Vertical Profiling of Aerosols With a Combined Raman-Elastic Backscatter Lidar in the Remote Southern Ocean Marine Boundary Layer (43–66?S, 132–150?E)

摘要

A combined Raman-elastic backscatter lidar, deployed aboard the research vessel RV Investigator for two campaigns for a total of 10 week's ship time, is used to quantify the properties of aerosols within the remote Southern Ocean marine boundary layer between Australia and Antarctica in the region 43–66?S and 132–150?E. Eleven Raman case studies are identified for analyses. Particle linear depolarization ratio and height-resolved lidar ratio S, calculated from the Raman retrievals, are consistent with values expected within the surface mixed layer for clean marine conditions.We determine S = (19 ± 7) sr across the Southern Ocean with the Raman lidar observations. Aerosol optical properties in the marine boundary layer close to Tasmania (43?S) sometimes indicate the influence of continental air masses. Aerosol optical depth at 355 nm calculated from the retrieved Raman extinction profiles within the surface mixed layer is τ = (0.11 ± 0.04). Boundary-layer height is determined from the lidar observations and decreases from (0.9 ± 0.4) km north of the Polar Front (around 55?S) to (0.7 ± 0.2) km south of the Polar Front. Dried sea salt is present above the midlatitude ocean in the dehumidified decoupled layer in different synoptic-scale atmospheric conditions including beneath a high-pressure system and in a post-frontal air mass. At all latitudes across the Southern Ocean, large aerosol backscatter, low depolarization ratio, and high relative humidity indicate the presence of sea salt droplets within the well-mixed near-surface layer.