Atmospheric Chemistry and Physics Climate effects of seasonally varying Biomass Burning emitted

Abstract. The climate impact of the seasonality of Biomass Burning emitted Carbonaceous Aerosols (BBCA) is 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, respec-tively. The model run with seasonally varying emission of BBCA leads to an increase in the external mixture of car-bonaceous aerosols as well as in the internal mixture of or-ganic carbon and sulfate but a decrease in the internal mix-ture of black carbon and sulfate relative to those in the run with constant annual BBCA emissions, as a result of differ-ent strengths of source/sink processes. The differences in atmospheric direct radiative forcing (DRF) caused by BBCA seasonality are in phase with the differences in column con-centrations of the external mixture of carbonaceous aerosols in space and time. In contrast, the differences in all-sky ra-diative forcing at the top of the atmosphere and at the earth’s surface extend beyond the BBCA source regions due to cli-mate feedback through cloud distribution and precipitation. The seasonality of biomass burning emissions uniquely af-fects the global distributions of convective clouds and pre-cipitation, indicating that these emissions have an impact on atmospheric circulation. In addition, the climate response to the periodic climate forcing of BBCA is not limited to biomass burning seasons but dynamically extends into non-biomass burning seasons as well.