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Acceleration of the southern African easterly jet driven by the radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA

Jean-Pierre Chaboureau 1, * Laurent Labbouz 1 Cyrille Flamant 2 Alma Hodzic 3 
* Corresponding author
2 TROPO - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : The direct and semi-direct radiative effects of biomass burning aerosols (BBA) are investigated over southern Africa and the southeast Atlantic during the Aerosols, Radiation and Clouds in southern Africa (AEROCLO-sA) field campaign in September 2017. A reference convection-permitting simulation has been performed using the Meso-NH model with an on-line dust emission scheme, a BBA tracer emitted using the daily Global Fire Emissions Database and online-computed backward Lagrangian trajectories. The simulation captures both the aerosol optical depth and the vertical distribution of aerosols as observed from airborne and space-borne lidars. It also reproduces the occurrence of stratocumulus over the southeast Atlantic, deep convective clouds over equatorial Africa and the large-scale circulation. In contrast, a sensitivity experiment where the radiative effect of BBA is not taken into account shows the smoke plume that is predicted too low in altitude, low-cloud cover that is too weak, deep convective activity that is too frequent but not intense enough, a Benguela jet that is too strong and a southern African easterly jet that is too weak. The Lagrangian analysis indicates that BBA are transported to higher altitudes, farther southwest and with a stronger diurnal oscillation when accounting of the radiative effects of BBA. The higher smoke plume altitude can be explained by a combination of three factors: increased upward motion induced by the stronger southern African easterly jet, self-lofting of BBA and reduced subsidence associated with a less frequent deep convective activity over equatorial Africa.
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Jean-Pierre Chaboureau, Laurent Labbouz, Cyrille Flamant, Alma Hodzic. Acceleration of the southern African easterly jet driven by the radiative effect of biomass burning aerosols and its impact on transport during AEROCLO-sA. Atmospheric Chemistry and Physics, European Geosciences Union, 2022, 22 (13), pp.8639-8658. ⟨10.5194/acp-22-8639-2022⟩. ⟨insu-03626051v2⟩

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