Global distribution and climate forcing of marine organic aerosol – Part 2: Effects on cloud properties and radiative forcing
1Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, NC, USA
2Chinese Research Academy of Environment Sciences, No. 8 Dayangfang, Beiyuan, Chaoyang District, Beijing 100012, China
3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
4School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
5Atmospheric Sciences & Global Change Division, Pacific Northwest National Laboratory, Richland, WA, USA
Abstract. In the first part of this paper series (Meskhidze et al., 2011), a treatment of marine organic aerosols (including primary organic aerosol, secondary organic aerosols, and methane sulfonate) was implemented into the Community Atmosphere Model version 5 (CAM5) with a 7-mode Modal Aerosol Module. A series of simulations was conducted to quantify the changes in aerosol and cloud condensation nuclei concentrations in the marine boundary layer. In this study, changes in the cloud microphysical properties and radiative forcing resulting from marine organic aerosols are assessed. Model simulations show that the anthropogenic aerosol indirect forcing (AIF) predicted by CAM5 is decreased in absolute magnitude by up to ~0.10 W m−2 (8%) when marine organic aerosols are included. Changes in the AIF from marine organic aerosols are associated with small global increases in low-level in-cloud droplet number concentration and liquid water path of ~1.3 cm−3 (~1.6%) and 0.2 g m−2 (0.5%), respectively. Areas especially sensitive to changes in cloud properties due to marine organic aerosol include the Southern Ocean, North Pacific Ocean, and North Atlantic Ocean, all of which are characterized by high marine organic emission rates. As climate models are particularly sensitive to the background aerosol concentration, this small but non-negligible change in the AIF due to marine organic aerosols provides a notable link for ocean-ecosystem marine low-level cloud interactions and may be a candidate for consideration in future earth system models.