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Ice-Sheet / Ocean Interaction Model for Greenland Fjords Using High-Order Discontinuous Galerkin Methods (Final Report)
This report summarizes the development and validation of the Non-hydrostatic Unified Model of the Ocean (NUMO). The overarching science goal of the project was to advance Earth System science by proposing a more realistic representation of physical processes in a Greenland fjord. To achieve this objective, we proposed to build a new, separate, high-resolution ocean model to realistically represent the complex three-dimensional physics of the fjord, its bathymetry, coastlines using continuous/discontinuous Galerkin (CG/DG) methods. The report describes the technical details of model components, i.e., choice of equations set, time integration scheme, boundary conditions, spatial discretization methods, mesh generation. We show a suite of validation results for test cases ranging from the Kovasznay flow, through the lock-exchange, simplified two-dimensional fjord, to a three-dimensional density current on a slope. Results are compared with the literature. The report is concluded with a discussion of efforts taken to perform a simulation of Sermilik Fjord with realistic bathymetry data.
Data initiatives for ocean-driven melt of Antarctic ice shelves
Ocean-driven melt of Antarctic ice shelves is an important control on mass loss from the ice sheet, but is complex to study due to significant variability in melt rates both spatially and temporally. Here we assess the strengths and weakness of satellite and field-based observations as tools for testing models of ice-shelf melt. We discuss how the complementary use of field, satellite and model data can be a powerful but underutilised tool for studying melt processes. Finally, we identify some community initiatives working to collate and publish coordinated melt rate datasets, which can be used in future for validating satellite-derived maps of melt and evaluating processes in numerical simulations.
Beyond the Stokes approximation: shallow visco-elastic ice-sheet models
Abstract The hypothesis that ice-sheet evolution is only controlled by the long-term non-Newtonian viscous behavior of ice has been challenged by observations indicating that effects like brittle failure, stick-slip sliding, tides and wave action may affect ice-sheet evolution on sub-daily timescales. Over these timescales, the quasi-static-creep approximation is no longer appropriate and elastic effects become important. Simulating elastic effects in ice-sheet models over relevant timescales, however, remains challenging. Here, we show that by including a visco-elastic rheology and reintroducing the oft neglected acceleration term back into the ice-sheet stress balance, we can create a visco-elastic system where the velocity is locally determined and information propagates at the elastic wave speed. Crucially, the elastic wave speed can be treated like an adjustable parameter and set to any value to reproduce a range of phenomena, provided the wave speed is large compared to the viscous velocity. We illustrate the system using three examples. The first two examples demonstrate that the system converges to the steady-state viscous and elastic limits. The third example examines ice-shelf rifting and iceberg calving. This final example hints at the utility of the visco-elastic formulation in treating both long-term evolution and short-term environmental effects.