31 Aug 2023
 | 31 Aug 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Evidence of a dual African and Australian biomass burning influence on the vertical distribution of aerosol and carbon monoxide over the Southwest Indian Ocean basin in early 2020

Nelson Bègue, Alexandre Baron, Gisèle Krysztofiak, Gwenaël Berthet, Hassan Bencherif, Corinna Kloss, Fabrice Jégou, Sergey Khaykin, Marion Ranaivombola, Tristan Millet, Thierry Portafaix, Valentin Duflot, Philippe Keckhut, Hélène Vérèmes, Guillaume Payen, Masha Kumar Sha, Pierre-François Coheur, Cathy Clerbaux, Michaël Sicard, Tetsu Sakai, Richard Querel, Ben Liley, Dan Smale, Isamu Morino, Osamu Ochino, Tomohiro Nagai, Penny Smale, and John Robinson

Abstract. The pristine atmosphere of the southwest Indian Ocean (SWIO) basin underwent significant perturbations during the 2020 austral summer. This study documents the complex variability of aerosols and carbon monoxide (CO) over this remote oceanic region and identifies the processes governing it in the upper troposphere – lower stratosphere (UT-LS). Aerosol profiles exhibit a multi-layer structure in the tropical UT-LS in January and February 2020. The numerical models (FLEXPART and MIMOSA) showed that the modulation of the aerosol content in the lower stratosphere is due to the intense and persistent stratospheric aerosol smoke layer generated during the 2019–20 extreme Australian bushfire events. One part of this stratospheric aerosol smoke layer was advected zonally by the prevailing easterly winds and its passage over Reunion was recorded by increased aerosol extinction profiles on 27th and 28th January. The analysis of the advected potential vorticity highlights an isentropic transport of air masses containing Australian biomass burning aerosol from extra-tropical latitudes to Reunion at the 400 K isentropic level, on 28th January. Interestingly, our results show that the biomass burning activity in eastern Africa, weak during this season, contributed to modulate (up to 90 %) the vertical distribution of CO and aerosols in the upper troposphere over the SWIO basin. The simultaneous presence of African and Australian aerosols smoke layers has been recorded by ground-based observations at Reunion. This study highlights for the first time the influence of the African emissions from biomass burning to the CO and aerosols distribution in the upper troposphere over the SWIO basin during the convective season. The results show that besides PyroCb -driven injection of biomass burning products to the stratosphere, an alternative pathway may exist during the regular deep-convection season in the tropics.

Nelson Bègue et al.

Status: open (until 02 Nov 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Nelson Bègue et al.

Nelson Bègue et al.


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Short summary
This study treats on the transport of the biomass burning (BB) products, induced during the 2019–20 extreme extreme Australian bushfire events, over the Southwest Indian Ocean. The BB activity in eastern Africa, weak during the wet season, contributed to modulate the atmospheric composition over this region. The simultaneous presence of African and Australian BB products has been recorded at Reunion. This reveals the complex variability of the atmospheric compostion over the SWIO basin.