A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Effect of smoke aerosol particles from biomass burning on the PARabsorbed by a primary forest in the AmazonMarcia Yamasoe 1 (akemi@model.iag.usp.br), Pierre Guillevic 2 , Brent Holben 3 , JoelSchafer 3 , Tom Eck 3 , Paulo Artaxo 41 Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de SãoPaulo, Rua do Matão, 1226, São Paulo, SP, Brazil, CEP 05508-900; 2 CETP – CNRS,10 Avenue de l’Europe, Vélizy, France; 3 NASA GSFC, Greenbelt Road, Greenbelt,MD, USA; 4 Instituto de Física da Universidade de São Paulo, Rua do Matão, Trav. R,187, São Paulo, SP, Brazil.A study of the influence of aerosol particles from biomass burning on thephotosynthetically active radiation (PAR) reaching the surface is being conducted in theAmazon region. The response of the vegetation for such forcing is also analyzed,through numerical calculations of the fraction of absorbed PAR inside the canopy.Experimental results showed a reduction of about 27% of PAR in the presence of thesmoke layer, with an aerosol optical depth of about 0.85 at 500 nm. Numericallycalculated results showed also that for such value of aerosol optical depth, the fractionof diffuse radiation in the PAR region increases from 0.16 (for a clear atmosphere) to0.54, for a solar zenith angle of 30 degrees. The combined effect on the PARdistribution within the cover of the decrease of total and increase of diffuse incomingradiation at the surface due to the smoke layer is evaluated using a 3D radiative transfermodel. The DART (Discrete Anisotropic Radiative Transfer) model simulates radiativetransfer within heterogeneous vegetation covers characterized by a three-dimensionalstructure. In the visible domain, the model predicts the surface directional reflectanceand the 3D distribution of absorbed PAR within the canopy. Simulations are performedfor a tropical primary forest at Jaru, in Rondonia state.