EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Open Access Climate Climate of the Past of the Past Discussions Open Access Open Access Earth System Earth System Dynamics Dynamics Discussions Open Access Geoscientific Geoscientific Open Access Instrumentation Instrumentation Methods and Methods and Data Systems Data Systems Discussions Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Open Access Open Access Geosci. Model Dev. Discuss., 6, 1689–1741, 2013 Geoscientific www.geosci-model-dev-discuss.net/6/1689/2013/Geoscientific Model Development GMDD doi:10.5194/gmdd-6-1689-2013Model Development Discussions © Author(s) 2013. CC Attribution 3.0 License. 6, 1689–1741, 2013 Open Access Open Access Hydrology and Hydrology and This discussion paper is/has been under review for the journal Geoscientific Model Elmer/Ice model Development (GMD). PleaseEarth refer toSystem the corresponding final paper in GMDEarth if available.System Sciences Sciences O. Gagliardini et al. Discussions Open Access Capabilities and performanceOpen Access of Ocean Science Ocean Science Title Page Elmer/Ice, a new generation ice-sheetDiscussions Abstract Introduction Open Access model Open Access Solid Earth Conclusions References O. Gagliardini1,2, T. ZwingerSolid3, F. Earth Gillet-Chaulet1, G. Durand1, L. Favier1, Discussions Tables Figures B. de Fleurian1, R. Greve4, M. Malinen3, C. Martín5, P. Råback3, J. Ruokolainen3, 1 6 4 7 M. Sacchettini , M. Schäfer , H. SeddikOpen Access , and J. Thies Open Access J I 1 Laboratoire de GlaciologieThe et Cryosphere Géophysique de l’Environnement, UJF-Grenoble,The Cryosphere CNRS – UMR5183, Saint-Martin-d’Hères, France Discussions J I 2Institut Universitaire de France, Paris, France Back Close 3CSC-IT Center for Science Ltd., Espoo, Finland 4 Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan Full Screen / Esc 5British Antarctic Survey, Cambridge, UK 6Arctic Centre, University of Lapland, Rovaniemi, Finland Printer-friendly Version 7Uppsala University, Uppsala, Sweden Received: 11 February 2013 – Accepted: 19 February 2013 – Published: 4 March 2013 Interactive Discussion Correspondence to: O. Gagliardini ([email protected]) Published by Copernicus Publications on behalf of the European Geosciences Union. 1689 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract GMDD The Fourth IPCC Assessment Report concluded that ice-sheet flow models are unable to forecast the current increase of polar ice sheet discharge and the associated contri- 6, 1689–1741, 2013 bution to sea-level rise. Since then, the glaciological community has undertaken a huge 5 effort to develop and improve a new generation of ice-flow models, and as a result, a Elmer/Ice model significant number of new ice-sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. O. Gagliardini et al. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to Title Page 10 solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger scale problems, earning the status of an Abstract Introduction ice-sheet model. Here, we summarise almost 10 yr of development performed by dif- ferent groups. We present the components already included in Elmer/Ice, its numerical Conclusions References performance, selected applications, as well as developments planned for the future. Tables Figures 15 1 Introduction J I Since the 2007 IPCC report (Solomon et al., 2007), the glaciological community has J I undertaken a huge effort to improve ice-sheet flow models, in order to provide reliable Back Close future estimates of the dynamical contribution of ice-sheets to sea level rise. These models were originally designed to reconstruct the evolution of ice-sheets over past Full Screen / Esc 20 glaciological cycles, neglecting short term responses and local features. The new chal- lenge of running ice-sheet models to provide estimates of future sea-level rise has cre- Printer-friendly Version ated the need for a new generation of ice-sheet models (Vaughan and Arthern, 2007; Interactive Discussion Gillet-Chaulet and Durand, 2010; Blatter et al., 2011; Kirchner et al., 2011; Alley and Joughin, 2012). This new generation of ice-sheet models includes a set of requisites 25 that are essential to provide a sufficiently accurate description of the ice flow dynamics. 1690 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | As a first requisite, these models must be able to describe the ice flow heterogeneity, and particularly the major contribution of individual ice streams to the total ice dis- GMDD charge. This requires the use of an unstructured mesh in the horizontal plane (e.g. 6, 1689–1741, 2013 Gillet-Chaulet et al., 2012; Larour et al., 2012; Seddik et al., 2012) or of adaptive multi- 5 grid methods (Cornford et al., 2013b). These mesh techniques are essential to pro- duce hundred-meter scale grid sizes in areas of interest, especially near the coast, Elmer/Ice model while for the interior regions where variations in velocity gradients are small, classic grid sizes can be kept to save computing resources. Grid refinement is even more es- O. Gagliardini et al. sential when considering the dynamics of the grounding line, i.e. the boundary between 10 the grounded ice sheet and the floating ice shelf, because a grid size that is too large Title Page gives inconsistent grounding line dynamics (Durand et al., 2009; Pattyn et al., 2013). The second important requisite is to have an accurate description of the complex Abstract Introduction state of stress prevailing in ice streams to solve the full-Stokes system, or at least to adopt a higher order asymptotic formulation. As shown by the ISMIP-HOM inter- Conclusions References 15 comparison exercise (Pattyn et al., 2008), higher-order models are needed to describe Tables Figures the ice flow in areas where the basal topography and slipperiness vary greatly, which are generally the most dynamic regions within ice sheets. Higher-order models are also J I necessary to properly describe the dynamics of the grounding line. The MISMIP inter- comparison (Pattyn et al., 2012) indicated the need to solve the full-Stokes equations J I 20 near the grounding line to obtain fully accurate results. Back Close The consequence of these first two requisites, i.e. high numerical resolution at places of interest and higher order formulations, is a high computing cost and the necessity Full Screen / Esc to develop parallel codes, able to run over hundreds of CPUs. Recent studies (Larour et al., 2012; Gillet-Chaulet et al., 2012; Seddik et al., 2012; Cornford et al., 2013b) have Printer-friendly Version 25 fulfilled these requirements and have shown that by deploying high performance com- puting (HPC) techniques this challenge can be successfully taken on. In this context, Interactive Discussion Elmer/Ice takes advantage of being backed by a large opens source community that also develops new numerical and HPC techniques for the code (e.g. Malinen, 2007). 1691 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The third requisite, and from the physical point of view the most challenging, is to implement physically-founded boundary conditions. These improvements are far more GMDD complex and it will take more time to fully address them in the ice-sheet flow models. 6, 1689–1741, 2013 The recently observed changes in coastal glacier dynamics (e.g. Moon et al., 2012) are 5 certainly driven by changes in ice sheet and ice shelf boundary conditions, and con- sequently linked to changes in the ocean and atmosphere components of the climatic Elmer/Ice model system. In the simplest cases, changes in the climatic components directly drive the changes at the boundaries of the ice mass. This is the case for surface air temperature O. Gagliardini et al. or ocean temperature which directly drive the temperature boundary condition of the 10 upper surface or the bottom ice/ocean interface, respectively. In other more complex Title Page cases, the link between changes in the ocean and/or atmosphere and changes in the ice flow is indirect. Intermediate processes (often not observable) are involved, as in the Abstract Introduction case for example of the link between surface runoff and basal sliding or ocean temper- ature and calving rate. Thus, a dedicated model is required to describe the processes Conclusions References 15 responsible for the transfer of these changes to the ice mass. Driving this dedicated Tables Figures transfer model might require to couple the ice sheet model with an atmosphere or an ocean model. J I The last important requisite for a forecast model is to be able to simulate present day observations with as much fidelity as possible (Aschwanden et al., 2012). This J I 20 point must be addressed clearly using data assimilation techniques and specific inverse Back Close methods to estimate the less well-known parameters of the model (e.g. Heimbach and Bugnion, 2009; Arthern and Gudmundsson, 2010; Morlighem et al., 2010). Full Screen / Esc Recent ice-sheet model developments have started to fulfil some of these priority requisites, leading the way toward the new generation of ice-sheet models (Bueler and Printer-friendly Version 25 Brown, 2009; Pollard and DeConto, 2009; Rutt et al., 2009; Larour et al., 2012; Leng et al., 2012; Winkelmann et al., 2011; Favier et al., 2012; Gillet-Chaulet et al., 2012).