Satellite assessment of sea salt aerosol productivity: The Southern Ocean case study

There is still a substantial ambiguity regarding Aerosol Optical Depths (AODs) over remote oceans, in particular over the pristine Southern Ocean. Satellite retrievals (e.g. MISR, MODIS) and global aerosol transport models show a distinct AOD maximum around the 60° South latitude band. In-situ measurements performed by the Marine Aerosol Network (MAN), on the other hand, indicate no increased AODs over the Southern Ocean. In this study elevated Southern Ocean AODs are examined from the modeling perspective. The primary aerosol component over the Southern Ocean is sea salt aerosol (SSA). Multiple simulations of SSA concentrations and optical depths are carried out using a single modeling framework, the Navy Aerosol Analysis and Prediction System (NAAPS) model. Several SSA emission functions are examined, including recently proposed formulations with sea surface temperature corrections. The differences between NAAPS simulations are primarily due to different SSA emission formulations. The results are compared against satellite-derived AODs, including MISR and MODIS instruments. MISR AOD retrievals are further filtered using a newly developed bias reduction procedure that eliminates retrievals affected by cloud contaminations and cloud adjacency effects. The results indicate a very large impact of emission parameterization on the simulated AODs. For some scenarios, the Southern Ocean AOD maximum almost completely disappears. Further MISR AOD quality screening substantially improves model/satellite agreement. Based on these comparisons the most optimal SSA emission function for global aerosol transport models is recommended.