The Impacts of Smoke Aerosols on South American Monsoon

Biomass burning season in tropical South America, which usually lasts over the dry Australia winter period, is followed by the onset of the wet season (summer monsoon). Recent studies indicate that smoke aerosols released from biomass burning in this region can significantly affect radiation, circulation, and land-surface processes during the burning season. This study seeks to understand the possible role of biomass burning in the monsoon development. The NCAR regional climate model is used to conduct simulations. The simulation domain has a resolution of 60 km with 91X91 grid points. The simulation period is August-November of 1995. A control simulation and a smoke simulation are conducted. There is no smoke aerosol loading in the control simulation throughout the simulation period. Smoke aerosol loading is added in the smoke simulation during the smoke phase of the integration period (August and September). The smoke optical properties, including total optical depth, single scattering albedo and asymmetric factor are specified based on the measurements during the Smoke, Cloud, and Radiation-Brazil (SCAR-B) experiment. The differences between the smoke and control simulations during the monsoon phase of the integration period (October and November) are used to measure the effects of biomass burning on monsoon. The preliminary results show that the Atlantic high becomes more intense due to biomass burning during the smoke phase. This perturbation is also seen in the first month of monsoon phase, indicating that biomass burning could affect adversely the development of the summer monsoon. Perturbation in the early time of the monsoon phase is negative over most of the region, probably resulting from the land-atmosphere interactions.