbed by human activity (Tegen and Fung, 1995; Sokolik and Toon, 1996). Continental aridity is indicated as the main cause of increased dust flux from the deserts (Rea et aI., 1985; Pye, 1989), that constitute the most relevant source of these particles. Hyper arid regions however (mean annual precipitation
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