Tutorial 11:

Aerosol-Cloud Interactions

Athanasios Nenes, Ecole Polytechnique Fédérale de Lausanne, Switzerland ; Foundation for Research and Technology, Greece.

Abstract: Every cloud droplet and almost every ice crystal in global clouds require an aerosol particle “seed” for its formation. Because of this, varying levels of aerosols from natural and anthropogenic sources can strongly modulate cloud properties and structure, with significant implications for precipitation, the hydrological cycle, regional & global climate. Quantitatively constraining such aerosol-cloud interactions and their impacts is riddled with uncertainty and significantly affects predictions of climate sensitivity to greenhouse gas levels. The large uncertainty originates largely from the complex and multi-scale coupling of aerosols and clouds. Added to this complexity is the large variability and range of aerosol types, each of which is characterized with its own ability to nucleate droplets and ice crystals.

This tutorial will provide an overview of what aerosol-cloud interactions are, the theoretical underpinnings of many key processes that govern them, and present approaches used to describe aerosol-cloud interactions in climate model frameworks through the combination of observations, theory and modeling. We will demonstrate how instrument development efforts and remote sensing helped constrain these interactions, especially when describing the processes of droplet and ice crystal formation. We will provide an assessment of what has been learned and point out key research challenges for the future.

Short bio: Athanasios Nenes is a Professor of Atmospheric Processes and heads the Laboratory of Atmospheric Processes and their Impacts (LAPI) at the École Polytechnique Fédérale de Lausanne, Switzerland. He is an affiliate researcher of the Institute of Chemical Engineering Science at the Foundation for Research and Technology Hellas in Patras, Greece and a founding member and co-director of the Center of Studies on Air quality and Climate Change at the institute. His research focuses on aerosol processes and their impacts on climate, health and ecosystems through a combination of theory, measurement and modelling. He is a Web of Science Highly Cited Researcher, and serves as President of the Atmospheric Sciences Division of the European Geophysical Union. In the past he served on the US National Academies Committee on the Future of Atmospheric Chemistry Research, Secretary of Atmospheric Sciences of the American Geophysical Union (AGU), the Board of the American Association for Aerosol Research (AAAR) and Editor in the Copernicus journal Atmospheric Chemistry and Physics. Prof. Nenes is a Fellow of the AAAR, a Fellow of the AGU and a member of the Academia Europaea. His has received the Copernicus Medal of the Copernicus Gesellschaft e.V., the Ascent Award of the Atmospheric Sciences Section of the AGU, the Kenneth T. Whitby and Sheldon K. Friedlander Awards of the AAAR, the Henry G. Houghton Award of the American Meteorological Society, a European Research Council Consolidator Award, a US National Science Foundation CAREER Award and a NASA New Investigator Award.