Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 8 22 2008 10.5194/acp-8-6839-2008 http://www.atmos-chem-phys.net/8/6839/2008/ http://www.atmos-chem-phys.net/8/6839/2008/acp-8-6839-2008.html http://www.atmos-chem-phys.net/8/6839/2008/acp-8-6839-2008.pdf 6839 6864 2008-11-28 Radiative budget in the presence of multi-layered aerosol structures in the framework of AMMA SOP-0 J.-C. Raut jean-christophe.raut@lsce.ipsl.fr P. Chazette Laboratoire des Sciences du Climat et de l'Environnement, Laboratoire mixte CEA-CNRS-UVSQ, CEA Saclay, 91191 Gif-sur-Yvette, France This paper presents radiative transfer calculations performed over Niamey in the UV-Visible range over the period 26th January–1st February 2006 during the African Multidisciplinary Monsoon Analysis (AMMA) international program. Climatic effects of aerosols along the vertical column have required an accurate determination of their optical properties, which are presented here for a variety of instrumented platforms: Ultralight aircraft, Facility for Airborne Atmospheric Measurements (FAAM) research aircraft, AERONET station. Measurements highlighted the presence of a multi-layered structure of mineral dust located below and biomass-burning particles in the more elevated layers. Radiative forcing was affected by both the scattering and absorption effects governed by the aerosol complex refractive index (ACRI). The best agreement between our results and AERONET optical thicknesses, ground-based extinction measurements and NO₂ photolysis rate coefficient was found using the synergy between all the instrumented platforms. The corresponding averaged ACRI at 355 nm were 1.53 (±0.04) −0.047i (±0.006) and 1.52 (±0.04) −0.008i (±0.001) for biomass-burning and mineral dust aerosols, respectively. 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