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Lattice Boltzmann modeling of air flow through firn from a megadunes area of East Antarctica


Recently, micro-computed tomography (micro-CT) techniques have been developed that permit the nondestructive imaging of snow samples. The micro-CT uses sequential x-ray scans to recreate three-dimensional (3-D) images of snow samples taken from the field. In conjunction with the radically improved ability to image 3-D microstructures, numerical techniques have been developed that use high resolution digital models to calculate heat conduction and gas flow through 3-D porous media microstructures. One of these numerical methods is the lattice-Boltzmann method (LBM), which is well suited to model viscous flow through porous media. We have used micro-CT imagery as the input for a LBM model of air flow through firn, and compared the modeled results to measured values. The samples used were from a Megadunes area of East Antarctica (81°S, 125°E), an area experiencing very low to no snow accumulation. Firn from regions experiencing low accumulation rates undergoes significant alteration due to long-term exposure near the surface, where large temperature gradients cause extensive post-depositional change. Measurements of the physical properties reveal significant variation in the top 10 meters due to dune migration. Relatively small differences in accumulation rate in areas in close proximity to one another result in large differences in physical properties, including grain size, density, and air permeability. Results of lattice Boltzmann modeling of the air flow through micro-CT 3D reconstructions of firn from two areas in a Megadune field experiencing different accumulation rates and a higher accumulation area (Hercules Dome, Antarctica), will be presented along with experimental results.