Aerosol–Radiation–Cloud Interactions in the Southeast Atlantic: Results from Three Years of ORACLES Deployments

Seasonal biomass burning (BB) in Southern Africa during the Southern hemisphere spring produces BB aerosol particles, that are lofted into the mid-troposphere and transported westward over the South-East (SE) Atlantic, where they interact with one of the three semi-permanent subtropical stratocumulus (Sc) cloud decks in the world. These interactions include cloud adjustments to aerosol-induced solar heating and microphysical effects. The representation of these interactions in climate models remains highly uncertain, because of the scarcity of observational constraints on both, the aerosol and cloud properties, and the governing physical processes. Three deployments involving the NASA P-3 and ER-2 aircraft in the ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) project in August/September of 2016, August 2017 and October 2018, are starting to fill this observational gap by providing an unprecedented look at the SE Atlantic cloud-aerosol system. We provide an overview of all deployments, highlighting aerosol absorptive and cloud-nucleating properties, their vertical distribution relative to clouds, the locations and degree of aerosol mixing into clouds, and cloud changes in response to such mixing. We will make an initial assessment of the differences and similarities of the BB plume and cloud properties as observed from the 2016 deployment site (Walvis Bay, Namibia), and the 2017 and 2018 deployment site (Sao Tômé and Príncipe) near the plume’s northern edge. We will conclude with an outlook for the integrative work we envision to address the overarching science questions regarding aerosol-radiation-climate interactions in the SE Atlantic and how the suborbital observations will aid long-term modeling and satellite measurement efforts. This presentation represents the entire ORACLES Science Team and only the listed authors.