Session U03: Physics Experiments in Antarctica, What They Tell Us About the South Pole and the Changing Climate

The Microphysics of Antarctic Clouds: what we know and what we’re trying to discover

Processes by which atmospheric aerosol particles – such as dusts, sea salt, or black carbon – interact with clouds are poorly understood, and contribute towards one of the largest uncertainties in future climate predictions in the Intergovernmental Panel on Climate Change (IPCC) assessment reports. Consequently, numerical models cannot accurately reproduce cloud fraction and lifetime, thus affecting atmospheric radiative interactions. This inadequate modelling capability is particularly problematic in the polar regions, where inaccurate radiative predictions hinder forecasts of, for example, the sea ice extent. Model development requires an improved understanding of the physical processes involved; however, a substantial hurdle in this effort is the scarcity of polar atmospheric measurements for model validation, particularly in Antarctica. By measuring cloud properties, such as liquid mass content, we can learn more about the clouds common to the region and develop a more realistic representation of their microphysical properties in models. In this presentation, I will discuss the methods by which we now make aircraft measurements of clouds and aerosol, and introduce the models we are using to try to understand our observations. Measurements from the Microphysics of Antarctic Clouds (MAC) campaign - conducted in the Weddell Sea, Antarctica - will be shown to illustrate the key questions we want to answer.   

Observing Antarctic Ice-sheet Conditions Using Ice-Penetrating Radar

Radio echo sounding is a uniquely powerful geophysical technique for~studying the interior of ice sheets, glaciers, and icy planetary bodies. It~can provide broad coverage and deep penetration as well as interpretable ice~thickness, basal topography, and englacial radio stratigraphy. However,~despite the long tradition of glaciological interpretation of radar images,~quantitative analyses of radar sounding data are rare and face several~technical challenges. These include attenuation uncertainty from unknown ice~temperature and chemistry, clutter and losses from surface and volume~scattering, and a lack of problem-specific radar theory. However, there is~rich, often underexploited, information in modern radar sounding data, which~is being collected over terrestrial and planetary ice at an unprecedented~rate. The development and application of hypothesis-driven analysis~approaches for these data can place observational constraints on the~morphologic, hydrologic, geologic, mechanical, thermal, and oceanographic~configurations of ice sheets and glaciers. These boundary conditions -- and~the physical processes which they express and control -- are filling a~fundamental gap our ability to understand the evolution of both marine ice~sheets and icy moons. These include the subglacial hydrology of marine ice~sheets and the thermophysical structure of planetary ice shells.   

Breaking the ice: an exploration of material behavior, boundary conditions, and (ice) failure in Antarctica.

Iceberg calving \textemdash or the mechanical removal of ice from glaciers and ice sheets \textemdash remains an important yet unresolved aspect of the dynamic ice flow. Providing more confident projections on global mean sea level rise will depend on our ability to more accurately simulate how ice is discharged into the ocean. This presentation focuses on the role that basal crevasses (fractures that form on the bottom sides of floating ice) play in the disintegration of glaciers, and explores the connection between calving, ocean-driven melting, and changes in glacier dynamics.\\ \\We begin with observations of basal crevasses in Antarctica that motivate simple material models, and finish with the presentation of a numerical model that accommodates multi-material model ice dynamics, exploring the effects that different initial geometries and boundary conditions play in the formation of cracks in the ice for some idealized experiments. Finally, we test the numerical model in a more realistic scenario, simulating the formation of cracks throughout time for Thwaites Glacier, Antarctica. Good agreement between observations of the distribution of cracks at Thwaites Glacier and our simulations encourage the notion that the material model formulation in our numerical model is appropriate for further prognostic simulation of glaciers.