scholarly journals On the Formulation of Basal Debris Drag for the Case of Sparse Debris

1988 ◽  
Vol 34 (118) ◽  
pp. 259-264 ◽  
Author(s):  
E.M. Snoemaker
Keyword(s):  
Melting Rate ◽  
Physical Processes ◽  
Rock Friction ◽  
Rock Fragments ◽  
Ice Velocity ◽  
Basal Melting ◽  
The Relationship

AbstractTwo models are presented for the formulation of abrasion and basal drag due to rock–rock friction (debris drag) for the case of sparse debris entrained in the basal layers of a temperate glacier resting on a bedrock bed. The first model is formulated in terms of average basal melting rate, va, and the concentration, C, of basal debris fragments which make intermittent bed contact. The second model is formulated in terms of vn the component of ice velocity normal to the bed flowing around rock fragments contacting the bed, and Cc, the concentration of debris actually in contact with the bed. The relationship between the two models is given for the case of a sinusoidal bed. Generalizations are discussed as well as potentially important physical processes which remain to be investigated.

scholarly journals On the Formulation of Basal Debris Drag for the Case of Sparse Debris

1988 ◽  
Vol 34 (118) ◽  
pp. 259-264 ◽  
Author(s):  
E.M. Snoemaker
Keyword(s):  
Melting Rate ◽  
Physical Processes ◽  
Rock Friction ◽  
Rock Fragments ◽  
Ice Velocity ◽  
Basal Melting ◽  
The Relationship

Abstract Two models are presented for the formulation of abrasion and basal drag due to rock–rock friction (debris drag) for the case of sparse debris entrained in the basal layers of a temperate glacier resting on a bedrock bed. The first model is formulated in terms of average basal melting rate, v a, and the concentration, C, of basal debris fragments which make intermittent bed contact. The second model is formulated in terms of v n the component of ice velocity normal to the bed flowing around rock fragments contacting the bed, and C c, the concentration of debris actually in contact with the bed. The relationship between the two models is given for the case of a sinusoidal bed. Generalizations are discussed as well as potentially important physical processes which remain to be investigated.

scholarly journals Basal melting and freezing under the Amery Ice Shelf, East Antarctica

2010 ◽  
Vol 56 (195) ◽  
pp. 81-90 ◽  
Author(s):  
Jiahong Wen ◽  
Yafeng Wang ◽  
Weili Wang ◽  
K.C. Jezek ◽  
Hongxing Liu ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Melting Rate ◽  
Scientific Basis ◽  
East Antarctica ◽  
Northwestern Part ◽  
Ice Shelf ◽  
Amery Ice Shelf ◽  
Velocity Surface ◽  
Ice Velocity ◽  
Basal Melting

AbstractThe basal melting and freezing rates under the Amery Ice Shelf, East Antarctica, are evaluated, and their spatial distributions mapped. Ice velocity, surface elevation and accumulation rate datasets are employed in the analysis, along with a column-averaged ice density model. Our analysis shows that the total area of basal melting is 34 700 km2, with a total annual melt of 62.5 ± 9.3 Gt and an average melting rate of 1.8 ± 0.3 m a−1. Basal freezing mainly occurs in the northwestern part of the ice shelf, over a total area of 26 100 km2 and with a maximum freezing rate of 2.4 ± 0.4 m a−1. The total marine ice that accretes to the ice-shelf base is estimated to be 16.2 ± 2.4 Gt a−1. Using a redefined grounding line and geometry of the Amery Ice Shelf, we estimate the net melt over the ice-shelf base is about 46.4 ± 6.9 G ta−1, which is higher than previous modeling and oceanographic estimates. Net basal melting accounts for about half of the total ice-shelf mass loss, with the rest being from iceberg discharge. Our basal melting and freezing distribution map provides a scientific basis for quantitative analysis of ice–ocean interaction at the ice-shelf–ocean interface.

scholarly journals Marine ice sheet model performance depends on basal sliding physics and sub-shelf melting

2016 ◽  
Author(s):  
Rupert Michael Gladstone ◽  
Roland Charles Warner ◽  
Benjamin Keith Galton-Fenzi ◽  
Olivier Gagliardini ◽  
Thomas Zwinger ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Model Performance ◽  
Effective Pressure ◽  
Physical Processes ◽  
Ice Shelf ◽  
Grounding Line ◽  
Basal Sliding ◽  
Power Law Function ◽  
Ice Velocity ◽  
Basal Melting

Abstract. Computer models are necessary for understanding and predicting marine ice sheet behaviour. However, there is uncertainty over implementation of physical processes at the ice base, both for grounded and floating glacial ice. Here we implement several sliding relations in a marine ice sheet flowline model accounting for all stress components, and demonstrate that model resolution requirements are strongly dependent on both the choice of basal sliding relation and the spatial distribution of ice shelf basal melting. Sliding relations that reduce the magnitude of the step change in basal drag from grounded ice to floating ice (where basal drag is set to zero) show reduced dependence on resolution compared to a commonly used relation, in which basal drag is purely a power law function of basal ice velocity. Sliding relations in which basal drag goes smoothly to zero as the grounding line is approached from inland (due to a physically motivated incorporation of effective pressure at the bed) provide further reduction to resolution dependence. A similar issue is found with the imposition of basal melt under the floating part of the ice shelf: melt parameterisations that reduce the abruptness of change in basal melting from grounded ice (where basal melt is set to zero) to floating ice provide improved convergence with resolution compared to parameterisations in which high melt occurs adjacent to the grounding line. Thus physical processes, such as sub-glacial outflow (which could cause high melt near the grounding line), would impact on capability to simulate marine ice sheets. For any given marine ice sheet the basal physics, both grounded and floating, governs the feasibility of simulating the system. The combination of a physical dependency of basal drag on effective pressure and low ice shelf basal melt rates near the grounding line mean that some marine ice sheet systems can be reliably simulated at a coarser resolution than currently thought necessary.

scholarly journals The Recent Advance of the Ross Ice Shelf Antarctica

1986 ◽  
Vol 32 (112) ◽  
pp. 464-474 ◽  
Author(s):  
S. S. Jacobs ◽  
D. R. Macayeal ◽  
J. L. Ardai
Keyword(s):  
Large Scale ◽  
Melting Rate ◽  
Spreading Rate ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Ross Ice Shelf ◽  
Front Position ◽  
Iceberg Calving ◽  
Basal Melting ◽  
Available Information

AbstractThe seaward edge of the Ross Ice Shelf advanced northward at a minimum average velocity of 0.8 km a–1 between 1962 and 1985. That advance approximated velocities that have been obtained from glaciological data, indicating little recent wastage by iceberg calving. West of long. 178° E., the ice shelf has attained its most northerly position in the past 145 years, and has not experienced a major calving episode for at least 75 years. Since 1841 the ice-front position has advanced and retreated within a zone from about lat. 77° 10’S. (near long. 171° E.) to lat. 78° 40’ S. (near long. 164° W.). The central ice front is now farthest south but has the highest advance rate. Calving may occur at more frequent intervals in that sector, which also overlies the warmest ocean currents that flow into the sub-ice-shelf cavity. Available information on ice-shelf advance, thickness, spreading rate, and surface accumulation indicates a basal melting rate around 3 m a–1 near the ice front. These data and independent estimates imply that basal melting is nearly as large a factor as iceberg calving in maintaining the ice-shelf mass balance. In recent years, the Ross, Ronne, and Filchner Ice Shelves have contributed few icebergs to the Southern Ocean, while projections from a contemporaneous iceberg census are that circumpolar calving alone may exceed accumulation on the ice sheet. Large-scale ice-shelf calving may have preceded historical sightings of increased numbers of icebergs at sea.

scholarly journals Physical controls on orographic cirrus inhomogeneity

2007 ◽  
Vol 7 (14) ◽  
pp. 3771-3781 ◽  
Author(s):  
J. E. Kay ◽  
M. Baker ◽  
D. Hegg
Keyword(s):  
Vertical Velocity ◽  
Cloud Cover ◽  
Particle Growth ◽  
Physical Processes ◽  
Velocity Fluctuations ◽  
Ice Nuclei ◽  
Weather Model ◽  
Model Cloud ◽  
Homogeneous Freezing ◽  
The Relationship

Abstract. Optical depth distributions (P(σ)) are a useful measure of radiatively important cirrus (Ci) inhomogeneity. Yet, the relationship between P(σ) and underlying cloud physical processes remains unclear. In this study, we investigate the influence of homogeneous and heterogeneous freezing processes, ice particle growth and fallout, and mesoscale vertical velocity fluctuations on P(σ) shape during an orographic Ci event. We evaluate Lagrangian Ci evolution along kinematic trajectories from a mesoscale weather model (MM5) using an adiabatic parcel model with binned ice microphysics. Although the presence of ice nuclei increased model cloud cover, our results highlight the importance of homogeneous freezing and mesoscale vertical velocity variability in controlling Ci P(σ) shape along realistic upper tropospheric trajectories.

scholarly journals Laboratory Simulations Of Glacial Abrasion: Comparison With Theory

1990 ◽  
Vol 36 (124) ◽  
pp. 304-314 ◽  
Author(s):  
Neal R. Iverson
Keyword(s):  
Water Film ◽  
Theoretical Models ◽  
Stress Concentrations ◽  
Creep Theory ◽  
Ice Flow ◽  
Rock Fragments ◽  
Roughness Elements ◽  
Ice Velocity ◽  
Pressure Melting ◽  
Ice Pressure

AbstractGlacial abrasion was simulated in experiments in which a small artificial glacier bed was pushed beneath a fixed ice block under pressure. The experiments provide a means of testing theoretical models of abrasion, particularly those factors that govern the magnitude of stress concentrations beneath abrading rock fragments. In preliminary experiments, vertical ice flow around a sphere mounted on the bed was studied. In subsequent experiments, marble tablets were pushed beneath granitic rock fragments frozen into the base of the ice block. Unlike previous abrasion experiments, the sliding velocity was realistic (25 mm d−1), and ice near the bed was at the pressure-melting temperature. Resultant striations closely resemble those observed on glaciated bedrock.As predicted by Hallet (1979), the component of the ice velocity towards the bed strongly influenced stresses beneath fragments, and classical regelation and creep theory provided an approximate estimate of the downward drag force on fragments. Half of the rock fragments rotated significantly, accounting for 10–50% of their motion relative to the bed and influencing abrasion rates and the shear stress supported along the ice-bed interface. Striation patterns indirectly suggest that fragment rotations were inhibited by increases in ice pressure, which presumably increased the drag on roughness elements on fragment surfaces. This may have resulted from a reduction in the thickness of the water film around fragments, facilitated by leakage of water from the bed.

On the relationship between the planetary radius and the equilibrium temperature for transiting exoplanets

2017 ◽  
Vol 26 (05) ◽  
pp. 1741012 ◽  
Author(s):  
Luigi Mancini
Keyword(s):  
Negative Correlation ◽  
Scaling Laws ◽  
Equilibrium Temperature ◽  
Least Squares Regression ◽  
Physical Processes ◽  
Transiting Planets ◽  
Astrophysical Objects ◽  
Best Fitting ◽  
The Relationship ◽  
Parent Star

Scaling laws have always played an important role in astronomy. They can give a general qualitative overview of common behaviors of many astrophysical objects, helping to understand the occurring physical processes. In the context of exoplanets, we study the possible correlation between (i) the planetary radius and the equilibrium temperature, [Formula: see text], and (ii) the planetary radius and the parent-star metallicity, [Formula: see text]. We considered a sample of transiting planets, for which their mass radius and equilibrium temperature are accurately determined. While we do not see any notable evidence of a correlation between [Formula: see text] and [Fe/H], the existence of a relationship between [Formula: see text] and [Formula: see text] is almost clear. We sub-divided our sample in different groups, based on their mass, and performed a least-squares regression of [Formula: see text] on [Formula: see text] for each sub-sample of planets. We found that the [Formula: see text] relation results very tight for two groups of intermediate-massive gas planets (i.e. for [Formula: see text] in the range between 0.5–1.0[Formula: see text][Formula: see text] and 1.0–1.5[Formula: see text][Formula: see text]) and that the slope of the best-fitting line gradually increases from the group of very massive to those of less massive planets, up to reverse in the Neptunian–Super-Earth regime, which has a negative correlation.

scholarly journals A Theoretical Model of Glacial Abrasion

1979 ◽  
Vol 23 (89) ◽  
pp. 39-50 ◽  
Author(s):  
Hallet Bernard
Keyword(s):  
Theoretical Model ◽  
Contact Force ◽  
Quantitative Model ◽  
Viscous Drag ◽  
Sliding Velocity ◽  
Dominant Contribution ◽  
Ice Flow ◽  
Preliminary Results ◽  
Rock Fragments ◽  
Basal Melting

AbstractPreliminary results of a quantitative model of glacial abrasion are presented. The analysis, which is constructed within a framework of modern glaciological views of processes near to the bed, is aimed at modeling abrasion under a temperate glacier whose basal layers contain only occasional rock fragments. It does not simulate abrasion by debris-rich ice or by subglacial drift. Calculations of abrasion-rates reduce to evaluations of the forces pressing rock fragments against the glacier bed and of the rates at which they are moved along the bed. The estimated viscous drag induced by ice flow toward the bed due to basal melting is generally the dominant contribution to this contact force. Although the analysis shares several important elements with the pioneering study of Boulton ([c1974]), sufficient fundamental differences in the modeling lead to distinctly different conclusions. Several new results are noteworthy: (1) other parameters being equal, abrasion will tend to be fastest where basal melting is most rapid, (2) glacier thickness does not affect abrasion through its influence on basal pressures, and (3) lodgement of rock fragments is only possible if the sliding velocity is very low, equivalent to the rate of basal melting.

scholarly journals Where is the 1-million-year-old ice at Dome A?

2018 ◽  
Vol 12 (5) ◽  
pp. 1651-1663 ◽  
Author(s):  
Liyun Zhao ◽  
John C. Moore ◽  
Bo Sun ◽  
Xueyuan Tang ◽  
Xiaoran Guo
Keyword(s):  
Heat Flux ◽  
Depth Profile ◽  
Ice Core ◽  
Three Dimensional ◽  
Melting Rate ◽  
Dome A ◽  
Geothermal Heat ◽  
Kunlun Station ◽  
Ice Fabrics ◽  
Basal Melting

Abstract. Ice fabric influences the rheology of ice, and hence the age–depth profile at ice core drilling sites. To investigate the age–depth profile to be expected of the ongoing deep ice coring at Kunlun station, Dome A, we use the depth-varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows for the simulation of the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which consequently control the age profile. Constraining modeled age–depth profiles with dated radar isochrones to 2∕3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 ka BP, limits the age of the deep ice at Kunlun to between 649 and 831 ka, a much smaller range than previously inferred. The simple interpretation of the polarimetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mW m−2. A heat flux of 50 mW m−2 is too low to fit the deeper radar layers, and 60 mW m−2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2–2.7 mm a−1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1-million-year-old ice may be found 200 m above the bed, and that there are large regions where even older ice is well above the bedrock within 5–6 km of the Kunlun station.

scholarly journals Documentary and ecosemiotics: Frames and faces in the work of Johan van der Keuken

2016 ◽  
Vol 44 (1/2) ◽  
pp. 186-208
Author(s):  
Hing Tsang
Keyword(s):  
Recent Work ◽  
20Th Century ◽  
Coastal Area ◽  
Western Europe ◽  
Urban Environments ◽  
Human Beings ◽  
Physical Processes ◽  
Natural Habitats ◽  
Late 20Th Century ◽  
The Relationship

This article argues that the work of the late Johan van der Keuken offers a contribution to ecological semiotics, and that it also defines the relationship between the semiotic animal and nature in ways that avoid glottocentricism. Taking from the recent work of Kalevi Kull, Jesper Hoffmeyer, and John Deely amongst others, I will argue that van der Keuken’s documentaries offer a view of ecology that is broader than a study of bio-physical processes that might reduce ecology to a narrow political issue.In order to support this argument, I will be looking at two contrasting films from van der Keuken – Flat Jungle (1978) and Face Value (1991). The first film examines natural habitats within a confined coastal area in Western Europe, while the second film looks at human beings in the different urban environments of late-20th-century Europe. I will then argue that van der Keuken does not collapse the vital distinctions between umwelt and Lebenswelt, yet his films also succeed at reminding us of their constant interdependence.

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