Abstract
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.
Highlights
Mineral dust represents the second largest component of primary particle emissions by mass, with an estimated global source strength of 1000 to 3000 Mt/yr (Ginoux et al, 2001; Houghton et al, 2001)
This paper describes the impact of vegetation anomalies on mineral dust particle sedimentation and entrainment observed during the African Monsoon Multidisciplinary Analyses (AMMA) experiment by using a combination of airborne observations and simulation exercises
Observations were interpreted using a mesoscale model simulation in order to explain the presence of high dust content over an area where local production is strongly inhibited by the surface cover
Summary
Mineral dust represents the second largest component of primary particle emissions by mass, with an estimated global source strength of 1000 to 3000 Mt/yr (Ginoux et al, 2001; Houghton et al, 2001). Prodi and Fea, 1979; Levin et al, 1980; Talbot et al, 1986; Guerzoni et al, 1997; Avila et al, 1997; Prospero, 1999; Gobbi et al, 2003). These particles contribute significantly to the global radiative budget through absorption and scattering of longwave and shortwave radiation (Houghton et al, 2001), and their indirect effect on cloud microphysics (Intergovernmental Panel in Climate Change, 2007; Twomey, 1977; Albrecht, 1989; Sandu et al, 2008).
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