L. Mac Cathles
Within New Zealand's Fox Glacier
Postdoctoral Scholar
E-mail: mcathles at uchicago.edu
Office: HGS 485
curriculum vitae
Research Interest: I am broadly interested in glacier physics and thermodynamics; particularly the intersection between experiments, either numerical or physical, and simple theories.
I began research in glaciology studying surface and seasonal snow properties, primarily by conducting in situ measurements of diffusivity, permeability thermal conductivity and density, while testing theories on how these properties are related. This research brought me to both Antarctica and Greenland, working at Megadunes and Summit Camp. After arriving at University of Chicago, I became involved with The Worlds Largest Icebergs Project, analyzing seismic data collected on icebergs and ice shelves. We correlated signals observed in the seismic record to distant storms, finding 86 seismic events generated from ocean wave ice sheet interactions. These waves propagated from storms distributed over the North and South Pacific Oceans.
Current Research: Recently I began working with Justin Burton on laboratory experiments investigating iceberg capsize and ice shelf collapse. I am continuing to work with Doug MacAyeal and Kristopher Darnell on producing models melt pond formation on ice sheets and ice shelves.
Dissertation: My dissertation examined radiative energy transport on the surface of an ice sheet or ice shelf. I looked at the energy transport for both different surface conditions and for rough surfaces. I explored feedbacks where the absorbed energy on the surface changes the surface in such a way that more energy is absorbed. One such feedback occurs when a supraglacial lake absorbs energy and sub-lake melting occurs, which deepens the lake, and reduces the albedo. While another feedback exists from topography which creates non-uniform absorption of sunlight, causing surface geometries to change as melting occurs, affecting how energy is absorbed on the surface. I developed an analytical solution for the albedo of a supraglacial lake as a function of water depth was derived, and showed that a supraglacial lake can reduce the albedo by fifty percent. I also established that a multi-spectral analysis is required for surfaces where liquid water is present, but little additional accuracy is gained beyond 18 spectral bands.
Complex surface topography has a significant effect on the absorption of energy due to multiple reflections between the surface and its self. A numerical model was developed to determine the absorption of insolation on an arbitrary two-dimensional surface. The absorbed radiation forces an ice ablation model evolving the surface topography through an ablation season. Results from numerical simulations show that there is a strong latitudinal dependence on how surface features evolve through an ablation season. At high latitudes, the aspect ratio of surface features decreases through the ablation season, reducing surface topography. At low latitudes, sinusoidal periodic surfaces grow in amplitude as the surface ablates. The surface evolves into a series of peaks and valleys,resembling penitentes, features observed in high alpine snow-packs in the tropics and sub-tropics. Further investigation of the range at which periodic surfaces grow in amplitude matches both the observed geographic range and orientation of penitentes. Analysis of model results suggest that penitentes require columnated insolation to grow, and this requirement is only met at lower latitudes and at north-south orientations. This is the first time the geographic range or orientation of penitentes have been quantitatively explained.
Recent publications
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Cathles, L. M., D. S. Abbot, J. N. Bassis, and D. R. MacAyeal, Modeling surface-roughness/solar- ablation feedback: Application to small-scale surface channels and crevasses of the Greenland Ice Sheet, Annals of Glaciology, 59, 2011. [pdf]
- Cathles, L. M., E. A. Okal and D. R. MacAyeal, 2009. Sea-swell arrival at the front of the Ross Ice Shelf, Antarctica, observed in a 2-year seismometer record. Journal of Geophysical Research, 114, F02015, doi:10.1029/2007JF000934. [pdf]
- Cathles, L. Maclagan, IV, L.M. Cathles, III, and M.R. Albert (2007) Instruments and methods - A physically based method for correcting temperature profile measurements made using thermocouples. Journal of Glaciology, 53 (181): 298-304, doi: 10.3189/172756507782202892 [pdf]
