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Current State of the Community Ice Sheet Model

Current State of the Community Ice Sheet Model. Stephen Price 1 , Bill Lipscomb 1 , Jesse Johnson 2 Tony Payne 3 , Ian Rutt 4 , Magnus Hagdorn 5 1 COSIM Project, Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory 2 Department of Computer Sciences, University of Montana

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Current State of the Community Ice Sheet Model

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  1. Current State of the Community Ice Sheet Model Stephen Price1, Bill Lipscomb1, Jesse Johnson2 Tony Payne3,Ian Rutt4, Magnus Hagdorn5 1COSIM Project, Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory 2Department of Computer Sciences, University of Montana 3Bristol Glaciology Centre, School of Geographical Sciences, University of Bristol 4School of the Environment and Society, Swansea University 5School of GeoSciences,University of Edinburgh Climate, Ocean, and Sea Ice Modeling Project

  2. Motivation for improved Ice Sheet Models • Current models do not capture observed ice sheet behaviour1, because: (1) Fundamental physics are missing (e.g. simplified gov. equations, negating realistic simulation of outlet glaciers and ice streams) (2) Processes of fundamental importance are not accounted for (e.g. simplified, static treatment of basal boundary conditions, ignoring atmos. and ocean coupling, explicit hydrology, etc.) Accurate predictions of future sea-level rise will require advanced models which can demonstrate skill at reproducing and explaining recent dramatic ice sheet behaviors. 1 IPCC (2007)

  3. Summary of Glimmer-CISM and development plans Model validation (higher-order dynamics) Tuning for initial conditions (Greenland) Summary Illulisat, Western Greenland

  4. Summary of Glimmer-CISM and development plans Model validation (higher-order dynamics) Tuning for initial conditions (Greenland) Summary Illulisat, Western Greenland

  5. Glimmer-CISM • The Glimmer ice sheet model (Rutt et al. 2009) was developed by Tony Payne et al. in the U.K. with the goal of coupling dynamic ice sheets to global climate models. • NSF has supported development of a Community Ice Sheet Model (CISM) based on Glimmer. • Jesse Johnson’s wiki: http://websrv.cs.umt.edu/isis • DOE has supported coupling of Glimmer to the Community Climate System Model (CCSM). • CCSM Land ice working group (meeting Feb. 2010 in Boulder): http://www.ccsm.ucar.edu/working_groups/Land+Ice/ • The U.S. and U.K. groups have recently combined efforts: • BerliOS repository: http://developer.berlios.de/projects/glimmer-cism/ • 6-member steering committee (M. Hagdorn, J. Johnson, W. Lipscomb, T. Payne, S. Price, I. Rutt)

  6. Ice sheets in the Community Climate System Model (CCSM) Atmosphere Land surface (Ice sheet surface mass balance) Coupler Sea Ice Ice sheet (Dynamics) Ocean Glimmer has been coupled to CCSM version 4 and will be used for IPCC runs with a dynamic Greenland ice sheet. The surface mass balance of ice sheets is computed by the land surface model on a coarse grid (~100 km) in multiple elevation classes, passed to Glimmer via the coupler, and downscaled to the ice sheet grid (~10 km).

  7. DOE IMPACTS IMPACTS - Investigation of the Magnitudes and Probabilities of Abrupt Climate Transitions • 5-year program on abrupt climate change • One part of the project (LANL and NYU) focuses on the potential instability of the West Antarctic ice sheet due to ice/ocean interactions • Couple Glimmer-CISM to the HYPOP ocean model on regional scales • Model ocean circulation beneath dynamic ice shelves

  8. DOE ISICLES ISICLES - Ice Sheet Initiative for CLimate at Extreme Scales • New 3-year program to develop advanced ice sheet models using efficient, scalable computational methods • Dynamical cores to be incorporated as options in Glimmer-CISM • Six projects with similar goals, different tools: - Matrix solvers and preconditioners (e.g., PETSc, Trilinos) - Adaptive mesh refinement (e.g., Chombo) - Unstructured grids (e.g., Voronoi meshes)

  9. Summary of Glimmer-CISM and development plans Model validation (higher-order dynamics) Tuning for initial conditions (Greenland) Summary Illulisat, Western Greenland

  10. ice stream with plastic till

  11. model vel (m/yr) observed vel (m/yr)

  12. Summary of Glimmer-CISM and development plans Model validation (higher-order dynamics) Tuning for initial conditions (Greenland) Summary field camp, central Greenland

  13. Tuning Procedure - Skipping the details, we have a simple procedure that allows us to “tune” basal sliding parameters to match a target velocity field - The resulting ice velocity, viscosity, and temperature fields are in a steady-state with modern day geometry, temperature, and geothermal flux fields (as well as those are known) - The result should be useful as an initial condition for a range of perturbation studies How do model and target1 velocity fields compare? 1Here, GIS balance velocities from Bamber et al. (J.Glac., 46, 2000)

  14. Summary We have a 3D ice sheet model (Glimmer-CISM) that can simulate the flow of inland ice, outlet glaciers and ice streams, and ice shelves using either of two higher-order flow schemes. The model is nearly ready for coupled climate experiments using CCSM. We plan to do experiments with dynamic, higher-order ice sheets in time to contribute to IPCC AR5. The model is evolving rapidly. Within a few years, scalable solvers and adaptive grids could make high-resolution, whole-ice-sheet simulations routine. We welcome collaborators.

  15. EXTRA

  16. Model framework

  17. Proposed CCSM4 experiments with GLIMMER(0.9o x 1.25o atm, 1o ocn) 1. Control 3. Long-term (asynchronous) Miren Vizcaino (UC Berkeley) et al. will analyze these runs. • Pre-industrial control, 230+ yrs • Pre-industrial control, 0.5o, ~100 yrs • 20th century (1870-2005) 2. IPCC AR5 scenarios • RCP4.5, 100-300 yrs • RCP8.5, 100-300 yrs Continuation of RCP4.5, 200 yrs (AOGCM), 2000 yrs (ice sheet) Branch runs of RCP4.5 and/or RCP8.5 (study irreversibility) Eemian interglacial: 1000 yr AOGCM w/ 10x accelerated Milankovich; 10,000 yr ice sheet

  18. Governing Equations Conservation of Momentum - 1st-order SIA (e.g. Blatter-Pattyn) using FDM (current) - 1st-order SIA (Dukowicz+) using FEM (under development) - full Stokes (next 2-4 yrs?) Conservation of Energy - standard heat equation solved for ice sheets (e.g. horiz diff neglected) - scalable improvement planned Conservation of Mass - standard, nonlinear diffusion equation in H (0-order SIA) - incremental remapping (1st-order SIA)

  19. Equations of Stress Equilibrium in Cartesian Coordinates (Stokes Flow) Assume static balance of forces by ignoring acceleration

  20. … apply some scaling based on H/L …

  21. First-Order SIA … integrate w.r.t. z to get explicit expression for P…

  22. First Order SIA …integrate in vertical from upper sfc through depth …

  23. First Order SIA …substitute vertical relation for P into horizontal balance …

  24. First Order SIA …use definition of deviatoric stress to eliminate vertical-normal stress deviator in horiz. equations …

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