Atmos. Chem. Phys. Discuss., 10, 9431-9462, 2010
© Author(s) 2010. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Climate effects of seasonally varying biomass burning emitted carbonaceous aerosols (BBCA)
G.-R. Jeong and C. Wang
Center for Global Change Science, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA

Abstract. The climate impact of the seasonality of Biomass Burning emitted Carbonaceous Aerosols (BBCA) has been studied using an aerosol-climate model coupled with a slab ocean model in a set of 60-year long simulations driven by BBCA emission data with and without seasonal variation, respectively. The model run with seasonally varying emission of BBCA leads to an increase in external mixture of carbonaceous aerosols and a decrease in internal mixtures of carbonaceous aerosols relative to those in the run with constant annual BBCA emissions, resulting from different strengths of source/sink processes. We find that the differences in atmospheric direct radiative forcing (DRF) caused by BBCA seasonality are in phase with the differences in column concentrations of an external mixture of carbonaceous aerosols in space and time; thus, the differences in surface temperature and heat fluxes are limited to the biomass burning source regions. In contrast, the differences in all-sky radiative forcing at the top of the atmosphere and at the earth's surface extend beyond the BBCA source regions due to climate feedback through cloud distribution and precipitation. The seasonality of biomass burning emissions uniquely affects the global distributions of high-level clouds and convective precipitation, which indicate an impact on atmospheric circulation. We especially find that the Inter-Tropical Convergence Zone (ITCZ) shifts northward when the seasonality of BBCA emissions is included in the model, compared to the case otherwise configured. In addition, the climate response to the periodic climate forcing of BBCA is not static in biomass burning seasons but dynamically extends into non-biomass seasons as well. The climate effects in contrasting biomass burning seasons occur in the springtime in northern Tropics with the largest difference in precipitation and mixed aerosol abundance caused by the seasonality of BBCA.

Citation: Jeong, G.-R. and Wang, C.: Climate effects of seasonally varying biomass burning emitted carbonaceous aerosols (BBCA), Atmos. Chem. Phys. Discuss., 10, 9431-9462, doi:10.5194/acpd-10-9431-2010, 2010.
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