Higher-order physics for modeling ice streams in ice sheets.

摘要

Ice streams are transitional between inland glaciers and ice shelves. Hence no stresses can be neglected. Ice streams are important dynamic features of a glacier; it is well known that ice streams drain up to 90% of the ice from an ice sheet. Herein I model ice streams as a multiphysics system of coupled components. This includes treating ice as a non-Newtonian fluid since empirical measurements show a power law relation between stress and strain rate. Sliding is a physical feature that must be included. This is done with a novel approach to sliding by way of a slippery layer. The slippery layer is given negligible thickness and rheology is tuned to the ice stream being modeled.;Testing and benchmarking verifies the model. The first comparison is made with the shallow ice approximation, a known analytical solution. The model is setup with a problem domain in which basal stress dominates. Comparison of the surface velocities shows excellent agreement. A second comparison involves a problem domain where longitudinal stress dominates. In this case a floating slab of is tested for creep via Weertman thinning. The model solution shows excellent agreement with the analytical solution of Weertman thinning.;Additional benchmarking tests other model parameters to ensure proper settings. These include proper discretization of the problem domain and analysis of aspect ratio effects, the ratio of width to height. The temperature solver is tested for conduction dominated problem domains as well as advection and strain heating dominated problem domains. Again the model yields expected results.;The model application to a real world ice stream is made with Whillans Ice Stream, which is located in Antarctica. Model results show that temperature is dominated by advection and that velocities show nearly plug-flow, in which vertical columns of ice move. The slippery layer tuned with a uniform softening shows better agreement with measured surface velocities [17] than tuning with a progressive softening.