Global distribution and climate forcing of marine organic aerosol – Part 2: Effects on cloud properties and radiative forcing

摘要

A series of simulations with the Community Atmosphere Model version 5 (CAM5)with a 7-mode Modal Aerosol Model were conducted to assess the changes incloud microphysical properties and radiative forcing resulting from marineorganic aerosols. Model simulations show that the anthropogenic aerosolindirect forcing (AIF) predicted by CAM5 is decreased in absolute magnitudeby up to 0.09 W m (7%) when marine organic aerosols are included.Changes in the AIF from marine organic aerosols are associated with smallglobal increases in low-level in-cloud droplet number concentration andliquid water path of 1.3 cm (1.5%) and 0.22 g m (0.5%),respectively. Areas especially sensitive to changes in cloud properties dueto marine organic aerosol include the Southern Ocean, North Pacific Ocean,and North Atlantic Ocean, all of which are characterized by high marineorganic emission rates. As climate models are particularly sensitive to thebackground aerosol concentration, this small but non-negligible change inthe AIF due to marine organic aerosols provides a notable link forocean-ecosystem marine low-level cloud interactions and may be a candidatefor consideration in future earth system models.