scholarly journals Enthalpy benchmark experiments for numerical ice sheet models

2015 ◽  
Vol 9 (1) ◽  
pp. 217-228 ◽  
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.

scholarly journals Enthalpy benchmark experiments for numerical ice sheet models

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.

scholarly journals Precise altimetric topography in ice-sheet flow studies

1993 ◽  
Vol 17 ◽  
pp. 195-200 ◽  
Author(s):  
F. Remy ◽  
J.F. Minster
Keyword(s):  
Activation Energy ◽  
Flow Direction ◽  
Ice Sheet ◽  
Rheological Parameters ◽  
Least Squares Regression ◽  
Sheet Flow ◽  
Ice Flow ◽  
Flow Models ◽  
Altimetric Data ◽  
Basal Shear

The precision of radar altimetry above an ice sheet can improve glaciological studies such as mass balance surveys or ice-sheet flow models, the first by comparing altimetric data at different times (see this issue), the second by testing or constraining models with data. This paper is a first step towards the latter. From a precise topography deduced by inversion of altimetric data (Remy and others, 1989), we calculate ice-flow direction, balance velocity and basal shear stress. The rheological parameters involved in the relation linking velocity, stress and temperature are then derived by least-squares regression. Ice flow is well represented by setting the Glen parameter,nto 1 ± 0.25 and the activation energy as 70 ± 10 kJ mol−1.

scholarly journals Towards a GIS assessment of numerical ice-sheet model performance using geomorphological data

2007 ◽  
Vol 53 (180) ◽  
pp. 71-83 ◽  
Author(s):  
Jacob Napieralski ◽  
Alun Hubbard ◽  
Yingkui Li ◽  
Jon Harbor ◽  
Arjen P. Stroeven ◽  
...  
Keyword(s):  
Flow Direction ◽  
Ice Sheet ◽  
Model Performance ◽  
Initial Step ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Directions ◽  
The Last Glacial Maximum ◽  
Basal Flow ◽  
The Last Glacial

AbstractA major difficulty in assimilating geomorphological information with ice-sheet models is the lack of a consistent methodology to systematically compare model output and field data. As an initial step in establishing a quantitative comparison methodology, automated proximity and conformity analysis (APCA) and automated flow direction analysis (AFDA) have been developed to assess the level of correspondence between modelled ice extent and ice-marginal features such as end moraines, as well as between modelled basal flow directions and palaeo-flow direction indicators, such as glacial lineations. To illustrate the potential of such an approach, an ensemble suite of 40 numerical simulations of the Fennoscandian ice sheet were compared to end moraines of the Last Glacial Maximum and the Younger Dryas and to glacial lineations in northern Sweden using APCA and AFDA. Model experiments evaluated in this manner were ranked according to level of correspondence. Such an approach holds considerable promise for optimizing the parameter space and coherence of ice-flow models by automated, quantitative assessment of multiple ensemble experiments against a database of geological or glaciological evidence.

scholarly journals Capabilities and performance of Elmer/Ice, a new generation ice-sheet model

2013 ◽  
Vol 6 (1) ◽  
pp. 1689-1741 ◽  
Author(s):  
O. Gagliardini ◽  
T. Zwinger ◽  
F. Gillet-Chaulet ◽  
G. Durand ◽  
L. Favier ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Element Model ◽  
Current Increase ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Problems ◽  
The Status ◽  
And Performance ◽  
New Generation

Abstract. 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 contribution to sea-level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice-flow models, and as a result, a 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. 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 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 ice-sheet model. Here, we summarise almost 10 yr of development performed by different groups. We present the components already included in Elmer/Ice, its numerical performance, selected applications, as well as developments planned for the future.

scholarly journals Laurentide Ice-Flow Patterns: A Historical Review, and Implications of the Dispersal of Belcher Islands Erratics

2007 ◽  
Vol 44 (2) ◽  
pp. 113-136 ◽  
Author(s):  
Victor K. Prest
Keyword(s):  
Ice Sheet ◽  
Historical Review ◽  
Flow Patterns ◽  
The Arctic ◽  
Laurentide Ice Sheet ◽  
Complex Nature ◽  
Hudson Bay ◽  
Ice Flow ◽  
Flow Models ◽  
The North

ABSTRACTThis paper deals with the evolution of ideas concerning the configuration of flow patterns of the great inland ice sheets east of the Cordillera. The interpretations of overall extent of Laurentide ice have changed little in a century (except in the Arctic) but the manner of growth, centres of outflow, and ice-flow patterns, remain somewhat controversial. Present geological data however, clearly favour the notion of multiple centres of ice flow. The first map of the extent of the North American ice cover was published in 1881. A multi-domed concept of the ice sheet was illustrated in an 1894 sketch-map of radial flow from dispersal areas east and west of Hudson Bay. The first large format glacial map of North America was published in 1913. The binary concept of the ice sheet was in vogue until 1943 when a single centre in Hudson Bay was proposed, based on the westward growth of ice from Labrador/Québec. This Hudson dome concept persisted but was not illustrated until 1977. By this time it was evident from dispersal studies that the single dome concept was not viable. Dispersal studies clearly indicate long-continued westward ice flow from Québec into and across southern Hudson Bay, as well as eastward flow from Keewatin into the northern part of the bay. Computer-type modelling of the Laurentide ice sheet(s) further indicates their complex nature. The distribution of two indicator erratics from the Proterozoicage Belcher Island Fold Belt Group help constrain ice flow models. These erratics have been dispersed widely to the west, southwest and south by the Labrador Sector of more than one Laurentide ice sheet. They are abundant across the Paleozoic terrain of the Hudson-James Bay lowland, but decrease in abundance across the adjoining Archean upland. Similar erratics are common in northern Manitoba in the zone of confluence between Labrador and Keewatin Sector ice. Scattered occurences across the Prairies occur within the realm of south-flowing Keewatin ice. As these erratics are not known, and presumably not present, in Keewatin, they indicate redirection and deposition by Keewatin ice following one or more older advances of Labrador ice. The distribution of indicator erratics thus test our concepts of ice sheet growth.

scholarly journals Using ice-flow models to evaluate potential sites of million year-old ice in Antarctica

2013 ◽  
Vol 9 (3) ◽  
pp. 2859-2887 ◽  
Author(s):  
B. Van Liefferinge ◽  
F. Pattyn
Keyword(s):  
Ice Sheet ◽  
Geothermal Heat ◽  
Ice Flow ◽  
Flow Models ◽  
Drill Site ◽  
Slow Moving ◽  
Basal Melting ◽  
The Antarctic ◽  
Suitable Potential

Abstract. Finding suitable potential sites for an undisturbed record of million-year old ice in Antarctica requires a slow-moving ice sheet (preferably an ice divide) and basal conditions that are not disturbed by large topographic variations. Furthermore, ice should be thick and cold basal conditions should prevail, since basal melting would destroy the bottom layers. However, thick ice (needed to resolve the signal at sufficient high resolution) increases basal temperatures, which is a conflicting condition in view of finding a suitable drill site. In addition, slow moving areas in the center of ice sheets are also low-accumulation areas, and low accumulation reduces potential cooling of the ice through vertical advection. While boundary conditions such as ice thickness and accumulation rates are relatively well constraint, the major uncertainty in determining basal conditions resides in the geothermal heat flow (GHF) underneath the ice sheet. We explore uncertainties in existing GHF datasets and their effect on basal temperatures of the Antarctic ice sheet and propose an updated method based on Pattyn (2010) to improve existing GHF datasets in agreement with known basal temperatures and their gradients to reduce this uncertainty. Both complementary methods lead to a better comprehension of basal temperature sensitivity and a characterization of potential ice coring sites within these uncertainties.

scholarly journals Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation

2014 ◽  
Vol 60 (222) ◽  
pp. 647-660 ◽  
Author(s):  
Claudia Ryser ◽  
Martin P. Lüthi ◽  
Lauren C. Andrews ◽  
Matthew J. Hoffman ◽  
Ginny A. Catania ◽  
...  
Keyword(s):  
Dynamical Behavior ◽  
Ice Sheet ◽  
Stress Transfer ◽  
Greenland Ice Sheet ◽  
Good Choice ◽  
Surface Velocity ◽  
Ice Streams ◽  
Ice Flow ◽  
Flow Models ◽  
Dependent Flow

AbstractIce deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.

Antarctic blue ice areas - towards extracting palaeoclimate information

2010 ◽  
Vol 22 (2) ◽  
pp. 99-115 ◽  
Author(s):  
Anna Sinisalo ◽  
John C. Moore
Keyword(s):  
Ice Sheets ◽  
Ice Sheet ◽  
Thermal Transition ◽  
Gas Composition ◽  
Accumulation Rates ◽  
Ice Flow ◽  
Flow Models ◽  
Flow Modelling ◽  
Substantial Progress ◽  
The Last Glacial

AbstractWe review the current scientific knowledge about Antarctic Blue Ice Areas (BIAs) with emphasis on their application for palaeoclimate studies. Substantial progress has been made since the review by Bintanja (1999), in particular dating the archive of ancient ice found on the surface of BIAs has progressed with advances in 14C measurements, tephrachronology, and geomorphological evidence giving better constraints to more sophisticated ice flow models. Flow modelling also provides information about past changes in ice flow velocities, accumulation rates and ice sheet elevation. The availability of gas composition in vertical cores from BIAs allows matching to well-dated global records of greenhouse gas variability over the last glacial-interglacial cycle and longer. It is clear from the limited number of studies to date that BIAs from different regions have quite different histories of formation and preservation, and that they are intimately linked to the response of their surrounding ice sheets to climate variability on glacial-interglacial time-scales. Looking to the future, climate records from BIAs are expected to provide information on variations in Southern Ocean processes as well as ice sheet evolution within the East Antarctic ice sheet at the thermal transition from cold based to warm based ice.

scholarly journals Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM

2020 ◽  
Author(s):  
Martin Rückamp ◽  
Heiko Goelzer ◽  
Angelika Humbert
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Higher Order ◽  
Initial State ◽  
Ice Flow ◽  
Outlet Glacier ◽  
Flow Models ◽  
High Emission

Abstract. Projections of the contribution of the Greenland ice sheet to future sea-level rise include uncertainties primarily due to the imposed climate forcing and the initial state of the ice sheet model. Several state-of-the-art ice flow models are currently being employed on various grid resolutions to estimate future mass changes in the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Here we investigate the sensitivity to grid resolution on centennial sea-level contributions from the Greenland ice sheet and study the mechanism at play. To this end, we employ the finite-element higher-order ice flow model ISSM and conduct experiments with four different horizontal resolutions, namely 4, 2, 1 and 0.75 km. We run the simulation based on the ISMIP6 core GCM MIROC5 under the high emission scenario RCP8.5 and consider both atmospheric and oceanic forcing in full and separate scenarios. Under the full scenarios, finer simulations unveil up to ~5 % more sea-level rise compared to the coarser resolution. The sensitivity depends on the magnitude of outlet glacier retreat, which is implemented as a series of retreat masks following the ISMIP6 protocol. Without imposed retreat under atmosphere-only forcing, the resolution dependency exhibits an opposite behaviour with about ~ 5 % more sea-level contribution in the coarser resolution. The sea-level contribution indicates a converging behaviour

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