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Can we apply 2.5-D model at a Dome?

Written by Olivier Gagliardini on .

2p5modelThree-dimensional ice flow modelling requires a large number of computing resources and observation data, such that 2-D simulations are often preferable. However, when there is significant lateral divergence, this must be accounted for (2.5-D models), and a flow tube is considered (volume between two horizontal flowlines). In the absence of velocity observations, this flow tube can be derived assuming that the flowlines follow the steepest slope of the surface, under a few flow assumptions. This method typically consists of scanning a digital elevation model (DEM) with a moving window and computing the curvature at the centre of this window. The ability of the 2.5-D models to account properly for a 3-D state of strain and stress has not clearly been established, nor their sensitivity to the size of the scanning window and to the geometry of the ice surface, for example in the cases of sharp ridges. Here, we study the applicability of a 2.5-D ice flow model around a dome, typical of the East Antarctic plateau conditions. A twin experiment is carried out, comparing 3-D and 2.5-D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical radius of this curvature. For isothermal ice, the error made by the 2.5-D model is in the range 0–10 % for weakly diverging flows, but is 2 or 3 times higher for highly diverging flows and could lead to a non-physical ice surface at the dome. For non-isothermal ice, assuming a linear temperature profile, the presence of a sharp ridge makes the 2.5-D velocity field unrealistic. In such cases, the basal ice is warmer and more easily laterally strained than the upper one, the walls of the flow tube are not vertical, and the assumptions of the 2.5-D model are no longer valid.

More information in  Passalacqua O., O. Gagliardini, F. Parrenin, J. Todd, F. Gillet-Chaulet and C. Ritz, 2016. Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome, Geosci. Model Dev., 9, 2301-2313, doi:10.5194/gmd-9-2301-2016.

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Elmer/Ice at EGU 2016

Written by Olivier Gagliardini on .

egu

Don't miss the talks and posters making use of Elmer/Ice:

** Monday
* CR1.4/AS4.3 Glaciers and ice caps under climate change (co-organized)
Poster: 17:30–19:00 / Hall X4
- Martina Schäfer, Marco Möller, Thomas Zwinger, and John Moore. The influence of topographic feedback on a coupled mass balance and ice-flow model for Vestfonna ice-cap, Svalbard


** Tuesday
* CR5.1 Modelling ice sheets and glaciers
Poster: 17:30–19:00 / Hall X4
- Julien Brondex, Olivier Gagliardini, Fabien Gillet-Chaulet, and Gael Durand. Influence of damage and basal friction on the grounding line dynamics

- Josefin Ahlkrona, Per Lötstedt, and Thomas Zwinger. Dynamically coupling the full Stokes equations and the SIA - the ISCAL method

* CR5.2 Subglacial Environments of Ice Sheets and Glaciers
Poster 17:30–19:00 / Hall X4

- Dorothée Vallot, Rickard Pettersson, Doug Benn, Adrian Luckman, Olivier Gagliardini, Fabien Gillet-Chaulet, Thomas Zwinger, Jack Kohler, Ward van Pelt, and Björn Claremar. Seasonal subglacial state under Kronebreen, Svalbard - inversion and sliding laws.


* CR5.3/OS2.10 Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling (co-organized)
Oral: 13:30–17:00 / Room L2
- 15h30-15h45: Martin O'Leary, Bernd Kulessa, Adam Booth, Paul Holland, Daniela Jansen, Ed King, Adrian Luckman, Dan McGrath, and Thomas Zwinger. Inferring the viscous and elastic properties of a suture zone in Larsen C

** Friday
* CR 13 Reconstructing paleo ice dynamics: Comparing and combining field-based evidence and numerical modeling
Oral: 10:30–12:00 / Room L2
- 10h30-10h45: Denis Cohen, Fabien Gillet-Chaulet, Thomas Zwinger, Horst Machguth, Wilfried Haeberli, and Urs H. Fischer Basal conditions and flow dynamics of the Rhine glacier, Alps, at the Last Glacial Maximum.

Poster: 13:30–15:00 / Hall X4
- Guillaume Jouvet, Denis Cohen, Julien Seguinot, and Fabien Gillet-Chaulet. Inconsistent Last Glacial Maximum ice thickness of the Rhine glacier between geomorphological reconstructions and two numerical models.

 

 

 

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Where shelf-ice turns passive

Written by Olivier Gagliardini on .

 

NCC JohannesThe decadal record of ice-shelf recession and break-up on the Antarctic Peninsula reveals that these vast slabs of floating ice restrain the sea-level relevant outflow from the upstream, well-grounded tributary glaciers. One of the key questions in projecting this outflow for the whole of Antarctica is how far ice-front recession may progress before important dynamic consequences are anticipated. This question is addressed in a recently published article in Nature Climate Change which relies on a continental-scale data assimilation with Elmer/Ice. Details of this assimilation were already presented in an accompanying article published earlier in The Cryosphere. The aim of the data assimilation was to quantify the buttressing effect on ice shelves relying on the inferred stress regime. If maximum buttressing showed values below a threshold, which itself was inferred from generic calving experiments, ice was considered dynamically passive. As long as the calving only removes this passive shelf-ice (PSI) portion, no important dynamic consequences are expected. The results show that 13 % of the total ice-shelf surface of Antarctica hold PSI with contrasting results across the continent. The presented analysis draws again the attention to the Amundsen and Bellingshausen sea sectors, where the PSI area fraction is notably lower, with regional averages of 7 and 5 %, respectively.

News written by Johannes J. Fürst.

Fürst, J. J., G. Durand, F. Gillet-Chaulet, L. Tavard, M. Rankl, M. Braun and O. Gagliardini, 2016. The safety band of Antarctic ice shelves, Nature Climate Change, doi:10.1038/NCLIMATE2912.

 

 

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