Influence of biomass burning aerosol on land-atmosphere interactions over Amazonia
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The impacts of biomass burning smoke on local rainfall and the structure of the atmospheric boundary layer have been actively studied in recent years. However, whether the large-scale biomass burning in the later dry season over Amazonia Region could influence the dry-to-wet transition season have not been examined. Previous observations have shown that the substantial increase of rainfall from dry to wet season over Amazonia are actually caused by small changes of the atmospheric thermodynamic structure relative to those over other monsoon regions. Consequently, the onset date of wet season can vary greatly as influenced by external or internal anomalous forcings. Thus, it is possible that the transition of the atmospheric thermodynamic structure and circulation from dry to wet season is also sensitive to the impacts of biomass burning smoke. To test this hypothesis, we have forced RegCM3 model with direct radiative forcing of smoke inferred from MODIS for the transition season (August to November). The comparison with control run helps us to examine the direct and semi-direct influences of smoke on the transition from dry to wet season. Our preliminary results show that the direct and semi-direct forcings of smoke could significantly influence the rainfall and related atmospheric and land surface conditions during the transition. However, these changes are sensitive to the prescribed vertical distribution of the aerosols.