Antarctica InSync Scientific Theme 6 - Aerosol-cloud-precipitation interactions and radiative feedbacks [white paper]

Insufficient understanding of the surface energy and mass budgets of the Southern Ocean and Antarctic Continent (SOAC) fundamentally limits our ability to estimate when, how fast and severely the region will respond to anthropogenic climate change. The recent abrupt sea ice decline raises a red flag. The SOAC surface energy and mass budgets are worryingly-inaccurately represented in predictive models. A key problem is the misrepresentation of aerosol-cloud-precipitation interactions and their impact on radiative feedbacks, systematically leading to gross surface temperature and precipitation biases. To mitigate these important shortcomings, Theme 6 aims at closing five critical knowledge gaps: (i) Quantifying aerosol sources, properties and processes; (ii) Characterizing cloud and precipitation properties; (iii) Understanding the surface energy budget and boundary layer structure; (iv) Constraining cloud-circulation coupling; and (v) Advancing the modelling of clouds and aerosols. Together, these five elements describe both the continuum of atmospheric processes and their impacts on the entire SOAC, as well as the large regional variability of these processes. We recommend an integrated ensemble of in situ and remote sensing observations targeted specifically at improving numerical representation and constraining model uncertainties. We emphasize the need for profile observations from the surface to low-level cloud altitude along latitudinal gradients, i.e., from the marginal sea ice zone towards the Antarctic plateau, while simultaneously covering East and West Antarctica as well as the Peninsula. Observations are categorized into three priority levels, where particularly priority 1 builds on existing long-term observations to build a strong legacy from existing efforts into future activities beyond Antarctica InSync. Priority 2 and 3 focus on process studies. Theme 6 will mitigate the present lack of structured data to constrain aerosol-cloud-precipitation processes and their radiative feedbacks.