Cloud-Aerosol Interactions and Aerosol Variability Near Southern Ocean Low Clouds

Climate models continue to exhibit a shortwave bias in the Southern Ocean associated with low clouds, especially those occurring in the cold sectors of cyclones. To improve the parameterizations of these clouds, one must first understand their formation and development processes. In the Southern Ocean, these clouds are strongly influenced by meteorological drivers (i.e. cold air outbreaks associated with mid-latitude cyclones). Aerosol particles are expected to play an important role as well, particularly sea salt, organics, and sulfates. In-situ observations of these clouds have been limited due to the remoteness of the region. However, the recent Southern Ocean Cloud Radiation Aerosol Transport Experimental Study (SOCRATES) sampled clouds and aerosols across a range of meteorological environments in January and February 2018. In-situ ship and aircraft measurements were made between 45 and 62°S during this campaign with a focus on observing clouds occurring in cold-sectors between 50-60°S. In this work, these observations are combined with HYSPLIT trajectories, ECMWF ERA-Interim reanalysis, and Himawari satellite retrievals to understand the role aerosols and meteorology play in developing low clouds, the vertical profiles of clouds and aerosols, and the sources and sinks of aerosol in this region. Possible new particle formation was observed above the low cloud layer during the campaign. High levels of cloud condensation nuclei and cloud droplet number concentrations greater than 100 cm^-3 were commonly observed near the sea surface, where 10-25 m s^-1 winds were typical.