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 (1) , Alexandre Baron (2, 3) , Gisèle Krysztofiak (4) , Gwenaël Berthet (4) , Corinna Kloss (4) , Fabrice Jégou (4) , Sergey Khaykin (5) , Marion Ranaivombola (1) , Tristan Millet (1) , Thierry Portafaix (1) , Valentin Duflot (1) , Philippe Keckhut (6) , Hélène Vérèmes (1) , Guillaume Payen (7) , Masha Kumar Sha (8) , Pierre-François Coheur (9) , Cathy Clerbaux (9, 5) , Michaël Sicard (1) , Tetsu Sakai (10) , Richard Querel (11) , Ben Liley (11) , Dan Smale (11) , Isamu Morino (12) , Osamu Ochino (12, 10) , Tomohiro Nagai (10) , Penny Smale (11) , John Robinson (11) , Hassan Bencherif (13, 1)

1 LACy - Laboratoire de l'Atmosphère et des Cyclones
2 CIRES - Cooperative Institute for Research in Environmental Sciences
3 CSL - NOAA Chemical Sciences Laboratory
4 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
5 TROPO - LATMOS
6 STRATO - LATMOS
7 OSU-Réunion - Observatoire des Sciences de l'Univers de La Réunion
8 BIRA-IASB - Belgian Institute for Space Aeronomy / Institut d'Aéronomie Spatiale de Belgique
9 SQUARES - Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing
10 MRI - Meteorological Research Institute [Tsukuba]
11 NIWA - National Institute of Water and Atmospheric Research [Lauder]
12 NIES - National Institute for Environmental Studies
13 School of Chemistry and Physics [Durban]

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 tropospherelower 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 27 th and 28 th 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 28 th January. Interestingly, our results show that the BB 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 BB to the CO and aerosols distribution in the upper troposphere over the SWIO basin during the convective season. The results show that besides PyroCbdriven injection of BB products to the stratosphere, an alternative pathway may exist during the regular deep-convection season in the tropics.

Domaines: Sciences de l'environnement

Nelson Bègue, Alexandre Baron, Gisèle Krysztofiak, Gwenaël Berthet, Corinna Kloss, et al.. 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. Atmospheric Chemistry and Physics, 2024, 24 (13), pp.8031-8048. ⟨10.5194/acp-24-8031-2024⟩. ⟨insu-04208981v2⟩