scholarly journals Description and Evaluation of the Community Ice Sheet Model (CISM) v2.1

2018 ◽  
Author(s):  
William H. Lipscomb ◽  
Stephen F. Price ◽  
Matthew J. Hoffman ◽  
Gunter R. Leguy ◽  
Andrew R. Bennett ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Standard Test ◽  
Higher Order ◽  
Third Party ◽  
Momentum Balance ◽  
Test Problems ◽  
Thermomechanical Model ◽  
Extensive Documentation ◽  
Basal Sliding

Abstract. We describe and evaluate version 2.1 of the Community Ice Sheet Model (CISM). CISM is a parallel, 3D thermomechanical model, written mainly in Fortran 90/95, that solves equations for the momentum balance and thickness and temperature evolution of ice sheets. CISM's velocity solver incorporates a hierarchy of Stokes-flow approximations, including shallow-shelf, depth-integrated higher-order, and 3D higher-order. CISM also includes a suite of test cases, links to third-party solver libraries, and parameterizations of physical processes such as basal sliding and iceberg calving. The model has been verified for standard test problems, including the ISMIP-HOM experiments for higher-order models, and has participated in the initMIP–Greenland initialization experiment. In multi-millennial simulations with modern climate forcing on a 4-km grid, CISM reaches a steady state that is broadly consistent with observed flow patterns of the Greenland ice sheet. CISM has been integrated into version 2.0 of the Community Earth System Model, where it is being used for Greenland simulations under past, present and future climates. The code is open-source with extensive documentation, and remains under active development.

scholarly journals Description and evaluation of the Community Ice Sheet Model (CISM) v2.1

2019 ◽  
Vol 12 (1) ◽  
pp. 387-424 ◽  
Author(s):  
William H. Lipscomb ◽  
Stephen F. Price ◽  
Matthew J. Hoffman ◽  
Gunter R. Leguy ◽  
Andrew R. Bennett ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Standard Test ◽  
Higher Order ◽  
Third Party ◽  
Momentum Balance ◽  
Test Problems ◽  
Thermomechanical Model ◽  
Extensive Documentation ◽  
Basal Sliding

Abstract. We describe and evaluate version 2.1 of the Community Ice Sheet Model (CISM). CISM is a parallel, 3-D thermomechanical model, written mainly in Fortran, that solves equations for the momentum balance and the thickness and temperature evolution of ice sheets. CISM's velocity solver incorporates a hierarchy of Stokes flow approximations, including shallow-shelf, depth-integrated higher order, and 3-D higher order. CISM also includes a suite of test cases, links to third-party solver libraries, and parameterizations of physical processes such as basal sliding, iceberg calving, and sub-ice-shelf melting. The model has been verified for standard test problems, including the Ice Sheet Model Intercomparison Project for Higher-Order Models (ISMIP-HOM) experiments, and has participated in the initMIP-Greenland initialization experiment. In multimillennial simulations with modern climate forcing on a 4 km grid, CISM reaches a steady state that is broadly consistent with observed flow patterns of the Greenland ice sheet. CISM has been integrated into version 2.0 of the Community Earth System Model, where it is being used for Greenland simulations under past, present, and future climates. The code is open-source with extensive documentation and remains under active development.

Greenland land-terminating glaciers velocity trends during the last two decades

2021 ◽  
Author(s):  
Paul Halas ◽  
Jeremie Mouginot ◽  
Basile de Fleurian ◽  
Petra Langebroek
Keyword(s):  
Water Pressure ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Surface Melting ◽  
Limited Area ◽  
Ice Dynamics ◽  
Basal Sliding ◽  
Surface Melt ◽  
Ice Sheet Dynamics ◽  
The Impact

<div> <p>Ice losses from the Greenland Ice Sheet have been increasing in the last two decades, leading to a larger contribution to the global sea level rise. Roughly 40% of the contribution comes from ice-sheet dynamics, mainly regulated by basal sliding. The sliding component of glaciers has been observed to be strongly related to surface melting, as water can eventually reach the bed and impact the subglacial water pressure, affecting the basal sliding.  </p> </div><div> <p>The link between ice velocities and surface melt on multi-annual time scale is still not totally understood even though it is of major importance with expected increasing surface melting. Several studies showed some correlation between an increase in surface melt and a slowdown in velocities, but there is no consensus on those trends. Moreover those investigations only presented results in a limited area over Southwest Greenland.  </p> </div><div> <p>Here we present the ice motion over many land-terminating glaciers on the Greenland Ice Sheet for the period 2000 - 2020. This type of glacier is ideal for studying processes at the interface between the bed and the ice since they are exempted from interactions with the sea while still being relevant for all glaciers since they share the same basal friction laws. The velocity data was obtained using optical Landsat 7 & 8 imagery and feature-tracking algorithm. We attached importance keeping the starting date of our image pairs similar, and avoided stacking pairs starting before and after melt seasons, resulting in multiple velocity products for each year.  </p> </div><div> <p>Our results show similar velocity trends for previously studied areas with a slowdown until 2012 followed by an acceleration. This trend however does not seem to be observed on the whole ice sheet and is probably specific to this region’s climate forcing. </p> </div><div> <p>Moreover comparison between ice velocities from different parts of Greenland allows us to observe the impact of different climatic trends on ice dynamics.</p> </div>

Greenland ice sheet hydrology

2013 ◽  
Vol 38 (1) ◽  
pp. 19-54 ◽  
Author(s):  
Vena W. Chu
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Field Studies ◽  
Ice Dynamics ◽  
Surface Water Hydrology ◽  
Basal Sliding ◽  
Hydrologic System ◽  
Global Sea Level

Understanding Greenland ice sheet (GrIS) hydrology is essential for evaluating response of ice dynamics to a warming climate and future contributions to global sea level rise. Recently observed increases in temperature and melt extent over the GrIS have prompted numerous remote sensing, modeling, and field studies gauging the response of the ice sheet and outlet glaciers to increasing meltwater input, providing a quickly growing body of literature describing seasonal and annual development of the GrIS hydrologic system. This system is characterized by supraglacial streams and lakes that drain through moulins, providing an influx of meltwater into englacial and subglacial environments that increases basal sliding speeds of outlet glaciers in the short term. However, englacial and subglacial drainage systems may adjust to efficiently drain increased meltwater without significant changes to ice dynamics over seasonal and annual scales. Both proglacial rivers originating from land-terminating glaciers and subglacial conduits under marine-terminating glaciers represent direct meltwater outputs in the form of fjord sediment plumes, visible in remotely sensed imagery. This review provides the current state of knowledge on GrIS surface water hydrology, following ice sheet surface meltwater production and transport via supra-, en-, sub-, and proglacial processes to final meltwater export to the ocean. With continued efforts targeting both process-level and systems analysis of the hydrologic system, the larger picture of how future changes in Greenland hydrology will affect ice sheet glacier dynamics and ultimately global sea level rise can be advanced.

scholarly journals The effect of the north-east ice stream on the Greenland ice sheet in changing climates

2007 ◽  
Vol 1 (1) ◽  
pp. 41-76 ◽  
Author(s):  
R. Greve ◽  
S. Otsu
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Simulation Code ◽  
North East ◽  
The North ◽  
Ice Stream ◽  
Basal Sliding ◽  
Speed Up ◽  
Fast Flow

Abstract. The north-east Greenland ice stream (NEGIS) was discovered as a large fast-flow feature of the Greenland ice sheet by synthetic aperture radar (SAR) imaginary of the ERS-1 satellite. In this study, the NEGIS is implemented in the dynamic/thermodynamic, large-scale ice-sheet model SICOPOLIS (Simulation Code for POLythermal Ice Sheets). In the first step, we simulate the evolution of the ice sheet on a 10-km grid for the period from 250 ka ago until today, driven by a climatology reconstructed from a combination of present-day observations and GCM results for the past. We assume that the NEGIS area is characterized by enhanced basal sliding compared to the "normal", slowly-flowing areas of the ice sheet, and find that the misfit between simulated and observed ice thicknesses and surface velocities is minimized for a sliding enhancement by the factor three. In the second step, the consequences of the NEGIS, and also of surface-meltwater-induced acceleration of basal sliding, for the possible decay of the Greenland ice sheet in future warming climates are investigated. It is demonstrated that the ice sheet is generally very susceptible to global warming on time-scales of centuries and that surface-meltwater-induced acceleration of basal sliding can speed up the decay significantly, whereas the NEGIS is not likely to dynamically destabilize the ice sheet as a whole.

Modelling the basal hydrology under the Greenland Ice Sheet

2020 ◽  
Author(s):  
Alexander Vanhulle ◽  
Sébastien Le Clec’h ◽  
Philippe Huybrechts
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Grid Cell ◽  
Sensitivity Analyses ◽  
Water Model ◽  
Ice Dynamics ◽  
Continental Scale ◽  
Basal Sliding ◽  
Smoothing Procedure ◽  
Individual Grid

<p>Subglacial hydrology plays an important role in the evolution of ice dynamics. Primarily, it affects basal processes such as basal sliding. Further, subglacial water exiting a calving front incites submarine melt, increasing calving, resulting in a thinning of the interior ice sheet. Knowledge of it is therefore crucial towards the development and improvement of ice sheet models. We implement a model representing the routing of subglacial water below the Greenland ice sheet in either a one, four or eight directional manner. Due to its computational efficiency, the model is suited for coupling with continental scale ice sheet models on very high resolutions (e.g. 150 m).</p><p>Routing depends on the hydraulic potential of individual grid cells which is therefore heavily dependent on accurate estimates of the ice thickness as well as the grid utilized. Sensitivity analyses brought to life that the routing exhibits artefacts resulting in significant flow diversions on high resolutions if the gradients are only considered over the distance of a single grid cell, this is overcome by incorporating a smoothing procedure.</p><p>With the basal water model in place and input of the basal melt rate from the VUB Greenland Ice Sheet Model (GISM) as well as runoff input from the Modèle Athmospherique Régional (MAR), we calculate the inflow of freshwater to several reference fjords for the last thirty years and investigate its temporal and spatial patterns. Jakobshavn Isbrae experiences by far the most freshwater inflow compared to the other reference fjords. Despite limited runoff in the northeast of Greenland, high basal melt rates and a significant catchment area provide the outlets of the Northeast Greenland Ice Stream (NEGIS) with substantial inflow too.</p>

scholarly journals A comparison of Eulerian and Lagrangian methods for dating in numerical ice-sheet models

2003 ◽  
Vol 37 ◽  
pp. 150-158 ◽  
Author(s):  
Oleg Rybak ◽  
Philippe Huybrechts
Keyword(s):  
Large Scale ◽  
Spline Approximation ◽  
Ice Sheet ◽  
Ice Age ◽  
Thermomechanical Model ◽  
Eulerian Approach ◽  
Basal Sliding ◽  
State Present ◽  
The Difference ◽  
Basal Melting

AbstractAccurate dating in ice sheets is required for a correct interpretation of palaeoclimatic records and for incorporation of material characteristics in the flow law which depend on ice age. In this paper, we make a comparison between a Lagrangian and Eulerian approach to the ice advection problem in numerical ice-sheet models. This comparison is first performed for a schematic two-dimensional ice sheet of Nye–Vialov type with a prescribed stationary velocity field. Severalcases are examined which incorporate basal melting, basal sliding and an undulating bed. A further comparison is made with an analytical solution for the ice divide. Both methods are also applied in a thermomechanical model of the Antarctic ice sheet for steady-state present-day conditions. Our main conclusion is that, for similar discretization parameters, the Lagrangian method produces less error than an Eulerian approach using a second-order upwinding finite-difference scheme, though the difference is small (<1%) for the largest part of the model domain. However, problems with the Lagrangian approach are introduced by the dispersion of tracers, necessitating the use of interpolation procedures that are a main source of additional error. It is also shown that a cubic-spline approximation of Lagrangian trajectories improves accuracy, but such a method is computationally hardly applicable in large-scale ice-sheet models.

scholarly journals Simulations of the Greenland ice sheet 100 years into the future with the full Stokes model Elmer/Ice

2012 ◽  
Vol 58 (209) ◽  
pp. 427-440 ◽  
Author(s):  
Hakime Seddik ◽  
Ralf Greve ◽  
Thomas Zwinger ◽  
Fabien Gillet-Chaulet ◽  
Olivier Gagliardini
Keyword(s):  
Global Warming ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Ice Streams ◽  
Simulation Code ◽  
Dynamic Scenario ◽  
The Future ◽  
Basal Sliding

AbstractIt is likely that climate change will have a significant impact on the mass balance of the Greenland ice sheet, contributing to future sea-level rise. Here we present the implementation of the full Stokes model Elmer/Ice for the Greenland ice sheet, which includes a mesh refinement technique in order to resolve fast-flowing ice streams and outlet glaciers. We discuss simulations 100 years into the future, forced by scenarios defined by the SeaRISE (Sea-level Response to Ice Sheet Evolution) community effort. For comparison, the same experiments are also run with the shallow-ice model SICOPOLIS (SImulation COde for POLythermal Ice Sheets). We find that Elmer/Ice is ~43% more sensitive (exhibits a larger loss of ice-sheet volume relative to the control run) than SICOPOLIS for the ice-dynamic scenario (doubled basal sliding), but ~61 % less sensitive for the direct global warming scenario (based on the A1 B moderate-emission scenario for greenhouse gases). The scenario with combined A1B global warming and doubled basal sliding forcing produces a Greenland contribution to sea-level rise of ~15cm for Elmer/Ice and ~12cm for SICOPOLIS over the next 100 years.

scholarly journals Effect of higher-order stress gradients on the centennial mass evolution of the Greenland ice sheet

2012 ◽  
Vol 6 (4) ◽  
pp. 2961-3010
Author(s):  
J. J. Fürst ◽  
H. Goelzer ◽  
P. Huybrechts
Keyword(s):  
Standard Model ◽  
Ice Sheet ◽  
Coupled Model ◽  
Greenland Ice Sheet ◽  
Signal Propagation ◽  
Higher Order ◽  
Force Balance ◽  
Appreciable Effect ◽  
Model Version ◽  
The Standard Model

Abstract. We use a three-dimensional thermo-mechanically coupled model of the Greenland ice sheet to assess the effects of marginal perturbations on volume changes on centennial time scales. The model is designed to allow for five ice dynamic formulations using different approximations to the force balance. The standard model is based on the shallow ice approximation for both ice deformation and basal sliding. A second model version relies on a higher-order Blatter/Pattyn type of core that resolves effects from gradients in longitudinal stresses and transverse horizontal shearing, i.e. membrane-like stresses. Together with three intermediate model versions, these five versions allow for gradually more dynamic feedbacks from membrane stresses. Idealised experiments were conducted on various resolutions to compare the time-dependent response to imposed accelerations at the marine ice front. If such marginal accelerations are to have an appreciable effect on total mass loss on a century time scale, a fast mechanism to transmit such perturbations inland is required. While the forcing is independent of the model version, inclusion of direct horizontal coupling allows the initial speedup to reach several tens of kilometres inland. Within one century, effects from gradients in membrane stress alter the inland signal propagation and transmit additional dynamic thinning to the ice sheet interior. But the centennial overall volume loss differs only by some percents from the standard model as the dominant response is a diffusive inland propagation of geometric changes. In our experiments, the volume response is even attenuated by direct horizontal coupling. The reason is a faster adjustment of the sliding regime by instant stress transmission in models that account for the effect of membrane stresses. Ultimately, horizontal coupling decreases the reaction time to perturbations at the ice sheet margin.

scholarly journals Three positive feedback mechanisms for ice-sheet melting in a warming climate

2011 ◽  
Vol 57 (206) ◽  
pp. 1057-1066 ◽  
Author(s):  
Diandong Ren ◽  
Lance M. Leslie
Keyword(s):  
21St Century ◽  
Positive Feedback ◽  
Climate Models ◽  
Sea Water ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Test Bed ◽  
Feedback Mechanisms ◽  
Warming Climate ◽  
Basal Sliding

AbstractThree positive feedback mechanisms that accelerate ice-sheet melting are assessed in a warming climate, using a numerical ice model driven by atmospheric climate models. The Greenland ice sheet (GrIS) is the modeling test-bed under accelerated melting conditions. The first feedback is the interaction of sea water with ice. It is positive because fresh water melts ice faster than salty water, owing primarily to the reduction in water heat capacity by solutes. It is shown to be limited for the GrIS, which has only a small ocean interface, and the grounding line of some fast glaciers becomes land-terminating during the 21st century. The second positive feedback, strain heating, is positive because it produces further ice heating inside the ice sheet. The third positive feedback, granular basal sliding, applies to all ice sheets and becomes the dominant feedback during the 21st century. A numerical simulation of Jakobshavn Isbræ over the 21st century reveals that all three feedback processes are active for this glacier. Compared with the year 2000 level, annual ice discharge into the ocean could increase by ∼1.4 km3 a−1 (∼5% of the present annual rate) by 2100. Granular basal sliding contributes ∼40% of this increase.

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