The South-East Atlantic aerosol-cloud system: gaps in our understanding of basic properties and physical processes

The low cloud deck over the South East Atlantic is one of three semi-permanent cloud decks in the world and plays a key role in the energetic balance of the region. It is highly important to the global climate system and has been shown in climate simulations to be extremely sensitive to climate forcings, such as a doubling of CO2. In the Southern hemisphere spring (July-October), this cloud deck interacts with dense layers of African biomass burning aerosols, which initially overlay the stratus deck, but eventually become mixed into the clouds as the marine boundary layer thickens and aerosols are transported across the South Atlantic. Preliminary modeling studies show that these interactions result in top of the atmosphere and atmospheric forcings which change the temperature and precipitation patterns of the region. In this paper, we will review the current knowledge of the spatial distributions of aerosols and clouds in the South-East Atlantic, on the basis of satellite observations, previous field experiments, and ground-based observations. We will show the vertical distribution of aerosols and clouds from CALIPSO/CloudSat measurements, and discuss the implications of limited spatial sampling. We present maps of the frequency of occurrence of aerosols located above clouds. We will discuss recent papers attempting to quantify the interactions between aerosols and clouds in the region, including their assumptions on basic aerosol properties. We will conclude by examining what types of measurements would be suitable to fill critical knowledge gaps regarding aerosol-cloud interactions in the South-East Atlantic, with a particular emphasis on the utility of remote sensing observations.