Abstract
Ice flow models used to project the mass balance of ice sheets in Greenland and Antarctica usually rely on the Shallow Ice Approximation (SIA) and the Shallow‐Shelf Approximation (SSA), sometimes combined into so‐called “hybrid” models. Such models, while computationally efficient, are based on a simplified set of physical assumptions about the mechanical regime of the ice flow, which does not uniformly apply everywhere on the ice sheet/ice shelf system, especially near grounding lines, where rapid changes are taking place at present. Here, we present a new thermomechanical finite element model of ice flow named ISSM (Ice Sheet System Model) that includes higher‐order stresses, high spatial resolution capability and data assimilation techniques to better capture ice dynamics and produce realistic simulations of ice sheet flow at the continental scale. ISSM includes several approximations of the momentum balance equations, ranging from the two‐dimensional SSA to the three‐dimensional full‐Stokes formulation. It also relies on a massively parallelized architecture and state‐of‐the‐art scalable tools. ISSM employs data assimilation techniques, at all levels of approximation of the momentum balance equations, to infer basal drag at the ice‐bed interface from satellite radar interferometry‐derived observations of ice motion. Following a validation of ISSM with standard benchmarks, we present a demonstration of its capability in the case of the Greenland Ice Sheet. We show ISSM is able to simulate the ice flow of an entire ice sheet realistically at a high spatial resolution, with higher‐order physics, thereby providing a pathway for improving projections of ice sheet evolution in a warming climate.
Highlights
[5] Here we present a new finite element, thermomechanical numerical model of ice flow named ISSM (Ice Sheet System Model) that includes higher-order stress components, high spatial resolution capability and relies on a massively parallelized architecture
We describe the equations adopted in ISSM to model ice flow, including its thermal regime, stress regime, boundary conditions and ice rheology
We present an application of ISSM to the modeling of the entire Greenland Ice Sheet (GIS) to illustrate the large scale applicability of ISSM
Summary
[2] Detailed and realistic modeling of the evolution of the Antarctic and Greenland Ice Sheets is needed to improve projections of sea level rise in a warming climate [Intergovernmental Panel on Climate Change (IPCC), 2007]. In case the margin retreats, ISSM assumes a minimum ice thickness of 1 m, which allows for the retreating ice to become dynamically decoupled from the rest of the ice sheet, without introducing instabilities in the ice flow dynamics, and without the need for actively imposing velocity constraints when the ice is fully retreated This scenario will be covered more efficiently when dynamic boundary migration is implemented. [30] our criteria for grounding line migration need to be further refined, using a full-Stokes computation of the stress-balance of the ice sheet/ice shelf system, and migration based on contact and pressure conditions at the grounding line [Nowicki and Wingham, 2008; Durand et al, 2009a, 2009b]. Further work is required to implement a scalable FS solver, similar to what was implemented by Leng et al [2010], but the performance of the MUMPS solver still ensures that reasonable computational times are reached, as shown later on
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