1Laboratoire de Météorologie Physique, Université Blaise Pascal, UMR 6016, Clermont-Ferrand, France
2Centre National de Recherches Météorologiques, GAME, Météo-France, Toulouse, France
3LACy, Université de La Réunion, Saint-Denis, France
4School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
5LATMOS/IPSL, CNRS-UPMC-UVSQ, Paris, France
6Frontier Science Organization, Kanazawa University, Japan
7LISA/IPSL, Universités Paris 12 et Paris 7, CNRS, UMR 6240, Créteil, France
Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in June 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to investigate a dynamical mechanism able to facilitate the sedimentation of dust particles from the Saharan Air Layer (SAL) into the boundary layer. A significant change in the dust particle concentration measured along the meridian between Niamey (Niger) and Cotonou (Benin) was found in the boundary layer (~700 m), where the dust particle concentration increased in a zone where local emission is not possible. Moreover, the boundary layer top observed with the dropsondes launched with the F-F20 shows a strong relationship with the surface cover anomalies, with higher Boundary Layer (BL) tops over the warmer surfaces, such as croplands, as opposed to adjacent forest. A mesoscale atmospheric model with a new on-line dust parameterization, resulting from the Alfaro and Gomes (2001) parametrisation and AMMA observations, was used to interpret the impact of vegetation anomalies on dust particle sedimentation. The results of the simulation are consistent with the observations, with higher dust concentration over the warm surface cover anomalies.