Aerosol-radiation-cloud Interactions in the South-east Atlantic: Future Suborbital Activities to Address Knowledge Gaps in Satellite and Model Assessments (Invited Presentation)

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles. Particles lofted into the mid-troposphere are transported westward over the South-East (SE) Atlantic, home to one of the three permanent subtropical stratocumulus (Sc) cloud decks in the world. The stratocumulus deck is critical to the regional and global climate system. It interacts with the dense layers of BB aerosols that initially overlay the cloud deck, but later subside and may mix into the clouds. These interactions include adjustments to aerosol-induced solar heating and microphysical effects, and their global representation in climate models remains one of the largest uncertainties in estimates of future climate. Hence, new observations over the SE Atlantic have significant implications for global climate change scenarios.

Our understanding of aerosol-cloud interactions in the SE Atlantic is hindered both by the lack of knowledge on aerosol and cloud properties, as well as the lack of knowledge about detailed physical processes involved. Most notably, we are missing knowledge on the absorptive and cloud nucleating properties of aerosols, including their vertical distribution relative to clouds, on the locations and degree of aerosol mixing into clouds, on the processes that govern cloud property adjustments, and on the importance of aerosol effects on clouds relative to co-varying synoptic scale meteorology.

We discuss the current knowledge of aerosol and cloud property distributions based on satellite observations and sparse suborbital sampling. Recent efforts to make full use of A-Train aerosol sensor synergies will be highlighted. We describe planned field campaigns in the region to address the existing knowledge gaps. Specifically, we describe the scientific objectives and implementation of the following five synergistic, international research activities aimed at providing some of the key aerosol and cloud properties and a process-level understanding of aerosol-cloud interactions over the SE Atlantic:

1) ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS), a five-year investigation between 2015 and 2019 with three Intensive Observation Periods (IOP), recently funded by the NASA Earth-Venture Suborbital Program, 2) CLARIFY-2016 (CLoud-Aerosol-Radiation Interactions and Forcing: Year 2016), a comprehensive observational and modeling programme funded by the UK's Natural Environment Research Council (NERC), and supported by the UK Met Office. 3) LASIC (Layered Atlantic Smoke Interactions with Clouds), a funded deployment of the DOE (Department of Energy) ARM Mobile Facility (AMF1) to Ascension Island, nominally for June 1 2016 - May 31 2017, 4) ONFIRE (ObservatioNs of Fireʼs Impact on the southeast atlantic REgion), a selected deployment of the NCAR C-130 aircraft to Sao Tome Island in 2017, and 5) AEROCLO-SA (AErosol RadiatiOn and CLOuds in Southern Africa), a collaborative French-South Africa-Namibian ground-based and airborne project to study boundary layer and above cloud aerosols in SA, funded by the Centre National des Recherches Scientifiques (CNRS) and the French National Research Agency (ANR), and supported by the SANUMARC Research Center of the University of Namibia and French Ministry of Foreign Affairs.