scholarly journals A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

2016 ◽  
Author(s):  
Tong Zhang ◽  
Stephen Price ◽  
Lili Ju ◽  
Wei Leng ◽  
Julien Brondex ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Ice Sheet ◽  
Model Intercomparison ◽  
Plan View ◽  
Grounding Line ◽  
Intercomparison Project ◽  
Simulation Results ◽  
Line Positions ◽  
Measure Of Uncertainty ◽  
Diagnostic Experiment

Abstract. We present a comparison of the numerics and simulation results for two "full" Stokes ice sheet models, FELIX-S (Leng et al., 2012) and Elmer/Ice (Gagliardini et al., 2013). The models are applied to the Marine Ice Sheet Model Intercomparison Project for planview models (MISMIP3D). For the diagnostic experiment (P75D) the two models give very similar results (<2 % difference with respect to along-flow velocities) when using identical geometries and computational meshes, which we interpret as an indication of inherent consistencies and similarities between the two models. For the Stnd, P75S, and P75R prognostic experiments, we find that FELIX-S (Elmer/Ice) grounding lines are relatively more retreated (advanced), results that are consistent with minor differences observed in the diagnostic experiment results and largely due to slightly different choices in the implementation of basal boundary conditions used by the two models. Based on current understanding, neither set of implementations is more or less favorable, in which case we propose that the span of different grounding line positions from these two models provides a measure of uncertainty when treating the results from full-Stokes models as a metric for accuracy in model intercomparison experiments. More importantly, we show that as grid resolution increases the grounding line positions for FELIX-S and Elmer/Ice appear to converge. We conclude that future model intercomparisons using full-Stokes models as a metric should include more than one model, to provide both additional confidence in the results from full-Stokes models and a measure of their uncertainty.

scholarly journals A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d)

2017 ◽  
Vol 11 (1) ◽  
pp. 179-190 ◽  
Author(s):  
Tong Zhang ◽  
Stephen Price ◽  
Lili Ju ◽  
Wei Leng ◽  
Julien Brondex ◽  
...  
Keyword(s):  
Truncation Error ◽  
Computational Cost ◽  
Ice Sheet ◽  
Model Resolution ◽  
Model Intercomparison ◽  
Plan View ◽  
Grounding Line ◽  
Intercomparison Project ◽  
Line Positions ◽  
Diagnostic Experiment

Abstract. We present a comparison of the numerics and simulation results for two "full" Stokes ice sheet models, FELIX-S (Leng et al. 2012) and Elmer/Ice (Gagliardini et al. 2013). The models are applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d). For the diagnostic experiment (P75D) the two models give similar results ( <  2 % difference with respect to along-flow velocities) when using identical geometries and computational meshes, which we interpret as an indication of inherent consistencies and similarities between the two models. For the standard (Stnd), P75S, and P75R prognostic experiments, we find that FELIX-S (Elmer/Ice) grounding lines are relatively more retreated (advanced), results that are consistent with minor differences observed in the diagnostic experiment results and that we show to be due to different choices in the implementation of basal boundary conditions in the two models. While we are not able to argue for the relative favorability of either implementation, we do show that these differences decrease with increasing horizontal (i.e., both along- and across-flow) grid resolution and that grounding-line positions for FELIX-S and Elmer/Ice converge to within the estimated truncation error for Elmer/Ice. Stokes model solutions are often treated as an accuracy metric in model intercomparison experiments, but computational cost may not always allow for the use of model resolution within the regime of asymptotic convergence. In this case, we propose that an alternative estimate for the uncertainty in the grounding-line position is the span of grounding-line positions predicted by multiple Stokes models.

scholarly journals Improvements in one-dimensional grounding-line parameterizations in an ice-sheet model with lateral variations (PSUICE3D v2.1)

2020 ◽  
Vol 13 (12) ◽  
pp. 6481-6500
Author(s):  
David Pollard ◽  
Robert M. DeConto
Keyword(s):  
Ice Sheet ◽  
Model Intercomparison ◽  
Structural Failure ◽  
Plan View ◽  
One Dimensional ◽  
West Antarctic ◽  
Grounding Line ◽  
Ice Retreat ◽  
Rcp 8.5 ◽  
Intercomparison Project

Abstract. The use of a boundary-layer parameterization of buttressing and ice flux across grounding lines in a two-dimensional ice-sheet model is improved by allowing general orientations of the grounding line. This and another modification to the model's grounding-line parameterization are assessed in three settings: rectangular fjord-like domains – the third Marine Ice Sheet Model Intercomparison Project (MISMIP+) and Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d) – and future simulations of West Antarctic ice retreat under Representative Concentration Pathway (RCP)8.5-based climates. The new modifications are found to have significant effects on the fjord-like results, which are now within the envelopes of other models in the MISMIP+ and MISMIP3d intercomparisons. In contrast, the modifications have little effect on West Antarctic retreat, presumably because dynamics in the wider major Antarctic basins are adequately represented by the model's previous simpler one-dimensional formulation. As future grounding lines retreat across very deep bedrock topography in the West Antarctic simulations, buttressing is weak and deviatoric stress measures exceed the ice yield stress, implying that structural failure at these grounding lines would occur. We suggest that these grounding-line quantities should be examined in similar projections by other ice models to better assess the potential for future structural failure.

scholarly journals Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP

2012 ◽  
Vol 6 (3) ◽  
pp. 573-588 ◽  
Author(s):  
F. Pattyn ◽  
C. Schoof ◽  
L. Perichon ◽  
R. C. A. Hindmarsh ◽  
E. Bueler ◽  
...  
Keyword(s):  
Steady State ◽  
Adaptive Mesh Refinement ◽  
Ice Sheet ◽  
Adaptive Mesh ◽  
Stable Steady State ◽  
Fixed Grid ◽  
Approximate Analytical Solutions ◽  
Grounding Line ◽  
Intercomparison Project ◽  
Line Positions

Abstract. Predictions of marine ice-sheet behaviour require models that are able to robustly simulate grounding line migration. We present results of an intercomparison exercise for marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no effects of lateral buttressing). Unique steady state grounding line positions exist for ice sheets on a downward sloping bed, while hysteresis occurs across an overdeepened bed, and stable steady state grounding line positions only occur on the downward-sloping sections. Models based on the shallow ice approximation, which does not resolve extensional stresses, do not reproduce the approximate analytical results unless appropriate parameterizations for ice flux are imposed at the grounding line. For extensional-stress resolving "shelfy stream" models, differences between model results were mainly due to the choice of spatial discretization. Moving grid methods were found to be the most accurate at capturing grounding line evolution, since they track the grounding line explicitly. Adaptive mesh refinement can further improve accuracy, including fixed grid models that generally perform poorly at coarse resolution. Fixed grid models, with nested grid representations of the grounding line, are able to generate accurate steady state positions, but can be inaccurate over transients. Only one full-Stokes model was included in the intercomparison, and consequently the accuracy of shelfy stream models as approximations of full-Stokes models remains to be determined in detail, especially during transients.

scholarly journals Grounding-line migration in plan-view marine ice-sheet models: results of the ice2sea MISMIP3d intercomparison

2013 ◽  
Vol 59 (215) ◽  
pp. 410-422 ◽  
Author(s):  
Frank Pattyn ◽  
Laura Perichon ◽  
Gaël Durand ◽  
Lionel Favier ◽  
Olivier Gagliardini ◽  
...  
Keyword(s):  
Extensional Flow ◽  
Ice Sheet ◽  
Model Approximation ◽  
Plan View ◽  
Transient Behaviour ◽  
Approximate Analytical Solutions ◽  
Grounding Line ◽  
Basal Sliding ◽  
Short Time ◽  
Line Positions

AbstractPredictions of marine ice-sheet behaviour require models able to simulate grounding-line migration. We present results of an intercomparison experiment for plan-view marine ice-sheet models. Verification is effected by comparison with approximate analytical solutions for flux across the grounding line using simplified geometrical configurations (no lateral variations, no buttressing effects from lateral drag). Perturbation experiments specifying spatial variation in basal sliding parameters permitted the evolution of curved grounding lines, generating buttressing effects. The experiments showed regions of compression and extensional flow across the grounding line, thereby invalidating the boundary layer theory. Steady-state grounding-line positions were found to be dependent on the level of physical model approximation. Resolving grounding lines requires inclusion of membrane stresses, a sufficiently small grid size (<500 m), or subgrid interpolation of the grounding line. The latter still requires nominal grid sizes of <5 km. For larger grid spacings, appropriate parameterizations for ice flux may be imposed at the grounding line, but the short-time transient behaviour is then incorrect and different from models that do not incorporate grounding-line parameterizations. The numerical error associated with predicting grounding-line motion can be reduced significantly below the errors associated with parameter ignorance and uncertainties in future scenarios.

scholarly journals Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

2020 ◽  
Vol 14 (7) ◽  
pp. 2283-2301 ◽  
Author(s):  
Stephen L. Cornford ◽  
Helene Seroussi ◽  
Xylar S. Asay-Davis ◽  
G. Hilmar Gudmundsson ◽  
Rob Arthern ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Model Intercomparison ◽  
Ice Streams ◽  
Important Distinction ◽  
Ice Flow ◽  
Flow Models ◽  
The Third ◽  
Grounding Line ◽  
Intercomparison Project ◽  
The Difference

Abstract. We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role.

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