Review of "Optimal numerical solvers for transient simulations of ice flow using the Ice Sheet System Model (ISSM)", by Habbal, et al

Abstract. Identifying fast and robust numerical solvers is a critical issue that needs to be addressed in order to improve projections of polar ice sheets evolving in a changing climate. This work evaluates the impact of using advanced numerical solvers for transient ice-flow simulations conducted with the JPL–UCI Ice Sheet System Model (ISSM). We identify optimal numerical solvers by testing a broad suite of readily available solvers, ranging from direct sparse solvers to preconditioned iterative methods, on the commonly used Ice Sheet Model Intercomparison Project for Higher-Order ice sheet Models benchmark tests. Three types of analyses are considered: mass transport, horizontal stress balance, and incompressibility. The results of the fastest solvers for each analysis type are ranked based on their scalability across mesh size and basal boundary conditions. We find that the fastest iterative solvers are ∼ 1.5–100 times faster than the default direct solver used in ISSM, with speed-ups improving rapidly with increased mesh resolution. We provide a set of recommendations for users in search of efficient solvers to use for transient ice-flow simulations, enabling higher-resolution meshes and faster turnaround time. The end result will be improved transient simulations for short-term, highly resolved forward projections (10–100 year time scale) and also improved long-term paleo-reconstructions using higher-order representations of stresses in the ice. This analysis will also enable a new generation of comprehensive uncertainty quantification assessments of forward sea-level rise projections, which rely heavily on ensemble or sampling approaches that are inherently expensive.

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Optimal numerical solvers for transient simulations of ice flow using the Ice Sheet System Model (ISSM)

10.5194/gmd-2016-111 ◽

2016 ◽

Author(s):

Feras Habbal ◽

Eric Larour ◽

Eric Rignot ◽

Christopher P. Borstad ◽

Helene Seroussi ◽

...

Keyword(s):

Ice Sheet ◽

Mesh Size ◽

Critical Issue ◽

Higher Order ◽

Iterative Solvers ◽

System Model ◽

Ice Flow ◽

Flow Simulations ◽

Transient Simulations ◽

The Impact

Abstract. Identifying fast and robust numerical solvers is a critical issue that needs to be addressed in order to improve projections of polar ice sheets evolving in a changing climate. This work evaluates the impact of using sophisticated numerical solvers for transient ice flow simulations using the NASA-JPL/UCI Ice Sheet System Model (ISSM). We identify optimal numerical solvers by testing them on a commonly used ice flow benchmark test, the Ice Sheet Model Intercomparison Project for Higher-Order ice sheet Models (ISMIP-HOM) Experiment F. Three types of analyses are considered: mass transport, horizontal stress balance, and vertical stress balance. A broad suite of solvers is tested, ranging from direct sparse solvers to preconditioned iterative methods. The results of the fastest solvers for each analysis type are ranked based on their scalability across mesh size for each basal sliding conditions specified in Experiment F. We find that the fastest iterative solvers are ~1.5–100 times faster than the default direct solver used in ISSM with speed-ups improving rapidly with increased mesh resolution. We provide a set of recommendations for users in search of efficient solvers to use for transient ice flow simulations, enabling higher-resolution meshes and faster turnaround time. The end result will be improved transient simulations for short-term, highly resolved forward projections (10–100 year time scale) and also improved long-term paleo-reconstructions using higher-order representation of stresses in the ice. This analysis will also enable a new generation of comprehensive uncertainty quantification assessments of forward sea-level rise projections, which rely heavily on ensemble or sampling approaches that are inherently expensive.

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Executive Editor Comment on "Optimal numerical solvers for transient simulations of ice flow using the Ice Sheet System Model (ISSM)"

10.5194/gmd-2016-111-sc1 ◽

2016 ◽

Author(s):

Astrid Kerkweg

Keyword(s):

Ice Sheet ◽

System Model ◽

Ice Flow ◽

Editor Comment ◽

Executive Editor ◽

Transient Simulations

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Enthalpy benchmark experiments for numerical ice sheet models

The Cryosphere ◽

10.5194/tc-9-217-2015 ◽

2015 ◽

Vol 9 (1) ◽

pp. 217-228 ◽

Cited By ~ 20

Author(s):

T. Kleiner ◽

M. Rückamp ◽

J. H. Bondzio ◽

A. Humbert

Keyword(s):

Analytical Solutions ◽

Ice Sheet ◽

Jump Conditions ◽

Cold Side ◽

Ice Flow ◽

Flow Models ◽

Transient Simulations ◽

Rate Calculation ◽

Transition Surface ◽

Simulation Results

Abstract. We present benchmark experiments to test the implementation of enthalpy and the corresponding boundary conditions in numerical ice sheet models. Since we impose several assumptions on the experiment design, analytical solutions can be formulated for the proposed numerical experiments. The first experiment tests the functionality of the boundary condition scheme and the basal melt rate calculation during transient simulations. The second experiment addresses the steady-state enthalpy profile and the resulting position of the cold–temperate transition surface (CTS). For both experiments we assume ice flow in a parallel-sided slab decoupled from the thermal regime. We compare simulation results achieved by three different ice flow-models with these analytical solutions. The models agree well to the analytical solutions, if the change in conductivity between cold and temperate ice is properly considered in the model. In particular, the enthalpy gradient on the cold side of the CTS goes to zero in the limit of vanishing temperate-ice conductivity, as required from the physical jump conditions at the CTS.

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Mechanisms and time scales of glacial inception simulated with an Earth system model of intermediate complexity

Climate of the Past ◽

10.5194/cp-5-245-2009 ◽

2009 ◽

Vol 5 (2) ◽

pp. 245-258 ◽

Cited By ~ 22

Author(s):

R. Calov ◽

A. Ganopolski ◽

C. Kubatzki ◽

M. Claussen

Keyword(s):

Transient Response ◽

Ice Sheet ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Intermediate Complexity ◽

Transient Simulations ◽

Ice Sheet Dynamics ◽

Inland Ice ◽

Equilibrium Simulation

Abstract. We investigate glacial inception and glacial thresholds in the climate-cryosphere system utilising the Earth system model of intermediate complexity CLIMBER-2, which includes modules for atmosphere, terrestrial vegetation, ocean and interactive ice sheets. The latter are described by the three-dimensional polythermal ice-sheet model SICOPOLIS. A bifurcation which represents glacial inception is analysed with two different model setups: one setup with dynamical ice-sheet model and another setup without it. The respective glacial thresholds differ in terms of maximum boreal summer insolation at 65° N (hereafter referred as Milankovitch forcing (MF)). The glacial threshold of the configuration without ice-sheet dynamics corresponds to a much lower value of MF compared to the full model. If MF attains values only slightly below the aforementioned threshold there is fast transient response. Depending on the value of MF relative to the glacial threshold, the transient response time of inland-ice volume in the model configuration with ice-sheet dynamics ranges from 10 000 to 100 000 years. Due to these long response times, a glacial threshold obtained in an equilibrium simulation is not directly applicable to the transient response of the climate-cryosphere system to time-dependent orbital forcing. It is demonstrated that in transient simulations just crossing of the glacial threshold does not imply large-scale glaciation of the Northern Hemisphere. We found that in transient simulations MF has to drop well below the glacial threshold determined in an equilibrium simulation to initiate glacial inception. Finally, we show that the asynchronous coupling between climate and inland-ice components allows one sufficient realistic simulation of glacial inception and, at the same time, a considerable reduction of computational costs.

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Inferred basal friction and surface mass balance of the Northeast Greenland Ice Stream using data assimilation of ICESat (Ice Cloud and land Elevation Satellite) surface altimetry and ISSM (Ice Sheet System Model)

The Cryosphere ◽

10.5194/tc-8-2335-2014 ◽

2014 ◽

Vol 8 (6) ◽

pp. 2335-2351 ◽

Cited By ~ 32

Author(s):

E. Larour ◽

J. Utke ◽

B. Csatho ◽

A. Schenk ◽

H. Seroussi ◽

...

Keyword(s):

Data Assimilation ◽

Mass Balance ◽

Ice Sheet ◽

System Model ◽

Surface Mass Balance ◽

Altimetry Data ◽

Ice Flow ◽

Surface Mass ◽

Ice Cloud ◽

Basal Friction

Abstract. We present a new data assimilation method within the Ice Sheet System Model (ISSM) framework that is capable of assimilating surface altimetry data from missions such as ICESat (Ice Cloud and land Elevation Satellite) into reconstructions of transient ice flow. The new method relies on algorithmic differentiation to compute gradients of objective functions with respect to model forcings. It is applied to the Northeast Greenland Ice Stream, where surface mass balance and basal friction forcings are temporally inverted, resulting in adjusted modeled surface heights that best fit existing altimetry. This new approach allows for a better quantification of basal and surface processes and a better understanding of the physical processes currently missing in transient ice-flow models to better capture the important intra- and interannual variability in surface altimetry. It also demonstrates that large spatial and temporal variability is required in model forcings such as surface mass balance and basal friction, variability that can only be explained by including more complex processes such as snowpack compaction at the surface and basal hydrology at the bottom of the ice sheet. This approach is indeed a first step towards assimilating the wealth of high spatial resolution altimetry data available from EnviSat, ICESat, Operation IceBridge and CryoSat-2, and that which will be available in the near future with the launch of ICESat-2.

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Enthalpy benchmark experiments for numerical ice sheet models

The Cryosphere Discussions ◽

10.5194/tcd-8-3207-2014 ◽

2014 ◽

Vol 8 (3) ◽

pp. 3207-3236

Author(s):

T. Kleiner ◽

M. Rückamp ◽

J. Bondzio ◽

A. Humbert

Keyword(s):

Analytical Solutions ◽

Ice Sheet ◽

Jump Conditions ◽

Cold Side ◽

Ice Flow ◽

Flow Models ◽

Transient Simulations ◽

Rate Calculation ◽

Transition Surface ◽

Simulation Results

Abstract. We present benchmark experiments to test the implementation of enthalpy and the corresponding boundary conditions in numerical ice sheet models. The first experiment tests particularly the functionality of the boundary condition scheme and the basal melt rate calculation during transient simulations. The second experiment addresses the steady-state enthalpy profile and the resulting position of the cold–temperate transition surface (CTS). For both experiments we assume ice flow in a parallel-sided slab decoupled from the thermal regime. Since we impose several assumptions on the experiment design, analytical solutions can be formulated for the proposed numerical experiments. We compare simulation results achieved by three different ice flow-models with these analytical solutions. The models agree well to the analytical solutions, if the change in conductivity between cold and temperate ice is properly considered in the model. In particular, the enthalpy gradient at the cold side of the CTS vanishes in the limit of vanishing conductivity in the temperate ice part as required from the physical jump conditions at the CTS.

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An approach to computing discrete adjoints for MPI-parallelized models applied to Ice Sheet System Model 4.11

Geoscientific Model Development ◽

10.5194/gmd-9-3907-2016 ◽

2016 ◽

Vol 9 (11) ◽

pp. 3907-3918 ◽

Cited By ~ 6

Author(s):

Eric Larour ◽

Jean Utke ◽

Anton Bovin ◽

Mathieu Morlighem ◽

Gilberto Perez

Keyword(s):

Ice Sheet ◽

Parallel Execution ◽

System Model ◽

Ice Flow ◽

Flow Models ◽

Adjoint State ◽

Expected Performance ◽

Polar Ice Sheets ◽

New Generation ◽

Discrete Adjoints

Abstract. Within the framework of sea-level rise projections, there is a strong need for hindcast validation of the evolution of polar ice sheets in a way that tightly matches observational records (from radar, gravity, and altimetry observations mainly). However, the computational requirements for making hindcast reconstructions possible are severe and rely mainly on the evaluation of the adjoint state of transient ice-flow models. Here, we look at the computation of adjoints in the context of the NASA/JPL/UCI Ice Sheet System Model (ISSM), written in C++ and designed for parallel execution with MPI. We present the adaptations required in the way the software is designed and written, but also generic adaptations in the tools facilitating the adjoint computations. We concentrate on the use of operator overloading coupled with the AdjoinableMPI library to achieve the adjoint computation of the ISSM. We present a comprehensive approach to (1) carry out type changing through the ISSM, hence facilitating operator overloading, (2) bind to external solvers such as MUMPS and GSL-LU, and (3) handle MPI-based parallelism to scale the capability. We demonstrate the success of the approach by computing sensitivities of hindcast metrics such as the misfit to observed records of surface altimetry on the northeastern Greenland Ice Stream, or the misfit to observed records of surface velocities on Upernavik Glacier, central West Greenland. We also provide metrics for the scalability of the approach, and the expected performance. This approach has the potential to enable a new generation of hindcast-validated projections that make full use of the wealth of datasets currently being collected, or already collected, in Greenland and Antarctica.

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