On the vertical distribution of smoke in the Amazonian atmosphere during the dry season

Franco Marenco (1) , Ben Johnson (1) , Justin M. Langridge (1) , Jane Mulcahy (1) , Angela Benedetti (2) , Samuel Remy (3) , Luke Jones (2) , Kate Szpek (1) , Jim Haywood (4, 1) , Karla Longo (5) , Paulo Artaxo (6)

1 United Kingdom Met Office [Exeter]
2 ECMWF - European Centre for Medium-Range Weather Forecasts
3 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)
4 University of Exeter
5 INPE - Instituto Nacional de Pesquisas Espaciais
6 USP - Universidade de São Paulo = University of São Paulo

Lidar observations of smoke aerosols have been analysed from six flights of the Facility for Airborne Atmospheric Measurements BAe-146 research aircraft over Brazil during the biomass burning season (September 2012). A large aerosol optical depth (AOD) was observed, typically ranging 0.4–0.9, along with a typical aerosol extinction coefficient of 100–400 Mm −1. The data highlight the persistent and widespread nature of the Amazonian haze, which had a consistent vertical structure, observed over a large distance (∼ 2200 km) during a period of 14 days. Aerosols were found near the surface; but the larger aerosol load was typically found in elevated layers that extended from 1–1.5 to 4– 6 km. The measurements have been compared to model predictions with the Met Office Unified Model (MetUM) and the ECMWF-MACC model. The MetUM generally reproduced the vertical structure of the Amazonian haze observed with the lidar. The ECMWF-MACC model was also able to reproduce the general features of smoke plumes albeit with a small overestimation of the AOD. The models did not always capture localised features such as (i) smoke plumes originating from individual fires, and (ii) aerosols in the vicinity of clouds. In both these circumstances, peak extinction coefficients of the order of 1000–1500 Mm −1 and AODs as large as 1–1.8 were encountered, but these features were either underestimated or not captured in the model predictions. Smoke injection heights derived from the Global Fire Assimilation System (GFAS) for the region are compatible with the general height of the aerosol layers.

Domaines: Météorologie

Franco Marenco, Ben Johnson, Justin M. Langridge, Jane Mulcahy, Angela Benedetti, et al.. On the vertical distribution of smoke in the Amazonian atmosphere during the dry season. Atmospheric Chemistry and Physics, 2016, 16 (4), pp.2155-2174. ⟨10.5194/acp-16-2155-2016⟩. ⟨hal-01306715⟩