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Biomass Burning in the Cuiabá-Santarém Area and Precipitation

Eder P. Vendrasco, University of São Paulo, eder@master.iag.usp.br (Presenting)
Pedro L. da Silva Dias, University of São Paulo, pldsdias@model.iag.usp.br

Numerical experiments with BRAMS were performed with two nested grids (50 and 10 km horizontal resolution, respectively) with and without the effect of biomass burning in 8 different situations for 96 hour integrations. Only the radiative effect of aerosols is included. The results were analyzed in large areas encompassing the Cuiabá-Santarém road in the north (A), two in the middle section (B1 and B2) and the southern area C where most of the burning takes place. In addition the whole area average was also analyzed. The precipitation change due to the radiative impact of biomass burning is generally negative. However, there are a few cases with a positive impact (up to 80% in one case). Two opposite forcing mechanisms were explored: (a) the thermodynamic forcing that is generaly negative in the sense that the aerosol tend to stabilize the lower atmosphere and (b) the dynamic impact associated with the low level horizontal pressure gradients produced by the aerosol plumes. In order to understand the non-linear relationship between the two effects, experiments were performed with double emissions. In these cases, the dynamic effect overcomes the stabilization produced by the radiative forcing and precipitation increase is observed in comparison with the control experiment. This result is robust in the sense that an ensemble of 8 cases were performed. The conclusion is that in the mean, the biomass burning radiative forcing tends to decrease the precipitation. However, very large concentrations of aerosols may lead to an increase in the precipitation due to the dynamical forcing associated to the horizontal pressure gradients.

Science Theme:  HY (Hydrometeorology)

Session:  2A: Hydrological and Meteorological Processes

Presentation Type:  Oral

Abstract ID: 142

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