Impact of dust aerosols on the radiative budget, surface heat fluxes, heating rate profiles and convective activity over West Africa during March 2006
1Université de Toulouse, UPS, LA (Laboratoire d'Aérologie), 14 avenue Edouard Belin, 31400 Toulouse, France
2CNRS, LA (Laboratoire d'Aérologie), 31400 Toulouse, France
3GAME/CNRM, METEO-FRANCE – CNRS, Toulouse, France
4Laboratoire d'Optique de l'Atmosphère, Université des Sciences et Technologies de Lille, CNRS, Villeneuve d'Ascq, France
5Service d'Aéronomie, Institut Pierre Simon Laplace, Paris, France
Abstract. The present work analyzes the effect of dust aerosols on the surface and top of atmosphere radiative budget, surface temperature, sensible heat fluxes, atmospheric heating rate and convective activity over West Africa. The study is focused on the regional impact of a major dust event over the period of 9–13 March. Numerical simulations have been performed with the MesoNH model in which full interactions between radiation and dynamics are introduced, through various components representing size-resolved aerosol and cloud microphysics, radiative properties of particles and clouds, dynamics, and a surface model. Due to its importance on radiative budgets, a specific attention has been paid to the representation of dust SSA in MesoNH by using AERONET inversions. The radiative impacts are estimated using two parallel simulations, one including radiative effects of dust and the other without them. The simulations of dust aerosol impacts on the radiative budget indicate remarkable instantaneous decrease of shortwave (SW) radiations, with regional (09°–17° N, 10° W–20° E) mean of −160 W/m2 during the 9 to 13 March period. The surface dimming resulting from the presence of dust is shown to cause important reduction of both surface temperature (up to 4°C over regions where high AODs occur) and sensible heat fluxes (up to 100 W/m2), which is consistent with experimental observations performed over the same region. At the top of the atmosphere, the SW cooling (regional mean of −13.5 W/m2) induced by mineral dust, although moderated by the longwave (LW) warming (regional mean of +5 W/m2), dominates the total net (shortwave + longwave) effect. The maximum SW heating occurs within the dusty layer with values comprised between 4 and 7°K by day and LW effect results in strong cooling (−6 to −16°K by day) below the dust layer. Finally, the simulations suggest the decrease of the convective available potential energy (CAPE) over the region in the presence of mineral dust.