An investigation into the origin of aerosol nucleation events observed in the Southern Ocean boundary layer

A clear picture of the physical processes involved in the nucle-ation of aerosol particles in the boundary layer (BL) over the remote Southern Ocean remains elusive due to the lack of definitive observations. A month-long observation aboard a ship during the first aerosol characterisation experiment (ACE-1) suggested that some enhanced aerosol nucleation events were linked to the passage of a frontal system. However, the cause of the link between frontal passages and nucleation events could not be determined from a statistical analysis of two years of surface observations at the Cape Grim Baseline Air-Pollution Station (CGBAPS). In this paper, numerical simulations are combined with satellite imagery, synoptic analysis and surface observations at CGBAPS to further investigate the origin of observed nucleation events during the passage of a frontal system. This analysis suggests that nanoparticles are formed at or just above the BL inversion by relatively common shallow post-frontal cumulus clouds. The BL then entrains these new particles in a process that helps maintain the overall aerosol population.