Climate Impacts of African Biomass Burning Aerosols

Biomass burning aerosols play an important role in the global energy budget. Unlike less absorbing aerosols, smoke from biomass burning can exert a positive direct radiative effect (DRE) over marine clouds. However, much is unknown about the extent, timing, and magnitude of these radiative effects owing to large model biases in simulating marine clouds. This presentation will provide observational benchmarks of aerosol direct radiative effects over the SE Atlantic Ocean from CloudSat's multi-sensor radiative fluxes and heating rates product. The satellite-based dataset leverages high-resolution vertical cloud and aerosol information from the active sensors aboard CloudSat and CALIPSO to mitigate challenges encountered by passive instruments. Over the SE Atlantic, we estimate an annual all-sky DRE of -1.7 W/m2, which is in good agreement with a coupled model simulation from CESM-CAM5. Large discrepancies in cloudy-sky DRE, though, suggest that regional estimates may be right for the wrong reasons. Results show significant differences in observed and modeled cloud cover, which likely contribute to differences in the extent and timing of aerosol direct radiative effects. Globally CESM-CAM5 predicts around 10% fewer clouds than observed, suggesting that model biases in DRE over ocean are driven primarily by errors in cloud cover as opposed to errors in aerosol optical properties. These findings highlight the importance of correctly representing cloud cover for accurate assessment of aerosol radiative effects.