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Elmer/Ice @EGU2017

Written by Olivier Gagliardini on .

egu plainThe fourth Elmer/Ice users splinter meeting will take place during EGU 2017 (Wednesday 25 April 2017, from 12:15 to 15:00, Room 0.51). The provisional agenda is here.

Don't miss the 15 Elmer/Ice related posters and orals that will be presented during EGU 2017:

Monday, 24 Apr

Eva de Andrés, Jaime Otero, Francisco Navarro, Agnieszka Prominska, Javier Lapazaran, and Waldemar Walczowski, A fjord-glacier coupled system model. Mon, 24 Apr, 13:30–13:45, Room G2

Joe Todd, Poul Christoffersen, Thomas Zwinger, Peter Råback, Nolwenn Chauché, Alun Hubbard, Nick Toberg, Adrian Luckman, Doug Benn, Donald Slater, and Tom Cowton. A 3D Full-Stokes Calving Model Applied to a West Greenland Outlet Glacier. Mon, 24 Apr, 14:30–14:45, Room G2

Tuesday, 25 Apr
Yongmei Gong, Thomas Zwinger, Jan Åström, Rupert Gladstone, Thomas Schellenberger, Bas Altena, and John Moore. Basal friction evolution and crevasse distribution during the surge of Basin 3, Austfonna ice-cap – offline coupling between a continuum ice dynamic model and a discrete element model. Tue, 25 Apr, 16:30–16:45, Room -2.32

Yasmina M. Martos, Carlos Martin, and David G. Vaughan. New basal temperature and basal melt rate maps of Antarctica. Tue, 25 Apr, 17:30–19:00, Hall X5

Wednesday, 26 Apr
Johannes J. Fürst, Thorsten Seehaus, Björn Sass, Kjetil Aas, Toby J. Benham, Julian Dowdeswell, Xavier Fettweis, Fabien Gillet-Chaulet, Geir Moholdt, Francisco Navarro, Christopher Nuth, Rickard Petterson, and Matthias Braun. A two-step mass-conservation approach to infer ice thickness maps: Performance for different glacier types on Svalbard. Wed, 26 Apr, 17:30–19:00, Hall X4

Thursday 27 Apr
Shahbaz Memon, Dorothée Vallot, Thomas Zwinger, and Helmut Neukirchen. Coupling of a continuum ice sheet model and a discrete element calving model using a scientific workflow system. Thu, 27 Apr, 08:45–09:00, Room L2

Doug Benn, Jan Åström, Thomas Zwinger, Joe Todd, and Faezeh Nick. Modelling tidewater glacier calving: from detailed process models to simple calving laws. Thu, 27 Apr, 08:45–09:00, Room G2

Mauro A. Werder, Basile de Fleurian, Timothy T. Creyts, Anders Damsgaard, Ian Delaney, Christine F. Dow, Olivier Gagliardini, Matthew J. Hoffman, Julien Seguinot, Aleah Sommers, Inigo Irarrazaval Bustos, and Jakob Downs. Subglacial Hydrology Model Intercomparison Project (SHMIP). Thu, 27 Apr, 09:45–10:00, Room G2

Olivier Passalacqua, Marie Cavitte, Massimo Frezzotti, Olivier Gagliardini, Fabien Gillet-Chaulet, Frédéric Parrenin, Catherine Ritz, Luca Vittuari, and Duncan Young. A mechanical diagnosis of the ice flow around Dome C: Elmer/Ice 3D simulations constrained by measured surface velocities and radar isochrones. Thu, 27 Apr, 17:30–19:00, Hall X5

Dorothée Vallot, Rickard Pettersson, Adrian Luckman, Douglas I. Benn, Thomas Zwinger (presenting), Ward van Pelt, Jack Kohler, Martina Schäfer, Björn Claremar, and Nicholas R. J. Hulton. Influence of surface changes on spatio-temporal variations of basal properties for Kronebreen, Svalbard. Thu, 27 Apr, 17:30–19:00, Hall X5

Rupert M. Gladstone, Thomas Zwinger (presenting), Fabien Gillet-Chaulet, and John C. Moore. Basal shear stress and choice of sliding relation in Antarctic Ice Sheet simulations. Thu, 27 Apr, 17:30–19:00, Hall X5

Denis Cohen, Thomas Zwinger, Wilfried Haeberli, and Urs H. Fischer. Did permafrost modify basal conditions during the Last Glacial Maximum? The case of the Rhine glacier, Swiss Alps. Thu, 27 Apr, 17:30–19:00, Hall X2

Fabien Gillet-Chaulet, Laure Tavard, Nacho Merino, Vincent Peyaud, Julien Brondex, Gael Durand, and Olivier Gagliardini. Anisotropic mesh adaptation for marine ice-sheet modelling. Thu, 27 Apr, 17:30–19:00, Hall X5

Lenneke Jong, Rupert Gladstone, and Ben Galton-Fenzi. Coupled ice sheet-ocean modelling to investigate ocean driven melting of marine ice sheets in Antarctica. Thu, 27 Apr, 17:30–19:00, Hall X5

Friday, 28 Apr
Reinhard Drews, Christoph Mayer, Olaf Eisen, Veit Helm, Todd A. Ehlers, Frank Pattyn, Sophie Berger, Lionel Favier, Ian H. Hewitt, Felix Ng, Johannes J. Fürst, Fabien Gillet-Chaulet, Nicolas Bergeot, and Kenichi Matsuoka. Fun at Antarctic grounding lines: Ice-shelf channels and sediment transport. Fri, 28 Apr, 08:52–08:54, PICO spot 3

Frédéric Parrenin, Marie Cavitte, Donald Blankenship, Jérôme Chappellaz, Hubertus Fischer, Olivier Gagliardini, Fabien Gillet-Chaulet, Valérie Masson-Delmotte, Olivier Passalacqua, Catherine Ritz, Jason Roberts, Martin Siegert, and Duncan Young. Is there 1.5 million-year old ice near Dome C, Antarctica? Fri, 28 Apr, 10:48–10:50, PICO spot 3

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Mesh sensitivity to friction law and sub-shelf melting

Written by Olivier Gagliardini on .

gladstone 2017Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flow-line model accounting for all stress components and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting.

Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction in resolution dependence.

A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line.

Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), impact on capability to simulate marine ice sheets. If there exists an abrupt change across the grounding line in either basal drag or basal melting, then high resolution will be required to solve the problem. However, the plausible combination of a physical dependency of basal drag on effective pressure, and the possibility of low ice shelf basal melt rates next to the grounding line, may mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary.

More information:  Gladstone, R.M., R.C. Warner, B.K. Galton-Fenzi, O. Gagliardini, T. Zwinger and R. Greve, 2017. Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting, The Cryosphere, 11, 319-329, doi:10.5194/tc-11-319-2017.

 

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A new full-Stokes model dealing with grounding line

Written by Olivier Gagliardini on .

zhang2017We 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.

More information: Zhang, T., S. Price, L. Ju, W. Leng, J. Brondex, G. Durand and O. Gagliardini, 2017. A comparison of two Stokes ice sheet models applied to the Marine Ice Sheet Model Intercomparison Project for plan view models (MISMIP3d), The Cryosphere, 11, 179-190, doi:10.5194/tc-11-179-2017.

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