Fog and aerosols over central Greenland

The Greenland Ice Sheet (GrIS) is losing mass at an accelerating rate and is the largest single contributor to global sea level rise. To understand the future of the ice sheet, we must understand the processes that drive the ice sheet surface energy budget (SEB). The central GrIS experiences strong radiative cooling that drives a stable boundary layer, dynamically isolating the lowest ∼100 m of the atmosphere. Fog regularly forms within this layer and can be difficult to detect. The particles that make up fog absorb and scatter radiation, with potentially large impacts on the SEB. The formation of these fog particles, whether they be liquid or ice, is related the population of aerosol particles, but our understanding of the role of aerosols in fog and cloud formation over central Greenland is limited by a lack of observations. In this thesis I use new and existing measurements, collected at Summit Station, to advance our understanding of surface aerosol concentrations, fog properties, and fog aerosol interactions over central Greenland. Firstly, I show that aerosol particle number concentrations are controlled by both local and synoptic processes, and that extremely low number concentrations can occur in all seasons. Secondly, I use ground-based infrared remote sensing to detect and characterise fog events, showing that some instruments that are often used to detect liquid water are not sufficiently sensitive to detect the optically thin shallow fogs that are common at Summit. Finally, by combining the results of these two studies, I present observational evidence supporting the hypotheses that (a) low surface aerosol particle number concentrations can limit fog liquid water path, (b) fog can act to increase near-surface aerosol particle number concentrations through enhanced mixing, and (c) multiple fog events in quiescent periods gradually deplete near-surface aerosol particle number concentrations. This thesis demonstrates the importance of dedicated instrumentation to monitor fog and the thermodynamic structure of the boundary layer over the ice sheet and highlights the need for vertical profiles of aerosol properties to better understand the relationship between aerosols, clouds, and the ice sheet SEB.