NUMERICAL MODELLING OF THE BIOMASS-BURNING AEROSOL DIRECT RADIATIVE EFFECTS ON THE THERMODYNAMICS STRUCTURE OF THE ATMOSPHERE AND PRECIPITATION Karla M. Longo*, Saulo R. Freitas, Maria A. Silva Dias, Pedro L. Silva Dias and Luiz Flavio Rodrigues Center for Weather Forecasting and Climate Studies - CPTEC/INPE 1. ABSTRACT The biomass burning aerosol direct radiative effect is studied through a numerical simulation using the CATT-BRAMS (Coupled Aerosol and Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System) model system. CATT-BRAMS is an on-line transport model fully consistent with the simulated atmospheric dynamics. The sources emission from biomass burning and technological activities for several gases and aerosol may be defined from several published dataset and remote sensing. The mass concentration prognoses accounts also for convective transport by shallow and deep cumulus, wet and dry deposition and plume rise. Also, an additional radiation parameterization, which takes the interaction between aerosol particles and short and long wave radiation into account, was implemented. The model is applied to simulate carbon monoxide (CO) and particulate material PM2.5 transport during the SMOCC/RACCI campaign during the 2002 dry season. We present preliminaries results of the direct effect of aerosol on the atmosphere thermodynamic structure, surface energy budget and precipitation. 2. INTRODUCTION The high concentration of aerosol particles and trace gases observed in the Amazon and Central Brazilian atmosphere during the dry season is associated with intense anthropogenic biomass burning activity (vegetation fires, Andreae, Erro! A origem da referência não foi encontrada.). Most of the particles are in the fine particle fraction of the size distribution, which can remain in the atmosphere for approximately a week (Kaufman, Erro! A origem da referência não foi encontrada.). In GOES-8 visible imagery Prins et al. Erro! A origem da referência não foi encontrada. have observed immense regional smoke plumes in South America covering an area of approximately 4 to 5 million km 2 during the biomass-burning season. Inhalable aerosol particles (d p <10 µm) with concentrations as high ______________________________________ Corresponding author address: Karla M. Longo, Centro de Previsão de Tempo e Estudos Climáticos (INPE), Cachoeira Paulista, São Paulo, Brazil. E-mail: longo@cptec.inpe.br. as 400 µg m -3 have been measured near the surface level and the vertically integrated smoke aerosol optical thickness column rises as high as 4.0 (440 nm channel) in Central Brazil (Artaxo et al. Erro! A origem da referência não foi encontrada., Erro! A origem da referência não foi encontrada.; Echalar et al. Erro! A origem da referência não foi encontrada.). On a regional and global scale, a persistent and heavy smoke layer over an extensive tropical region may alter the radiation balance and hydrologic cycling. Modeling efforts of Jacobson Erro! A origem da referência não foi encontrada. and Sato et al. Erro! A origem da referência não foi encontrada. have suggested that black-carbon radiative forcing could balance the cooling effects of the global anthropogenic sulfate emissions. The direct global radiative forcing of black-carbon is estimated to be 0.55 Wm -2 , corresponding to 1/3 of the CO 2 forcing. In terms of direct radiative forcing, this would elevate black-carbon to one of the most important elements in global warming, second only to CO 2 (Andreae Erro! A origem da referência não foi encontrada.). The presence of biomass burning particles in the atmosphere may also modify the solar radiative balance by changing cloud microphysics. These particles act as cloud condensation and ice nuclei, promoting changes in the cloud drops spectrum and so altering the cloud albedo and precipitation (Cotton and Pielke Erro! A origem da referência não foi encontrada.; Rosenfeld Erro! A origem da referência não foi encontrada.). This suggests that biomass burning effects may extrapolate from the local scale and be determinant in the pattern of planetary redistribution of energy from the tropics to medium and high latitudes via convective transport processes. Koren et al. Erro! A origem da referência não foi encontrada. using satellite images of the Amazon rainforest suggested that smoke and cumulus clouds rarely occur together. Figure 1 shows an example of this situation for 2005. In this paper the direct effect of biomass burning aerosols is investigated using the CATT- 283 Proceedings of 8 ICSHMO, Foz do Iguaçu, Brazil, April 24-28, 2006, INPE, p. 283-289.