Transport of dust particles from the Bodélé region to the monsoon layer – AMMA case study of the 9–14 June 2006 period

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.

Interactions of atmospheric gases and aerosols with the monsoon dynamics over the Sudano-Guinean region during AMMA

“…During these 2 days, the WAM dynamics over the area were perturbed by the presence of a MCS. It developed over the Jos Plateau (Nigeria) around 16:00 UTC, reaching the Benin-Nigeria border at 20:00 UTC and moving southwestward across Benin overnight and into central Ghana, as already described in Flamant et al (2009) and (Crumeyrolle et al, 2011). The model reproduces the location of this MCS but earlier than in the observations, i.e., reaching the Benin-Nigeria border at 10:00 UTC (Fig.…”

Dust emission size distribution impact on aerosol budget and radiative forcing over the Mediterranean region: a regional climate model approach

“…Zender et al, 2003), which could be potentially unrealistic close to emitting regions. When local emission distribution data are available, this approach has proved to be regionally more realistic (Crumeyrolle et al, 2011) but is a priori tied to a specific domain of study. A second approach, notably used by Alfaro and Gomes (2001) and Shao (2001), consists of using a physically explicit scheme to link the emission size distribution to both the wind speed at emission and soil properties such as the size distribution, aggregate binding energy, and soil plastic pressure.…”

Modelling of primary aerosols in the chemical transport model MOCAGE: development and evaluation of aerosol physical parameterizations

“…The size distribution used in SIM1 has the number median diameters r 1 = 1.7 × 10 −6 m, r 2 = 6.7 × 10 −6 m, and r 3 = 14.2 × 10 −6 m; geometric standard deviations σ 1 = 1.7, σ 2 = 1.6, and σ 3 = 1.5; and mass fractions frac 1 = 0.3, frac 2 = 0.4, and frac 3 = 0.3. In this study we modified the size distribution following Alfaro et al (1998) and Crumeyrolle et al (2011), and in SIM2 our distribution is shifted towards smaller sizes with number median diameters r 1 = 6.4 × 10 −7 m, r 2 = 3.45 × 10 −6 m, and r 3 = 8.67×10…”