Science.gov

Sample records for ice flow patterns

  1. Flow-pattern evolution of the last British Ice Sheet

    NASA Astrophysics Data System (ADS)

    Hughes, Anna L. C.; Clark, Chris D.; Jordan, Colm J.

    2014-04-01

    We present a 10-stage reconstruction of the evolution in ice-flow patterns of the last British Ice Sheet from build-up to demise derived from geomorphological evidence. 100 flowsets identified in the subglacial bedform record (drumlins, mega-scale glacial lineations, and ribbed moraine) are combined with ancillary evidence (erratic-transport paths, absolute dates and a semi-independently reconstructed retreat pattern) to define flow patterns, ice divides and ice-sheet margins during build-up, maximum glaciation and retreat. Overprinting and cross-cutting of landform assemblages are used to define the relative chronology of flow patterns and a tentative absolute chronology is presented based on a collation of available dates for ice advance and retreat. The ice-flow configuration of the last British Ice Sheet was not static. Some ice divides were remarkably stable, persisting through multiple stages of the ice-sheet evolution, whereas others were transient features existing for a short time and/or shifting in position 10s km. The 10 reconstructed stages of ice-sheet geometry capture two main modes of operation; first as an integrated ice sheet with a broadly N-S orientated ice divide, and second as a multi-domed ice sheet orientated parallel with the shelf edge. A thick integrated ice sheet developed as ice expanded out of source areas in Scotland to envelop southerly ice caps in northern England and Wales, and connect with the Irish Ice Sheet to the west and the Scandinavian Ice Sheet across the North Sea. Following break-up of ice over the North Sea, ice streaming probably drove mass loss and ice-sheet thinning to create a more complex divide structure, where ice-flow patterns were largely controlled by the form of the underlying topography. Ice surface lowering occurred before separation of, and retreat to, multiple ice centres centred over high ground. We consider this 10-stage reconstruction of the evolution in ice-sheet configuration to be the simplest palaeo

  2. Amazonian mid- to high-latitude glaciation on Mars: Supply-limited ice sources, ice accumulation patterns, and concentric crater fill glacial flow and ice sequestration

    NASA Astrophysics Data System (ADS)

    Fastook, James L.; Head, James W.

    2014-02-01

    Crater deposit thicknesses (~50 m) cannot fill the craters in a time period compatible with the interpreted formation times of the Pedestal Crater mantled ice layers. We use a representative obliquity solution to drive an ice flow model and show that a cyclical pattern of multiply recurring layers can both fill the craters with a significant volume of ice, as well as transport debris from the crater walls out into the central regions of the craters. The cyclical pattern of waxing and waning mantling layers results in a rippled pattern of surface debris extending out into the crater interiors that would manifest itself as an observable concentric pattern, comparable in appearance to concentric crater fill. In this scenario, the formation of mantling sublimation till layers seals the accumulating ice and sequesters it from significant temperature variations at diurnal, annual and spin-axis/orbital cycle time scales, to produce ancient ice records preserved today below CCF crater floors. Lack of meltwater features associated with concentric crater fill provides evidence that the Late Amazonian climate did not exceed the melting temperature in the mid- to high-latitudes for any significant period of time. Continued sequestration of ice with time in CCF and related deposits (lobate debris aprons and lineated valley fill) further reduces the already supply-limited polar ice sources, suggesting that there has been a declining reservoir of available ice with each ensuing glacial period. Together, these deposits represent a candidate library of climate chemistry and global change dating from the Late Amazonian, and a non-polar water resource for future exploration.

  3. Subglacial conditions and ice-flow patterns reconstructed from petrographic composition

    NASA Astrophysics Data System (ADS)

    Lipka, Ewelina; Szuman, Izabela

    2010-05-01

    Usually the petrographic composition of sediments give a basis to distinguish sediments horizons and correlate them. In this study clasts petrography contributes to reconstruction of subglacial conditions as well. Together with till fabric analysis and geomorphological facts it can also give a valuable evidence for ice-flow patterns. The study concerns the Great Poland region, located in central-western Poland. The research area extnents are 53.149 °N and 51.849 °N paralells and 15.899 °E and 18.249 °E meridians. The area lies within the range of the Last Glacial Maximum phase (in Poland known as the Leszno Phase) and the Poznan Phase, which is the succeeding stage of the Weichselian Ice Sheet in Poland. The purpose of the study was twofold. Firstly, the authors aimed at revealing and reconstructing the vertical diversity of subglacial dynamics. Secondly it was intended to distinguish lower-scale flowline patterns within the major ice streams as well. A set of data was acquired from subglacial tills deposited by an active ice sheet sole (deformation and lodgement till). The data set included results of: lithofacies analysis results, till fabric measurements (a-axes of at least 30 elongated clasts), clasts-compositional data derived from 5-10 mm gravels and grain-size distribution obtained with wet and dry (mechanical) sieving techniques. Changes in the petrographic composition of gravels were investigated in two ways. At first, in parallel profiles, to detect a spatial tendency in the petrographic composition. The latter way concerned vertical profiles within subglacial till horizons with the purpose of revealing some trends induced by vertical changes of subglacial conditions. Subsequently all the textural features were associated with geomorphic traces, demonstrated by subglacial channels and other glacial lineations, obtained from Digital Elevation Model, in order to distinguish ice-flow patterns. The clasts petrography analysed in vertical profiles revealed

  4. Reorganization of ice sheet flow patterns in Arctic Canada and the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Refsnider, Kurt A.; Miller, Gifford H.

    2010-07-01

    Evidence for the evolution of Laurentide Ice Sheet (LIS) basal thermal regime patterns during successive glaciations is poorly preserved in the geologic record. Here we explore a new approach to constrain the distribution of cold-based ice across central Baffin Island in the eastern Canadian Arctic over many glacial-interglacial cycles by combining till geochemistry and cosmogenic radionuclide (CRN) data. Parts of the landscaped with geomorphic evidence for limited glacial erosion are covered by till characterized by high chemical index of alteration (CIA) values and CRN concentrations requiring complicated burial-exposure histories. Till from regions scoured by glacial erosion have CIA values indistinguishable from local bedrock and CRN concentrations that can be explained by simple exposure following deglaciation. CRN modeling results based on these constraints suggest that the weathered tills were deposited by 1.9 to 1.2 Ma, and by that time the fiorded Baffin Island coastline must have developed close to its modern configuration as piracy of ice flow by the most efficient fiord systems resulted in a major shift in the basal thermal regime across the northeastern LIS. The resultant concentration of ice flow in fewer outlet systems may help explain the cause of the mid-Pleistocene transition from 41- to 100-kyr glacial cycles.

  5. Greenland Ice Flow

    NASA Video Gallery

    Greenland looks like a big pile of snow seen from space using a regular camera. But satellite radar interferometry helps us detect the motion of ice beneath the snow. Ice starts flowing from the fl...

  6. Influence of ice sheet bed morphology on spatial and seasonal patterns of ice flow in Greenland: preliminary results from an automated method for interpreting high resolution ice velocity data derived from Landsat imagery.

    NASA Astrophysics Data System (ADS)

    Jones, Andrew H.; Swift, Darrel A.; Livingstone, Stephen J.

    2016-04-01

    Ice sheet bed morphology affects ice flow rates and patterns by topographically directing and resisting ice flow and by modulating rates of basal sliding. Notably, reverse bedslopes are anticipated to modulate basal sliding rates and mechanisms through their control on subglacial drainage system morphology and efficiency. In ice sheet contexts, understanding of the significance of these controls, their relative importance and ubiquity, remains weak. We aim to use contemporary remote sensing data products that provide high spatial and temporal resolution ice velocity and bed data for the Greenland ice sheet to attempt a comprehensive and systematic analysis of spatial and seasonal variation in flow behaviour and its links to bed morphology. Here we present an automated method for high resolution 4-dimensional analysis of a large archive dataset (Rosenau et al, 2015) of Landsat-derived ice velocity that enables the extraction of velocity data along a large number of longitudinal flowlines for individual glacier catchments and the analysis of along-flow velocity patterns. Analysis can be undertaken on individual flowlines, or adjacent flowlines can be custom aggregated both spatially and temporarily to investigate factors such as intra-annual or inter-annual seasonal patterns. We present initial analyses of seasonal velocity changes at a sample of glacier catchments and their relationship to glacier bed characteristics.

  7. Ice Flow in the North East Greenland Ice Stream

    NASA Technical Reports Server (NTRS)

    Joughin, Ian; Kwok, Ron; Fahnestock, M.; MacAyeal, Doug

    1999-01-01

    Early observations with ERS-1 SAR image data revealed a large ice stream in North East Greenland (Fahnestock 1993). The ice stream has a number of the characteristics of the more closely studied ice streams in Antarctica, including its large size and gross geometry. The onset of rapid flow close to the ice divide and the evolution of its flow pattern, however, make this ice stream unique. These features can be seen in the balance velocities for the ice stream (Joughin 1997) and its outlets. The ice stream is identifiable for more than 700 km, making it much longer than any other flow feature in Greenland. Our research goals are to gain a greater understanding of the ice flow in the northeast Greenland ice stream and its outlet glaciers in order to assess their impact on the past, present, and future mass balance of the ice sheet. We will accomplish these goals using a combination of remotely sensed data and ice sheet models. We are using satellite radar interferometry data to produce a complete maps of velocity and topography over the entire ice stream. We are in the process of developing methods to use these data in conjunction with existing ice sheet models similar to those that have been used to improve understanding of the mechanics of flow in Antarctic ice streams.

  8. Revealing the early ice flow patterns with historical Declassified Intelligence Satellite Photographs back to 1960s

    NASA Astrophysics Data System (ADS)

    Wang, Shujie; Liu, Hongxing; Yu, Bailang; Zhou, Guoqing; Cheng, Xiao

    2016-06-01

    The reconnaissance ARGON satellites collected the earliest images of Antarctica from space dating back to the 1960s, providing valuable historical baseline information for studying polar ice sheets. Those photographs are underutilized for ice motion mapping, due to lack of sufficient ground controls for image orthorectification. In this study, we orthorectified the ARGON photographs by fully exploiting the metric qualities of WorldView satellite images: very high spatial resolution and precise geolocation. Through a case study over Larsen Ice Shelf, we demonstrated that the camera model with bundle block adjustment can achieve geolocation accuracy of better than the nominal resolution (140 m) for orthorectifying ARGON images, with WorldView imagery as ground control source. This allowed us to extend the ice velocity records of Larsen Ice Shelf back into 1960s~1970s for the first time. The retrospective analysis revealed that acceleration of the collapsed Larsen B occurred much earlier than previously thought.

  9. Glaciation in the Late Noachian Icy Highlands: Ice accumulation, distribution, flow rates, basal melting, and top-down melting rates and patterns

    NASA Astrophysics Data System (ADS)

    Fastook, James L.; Head, James W.

    2015-02-01

    pattern was disorganized and followed topography, with no radial flow pattern typical of an equilibrium ice sheet. Virtually the entire ice sheet is predicted to be cold-based, and thus the range of wet-based features typically associated with temperate glaciers (e.g., drumlins, eskers, etc.) is not predicted to occur. Wet-based conditions are predicted only locally in the thickest ice (on the floors of the deepest craters), where limited subglacial lakes may have formed. These LNIH regional ice-sheets provide a huge reservoir of potential meltwater as a source for forming the observed fluvial and lacustrine features and deposits. Top-down melting scenarios applied to our LNIH ice sheet model predict that periods of punctuated warming could lead to elevated temperatures sufficient to melt enough snow and ice to readily account for the observed fluvial and lacustrine features and deposits. Our model indicates that such melting should take place preferentially at the margins of the ice sheets, a prediction that can be tested with further analyses.

  10. Seasonal-scale abrasion and quarrying patterns from a two-dimensional ice-flow model coupled to distributed and channelized subglacial drainage

    NASA Astrophysics Data System (ADS)

    Beaud, Flavien; Flowers, Gwenn E.; Pimentel, Sam

    2014-08-01

    Field data and numerical modeling show that glaciations have the potential either to enhance relief or to dampen topography. We aim to model the effect of the subglacial hydraulic system on spatiotemporal patterns of glacial erosion by abrasion and quarrying on time scales commensurate with drainage system fluctuations (e.g., seasonal to annual). We use a numerical model that incorporates a dual-morphology subglacial drainage system coupled to a higher-order ice-flow model and process-specific erosion laws. The subglacial drainage system allows for a dynamic transition between two morphologies: the distributed system, characterized by an increase in basal water pressure with discharge, and the channelized system, which exhibits a decrease in equilibrium water pressure with increasing discharge. We apply the model to a simple synthetic glacier geometry, drive it with prescribed meltwater input variations, and compute sliding and erosion rates over a seasonal cycle. When both distributed and channelized systems are included, abrasion and sliding maxima migrate ~ 20% up-glacier compared to simulations with distributed drainage only. Power-law sliding generally yields to a broader response of abrasion to water pressure changes along the flowline compared to Coulomb-friction sliding. Multi-day variations in meltwater input elicit a stronger abrasion response than either diurnal- or seasonal variations alone for the same total input volume. An increase in water input volume leads to increased abrasion. We find that ice thickness commensurate with ice sheet outlet glaciers can hinder the up-glacier migration of abrasion. Quarrying patterns computed with a recently published law differ markedly from calculated abrasion patterns, with effective pressure being a stronger determinant than sliding speeds of quarrying rates. These variations in calculated patterns of instantaneous erosion as a function of hydrology-, sliding-, and erosion-model formulation, as well as model

  11. Spatial complexity of ice flow across the Antarctic Ice Sheet

    NASA Astrophysics Data System (ADS)

    Ng, Felix S. L.

    2015-11-01

    Fast-flowing ice streams carry ice from the interior of the Antarctic Ice Sheet towards the coast. Understanding how ice-stream tributaries operate and how networks of them evolve is essential for developing reliable models of the ice sheet’s response to climate change. A particular challenge is to unravel the spatial complexity of flow within and across tributary networks. Here I define a measure of planimetric flow convergence, which can be calculated from satellite measurements of the ice sheet’s surface velocity, to explore this complexity. The convergence map of Antarctica clarifies how tributaries draw ice from its interior. The map also reveals curvilinear zones of convergence along lateral shear margins of streaming, and abundant ripples associated with nonlinear ice rheology and changes in bed topography and friction. Convergence on ice-stream tributaries and their feeding zones is uneven and interspersed with divergence. For individual drainage basins, as well as the ice sheet as a whole, fast flow cannot converge or diverge as much as slow flow. I therefore deduce that flow in the ice-stream networks is subject to mechanical regulation that limits flow-orthonormal strain rates. These findings provide targets for ice-sheet simulations and motivate more research into the origin and dynamics of tributarization.

  12. Ice-Confined Basaltic Lava Flows: Review and Discussion

    NASA Astrophysics Data System (ADS)

    Skilling, I.; Edwards, B. R.

    2012-12-01

    Basaltic lavas that are interpreted as having been emplaced in subglacial or ice-confined subaerial settings are known from several localities in Iceland, British Columbia and Antarctica. At least four different types of observations have been used to date to identify emplacement of basaltic lavas in an ice-rich environment: i) gross flow morphology, ii) surface structures, iii) evidence for ice-confined water during emplacement, and iv) lava fracture patterns. Five types of ice-confined lava are identified: sheets, lobes, mounds, linear ridges and sinuous ridges. While the appearance of lavas is controlled by the same factors as in the submarine environment, such as the geometry and configuration of vents and lava tubes, flow rheology and rates, and underlying topography, the presence of ice can lead to distinct features that are specific to the ice-confined setting. Other types have very similar or identical equivalents in submarine environment, albeit with some oversteepening/ice contact surfaces. Ice-confined lavas can form as (1) subaerial or subaqueous lavas emplaced against ice open to the air, (2) subaqueous lavas emplaced into pre-existing sub-ice drainage networks, and (3) subaqueous lavas emplaced into ponded water beneath ice. Their surface structures reflect the relationship between rates of lava flow emplacement at the site of ice-water-lava contact, ice melting and water drainage. Variations in local lava flow rates could be due to lava cooling, constriction, inflation, tube development, ice melting, ice collapse, lava collapse, changes in eruption rate etc. Episodes of higher lava flow rate would favour direct ice contact and plastic compression against the ice, generating oversteepened and/or overthickened chilled margins, cavities in the lava formed by melting of enveloped ice blocks (cryolith cavities) and structures such as flattened pillows and lava clasts embedded into the glassy margins. Melting back of the confining ice generates space to

  13. Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record

    NASA Astrophysics Data System (ADS)

    Greenwood, Sarah L.; Clark, Chris D.

    2009-12-01

    The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one 'flowsets' comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset cross-cutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative 'age-stack' of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset - its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, 'smudged' landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories

  14. The calculation of flow over iced airfoils

    NASA Technical Reports Server (NTRS)

    Cebeci, Tuncer

    1988-01-01

    Progress toward the development of a method for predicting the flowfield of an iced airfoil is described and shown to offer the prospect of a priori calculations of the effects of ice accretion and roughness on airfoil performance. The approach is based on interaction of inviscid flow solutions obtained by a panel method and improved upon by a finite-difference boundary-layer method which, operating in an inverse mode, incorporates viscous effects including those associated with separated flows. Results are presented for smooth, rough and iced airfoils as a function of angle of attack. Those for smooth and rough airfoils confirm the accuracy of the method and its applicability to surfaces with roughness similar to that associated with insect deposition and some forms of ice. Two procedures have been developed to deal with large ice accretion and their performance is examined and shown to be appropriate to the engineering requirements.

  15. Ice patterns and hydrothermal plumes, Lake Baikal, Russia - Insights from Space Shuttle hand-held photography

    NASA Technical Reports Server (NTRS)

    Evans, Cynthia A.; Helfert, Michael R.; Helms, David R.

    1992-01-01

    Earth photography from the Space Shuttle is used to examine the ice cover on Lake Baikal and correlate the patterns of weakened and melting ice with known hydrothermal areas in the Siberian lake. Particular zones of melted and broken ice may be surface expressions of elevated heat flow in Lake Baikal. The possibility is explored that hydrothermal vents can introduce local convective upwelling and disrupt a stable water column to the extent that the melt zones which are observed in the lake's ice cover are produced. A heat flow map and photographs of the lake are overlaid to compare specific areas of thinned or broken ice with the hot spots. The regions of known hydrothermal activity and high heat flow correlate extremely well with circular regions of thinned ice, and zones of broken and recrystallized ice. Local and regional climate data and other sources of warm water, such as river inlets, are considered.

  16. Distinct Seasonal Velocity Patterns Based on Ice-Sheet-Wide Analysis of Greenland Outlet Glaciers

    NASA Astrophysics Data System (ADS)

    Moon, T. A.; Joughin, I. R.; Smith, B. E.; van den Broeke, M. R.; Usher, M.

    2014-12-01

    Mass loss from the Greenland Ice Sheet increased significantly over the last several decades and current mass losses of 260-380 Gt ice/yr contribute 0.7-1.1 mm/yr to global sea-level rise. Greenland mass loss includes ice discharge via marine-terminating outlet glaciers and surface meltwater runoff, the former now making up a third to a half of total ice loss. The magnitude of ice discharge depends in part on ice-flow speed, which has broadly increased since 2000 but varies locally, regionally, and from year to year. Research on a limited set of Greenland glaciers also shows that speeds vary seasonally. However, for much of the west, northwest, and southeast coasts where ice loss is increasing most rapidly, there are few or no records of seasonal velocity variation. Ice velocity is influenced by several key components of the ice-sheet-ocean-climate system: subglacial environment, surface melt and runoff, and ice-ocean interaction at the ice-front (terminus). Thus, knowledge of seasonal velocity patterns is important for predicting annual ice discharge, understanding the effects of increased surface melt on total mass loss, and establishing how ice-flow responds to other climatic changes. We developed 5-year records of seasonal velocity measurements for 55 glaciers around the ice-sheet margin. Among glaciers with significant speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position, with seasonal summer speedup sustained through fall. The other two patterns appear to be meltwater controlled and indicate regional differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. These differences in dominant velocity control mechanisms reveal likely spatiotemporal variations in the dynamic response of the ice sheet to climate change.

  17. Flow Dynamics and Stability of the NE Greenland Ice Stream from Active Seismics and Radar

    NASA Astrophysics Data System (ADS)

    Riverman, K. L.; Alley, R. B.; Anandakrishnan, S.; Christianson, K. A.; Peters, L. E.; Muto, A.

    2015-12-01

    We find that dilatant till facilitates rapid ice flow in central Greenland, and regions of dryer till limit the expansion of ice flow. The Northeast Greenland Ice Stream (NEGIS) is the largest ice stream in Greenland, draining 8.4% of the ice sheet's area. Fast ice flow initiates near the ice sheet summit in a region of high geothermal heat flow and extends some 700km downstream to three outlet glaciers along the NE Coast. The flow pattern and stability mechanism of this ice stream are unique to others in Greenland and Antarctica, and merit further study to ascertain the sensitivity of this ice stream to future climate change. In this study, we present the results of the first-ever ground-based geophysical survey of the initiation zone of NEGIS. Based on radar and preliminary seismic data, Christianson et al. (2014, EPSL) propose a flow mechanism for the ice stream based on topographically driven hydropotential lows which generate 'sticky' regions of the bed under the ice stream margins. We further test this hypothesis using a 40km reflection seismic survey across both ice stream margins. We find that regions of 'sticky' bed as observed by the radar survey are coincident with regions of the bed with seismic returns indicating drier subglacial sediments. These findings are further supported by five amplitude-verses-offset seismic surveys indicating dilatant till within the ice stream and consolidated sediments within its margins.

  18. Determining the Orientations of Ice Crystals Using Electron Backscatter Patterns

    NASA Astrophysics Data System (ADS)

    Iliescu, D.; Baker, I.; Chang, H.

    2004-05-01

    The presentation will show how electron backscatter diffraction can be employed to determine crystal orientations in ice. The technique involves obtaining and indexing electron back-scatter patterns (EBSPs) from uncoated ice using a scanning electron microscope equipped with a custom-built cold-stage and an Orientation Imaging System. Unlike any of the currently-used methods, the EBSP-based technique has considerably higher angular and spatial resolution and is significantly faster. We also present an orientation image map of a muti-grain region in laboratory-grown ice constructed by automatically indexing the EBSPs using an HKL, Inc Channel 5 Orientation Imaging System and discuss possible applications of the technique to the study of natural ice. Primarily, the focus will be on the characterization of the microstructure of dynamically recrystallized glacier ice whose texture is intrinsically related the flow process. Other applications include obtaining orientation images from frozen water-containing materials, such as clathrate hydrates. This research was supported by Army Research Office grant DAAD 19-03-1-0110 and National Science Foundation grants OPP-9981379 and OPP-0221120.

  19. Flow of Ice near a Large Melt Channel in the Ross Ice Shelf

    NASA Astrophysics Data System (ADS)

    Conway, H.; Hindmarsh, R. C. A.; Koutnik, M. R.; Stevens, C.; Winberry, J. P.

    2014-12-01

    There is increasing evidence for the existence of large channels incised beneath ice shelves in West Antarctica. However, the genesis of these channels is still not clear. Measurements from the floating tongue of Pine Island Glacier show that sub-shelf channels formed by localized melting (Stanton et al., 2013); oceanographic models of flow in sub-ice-shelf cavities are capable of producing sub-shelf channels through non-linear feed-back mechanisms (Gladish et al. 2012; Sergienko, 2013). On the other hand, other evidence suggests that sub-shelf channels can initiate at locations where melt water beneath grounded ice crosses the grounding line (Le Brocq et al. 2013). Here we use ground-based radar to map a channel incised into the base of the Ross Ice Shelf proximal to the grounding zone of Beardmore Glacier, West Antarctica. Results show that in the grounding zone (ice thickness is 1150m), the channel is 100m deep and 0.5 km wide. On the shelf, the channel widens and deepens down stream; 8km down from the grounding line (ice thickness is 600-800 m), the channel is 200m deep and 1 km wide (see Figure); apparently in this case, the channel originates from beneath the grounded ice. Although there is some indication of radar-detected internal stratigraphy dipping toward the channels indicative of meltin, the pattern of the stratigraphy suggests significant accumulated strain (see Figure). Further, vertical strain-rates calculated from repeat measurements using phase-sensitive radar (pRES), show a more complex pattern over melt-channels than is usually assumed for ice shelves. Specifically, 57 of the 69 pRES measurements exhibit a pattern of compression in the upper 75% of the ice column and extension in the lower 25%. This observation is important because such a pattern affects the ratio of surface- to mean-velocity, which is usually assumed to be unity in shelf-mass balance calculations. FIGURE CAPTION: Unmigrated, across-channel radar profile 8km downstream from the

  20. How does ice sheet loading affect ocean flow around Antarctica?

    NASA Astrophysics Data System (ADS)

    Dijkstra, H. A.; Rugenstein, M. A.; Stocchi, P.; von der Heydt, A. S.

    2012-12-01

    Interactions and dynamical feedbacks between ocean circulation, heat and atmospheric moisture transport, ice sheet evolution, and Glacial Isostatic Adjustment (GIA) are overlooked issues in paleoclimatology. Here we will present first results on how ocean flows were possibly affected by the glaciation of Antarctica across the Eocene-Oligocene Transition (~ 34 Ma) through GIA and bathymetry variations. GIA-induced gravitationally self-consistent bathymetry variations are determined by solving the Sea Level Equation (SLE), which describes the time dependent shape of (i) the solid Earth and (ii) the equipotential surface of gravity. Since the ocean circulation equations are defined relative to the equipotential surface of gravity, only bathymetry variations can influence ocean flows, although the sea surface slope will also change through time due to gravitational attraction. We use the Hallberg Isopycnal Model under late Eocene conditions to calculate equilibrium ocean flows in a domain in which the bathymetry evolves under ice loading according to the SLE. The bathymetric effects of the glaciation of Antarctica lead to substantial spatial changes in ocean flows, and close to the coast, the flow even reverses direction. Volume transports through the Drake Passage and Tasman Seaway adjust to the new bathymetry. The results indicate that GIA-induced ocean flow variations alone may have had an impact on sedimentation and erosion patterns, the repositioning of fronts, ocean heat transport and grounding line and ice sheet stability.

  1. Geological control of flow in the Institute and Möller Ice Streams, West Antarctica

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Ross, N.; Corr, H.; Bingham, R. G.; Rippin, D. M.; Le Brocq, A.; Siegert, M. J.

    2012-12-01

    The conditions at the base of an ice sheet influence its flow, and reflect the ongoing interaction between moving ice and the underlying geology. Critical influences on ice flow include subglacial topography, bed lithology, and geothermal heat flux. These factors are influenced either directly by local geology, or by the regional tectonic setting. Geophysical methods have been used in many parts of Antarctica, such as the Siple Coast, to reveal the role subglacial geology plays in influencing ice flow. Until recently, however, the Institute and Möller Ice Streams, which drain ~20% of the West Antarctic Ice Sheet into the Weddell Sea, were only covered by sparse airborne radar (~50 km line spacing), and reconnaissance aeromagnetic data, limiting our understanding of the geological template for this sector of the West Antarctic Ice Sheet. Here we present our geological interpretation of the first integrated aerogeophysical survey over the catchments of the Institute and Möller Ice Streams, which collected ~25,000 km of new aerogeophysical data during the 2010/11 field season. These new airborne radar, magnetic and gravity data reveals both the subglacial topography, and the subglacial geology. Our maps show the fastest flowing coastal part of the Institute Ice Stream crosses a sedimentary basin underlain by thinned continental crust. Further inland two distinct ice flow provinces are recognised: the Pagano Ice Flow Province, which follows the newly identified, ~75 km wide, sinistral strike-slip Pagano Fault Zone at the boundary between East and West Antarctica; and the Ellsworth Ice Flow Province, which is controlled by the Permo-Triassic structural grain of folded Middle Cambrian-Permian meta-sediments, and Jurassic granitic rocks which form significant subglacial highlands. Our new data highlight the importance of understanding subglacial geology when explaining the complex pattern of ice flow observed in the ice sheet interior.

  2. Representation of sharp rifts and faults mechanics in modeling ice shelf flow dynamics: Application to Brunt/Stancomb-Wills Ice Shelf, Antarctica

    NASA Astrophysics Data System (ADS)

    Larour, E.; Khazendar, A.; Borstad, C. P.; Seroussi, H.; Morlighem, M.; Rignot, E.

    2014-09-01

    Ice shelves play a major role in buttressing ice sheet flow into the ocean, hence the importance of accurate numerical modeling of their stress regime. Commonly used ice flow models assume a continuous medium and are therefore complicated by the presence of rupture features (crevasses, rifts, and faults) that significantly affect the overall flow patterns. Here we apply contact mechanics and penalty methods to develop a new ice shelf flow model that captures the impact of rifts and faults on the rheology and stress distribution of ice shelves. The model achieves a best fit solution to satellite observations of ice shelf velocities to infer the following: (1) a spatial distribution of contact and friction points along detected faults and rifts, (2) a more realistic spatial pattern of ice shelf rheology, and (3) a better representation of the stress balance in the immediate vicinity of faults and rifts. Thus, applying the model to the Brunt/Stancomb-Wills Ice Shelf, Antarctica, we quantify the state of friction inside faults and the opening rates of rifts and obtain an ice shelf rheology that remains relatively constant everywhere else on the ice shelf. We further demonstrate that better stress representation has widespread application in examining aspects affecting ice shelf structure and dynamics including the extent of ice mélange in rifts and the change in fracture configurations. All are major applications for better insight into the important question of ice shelf stability.

  3. Holocene accumulation and ice flow near the West Antarctic Ice Sheet Divide ice core site

    NASA Astrophysics Data System (ADS)

    Koutnik, Michelle R.; Fudge, T. J.; Conway, Howard; Waddington, Edwin D.; Neumann, Thomas A.; Cuffey, Kurt M.; Buizert, Christo; Taylor, Kendrick C.

    2016-05-01

    The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 kyr of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 km from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20% lower than modern at 9.2 kyr before present (B.P.), increased by 40% from 9.2 to 2.3 kyr B.P., and decreased by at least 10% over the past 2 kyr B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 km of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.

  4. Experimental investigation of ice slurry flow pressure drop in horizontal tubes

    SciTech Connect

    Grozdek, Marino; Khodabandeh, Rahmatollah; Lundqvist, Per

    2009-01-15

    Pressure drop behaviour of ice slurry based on ethanol-water mixture in circular horizontal tubes has been experimentally investigated. The secondary fluid was prepared by mixing ethyl alcohol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 C). The pressure drop tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 30% depending on test conditions. Results from flow tests reveal much higher pressure drop for higher ice concentrations and higher velocities in comparison to the single phase flow. However for ice concentrations of 15% and higher, certain velocity exists at which ice slurry pressure drop is same or even lower than for single phase flow. It seems that higher ice concentration delay flow pattern transition moment (from laminar to turbulent) toward higher velocities. In addition experimental results for pressure drop were compared to the analytical results, based on Poiseulle and Buckingham-Reiner models for laminar flow, Blasius, Darby and Melson, Dodge and Metzner, Steffe and Tomita for turbulent region and general correlation of Kitanovski which is valid for both flow regimes. For laminar flow and low buoyancy numbers Buckingham-Reiner method gives good agreement with experimental results while for turbulent flow best fit is provided with Dodge-Metzner and Tomita methods. Furthermore, for transport purposes it has been shown that ice mass fraction of 20% offers best ratio of ice slurry transport capability and required pumping power. (author)

  5. Self-stabilzing ice-stream flow in Northeast Greenland

    NASA Astrophysics Data System (ADS)

    Christianson, Knut; Alley, Richard; Peters, Leo; Anandakrishnan, Sridhar; Jacobel, Robert; Riverman, Kiya; Muto, Atsuhiro

    2013-04-01

    We present radio-echo sounding (RES), global positioning system (GPS), and active-source seismic data from the central portion of the Northeast Greenland Ice Stream (NEGIS) showing that the dynamic effects of the streaming flow control ice-stream extent. NEGIS is the sole fast-flowing ice-stream to initiate deep in the interior (~700 km) of the Greenland Ice Sheet (GIS), and was previously shown to widen downglacier from a small region of high geothermal flux near the ice-divide. Our data reveal water-saturated till lubricating the ice-stream, with the ice-stream likely widening toward the coast from flow around basal roughness and other processes. Ice accelerates and thus thins as it flows into the efficiently lubricated NEGIS, producing marginal troughs in surface topography. These marginal troughs, which lack strong control in the basal topography, create steep gradients in the subglacial hydropotential that generate parallel well-lubricated and 'sticky' bands beneath the ice-stream margins. The 'sticky' bands limit ice entrainment across the margin and thus restrict further widening, producing the long, narrow, and relatively stable ice-stream. However, it remains possible that a sufficiently strong perturbation from the coast could thin the central ice-stream enough to remove the marginal troughs, allowing more efficient flow of ice into the stream and thus drawdown of the ice-sheet.

  6. Recent changes in the flow of the Ross Ice Shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Hulbe, Christina L.; Scambos, Ted A.; Lee, Choon-Ki; Bohlander, Jennifer; Haran, Terry

    2013-08-01

    Comparison of surface velocities measured during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973 to 1978) and velocities measured via feature tracking between two Moderate-resolution Imaging Spectroradiometer (MODIS) mosaics (compiled from 2003/4 and 2008/9 images) reveals widespread slowing and minor areas of acceleration in the Ross Ice Shelf (RIS) over the approximately 30 year interval. The largest changes (-13 ma) occur near the Whillans and Mercer Ice Streams grounding line in the southernmost part of the ice shelf. Speed has increased over the interval (up to 5 ma) between the MacAyeal Ice Stream grounding line and the shelf front, and along the eastern shelf front. Changes in ice thickness computed using ICESat laser altimetry are used together with a well-tested model of the ice shelf to investigate underlying causes of change in the flow of the ice shelf over time. The observed transients represent a combination of recent forcings and ongoing response to ice stream discharge variations over the past millennium. While evidence of older events may be present, the modern signal is dominated by shorter time scale events, including the stagnation of Kamb Ice Stream about 160 years ago, recent changes in basal drag on the Whillans Ice Stream ice plain and, perhaps, iceberg calving. Details in embayment geometry, for example the shallow sea floor below Crary Ice Rise, modulate the spatial pattern of ice shelf response to boundary condition perturbations.

  7. Investigations on the origins and maintenance of the Scharffenbergbotnen blue ice area by combined surface wind and ice flow simulations

    NASA Astrophysics Data System (ADS)

    Zwinger, Thomas; Malm, Torsten; Schäfer, Martina; Martín, Carlos; Moore, John C.

    2015-04-01

    Using the turbulent flow modeling capabilities of the Finite Element code Elmer we model the spatial and temporal distributions of wind impact speeds caused by a katabatic wind front on the by nunataks surrounded glacier valley of Scharffenbergbotnen (SBB), Dronning Maud Land, East Antarctica. Comparison of these patterns to the steady state mass balance distribution obtained using a prescribed fabric distribution to solve the prognostic ice flow problem with a the full-stress code Elmer/Ice reveal a significant correspondence over the inner part of the valley and in particular the blue ice area (BIA) where the snow and even multi-year firn is removed by very high winds. This leads us to the conclusion that topographically accelerated winds are the dominant factor determining the mass balance of high elevation BIA's. Based on geomorphological evidence we further reconstruct the surface terrain to resemble the situation at the Late Glacial Maximum (LGM), where the ice inside the valley was ~200 m thicker and the nunataks were smoothed out by the ice cover. The same turbulent flow simulation, utilizing the Virtual Multi-Scale (VMS) method, on this altered terrain reveals that the focusing effect of the present day surface did not exist at the LGM. This supports the finding of ice sample ages and flow model results that the inner BIA at SBB was created as a consequence of the lowering ice surface clearly after LGM.

  8. Ice-flow evolution of the Labrador Sector of the Laurentide Ice Sheet: a review, with new evidence from northern Quebec

    NASA Astrophysics Data System (ADS)

    Veillette, J. J.; Dyke, A. S.; Roy, M.

    1999-07-01

    Outcrops bearing stained, striated facets indicative of north-northeastward moving ice, truncated by unstained, striated facets indicative of various younger flows occur in the Caniapiscau area of north-central Quebec. This is the first report of differential staining of striated facets in the region. We propose that the staining occurred in an ice-free interval of probable interglacial age. This early ice flow probably occurred during ice retreat toward the Quebec highlands. Ice flow and glacial transport data from the southern Hudson Bay and James Bay basins indicate that the next major regional ice flow was toward the northwest and resulted from the expansion of an Early Wisconsinan glacier in the Quebec highlands. The northern part of this flow was diverted northwestward through Hudson Bay, and the southern part southwestward across James Bay, following a progressive counterclockwise rotation of flow. A zone of intersection (ZI) of two major glacier bedform systems, often referred to as the horseshoe-shaped Labrador Ice Divide, represents the head of a large northward convergent ice-flow system that extended to Ungava Bay and beyond. The Ungava flow propagated southward and captured the head of the opposing flow from an outflow centre located east of Caniaspiscau reservoir. We propose that this capture event correlates with the Gold Cove Advance in Ungava Bay and on Baffin Island at about 9900 14C yr BP. It is the largest advance of Quebec-Labrador ice yet proposed for the region. This correlation is based on the relative ice-flow chronology, accommodation of glacial lakes Naskaupi and McLean in the deglaciation sequence, the constraints placed on Last Glacial Maximum (LGM) ice configuration by the postglacial uplift pattern and events in the deep-sea record. Therefore, the Ungava ice-flow pattern is not a relict pre-Wisconsinan glacial landscape as recently proposed.

  9. Satellite imagery of the onset of streaming flow of ice streams C and D, West Antarctica

    USGS Publications Warehouse

    Hodge, S.M.; Doppelhammer, S.K.

    1996-01-01

    Five overlapping Landsat multispectral scanner satellite images of the interior of the West Antarctic ice sheet were enhanced with principal component analysis, high-pass filtering, and linear contrast stretching and merged into a mosaic by aligning surface features in the overlap areas. The mosaic was registered to geodetic coordinates, to an accuracy of about 1 km, using the five scene centers as control points. The onset of streaming flow of two tributaries of ice stream C and one tributary of ice stream D is visible in the mosaic. The onset appears to occur within a relatively short distance, less than the width of the ice stream, typically at a subglacial topographic feature such as a step or ridge. The ice streams extend farther up into the interior than previously mapped. Ice stream D starts about 150 km from the ice divide, at an altitude of about 1500 m, approximately halfway up the convex-upward dome shape of the interior ice sheet. Ice stream D is relatively much longer than ice stream C, possibly because ice stream D is currently active whereas ice stream C is currently inactive. The grounded portion of the West Antarctic ice sheet is perhaps best conceptualized as an ice sheet in which ice streams are embedded over most of its area, with slow moving ice converging into fast moving ice streams in a widely distributed pattern, much like that of streams and rivers in a hydrologic basin. A relic margin appears to parallel most of the south margin of the tributary of ice stream D, separated from the active shear margin by about 10 km or less for a distance of over 200 km. This means there is now evidence for recent changes having occurred in three of the five major ice streams which drain most of West Antarctica (B, C, and D), two of which (B and D) are currently active.

  10. Small-scale modeling of ice flow perturbations induced by sudden ice shelf breakup

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; Zeoli, Antonio; Iandelli, Irene

    2014-08-01

    The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. In this paper, this process is analyzed by means of scaled analogue experiments reproducing the flow of a valley glacier draining an ice sheet grounded above sea level into an ice shelf, and analyzing the dynamic perturbations resulting from ice shelf disintegration and removal of buttressing effect. Models show a significant increase in glacier velocity close to its outlet following ice shelf breakup, a transient effect that does not significantly propagate upstream towards the ice sheet and rapidly decays with time. Basal lubrication and variations in ice thickness do not significantly influence the process that thus leaves the ice sheet almost unaffected by flow perturbations.

  11. The influence of subglacial hydrology on the flow of Kamb Ice Stream, West Antarctica

    NASA Astrophysics Data System (ADS)

    Wel, Narelle; Christoffersen, Poul; Bougamont, Marion

    2013-03-01

    Ice streams on the Siple Coast, West Antarctica, have a complex history of flow because their basal motion is governed by time-varying basal conditions. Although the mechanical interaction between ice and till is well established, very little is known about the potential effect of regionally scaled water transport in a basal water system, which has only recently become apparent. To investigate the combined effect of hydrological and mechanical processes, we developed the Hydrology, Ice and Till model, in which ice flow is coupled to a Coulomb-plastic till layer and a basal water system consisting of discrete conduits. When the model is applied to Kamb Ice Stream (KIS), results confirm that it is capable of oscillating between fast and stagnant modes of flow. We show that when subglacial conduits are disregarded or do not extend to the grounding line, the oscillatory behavior of the ice stream is governed by the basal thermal regime. When conduits extend to the grounding line, the modelled ice stream oscillation period is increased, peak speeds are reduced, and oscillations may ultimately cease if the volume of water supplied is sufficiently high. Three different hydrological states characterize the behavioral patterns of ice flow and these states are distinguished by conditions at the grounding line. Modelled ice stream velocities were found to oscillate with fast and slow periods typically lasting a few hundred years, although varying according to hydrological activity. Our results indicate that KIS could reactivate this century, given its hydrological setting and ~170 years of stagnation.

  12. Seasonal Greenland Ice Sheet ice flow variations in regions of differing bed and surface topography

    NASA Astrophysics Data System (ADS)

    Sole, A. J.; Livingstone, S. J.; Rippin, D. M.; Hill, J.; McMillan, M.; Quincey, D. J.

    2015-12-01

    The contribution of the Greenland Ice Sheet (GrIS) to future sea-level rise is uncertain. Observations reveal the important role of basal water in controlling ice-flow to the ice sheet margin. In Greenland, drainage of large volumes of surface meltwater to the ice sheet bed through moulins and hydrofracture beneath surface lakes dominates the subglacial hydrological system and provides an efficient means of moving mass and heat through the ice sheet. Ice surface and bed topography influence where meltwater can access the bed, and the nature of its subsequent flow beneath the ice. However, no systematic investigation into the influence of topographic variability on Greenland hydrology and dynamics exists. Thus, physical processes controlling storage and drainage of surface and basal meltwater, and the way these affect ice flow are not comprehensively understood. This presents a critical obstacle in efforts to predict the future evolution of the GrIS. Here we present high-resolution satellite mapping of the ice-surface drainage network (e.g. lakes, channels and moulins) and measurements of seasonal variations in ice flow in south west Greenland. The region is comprised of three distinct subglacial terrains which vary in terms of the amplitude and wavelength and thus the degree to which basal topography is reflected in the ice sheet surface. We find that the distribution of surface hydrological features is related to the transfer of bed topography to the ice sheet surface. For example, in areas of thinner ice and high bed relief, moulins occur more frequently and are more uniformly dispersed, indicating a more distributed influx of surface-derived meltwater to the ice sheet bed. We investigate the implications of such spatial variations in surface hydrology on seasonal ice flow rates.

  13. Antarctic Sea Ice Patterns and Its Relationship with Climate

    NASA Astrophysics Data System (ADS)

    Barreira, S.

    2015-12-01

    Antarctic sea ice concentration fields show a strong seasonal and interannual variation closely tied to changes in climate patterns. The Ross, Amundsen, Bellingshausen, and Weddell Seas during Summer-Autumn and the Southern Ocean regions north of these areas during Winter-Spring have the greatest sea ice variability. Principal components analysis in T- mode, Varimax-rotated applied on Antarctic monthly sea ice concentration anomaly (SICA) fields for 1979-2015 (NASA Team algorithm data sets available at nsidc.org) revealed the main spatial characteristics of Antarctic sea ice patterns and their relationship with atmospheric circulation. This analysis yielded five patterns of sea ice for winter-spring and three patterns for summer-autumn, each of which has a positive and negative phase. To understand the links between the SICA patterns and climate, we extracted the mean pressure and temperature fields for the months with high loadings (positive or negative) of the sea ice patterns. The first pattern of winter-spring sea ice concentration is a dipole structure between the Drake Passage and northern regions of the Bellingshausen and Weddell Seas and, the South Atlantic Ocean. The negative phase shows a strong negative SICA over the Atlantic basin. This pattern can be associated with to the atmospheric structures related to a positive SAM index and a wave-3 arrangement around the continent. That is, a strong negative pressure anomaly centered over the Bellingshausen Sea accompanied by three positive pressure anomalies in middle-latitudes. For summer-autumn, the first pattern shows two strong positive SICA areas, in the eastern Weddell Sea and the northwestern Ross Sea. A negative SICA covers the Amundsen-Bellingshausen Seas and northwest of the Antarctic Peninsula. This pattern, frequently seen in summers since 2008, is associated with cool conditions over the Weddell Sea but warmer temperatures and high surface air pressure west, north and northwest of the Peninsula.

  14. Ice flow and precipitation change over the Swiss Alps during the last glaciation, a modeling approach

    NASA Astrophysics Data System (ADS)

    Becker, Patrick; Jouvet, Guillaume; Funk, Martin; Seguinot, Julien

    2015-04-01

    About 20,000 years before present at the end of the Würm glaciation, glaciers in Europe have reached their maximum extent and wide parts of the forelands were covered by ice. Our goal is to reconstruct the European alpine ice cap during the last glaciation using numerical simulations of the ice flow. To do that, we use the Parallel Ice Sheet Model (PISM) to simulate the ice flow. PISM is capable to simulate the time evolution of a large scale ice sheet for millenniums by accounting for the dynamics of ice, englacial temperature, bedrock temperature, lithosphere deformation and surface mass balance. The latter is computed using a positive degree day model that is forced by climate data. A classical approach consists of applying a constant temperature offset to present-day temperature data, while keeping constant today's precipitation patterns. However, geomorphological hints show that the prevailing precipitation regime during the last glaciation was dominated by a southerly atmospheric circulation pattern, in contrast to today's prevalent westerly airflow. Due to this fact we propose several empirical corrections to the present-day precipitation patterns and select those which yield the best match between modeled ice cap extents and geomorphologically-based margin reconstructions.

  15. Investigating the Flow Dynamics at Ice Shelf Calving Fronts

    NASA Astrophysics Data System (ADS)

    Wearing, Martin; Hindmarsh, Richard; Worster, Grae

    2015-04-01

    Ice-shelf calving-rates and the buttressing ice shelves provide to grounded ice are both difficult to model and quantify. An increased understanding of the mechanics of this process is imperative in determining the dynamics of marine ice sheets and consequently predicting their future extent, thickness and discharge. Alley et al. (2008) proposed an empirically derived calving law, relating the calving rate to the strain rate at the calving front. However, Hindmarsh (2012) showed that a similar relationship could be deduced by considering the viscous flow of the ice shelf. We investigate the relationship between the ice shelf flow field and the strain rate field in the area close to the calving front. Analysis is undertaken of ice surface velocity data for a range of Antarctic ice shelves (data from Rignot et al., 2011) and an inferred strain rate field produced from that data. These geophysical results are compared with a simple mathematical model for laterally confined ice shelf flow. Correlations are calculated between the same variables as Alley et al. but using a new and larger data compilation, which gives a greater degree of scatter. Good agreement is observed between the expected theoretical scaling and geophysical data for the flow of ice near the calving front in the case of laterally confined ice shelves. This lateral confinement ensures flow is aligned in the along-shelf direction and resistance to flow is provided by near stationary ice in the grounded margins. In other cases, the velocity is greater than predicted, which we attribute on a case-by-case basis to marginal weakening or the presence of ice tongues. We develop statistical methodologies for identifying these outliers.

  16. Effects of Inlet Icing on Performance of Axial-flow Turbojet Engine in Natural Icing Conditions

    NASA Technical Reports Server (NTRS)

    Acker, Loren W; Kleinknecht, Kenneth S

    1950-01-01

    A flight investigation in natural icing conditions was conducted to determine the effect of inlet ice formations on the performance of axial-flow turbojet engines. The results are presented for icing conditions ranging from a liquid-water content of 0.1 to 0.9 gram per cubic meter and water-droplet size from 10 to 27 microns at ambient-air temperature from 13 to 26 degrees F. The data show time histories of jet thrust, air flow, tail-pipe temperature, compressor efficiency, and icing parameters for each icing encounter. The effect of inlet-guide-vane icing was isolated and shown to account for approximately one-half the total reduction in performance caused by inlet icing.

  17. Insights into ice shelf buttressing and ice rheology on Rutford Ice Stream, West Antarctica, from synoptic-scale observations of tidally driven ice flow variations

    NASA Astrophysics Data System (ADS)

    Minchew, Brent; Simons, Mark; Riel, Bryan; Millio, Pietro

    2016-04-01

    Synoptic-scale observations of the response of ice streams to well-constrained forcing functions provide unique insights into ice stream dynamics and the underlying mechanics of glacier flow. Rutford Ice Stream, West Antarctica, is one of the few recognized ice streams with strong, observed, periodic ice-flow variability (e.g., Gudmundsson, 2006; Murray et al., 2007); numerous in situ observations of the subglacial environment (e.g., Smith et al., 2015); and extensive modeling efforts focused on understanding the mechanisms that drive the observed variations in glacier flow (e.g. Thompson et al., 2014; Rosier et al., 2014; 2015). Despite these efforts, the processes underlying the ~20% modulation in horizontal ice flow at Msf (14.77-day) periods - which corresponds to the beat frequency of the lunar and solar semi-diurnal ocean tides - remain a mystery. To help resolve the salient processes, we contribute a first-of-its-kind observational dataset that provides ice-stream-scale measurements of 3D secular and time-varying ice flow on Rutford with ~40-m spatial resolution. These data were inferred from 9 months of continuous synthetic aperture radar observations collected with the COSMO-SkyMed 4-satellite constellation from multiple satellite viewing geometries. The resulting velocity fields provide constraints on ice flow in all three spatial dimensions and in time, making them true 4D surface velocity fields. The time-varying velocity field components elucidate the spatial characteristics of the response of ice flow on Rutford to ocean tidal forcing and agree with collocated GPS measurements. We show that the response of horizontal ice flow to ocean tidal forcing is most pronounced over the ice shelf and subsequently propagates through the grounded ice stream at ~29 km/day, decaying quasi-linearly with distance over ~85 km upstream of the grounding zone. We observe multiple regions over the ice shelf whose motion is consistent with subglacial pinning points and that

  18. Fast-flowing outlet glaciers on Svalbard ice caps

    SciTech Connect

    Dowdeswell, J.A. ); Collin, R.L. )

    1990-08-01

    Four well-defined outlet glaciers are present on the 2510 km{sup 2} cap of Vestfonna in Nordaustlandet, Svalbard. Airborne radio echo sounding and aerial-photograph and satellite-image analysis methods are used to analyze the morphology and dynamics of the ice cap and its component outlet glaciers. The heavily crevassed outlets form linear depressions in the ice-cap surface and flow an order of magnitude faster than the ridges of uncrevassed ice between them. Ice flow on the ridges is accounted for by internal deformation alone, whereas rates of outlet glacier flow require basal motion. One outlet has recently switched into and out of a faster mode of flow. Rapid terminal advance, a change from longitudinal compression to tension, and thinning in the upper basin indicate surge behavior. Observed outlet glacier discharge is significantly greater than current inputs of mass of the ice cap, indicating that present rates of flow cannot be sustained under the contemporary climate.

  19. recent changes the in flow of the Ross Ice Shelf, West Antarctica

    NASA Astrophysics Data System (ADS)

    Hulbe, C. L.; Scambos, T. A.; Bohlander, J. A.; Lee, C.

    2012-12-01

    Comparison of surface velocities measured during the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS, 1973 to 1978) and velocities measured via feature tracking between two Moderate-resolution Imaging Spectroradiometer (MODIS) mosaics (compiled from 2003-4 and 2008-9 images) reveals widespread slowing and minor areas of acceleration in the Ross Ice Shelf (RIS) over the \\~30 year interval. The largest changes (-13 m/a/a) occur near the Whillans and Mercer Ice Streams grounding line in the southernmost part of the ice shelf. Speed has increased over the interval (up to 5 m/a/a) between the MacAyeal Ice Stream grounding line and the shelf front, and along the eastern part of the shelf front. Here, a well-tested model of the ice shelf is used to discern between longer and shorter time scale transients in ice shelf flow. Changes in ice thickness computed using ICESat laser altimetry are used to test various model outcomes. The observed transients represent a combination of ongoing response to ice stream discharge variations and resulting shelf thickness changes over the past millennium and while faint impressions of past events are evident, the modern signal is dominated by shorter time scale events, including the stagnation of Kamb Ice Stream about 160 years ago, recent changes in basal drag on the Whillans Ice Stream ice plain and, apparently, iceberg calving. Details in embayment geometry, for example the shallow sea floor below Crary Ice Rise, modulate the spatial pattern of ice shelf response to flow perturbations.

  20. Tidal Modulation of Ice-shelf Flow: a Viscous Model of the Ross Ice Shelf

    NASA Technical Reports Server (NTRS)

    Brunt, Kelly M.; MacAyeal, Douglas R.

    2014-01-01

    Three stations near the calving front of the Ross Ice Shelf, Antarctica, recorded GPS data through a full spring-neap tidal cycle in November 2005. The data revealed a diurnal horizontal motion that varied both along and transverse to the long-term average velocity direction, similar to tidal signals observed in other ice shelves and ice streams. Based on its periodicity, it was hypothesized that the signal represents a flow response of the Ross Ice Shelf to the diurnal tides of the Ross Sea. To assess the influence of the tide on the ice-shelf motion, two hypotheses were developed. The first addressed the direct response of the ice shelf to tidal forcing, such as forces due to sea-surface slopes or forces due to sub-ice-shelf currents. The second involved the indirect response of ice-shelf flow to the tidal signals observed in the ice streams that source the ice shelf. A finite-element model, based on viscous creep flow, was developed to test these hypotheses, but succeeded only in falsifying both hypotheses, i.e. showing that direct tidal effects produce too small a response, and indirect tidal effects produce a response that is not smooth in time. This nullification suggests that a combination of viscous and elastic deformation is required to explain the observations.

  1. Zonal flow as pattern formation

    NASA Astrophysics Data System (ADS)

    Parker, Jeffrey B.; Krommes, John A.

    2013-10-01

    Zonal flows are well known to arise spontaneously out of turbulence. We show that for statistically averaged equations of the stochastically forced generalized Hasegawa-Mima model, steady-state zonal flows, and inhomogeneous turbulence fit into the framework of pattern formation. There are many implications. First, the wavelength of the zonal flows is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.

  2. Zonal flow as pattern formation

    SciTech Connect

    Parker, Jeffrey B.; Krommes, John A.

    2013-10-15

    Zonal flows are well known to arise spontaneously out of turbulence. We show that for statistically averaged equations of the stochastically forced generalized Hasegawa-Mima model, steady-state zonal flows, and inhomogeneous turbulence fit into the framework of pattern formation. There are many implications. First, the wavelength of the zonal flows is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.

  3. West-Antarctic Ice Streams: Analog to Ice Flow in Channels on Mars

    NASA Technical Reports Server (NTRS)

    Lucchitta, B. K.

    1997-01-01

    Sounding of the sea floor in front of the Ross Ice Shelf in Antarctica recently revealed large persistent patterns of longitudinal megaflutes and drumlinoid forms, which are interpreted to have formed at the base of ice streams during the list glacial advance. The flutes bear remarkable resemblance to longitudinal grooves and highly elongated streamlined islands found on the floors of some large martian channels, called outflow channels. ln addition, other similarities exist between Antarctic ice streams and outflow channels. Ice streams are 30 to 80 km wide and hundreds of kilometers long, as are the martian channels. Ice stream beds are below sea level. Floors of many martian outflow channels lie below martian datum, which may have been close to or below past martian sea levels. The Antarctic ice stream bed gradient is flat and locally may go uphill, and surface slopes are exceptionally low. So are gradients of martian channels. The depth to the bed in ice streams is 1 to 1.5 km. At bankful stage, the depth of the fluid in outflow channels would have been 1 to 2 km. These similarities suggest that the martian outflow channels, whose origin is commonly attributed to gigantic catastrophic floods, were locally filled by ice that left a conspicuous morphologic imprint. Unlike the West-Antarctic-ice streams, which discharge ice from an ice sheet, ice in the martian channels came from water erupting from the ground. In the cold martian environment, this water, if of moderate volume, would eventually freeze. Thus it may have formed icings on springs, ice dams and jams on constrictions in the channel path, or frozen pools. Given sufficient thickness and downhill surface gradient, these ice masses would have moved; and given the right conditions, they could have moved like Antarctic ice streams.

  4. Preferred crystallographic orientation in the ice I ← II transformation and the flow of ice II

    USGS Publications Warehouse

    Bennett, K.; Wenk, H.-R.; Durham, W.B.; Stern, L.A.; Kirby, S.H.

    1997-01-01

    The preferred crystallographic orientation developed during the ice I ← II transformation and during the plastic flow of ice II was measured in polycrystalline deuterium oxide (D2O) specimens using low-temperature neutron diffraction. Samples partially transformed from ice I to II under a non-hydrostatic stress developed a preferred crystallographic orientation in the ice II. Samples of pure ice II transformed from ice I under a hydrostatic stress and then when compressed axially, developed a strong preferred orientation of compression axes parallel to (1010). A match to the observed preferred orientation using the viscoplastic self-consistent theory was obtained only when (1010) [0001] was taken as the predominant slip system in ice II.

  5. Flow and fracture of ice and ice mixtures

    NASA Technical Reports Server (NTRS)

    Durham, W. B.; Kirby, S. H.

    1991-01-01

    Frozen volatiles make up an important volume fraction of the low density moons of the outer solar system. Understanding the tectonic history of the surfaces of these moons, as well as the evolution of their interiors, requires knowledge of the mechanical strength of these icy materials under the appropriate planetary conditions (temperature, hydrostatic pressure, strain rate). Ongoing lab research is being conducted to measure mechanical properties of several different ices under conditions that faithfully reproduce condition both at the moons' surfaces (generally low temperature, to about 100 K, and low pressures) and in the deep interiors (warmer temperatures, pressures to thousands of atmospheres). Recent progress is reported in two different phases of the work: rheology of ices in the NH3-H2O system at temperatures and strain rates lower than ever before explored, with application to the ammonia-rich moons of Saturn and Uranus; and the water ice I yields II phase transformation, which not only applies directly to process deep in the interiors of Ganymede and Callisto, but holds implications for deep terrestrial earthquakes as well.

  6. connecting the dots between Greenland ice sheet surface melting and ice flow dynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Box, J. E.; Colgan, W. T.; Fettweis, X.; Phillips, T. P.; Stober, M.

    2013-12-01

    This presentation is of a 'unified theory' in glaciology that first identifies surface albedo as a key factor explaining total ice sheet mass balance and then surveys a mechanistic self-reinforcing interaction between melt water and ice flow dynamics. The theory is applied in a near-real time total Greenland mass balance retrieval based on surface albedo, a powerful integrator of the competing effects of accumulation and ablation. New snowfall reduces sunlight absorption and increases meltwater retention. Melting amplifies absorbed sunlight through thermal metamorphism and bare ice expansion in space and time. By ';following the melt'; we reveal mechanisms linking existing science into a unified theory. Increasing meltwater softens the ice sheet in three ways: 1.) sensible heating given the water temperature exceeds that of the ice sheet interior; 2.) Some infiltrating water refreezes, transferring latent heat to the ice; 3.) Friction from water turbulence heats the ice. It has been shown that for a point on the ice sheet, basal lubrication increases ice flow speed to a time when an efficient sub-glacial drainage network develops that reduces this effect. Yet, with an increasing melt duration the point where the ice sheet glides on a wet bed increases inland to a larger area. This effect draws down the ice surface elevation, contributing to the ';elevation feedback'. In a perpetual warming scenario, the elevation feedback ultimately leads to ice sheet loss reversible only through much slower ice sheet growth in an ice age environment. As the inland ice sheet accelerates, the horizontal extension pulls cracks and crevasses open, trapping more sunlight, amplifying the effect of melt accelerated ice. As the bare ice area increases, the direct sun-exposed crevassed and infiltration area increases further allowing the ice warming process to occur more broadly. Considering hydrofracture [a.k.a. hydrofracking]; surface meltwater fills cracks, attacking the ice integrity

  7. Potential flow analysis of glaze ice accretions on an airfoil

    NASA Technical Reports Server (NTRS)

    Zaguli, R. J.

    1984-01-01

    The results of an analytical/experimental study of the flow fields about an airfoil with leading edge glaze ice accretion shapes are presented. Tests were conducted in the Icing Research Tunnel to measure surface pressure distributions and boundary layer separation reattachment characteristics on a general aviation wing section to which was affixed wooden ice shapes which approximated typical glaze ice accretions. Comparisons were made with predicted pressure distributions using current airfoil analysis codes as well as the Bristow mixed analysis/design airfoil panel code. The Bristow code was also used to predict the separation reattachment dividing streamline by inputting the appropriate experimental surface pressure distribution.

  8. Biogeomorphic interactions and patterns on Little Ice Age lateral moraines

    NASA Astrophysics Data System (ADS)

    Eichel, Jana; Schmidtlein, Sebastian; Dikau, Richard

    2014-05-01

    Glaciers and their forefields are strongly affected by climate change. This leads to increasing geomorphological and ecological dynamics in these environments. Glacier recession exposes high volumes of unconsolidated sediments, with lateral moraines being among the most important sediment storages. Their sediment is reworked by a variety of slope processes, e.g. sheet wash, debris flows or gullying. At the same time, these landforms are colonized by plants and other organisms, proceeding into vegetation succession. It is believed that this process ultimately leads to sediment stabilization which is an important factor for reservoir management in glacier forefields. Recent biogeomorphic research revealed a strong coupling of geomorphic and ecologic processes and complex feedbacks. Geomorphic processes disturb vegetation while at the same time, certain plant species, 'geomorphic-engineer species', can influence geomorphic properties and processes. The strength of these interactions changes during biogeomorphic succession. Corresponding patterns of vegetation and geomorphic forms and processes arise at the mesoscale. The resulting spatial heterogeneity can be mapped as patches. In our study, we investigate patterns of vegetation and geomorphic forms and processes on Little Ice Age lateral moraines in the Turtmann glacier forefield, Switzerland. Despite higher terrain age, these landforms show strongly heterogeneous vegetation as well as geomorphic activity patterns, indicating that sediment stabilization has not yet been accomplished. This could result from varying strengths of biogeomorphic interactions. To assess this influence, vegetation and geomorphic properties of 50 vegetation plots were sampled and statistically analyzed. Results showed that vegetation composition does not relate to terrain age, rather, geomorphic disturbances seem to be a dominant influencing factors, producing patch dynamics. Certain species compositions can be related to specific geomorphic

  9. Examination of upstream flow dynamics in response to the front retreat of ice shelves with different geometric configurations

    NASA Astrophysics Data System (ADS)

    Wang, S.; Liu, H.

    2015-12-01

    Ice shelves fringe ~75% of Antarctica's coastline, nourished by numerous terrestrial glacier systems. The ice-shelf disintegrations in recent decades and the observed thinning trends have revealed their susceptibility to the atmospheric and oceanic changes in the climate warming context. The buttressing effect of an ice shelf constrains the ice discharge of its upstream land ice, thus regulating the contribution to sea level of the terrestrial glaciers. The important role of ice shelves in stabilizing the upstream glacier flow dynamics is emphasized by the rapid accelerations and thinning of the tributary glaciers in response to the collapses of the northern Larsen Ice Shelf in Antarctic Peninsula. However, this buttressing effect is determined by the stress balance conditions of an ice shelf, which is further affected by the ice-shelf geometric configurations. The ice shelves confined by fjords, islands, promontories or seabed topographic highs exert greater buttressing effects than those less confined by the lateral or basal shear stresses. This research aims to assess the influences of different ice-shelf configurations on upstream flow dynamics in response to large ice-shelf retreat events. By using remotely sensed imagery acquired by multiple satellite missions, we derived the time series surface velocity records for the Larsen B glacier-ice shelf system in Antarctic Peninsula during 1995 - 2015 and for the Mertz glacier-ice shelf system in East Antarctica during 1997 - 2015, respectively. The former was well confined in the embayment, while the latter is unconfined by lateral margins. We compared the different temporal variation patterns in flow dynamics between these two sites before and after their large retreating events, i.e. the collapse event of Larsen B Ice Shelf in 2002 and the large calving event of Mertz Ice Shelf in 2010. The surface velocity profiles reveal the less sensitivity of upstream responses to the front retreat for the Mertz Ice Shelf.

  10. Patterns of Quaternary ice sheet erosion and deposition in Fennoscandia and a theoretical framework for explanation

    NASA Astrophysics Data System (ADS)

    Kleman, Johan; Stroeven, Arjen P.; Lundqvist, Jan

    2008-05-01

    middle Quaternary. The scouring zones formed under conditions of rapid ice flow towards bathymetrically-defined calving margins of FIS style ice sheets. They likely reflect process patterns of the last two or three FIS style ice sheets. The three landscape zones differ in their degree of permanence, with the deep erosion zones being a long-lasting legacy in the landscape, more likely to be enhanced than obliterated by subsequent glacial events. The thick drift cover zone, once established, appears to have been surprisingly robust to erosion by subsequent glacial events. The scouring zones appear to be the most recent and ephemeral of the three zones, with possible major alterations during single glacial events.

  11. Modelling water flow under glaciers and ice sheets

    PubMed Central

    Flowers, Gwenn E.

    2015-01-01

    Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082

  12. Application of GRACE to the Evaluation of an Ice Flow Model of the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Schlegel, N.; Wiese, D. N.; Watkins, M. M.; Larour, E. Y.; Box, J. E.; Fettweis, X.; van den Broeke, M. R.; Morlighem, M.; Boening, C.; Seroussi, H. L.

    2014-12-01

    Quantifying Greenland's future contribution to sea level rise is a challenging task and requires accurate estimates of ice flow sensitivity to climate change. Transient ice flow models are promising tools for estimating future ice sheet behavior. However, confidence in these types of future projections is low, especially because evaluation of model historical runs is so challenging due to the scarcity of continental-wide data for validation. For more than a decade, NASA's GRACE has continuously acquired time-variable measurements of the Earth's gravity field and has provided unprecedented surveillance of mass balance of the ice sheets, offering an opportunity for ice sheet model evaluation. Here, we take advantage of a new high-resolution (~300 km) monthly mascon solution for the purpose of mass balance comparison with an independent, historical ice flow model simulation using the Ice Sheet System Model (ISSM). The comparison highlights which regions of the ice sheet differ most from GRACE. Investigation of regional differences in trends and seasonal amplitudes between simulations forced with three different Regional Climate Model (RCM)-based estimates of surface mass balance (SMB) allows us to make conclusions about the relative contributions of various error sources in the model hindcast. This study constitutes the first regional comparison of GRACE data and an ice sheet model. Conclusions will aid in the improvement of RCM SMB estimates as well as ice sheet simulation estimates of present and future rates of sea level rise. This work was performed at the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration's Cryosphere Program and President's and Director's Fund Program.

  13. Airborne radar evidence for tributary flow switching in Institute Ice Stream, West Antarctica: Implications for ice sheet configuration and dynamics

    NASA Astrophysics Data System (ADS)

    Winter, Kate; Woodward, John; Ross, Neil; Dunning, Stuart A.; Bingham, Robert G.; Corr, Hugh F. J.; Siegert, Martin J.

    2015-09-01

    Despite the importance of ice streaming to the evaluation of West Antarctic Ice Sheet (WAIS) stability we know little about mid- to long-term dynamic changes within the Institute Ice Stream (IIS) catchment. Here we use airborne radio echo sounding to investigate the subglacial topography, internal stratigraphy, and Holocene flow regime of the upper IIS catchment near the Ellsworth Mountains. Internal layer buckling within three discrete, topographically confined tributaries, through Ellsworth, Independence, and Horseshoe Valley Troughs, provides evidence for former enhanced ice sheet flow. We suggest that enhanced ice flow through Independence and Ellsworth Troughs, during the mid-Holocene to late Holocene, was the source of ice streaming over the region now occupied by the slow-flowing Bungenstock Ice Rise. Although buckled layers also exist within the slow-flowing ice of Horseshoe Valley Trough, a thicker sequence of surface-conformable layers in the upper ice column suggests slowdown more than ~4000 years ago, so we do not attribute enhanced flow switch-off here, to the late Holocene ice-flow reorganization. Intensely buckled englacial layers within Horseshoe Valley and Independence Troughs cannot be accounted for under present-day flow speeds. The dynamic nature of ice flow in IIS and its tributaries suggests that recent ice stream switching and mass changes in the Siple Coast and Amundsen Sea sectors are not unique to these sectors, that they may have been regular during the Holocene and may characterize the decline of the WAIS.

  14. Convective Enhancement of Icing Roughness Elements in Stagnation Region Flows

    NASA Technical Reports Server (NTRS)

    Hughes, Michael T.; McClain, Stephen T.; Vargas, Mario; Broeren, Andy

    2015-01-01

    To improve existing ice accretion simulation codes, more data regarding ice roughness and its effects on convective heat transfer are required. To build on existing research on this topic, this study used the Vertical Icing Studies Tunnel (VIST) at NASA Glenn Research to model realistic ice roughness in the stagnation region of a NACA 0012 airfoil. Using the VIST, a test plate representing the leading 2% chord of the airfoil was subjected to flows of 7.62 m/s (25 ft/s), 12.19 m/s (40 ft/s), and 16.76 m/s (55 ft/s). The test plate was fitted with 3 surfaces, each with a different representation of ice roughness: 1) a control surface with no ice roughness, 2) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 10x, and 3) a surface with ice roughness with element height scaled by 10x and streamwise rough zone width from the stagnation point scaled by 25x. Temperature data from the tests were recorded using an infrared camera and thermocouples imbedded in the test plate. From the temperature data, a convective heat transfer coefficient map was created for each case. Additional testing was also performed to validate the VIST's flow quality. These tests included five-hole probe and hot-wire probe velocity traces to provide flow visualization and to study boundary layer formation on the various test surfaces. The knowledge gained during the experiments will help improve ice accretion codes by providing heat transfer coefficient validation data and by providing flow visualization data helping understand current and future experiments performed in the VIST.

  15. Flow speed within the Antarctic ice sheet and its controls inferred from satellite observations

    NASA Astrophysics Data System (ADS)

    Arthern, Robert J.; Hindmarsh, Richard C. A.; Williams, C. Rosie

    2015-07-01

    Accurate dynamical models of the Antarctic ice sheet with carefully specified initial conditions and well-calibrated rheological parameters are needed to forecast global sea level. By adapting an inverse method previously used in electric impedance tomography, we infer present-day flow speeds within the ice sheet. This inversion uses satellite observations of surface velocity, snow accumulation rate, and rate of change of surface elevation to estimate the basal drag coefficient and an ice stiffness parameter that influences viscosity. We represent interior ice motion using a vertically integrated approximation to incompressible Stokes flow. This model represents vertical shearing within the ice and membrane stresses caused by horizontal stretching and shearing. Combining observations and model, we recover marked geographical variations in the basal drag coefficient. Relative changes in basal shear stress are smaller. No simple sliding law adequately represents basal shear stress as a function of sliding speed. Low basal shear stress predominates in central East Antarctica, where thick insulating ice allows liquid water at the base to lubricate sliding. Higher shear stress occurs in coastal East Antarctica, where a frozen bed is more likely. Examining Thwaites glacier in more detail shows that the slowest sliding often coincides with elevated basal topography. Differences between our results and a similar adjoint-based inversion suggest that inversion or regularization methods can influence recovered parameters for slow sliding and finer scales; on broader scales we recover a similar pattern of low basal drag underneath major ice streams and extensive regions in East Antarctica that move by basal sliding.

  16. Driving Stresses in Mars Polar Ice Caps and Conditions for Ice Flow

    NASA Technical Reports Server (NTRS)

    Zwally, H. Jay; Saba, Jack L.

    1999-01-01

    Measurements of the topography of the North polar ice cap by the Mars Orbiter Laser Altimeter (MOLA) show that the ice cap is 2950 +/- 200 meters thick. The volume of the cap is about 1.2 x 10(exp 6) cu km covering an area of 1.04 x 10(exp 6) sq km, which is about 40 percent of the Greenland ice sheet in volume and 62 percent in area. The composition of the Northern cap was previously concluded to be predominately H2O, rather than CO2 ice, based on thermodynamic considerations of the insustainablity of CO2 during summer. Principal questions about the cap are: does the ice move and at what rate, is the cap currently growing or depleting in volume, and how and when was the cap formed? Recent research on terrestrial ice sheets indicates that rates of ice deformation at the low stress values characteristic of ice sheets are significantly higher than the rates given by the classic viscous-plastic flow laws commonly used.

  17. Bayesian Inversion for Large Scale Antarctic Ice Sheet Flow

    NASA Astrophysics Data System (ADS)

    Ghattas, O.; Isaac, T.; Petra, N.; Stadler, G.

    2014-12-01

    The flow of ice from the interior of polar ice sheets is the primarycontributor to projected sea level rise. One of the main difficultiesfaced in modeling ice sheet flow is the uncertain spatially-varyingRobin boundary condition that describes the resistance to sliding atthe base of the ice. Satellite observations of the surface ice flowvelocity, along with a model of ice as a creeping incompressibleshear-thinning fluid, can be used to infer this uncertain basalboundary condition. We cast this ill-posed inverse problem in theframework of Bayesian inference, which allows us to infer not only thebasal sliding parameters, but also the associated uncertainty. Toovercome the prohibitive nature of Bayesian methods for large-scaleinverse problems, we exploit the fact that, despite the large size ofobservational data, they typically provide only sparse information onmodel parameters. We show results for Bayesian inversion of the basalsliding parameter field for the full Antarctic continent, anddemonstrate that the work required to solve the inverse problem,measured in number of forward (and adjoint) ice sheet model solves, isindependent of the parameter dimension, data dimension, and number ofprocessor cores.

  18. Rotation of melting ice disks due to melt fluid flow

    NASA Astrophysics Data System (ADS)

    Dorbolo, S.; Adami, N.; Dubois, C.; Caps, H.; Vandewalle, N.; Darbois-Texier, B.

    2016-03-01

    We report experiments concerning the melting of ice disks (85 mm in diameter and 14 mm in height) at the surface of a thermalized water bath. During the melting, the ice disks undergo translational and rotational motions. In particular, the disks rotate. The rotation speed has been found to increase with the bath temperature. We investigated the flow under the bottom face of the ice disks by a particle image velocimetry technique. We find that the flow goes downwards and also rotates horizontally, so that a vertical vortex is generated under the ice disk. The proposed mechanism is the following. In the vicinity of the bottom face of the disk, the water eventually reaches the temperature of 4°C for which the water density is maximum. The 4°C water sinks and generates a downwards plume. The observed vertical vorticity results from the flow in the plume. Finally, by viscous entrainment, the horizontal rotation of the flow induces the solid rotation of the ice block. This mechanism seems generic: any vertical flow that generates a vortex will induce the rotation of a floating object.

  19. Flow quality studies of the NASA Lewis Research Center Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Arrington, E. Allen; Pickett, Mark T.; Sheldon, David W.

    1994-01-01

    A series of studies have been conducted to determine the flow quality in the NASA Lewis Icing Research Tunnel. The primary purpose of these studies was to document airflow characteristics, including flow angularity, in the test section and tunnel loop. A vertically mounted rake was used to survey total and static pressure and two components of flow angle at three axial stations within the test section (test section inlet, test plane, and test section exit; 15 survey stations total). This information will be used to develop methods of improving the aerodynamic and icing characteristics within the test section. The data from surveys made in the tunnel loop were used to determine areas where overall tunnel flow quality and efficiency can be improved. A separate report documents similar flow quality surveys conducted in the diffuser section of the Icing Research Tunnel. The flow quality studies were conducted at several locations around the tunnel loop. Pressure, velocity, and flow angularity measurements were made by using both fixed and translating probes. Although surveys were made throughout the tunnel loop, emphasis was placed on the test section and tunnel areas directly upstream of the test section (settling chamber, bellmouth, and cooler). Flow visualization, by video recording smoke and tuft patterns, was also used during these studies. A great deal of flow visualization work was conducted in the area of the drive fan. Information gathered there will be used to improve the flow quality upstream and downstream of the fan.

  20. Reactivation of Kamb Ice Stream tributaries triggers century-scale reorganization of Siple Coast ice flow in West Antarctica

    SciTech Connect

    Bougamont, M.; Christoffersen, P.; Price, S. F.; Fricker, H. A.; Tulaczyk, S.; Carter, S. P.

    2015-10-21

    Ongoing, centennial-scale flow variability within the Ross ice streams of West Antarctica suggests that the present-day positive mass balance in this region may reverse in the future. Here we use a three-dimensional ice sheet model to simulate ice flow in this region over 250 years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb Ice Stream is a source of internal ice flow instability, which reorganizes all ice streams in this region, leading to a reduced (positive) mass balance within decades and a net loss of ice within two centuries. This hitherto unaccounted for flow variability could raise sea level by 5 mm this century. Furthermore, better constraints on future sea level change from this region will require improved estimates of geothermal heat flux and subglacial water transport.

  1. Instability of water-ice interface under turbulent flow

    NASA Astrophysics Data System (ADS)

    Izumi, Norihiro; Naito, Kensuke; Yokokawa, Miwa

    2015-04-01

    It is known that plane water-ice interface becomes unstable to evolve into a train of waves. The underside of ice formed on the water surface of rivers are often observed to be covered with ice ripples. Relatively steep channels which discharge melting water from glaciers are characterized by beds covered with a series of steps. Though the flowing agent inducing instability is not water but gas including water vapor, a similar train of steps have been recently observed on the Polar Ice Caps on Mars (Spiral Troughs). They are expected to be caused by the instability of water-ice interface induced by flowing fluid on ice. There have been some studies on this instability in terms of linear stability analysis. Recently, Caporeale and Ridolfi (2012) have proposed a complete linear stability analysis in the case of laminar flow, and found that plane water-ice interface is unstable in the range of sufficiently large Reynolds numbers, and that the important parameters are the Reynolds number, the slope angle, and the water surface temperature. However, the flow inducing instability on water-ice interface in the field should be in the turbulent regime. Extension of the analysis to the case of fully developed turbulent flow with larger Reynolds numbers is needed. We have performed a linear stability analysis on the instability of water-ice interface under turbulent flow conditions with the use of the Reynolds-averaged Navier-Stokes equations with the mixing length turbulent model, the continuity equation of flow, the diffusion/dispersion equation of heat, and the Stefan equation. In order to reproduce the accurate velocity distribution and the heat transfer in the vicinity of smooth walls with the use of the mixing length model, it is important to take into account of the rapid decrease in the mixing length in the viscous sublayer. We employ the Driest model (1956) to the formulation. In addition, as the thermal boundary condition at the water surface, we describe the

  2. Simulation of air-droplet mixed phase flow in icing wind-tunnel

    NASA Astrophysics Data System (ADS)

    Mengyao, Leng; Shinan, Chang; Menglong, Wu; Yunhang, Li

    2013-07-01

    Icing wind-tunnel is the main ground facility for the research of aircraft icing, which is different from normal wind-tunnel for its refrigeration system and spraying system. In stable section of icing wind-tunnel, the original parameters of droplets and air are different, for example, to keep the nozzles from freezing, the droplets are heated while the temperature of air is low. It means that complex mass and heat transfer as well as dynamic interactive force would happen between droplets and air, and the parameters of droplet will acutely change along the passageway. Therefore, the prediction of droplet-air mixed phase flow is necessary in the evaluation of icing researching wind-tunnel. In this paper, a simplified droplet-air mixed phase flow model based on Lagrangian method was built. The variation of temperature, diameter and velocity of droplet, as well as the air flow field, during the flow process were obtained under different condition. With calculating three-dimensional air flow field by FLUENT, the droplet could be traced and the droplet distribution could also be achieved. Furthermore, the patterns about how initial parameters affect the parameters in test section were achieved. The numerical simulation solving the flow and heat and mass transfer characteristics in the mixing process is valuable for the optimization of experimental parameters design and equipment adjustment.

  3. Dilatant till facilitates ice-stream flow in northeast Greenland

    NASA Astrophysics Data System (ADS)

    Christianson, Knut; Peters, Leo E.; Alley, Richard B.; Anandakrishnan, Sridhar; Jacobel, Robert W.; Riverman, Kiya L.; Muto, Atsuhiro; Keisling, Benjamin A.

    2014-09-01

    We present radio-echo sounding (RES), global positioning system (GPS), and active-source seismic data across the central portion of the Northeast Greenland Ice Stream (NEGIS). NEGIS widens downglacier from a small region of high geothermal flux near the ice divide. Our data reveal high-porosity (40+%) water-saturated till lubricating the ice stream. Ice accelerates and thins as it flows into NEGIS, producing marginal troughs in surface topography. These troughs create steep gradients in the subglacial hydropotential that generate parallel “sticky” and “slippery” bands beneath the shear margins. The low-porosity “sticky” sediment bands limit ice entrainment across the margins and thus restrict further widening, producing the long, narrow, and relatively stable ice stream. However, the observed relations among surface elevation, basal water routing, broad sedimentary drape, and till dilatancy suggest that rapid shifts in ice dynamics are possible, including rapid transmission of ocean forcing inland. The source and routing of the subglacial till are unclear, but our data help constrain hypotheses.

  4. Tidal controls on the flow of ice streams

    NASA Astrophysics Data System (ADS)

    Rosier, Sebastian H. R.; Gudmundsson, G. Hilmar

    2016-05-01

    The flow of many Antarctic ice streams is known to be significantly influenced by tides. In the past, modeling studies have implemented the tidal forces acting on a coupled ice stream/ice shelf system in a number of different ways, but the consequences that this has on the modeled response of ice streams to tides have, until now, not been considered. Here we investigate for the first time differences in model response that are only due to differences in the way tidal forcings are implemented. We find that attempts to simplify the problem by neglecting flexural stresses are generally not valid and forcing models with only changes in ocean back pressure will not capture either the correct amplitudes or length scale.

  5. Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics.

    PubMed

    Csatho, Beata M; Schenk, Anton F; van der Veen, Cornelis J; Babonis, Gregory; Duncan, Kyle; Rezvanbehbahani, Soroush; van den Broeke, Michiel R; Simonsen, Sebastian B; Nagarajan, Sudhagar; van Angelen, Jan H

    2014-12-30

    We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993-2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt ⋅ y(-1), equivalent to 0.68 mm ⋅ y(-1) sea level rise (SLR) for 2003-2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004-2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland's outlet glaciers. PMID:25512537

  6. Magnetically stimulated fluid flow patterns

    ScienceCinema

    Martin, Jim; Solis, Kyle

    2014-08-06

    Sandia National Laboratories' Jim Martin and Kyle Solis explain research on the effects of magnetic fields on fluid flows and how they stimulate vigorous flows. Fluid flow is a necessary phenomenon in everything from reactors to cooling engines in cars.

  7. Magnetically stimulated fluid flow patterns

    SciTech Connect

    Martin, Jim; Solis, Kyle

    2014-03-06

    Sandia National Laboratories' Jim Martin and Kyle Solis explain research on the effects of magnetic fields on fluid flows and how they stimulate vigorous flows. Fluid flow is a necessary phenomenon in everything from reactors to cooling engines in cars.

  8. Assessing the Influence of Tributary Glaciers on Ice Properties and Flow Dynamics

    NASA Astrophysics Data System (ADS)

    Quick, A. M.; Rupper, S.; McBride, J. H.; Ritter, S.; Tingey, D. G.; McKean, A.; Parks, E.

    2009-12-01

    Ice flow models designed to simulate glacier changes in response to changes in climatic forcing, past or present, must accurately predict glacier flow rates, which can only be determined if ice rheology is well constrained. In the commonly used flow-law models that assume strain rates are proportional to a power-law dependence on stress, the flow-law parameters are dependent upon numerous ice properties, some of which include temperature, impurities, liquid water fraction, crystal size and fabric. The aim of this study is to measure the ice properties between tributary glaciers within a single glacier system and assess the impact of the differences in these properties on the flow rates of the system as a whole. The preliminary study was done on the Gornergletscher, located in Valais, Switzerland. The Gornergletscher is the second largest glacier system in the European Alps, and results from the confluence of several tributary glaciers. Forty-three shallow ice cores (.30-3 m) were drilled in the ablation zone down-flow of the confluence of two of the tributary glaciers in the Gornergletscher system - fifteen ice cores on Grenzgletscher and twenty-eight on Zwillingsgletscher. Physical (density, grain size), chemical (stable isotopes, solutes, dust), and thermal (temperature) properties of ice were measured in all cores. Preliminary chemical analyses indicate statistically significant differences in the isotopic composition of the ice. In particular, there is a 20‰ difference in the mean δD between the two glaciers which can not be easily explained by isotopic lapse rates and elevation differences of the source regions. The isotopic difference may be evidence of flow pattern differences giving rise to differences in surface ice ages between the adjacent glaciers. In addition to the ice cores, a ground-penetrating radar survey using a 200-MHz bistatic antenna in continuous mode with a fixed transmitter-receiver offset was completed extending 1200 meters down

  9. Late Wisconsinan ice sheet flow across northern and central Vermont, USA

    NASA Astrophysics Data System (ADS)

    Wright, Stephen F.

    2015-12-01

    A compilation of over 2000 glacial striation azimuths across northern and central Vermont, northeastern USA, provides the basis for interpreting a sequence of ice flow directions across this area. The oldest striations indicate widespread ice flow to the southeast, obliquely across the mountains. Similarly oriented striations between northern Vermont and the ice sheet's terminus in the Gulf of Maine suggest that a broad area of southeast ice flow existed at the Last Glacial Maximum. Younger striations with more southerly azimuths on both the mountain ridgelines and within adjacent valleys indicate that ice sheet flow trajectories in most areas rotated from southeast to south, parallel to the North-South alignment of the mountains, as the ice sheet thinned. This transition in ice flow direction was time transgressive from south to north with the Green Mountains eventually separating a thick south-flowing lobe of ice in the Champlain Valley from a much thinner lobe of south-flowing ice east of the mountains. While this transition was taking place yet ice was still thick enough to flow across the mountains, ice flow along a narrow ˜65 km long section of the Green Mountains shifted to the southwest such that ice was flowing into the Champlain Valley. The most likely process driving this change was a limited period of fast ice flow in the Champlain Valley, a short-lived ice streaming event, that drew down the ice surface in the valley. The advancing ice front during this period of fast ice flow may be responsible for the Luzerne Readvance south of Glens Falls, New York. Valley-parallel striations across the area indicate strong topographic control on ice flow as the ice sheet thinned.

  10. Paleo-Ice flow and overdeepenings in an Alpine setting: Examples from the Tyrolian Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Reitner, J. M.; Gruber, W.

    2009-04-01

    Overdeepened valleys and basins are the most interesting features of former glacial action in Alpine areas. Understanding the formation of such phenomena are not only a scientific task but also an important challenge for a society increasingly exploiting sustainable natural resources even in remote areas. The feasibility of hydrogeological or geothermal projects, for instance, depends on the bedrock depth and the sedimentary infill of such valleys. Generally, overdeepened valleys are formed in areas where the ice discharge was high, such as near the equilibrium line, at valley junctions, or at narrowings of the valley profile. The long known overdeepened tongue basins in the Eastern Alps are regarded as typical examples of the impact of high ice flow velocities combined with increased debris load and running water under hydrostatic pressure around the former (LGM, and older glaciations) equilibrium lines (e.g. van Husen, 2000). However, within a highly dissected mountain topography like that of the Eastern Alps the existence of overdeepened valleys-parts supposedly also reflects changes in ice flow direction and velocity during glacial history within one glacial event (like the LGM) as well as during the Pleistocene. For example, ice flow in the phase of ice build-up at the beginning of major glaciations is controlled by the topography and trend of the valleys whereas during the climax of the big glaciations a mountain ice cap exists with a continuous discharge across water divides. Thus, the onsets of ice transfluences as well as the valley orientation in relation to the changing ice flow direction are regarded as major conditions for overdeepenings in an inneralpine setting. Such a complex and changing pattern of ice flow will be shown by the example of the Inn valley and its tributary valleys in the S and E (valley of the Wildschönauer Ache and of the Brixentaler Ache). Based on extensive geological mapping and lithostratigraphy in combination with geophysical

  11. Submarine landforms and ice-sheet flow in the Kvitøya Trough, northwestern Barents Sea

    NASA Astrophysics Data System (ADS)

    Hogan, K. A.; Dowdeswell, J. A.; Noormets, R.; Evans, J.; Cofaigh, C. Ó.; Jakobsson, M.

    2010-12-01

    High-resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in Kvitøya Trough, northwestern Barents Sea. A new swath-bathymetric dataset identifies three types of submarine landform in the study area (streamlined landforms, meltwater channels and cavities, iceberg scours). Subglacially produced streamlined landforms provide a record of ice flow through Kvitøya Trough during the last glaciation. Flow directions are inferred from the orientations of streamlined landforms (drumlins, crag-and-tail features). Ice flowed northward for at least 135 km from an ice divide at the southern end of Kvitøya Trough. A large channel-cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice-sheet base. Modest landform elongation ratios and a lack of mega-scale glacial lineations suggest that, although ice in Kvitøya Trough was melting at the bed and flowed faster than the likely thin and cold-based ice on adjacent banks, a major ice stream probably did not occupy the trough. Retreat was relatively rapid after 14-13.5 14C kyr B.P. and probably progressed via ice sheet-bed decoupling in response to rising sea level. There is little evidence for still stands during ice retreat or of ice-proximal deglacial sediments. Relict iceberg scours in present-day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat.

  12. Changes in Ice Flow Dynamics of Totten Glacier, East Antarctica and Impacts on Ice Mass Balance

    NASA Astrophysics Data System (ADS)

    Li, X.; Rignot, E. J.; Mouginot, J.; Scheuchl, B.; An, L.

    2014-12-01

    Totten Glacier, East Antarctica is one of the largest glaciers in Antarctica, draining an area of 5.3*105 km2 and containing ice at an equivalent 9 m sea level rise. Lidar/radar altimetry data from 2003-2009 suggests that the glacier is thinning. Thinning is concentrated in areas of fast flow and therefore indicative of changes in ice dynamics. Here, we employ time series of ice velocity from ERS-1/2, RADARSAT-1, LANDSAT-7, ALOS PALSAR, TanDEM/TerraSAR-X and COSMO-Skymed to measure the glacier velocity from 1996 till present. We find significant temporal changes in ice velocity, especially in 1996-2007, followed by a period of slow decrease in 2010-2013. Comparing the results with RACMO2 surface mass balance in the interior suggests that the glacier mass balance was already negative in 1996 and became more negative into the 2000s. The resulting mass loss and stretching of the ice is compatible with the 1.5 m/yr thinning detected by the radar altimeters near the grounding zone. The grounding zone of the glacier includes a vast 15 km long ice plain where the glacier is only grounded a few 10m above hydrostatic equilibrium. We detect a retreat of the region of partial floatation with time, but not solid migration of the grounding line of the glacier. Inverted bathymetry results from gravity data collected offshore suggest the presence of a paleo subglacial channel conducive to the transfer of surface ocean heat, likely diluted circumpolar deep water, whose transfer to the ice shelf cavity may have affected the glacier stability. We suggest that further transfer of ocean heat to the ice shelf could trigger a rapid glacier retreat in this region.

  13. Analogue modelling of the influence of ice shelf collapse on the flow of ice sheets grounded below sea-level

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; Zeoli, Antonio

    2016-04-01

    The sudden breakup of ice shelves is expected to result in significant acceleration of inland glaciers, a process related to the removal of the buttressing effect exerted by the ice shelf on the tributary glaciers. This effect has been tested in previous analogue models, which however applied to ice sheets grounded above sea level (e.g., East Antarctic Ice Sheet; Antarctic Peninsula and the Larsen Ice Shelf). In this work we expand these previous results by performing small-scale laboratory models that analyse the influence of ice shelf collapse on the flow of ice streams draining an ice sheet grounded below sea level (e.g., the West Antarctic Ice Sheet). The analogue models, with dimensions (width, length, thickness) of 120x70x1.5cm were performed at the Tectonic Modelling Laboratory of CNR-IGG of Florence, Italy, by using Polydimethilsyloxane (PDMS) as analogue for the flowing ice. This transparent, Newtonian silicone has been shown to well approximate the rheology of natural ice. The silicone was allowed to flow into a water reservoir simulating natural conditions in which ice streams flow into the sea, terminating in extensive ice shelves which act as a buttress for their glaciers and slow their flow. The geometric scaling ratio was 10(-5), such that 1cm in the models simulated 1km in nature; velocity of PDMS (a few mm per hour) simulated natural velocities of 100-1000 m/year. Instability of glacier flow was induced by manually removing a basal silicone platform (floating on water) exerting backstresses to the flowing analogue glacier: the simple set-up adopted in the experiments isolates the effect of the removal of the buttressing effect that the floating platform exerts on the flowing glaciers, thus offering insights into the influence of this parameter on the flow perturbations resulting from a collapse event. The experimental results showed a significant increase in glacier velocity close to its outlet following ice shelf breakup, a process similar to what

  14. Comparison of Ice-shelf Creep Flow Simulations with Ice-front Motion of Filchner-Ronne Ice Shelf, Antarctica, Detected by SAR Interferometry

    NASA Technical Reports Server (NTRS)

    Hulbe, C. L.; Rignot, E.; MacAyeal, D. R.

    1998-01-01

    Comparison between numerical model ice-shelf flow simulations and synthetic aperture radar (SAR) interferograms is used to study the dynamics at the Hemmen Ice Rise (HIR) and Lassiter Coast (LC) corners of the iceberg-calving front of the Filchner-Ronne Ice Shelf (FRIS).

  15. Multiphase flow of the late Wisconsinan Cordilleran ice sheet in Western Canada

    USGS Publications Warehouse

    Stumpf, A.J.; Broster, B.E.; Levson, V.M.

    2000-01-01

    In central British Columbia, ice flow during the late Wisconsinan Fraser glaciation (ca. 25-10 ka) occurred in three phases. The ice expansion phase occurred during an extended period when glaciers flowed westward to the Pacific Ocean and east-southeastward onto the Nechako Plateau from ice centers in the Skeena, Hazelton, Coast, and Omineca Mountains. Initially, glacier flow was confined by topography along major valleys, but eventually piedmont and montane glaciers coalesced to form an integrated glacier system, the Cordilleran ice sheet. In the maximum phase, a Cordilleran ice divide developed over the Nechako Plateau to 300 km inland from the Pacific coast. At this time, the surface of the ice sheet extended well above 2500 m above sea level, and flowed westward over the Skeena, Hazelton, and Coast Mountains onto the continental shelf, and eastward across the Rocky Mountains into Alberta. In the late glacial phase, a rapid rise of the equilibrium line caused ice lobes to stagnate in valleys, and restricted accumulation centers to high mountains. Discordant directions in ice flow are attributed to fluctuations of the ice divide representing changes in the location of accumulation centers and ice thickness. Ice centers probably shifted in response to climate, irregular growth in the ice sheet, rapid calving, ice streaming, and drainage of proglacial and subglacial water bodies. Crosscutting ice-flow indicators and preservation of early (valley parallel) flow features in areas exposed to later (cross-valley) glacier erosion indicate that the ice expansion phase was the most erosive and protracted event.

  16. Flow resistance of ice slurry in bends and elbow pipes

    NASA Astrophysics Data System (ADS)

    Niezgoda-Żelasko, B.; Żelasko, J.

    2014-08-01

    The present paper covers the flow of ice slurry made of a 10.6% ethanol solution through small-radius bends and elbow pipes. The paper presents the results of experimental research on the flow resistances of Bingham-fluid ice slurry in bends and elbows. The research, performed for three pipe diameters and a relative bend radius of 1<=D/di<=2, has made it possible to take into consideration the influence of friction resistances as well the of the flow geometry on the total local resistance coefficients. The study attempts to make the local resistance coefficient dependent on the Dean number defined for a generalized Reynolds number according to Metzner-Reade

  17. The Evolution of Flow Stripes and Internal Layers on Kamb Ice Stream, Antarctica

    NASA Astrophysics Data System (ADS)

    Campbell, I.; Welch, B.; Jacobel, R.; Pettersson, R.

    2006-12-01

    Flowstripes are ubiquitous features indicating fast ice flow on glaciers, ice streams and floating ice shelves. Model studies show that they are an expected consequence where flow is strongly convergent, or whenever velocity at the bed is large compared to shearing through the ice thickness (Gudmundsson et al., 1998). Under these conditions, basal undulations are effectively transmitted to the surface where they are advected for long distances downstream. Folding of internal layers depicted in radar profiles is also a common occurrence in ice streams. In the case of Kamb Ice Stream (KIS), "stacks" of internal layers folds on the scale of 1-3 kilometers in wavelength in the cross-flow direction have been traced for over 100 kilometers (Ng and Conway, 2004). The question is: What relationship, if any, do these folds have with respect to surface flowstripes? We have traced surface flowstripes in Radarsat and MODIS imagery for several hundred kilometers on KIS from the onset of streaming flow into the stagnant trunk. We compare the morphology and evolution of these features at the surface to the internal layer folds in cross-ice stream profiles at five transects along the length of KIS, including those analyzed by Ng and Conway (2004). We find little correspondence between the internal layer folds in the cross-flow radar profiles and the flowstripes seen on the surface directly above. The initial wavelengths of internal layer folds are generally in the range of 1-3 km and tend to converge downstream, ending with wavelengths typically less than a kilometer. Surface flowstripes, though having similar wavelengths (on the order of 1.5 to 3 km at onset), remain roughly subparallel for tens to hundreds of kilometers, eventually becoming less distinct as the ice stagnates but retaining their wavelength and spacing. We are thus able to identify examples where flowstripes cross above internal layers. The amplitude of internal layer folds we have measured decreases towards the

  18. An ice-rich flow origin for the banded terrain in the Hellas basin, Mars

    NASA Astrophysics Data System (ADS)

    Diot, X.; El-Maarry, M. R.; Guallini, L.; Schlunegger, F.; Norton, K. P.; Thomas, N.; Sutton, S.; Grindrod, P. M.

    2015-12-01

    The interior of Hellas Basin displays a complex landscape and a variety of geomorphological domains. One of these domains, the enigmatic banded terrain covers much of the northwestern part of the basin. We use high-resolution (Context Camera and High-Resolution Imaging Science Experiment) Digital Terrain Models to show that most of the complex viscous flowing behavior exhibited by the banded terrain is controlled by topography and flow-like interactions between neighboring banded terrain. Furthermore, the interior of the basin hosts several landforms suggestive of the presence of near-surface ice, which include polygonal patterns with elongated pits, scalloped depressions, isolated mounds, and collapse structures. We suggest that thermal contraction cracking and sublimation of near-surface ice are responsible for the formation and the development of most of the ice-related landforms documented in Hellas. The relatively pristine form, lack of superposed craters, and strong association with the banded terrain, suggest an Amazonian (<3 Ga) age of formation for these landforms. Finally, relatively high surface pressures (above the triple point of water) expected in Hellas and summertime temperatures often exceeding the melting point of water ice suggest that the basin may have recorded relatively "temperate" climatic conditions compared to other places on Mars. Therefore, the potentially ice-rich banded terrain may have deformed with lower viscosity and stresses compared to other locations on Mars, which may account for its unique morphology.

  19. Ice flow velocities and elevation change at Fleming Glacier, Wordie Ice Shelf, Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Wendt, A.; Wendt, J.; Bown, F.; Rivera, A.; Zamora, R.; Bravo, C.; Casassa, G.

    2009-04-01

    Glaciers in the Antarctic Peninsula have been responding to the pronounced atmospheric warming in the region (Vaughan et al. 2003) with frontal retreat (Cook et al. 2005), ice shelf collapse (Rott et al. 1996) and ice flow acceleration and thinning (Rignot et al. 2004; Shepherd et al. 2003; Pritchard & Vaughan 2007). These trends have progressively migrated southwards along the Antarctic Peninsula causing, for instance, a substantial retreat of Wilkins Ice Shelf (70.2˚ S) in 2008. At 69.3˚ S, but 300 km to the east, Wordie Ice Shelf experienced a major reduction in size in the 1980s (Doake & Vaughan 1991). Available information about this ice shelf and its feeding glaciers dates back to the 1970s when ice thickness and velocity measurements were carried out on Fleming Glacier (Doake 1975). Although initially it was thought that the post-collapse conditions of the feeding glaciers remained unchanged (Vaughan 1993), more recent evidence shows that glaciers accelerated after the ice shelf collapse and substantial glacier thinning has occurred (Rignot et al. 2005). We present data acquired during two field expeditions to Fleming Glacier. During the first season in November 2007, we installed an Automatic Weather Station (AWS) and a permanent GPS site. Additional data including a local GPS network, ground penetrating radar measurements and snow densities were collected. In December 2008, during the second field campaign, surface elevation data were acquired using an airborne laser scanner along a trajectory between Gibbs Glacier and Airy Glacier, along the ice divide between both sides of the Peninsula and on Fleming Glacier. The AWS was found protruding only 20 cm above the snow surface, demonstrating the high snow accumulation in the area, which was sufficient to cover the 4 m high tower installed in 2007 and that annual variability in the mass accumulation is significant. The station collected data for 250 days. The permanent GPS stopped collecting data after

  20. Coupling and feedback between Pacific sea ice and the Western Pacific pattern

    NASA Astrophysics Data System (ADS)

    Matthewman, N. J.; Magnusdottir, G.

    2010-12-01

    Coupling between sea ice variability in the Pacific basin and large scale modes of atmospheric variability are examined using weekly averaged data for December-April between 1979 and 2008. We define the large scale patterns of variability for sea ice concentration and 500hPa geopotential height over the Pacific basin and North America using Empirical Orthogonal Functions (EOFs). The patterns associated with the leading two EOFs of sea ice variability are a dipole in sea ice concentration with centers of action in the Bering Sea and Sea of Okhotsk (first EOF, ICE1), and an advance or retreat of sea ice in both seas simultaneously (second EOF, ICE2). Correlation analysis between the 500hPa geopotential height field and the principal component of the ICE2 pattern shows a large non-local response in geopotential height to changes in the ICE2 sea ice pattern. At extratropical latitudes this response in 500hPa geopotential height has two strong centers of action over the Bering Strait and Hudson Bay, with two somewhat weaker centers of action in the subtropics over the Western Pacific Ocean and the Atlantic Ocean. Further analysis suggests this response is due to sea ice in the Bering Sea region of the the ICE2 pattern, rather than the Sea of Okhotsk. This response pattern closely resembles a leading mode of 500hPa geopotential height variability, the Western Pacific (WP) pattern, indicating a coupled relationship between the WP pattern and the overall advance and retreat of sea ice in the Pacific basin. By considering intraseasonal time series of the principal components (indices) associated with the ICE2 and WP patterns, causality and coupling between the two is quantified using a stochastically forced Vector Autoregressive (VAR) model. Fitting the VAR model to observed time series for each index, we find that co-dependence between the ICE2 and WP significantly improves model performance compared with model configurations where dependence in either direction is

  1. Englacial Structures as Indicators of the Controls on Ice Flow

    NASA Astrophysics Data System (ADS)

    Holschuh, N.; Parizek, B. R.; Alley, R. B.; Anandakrishnan, S.

    2015-12-01

    Direct sampling of the subglacial environment is costly, and will therefore never supply the spatial coverage needed to determine the basal boundary conditions required for large-scale ice-sheet modeling. Studies of the West Antarctic Ice Sheet (WAIS) show that the frictional and rheologic properties of the bed are a leading control on the evolution of the system, so developing geophysical methods to help constrain the basal characteristics of WAIS will reduce uncertainty in predictions of the timing and magnitude of future sea-level rise. Radar-imaged structures within the ice are an attractive data set for this pursuit, as they contain information about the flow dynamics that transform the horizontally deposited layers to their modern configuration; however, they can be challenging to interpret, given the number of processes acting to deform the internal layers and the difficulty in automating their analysis. In this study, we move away from the layer-tracing paradigm in favor of an automated slope extraction algorithm. This has several advantages: it does not require feature-continuity, providing a more stable result in regions of intense deformation, and it results in a data product that maps directly to model output. For steady-state features, layer slopes reflect the horizontal and vertical velocity structure, making quantitative comparison of the model and observations simple compared to the more qualitative, particle tracer comparisons done in the past. Using a higher order ice-flow model, we attempt to refine our understanding of basal properties using reflector slope fields at the grounding line of Whillans Ice Stream and the shear margin of the North East Greenland Ice Stream, with the hope of eventually using this method for basin-scale inversions.

  2. Geomorphological Evidence for Pervasive Ground Ice on Ceres from Dawn Observations of Craters and Flows.

    NASA Astrophysics Data System (ADS)

    Schmidt, B. E.; Chilton, H.; Hughson, K.; Scully, J. E. C.; Russell, C. T.; Sizemore, H. G.; Nathues, A.; Platz, T.; Bland, M. T.; Schenk, P.; Hiesinger, H.; Jaumann, R.; Byrne, S.; Schorghofer, N.; Ammannito, E.; Marchi, S.; O'Brien, D. P.; Sykes, M. V.; Le Corre, L.; Capria, M. T.; Reddy, V.; Raymond, C. A.; Mest, S. C.; Feldman, W. C.

    2015-12-01

    Five decades of observations of Ceres' albedo, surface composition, shape and density suggest that Ceres is comprised of both silicates and tens of percent of ice. Historical suggestions of surficial hydrated silicates and evidence for water emission, coupled with its bulk density of ~2100 kg/m3 and Dawn observations of young craters containing high albedo spots support this conclusion. We report geomorphological evidence from survey data demonstrating that evaporative and fluid-flow processes within silicate-ice mixtures are prevalent on Ceres, and indicate that its surface materials contain significant water ice. Here we highlight three classes of features that possess strong evidence for ground ice. First, ubiquitous scalloped and "breached" craters are characterized by mass wasting and by the recession of crater walls in asymmetric patterns; these appear analogous to scalloped terrain on Mars and protalus lobes formed by mass wasting in terrestrial glaciated regions. The degradation of crater walls appears to be responsible for the nearly complete removal of some craters, particularly at low latitudes. Second, several high latitude, high elevation craters feature lobed flows that emanate from cirque-shaped head walls and bear strikingly similar morphology to terrestrial rock glaciers. These similarities include lobate toes and indications of furrows and ridges consistent with ice-cored or ice-cemented material. Other lobed flows persist at the base of crater walls and mass wasting features. Many flow features evidently terminate at ramparts. Third, there are frequent irregular domes, peaks and mounds within crater floors that depart from traditional crater central peaks or peak complexes. In some cases the irregular domes show evidence for high albedo or activity, and thus given other evidence for ice, these could be due to local melt and extrusion via hydrologic gradients, forming domes similar to pingos. The global distribution of these classes of features

  3. Two-dimensional numerical ice flow modelling of an empirically reconstructed martian glacier-like form

    NASA Astrophysics Data System (ADS)

    Brough, Stephen; Hubbard, Bryn; Hubbard, Alun

    2016-04-01

    Although a substantial reservoir of glacier ice has been identified in the mid-latitudes of Mars, debate still persists regarding the formation, current and former extent, and dynamic evolution of these ice masses. Here we present initial results from a higher-order, two-dimensional (2D) numerical model of ice flow for an empirically reconstructed glacier-like form (GLF), a distinctive ice related landform, similar in planform appearance to valley or debris-covered glaciers on Earth, in eastern Hellas Planitia, Mars (˜38.65 oS and 113.16 oE). The main aim of this study is to investigate the long-term temperature requirement to yield surface ice flow rates consistent with those recently reconstructed from boulder trails observed in a comparable GLF. We apply our numerical model to the GLF's central flowline under steady-state conditions and vary the viscosity related rate factor parameter, A, for a range of temperatures from 0 to -100 oC for our three reconstruction scenarios (lower [12 kPa], mean [22 kPa] and upper [38 kPa]; Karlsson et al. [2015] Geophys. Res. Lett., 42[8]). The model converges for all realistic temperatures yielding a range of 2D stress and strain configurations for our reconstructed GLF. The mean annual surface velocities across the three reconstruction scenarios show a similar pattern, with motion recorded at temperatures ranging from 0 oC to ˜ -70 oC, below which motion reduces to <10-5 m a‑1. In order to simulate flow rates to 7.5 mm a‑1 (Hubbard et al. [2014] The Cryosphere, 8), as determined for other martian GLFs, the model experiments reveal a required ice temperature for the GLF of between ˜ -7.5 and -27 oC.

  4. High Resolution Continuous Flow Analysis System for Polar Ice Cores

    NASA Astrophysics Data System (ADS)

    Dallmayr, Remi; Azuma, Kumiko; Yamada, Hironobu; Kjær, Helle Astrid; Vallelonga, Paul; Azuma, Nobuhiko; Takata, Morimasa

    2014-05-01

    In the last decades, Continuous Flow Analysis (CFA) technology for ice core analyses has been developed to reconstruct the past changes of the climate system 1), 2). Compared with traditional analyses of discrete samples, a CFA system offers much faster and higher depth resolution analyses. It also generates a decontaminated sample stream without time-consuming sample processing procedure by using the inner area of an ice-core sample.. The CFA system that we have been developing is currently able to continuously measure stable water isotopes 3) and electrolytic conductivity, as well as to collect discrete samples for the both inner and outer areas with variable depth resolutions. Chemistry analyses4) and methane-gas analysis 5) are planned to be added using the continuous water stream system 5). In order to optimize the resolution of the current system with minimal sample volumes necessary for different analyses, our CFA system typically melts an ice core at 1.6 cm/min. Instead of using a wire position encoder with typical 1mm positioning resolution 6), we decided to use a high-accuracy CCD Laser displacement sensor (LKG-G505, Keyence). At the 1.6 cm/min melt rate, the positioning resolution was increased to 0.27mm. Also, the mixing volume that occurs in our open split debubbler is regulated using its weight. The overflow pumping rate is smoothly PID controlled to maintain the weight as low as possible, while keeping a safety buffer of water to avoid air bubbles downstream. To evaluate the system's depth-resolution, we will present the preliminary data of electrolytic conductivity obtained by melting 12 bags of the North Greenland Eemian Ice Drilling (NEEM) ice core. The samples correspond to different climate intervals (Greenland Stadial 21, 22, Greenland Stadial 5, Greenland Interstadial 5, Greenland Interstadial 7, Greenland Stadial 8). We will present results for the Greenland Stadial -8, whose depths and ages are between 1723.7 and 1724.8 meters, and 35.520 to

  5. Ice melting and downward transport of meltwater by two-phase flow in Europa's ice shell

    NASA Astrophysics Data System (ADS)

    Kalousová, Klára; Souček, Ondřej; Tobie, Gabriel; Choblet, Gaël.; Čadek, Ondřej

    2014-03-01

    With its young surface, very few impact craters, and the abundance of tectonic and cryovolcanic features, Europa has likely been subjected to relatively recent endogenic activity. Morphological analyses of chaos terrains and double ridges suggest the presence of liquid water within the ice shell a few kilometers below the surface, which may result from enhanced tidal heating. A major issue concerns the thermal/gravitational stability of these water reservoirs. Here we investigate the conditions under which water can be generated and transported through Europa's ice shell. We address particularly the downward two-phase flow by solving the equations for a two-phase mixture of water ice and liquid water in one-dimensional geometry. In the case of purely temperate ice, we show that water is transported downward very efficiently in the form of successive porosity waves. The time needed to transport the water from the subsurface region to the underlying ocean varies between ˜1 and 100 kyr, depending mostly on the ice permeability. We further show that water produced in the head of tidally heated hot plumes never accumulates at shallow depths and is rapidly extracted from the ice shell (within less than a few hundred kiloyears). Our calculations indicate that liquid water will be largely absent in the near subsurface, with the possible exception of cold conductive regions subjected to strong tidal friction. Recently active double ridges subjected to large tidally driven strike-slip motions are perhaps the most likely candidates for the detection of transient water lenses at shallow depths on Europa.

  6. Paleo-ice flow directions of the Northern Antarctic Peninsula ice sheet based upon a new synthesis of seabed imagery

    NASA Astrophysics Data System (ADS)

    Lavoie, C.; Domack, E. W.; Pettit, E. C.; Scambos, T. A.; Larter, R. D.; Schenke, H.-W.; Yoo, K. C.; Gutt, J.; Wellner, J.; Canals, M.; Anderson, J. B.; Amblas, D.

    2014-10-01

    We present a new seafloor map for the northern Antarctic Peninsula (AP), including swath multibeam data sets from five national programs. Our map allows for the examination and interpretation of Last Glacial Maximum (LGM) paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes) on the AP continental shelf. The results show a flow bifurcation as ice exits the Larsen-B embayment. Flow emanating off the Seal Nunataks (including Robertson Island) is directed toward the southeast, then eastward as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" is directed toward the southeast then southward, as ice overflowed the tip of the Jason Peninsula to reach the southern perimeter of the embayment. Our reconstruction also refines the extent of at least five other distinct paleo-ice stream systems which, in turn, serve to delineate seven broad regions where contemporaneous ice domes must have been centered on the continental shelf during the LGM time interval. Our reconstruction is more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel.

  7. Unraveling Flow Patterns through Nonlinear Manifold Learning

    PubMed Central

    Tauro, Flavia; Grimaldi, Salvatore; Porfiri, Maurizio

    2014-01-01

    From climatology to biofluidics, the characterization of complex flows relies on computationally expensive kinematic and kinetic measurements. In addition, such big data are difficult to handle in real time, thereby hampering advancements in the area of flow control and distributed sensing. Here, we propose a novel framework for unsupervised characterization of flow patterns through nonlinear manifold learning. Specifically, we apply the isometric feature mapping (Isomap) to experimental video data of the wake past a circular cylinder from steady to turbulent flows. Without direct velocity measurements, we show that manifold topology is intrinsically related to flow regime and that Isomap global coordinates can unravel salient flow features. PMID:24614890

  8. A numerical simulation of the flow in the diffuser of the NASA Lewis icing research tunnel

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.; Keith, Theo G., Jr.

    1990-01-01

    The flow in the diffuser section of the Icing Research Tunnel at the NASA Lewis Research Center is numerically investigated. To accomplish this, an existing computer code is utilized. The code, known as PARC3D, is based on the Beam-Warming algorithm applied to the strong conservation law form of the complete Navier-Stokes equations. The first portion of the paper consists of a brief description of the diffuser and its current flow characteristics. A brief discussion of the code work follows. Predicted velocity patterns are then compared with the measured values.

  9. Precipitation patterns during channel flow

    NASA Astrophysics Data System (ADS)

    Jamtveit, B.; Hawkins, C.; Benning, L. G.; Meier, D.; Hammer, O.; Angheluta, L.

    2013-12-01

    Mineral precipitation during channelized fluid flow is widespread in a wide variety of geological systems. It is also a common and costly phenomenon in many industrial processes that involve fluid flow in pipelines. It is often referred to as scale formation and encountered in a large number of industries, including paper production, chemical manufacturing, cement operations, food processing, as well as non-renewable (i.e. oil and gas) and renewable (i.e. geothermal) energy production. We have studied the incipient stages of growth of amorphous silica on steel plates emplaced into the central areas of the ca. 1 meter in diameter sized pipelines used at the hydrothermal power plant at Hellisheidi, Iceland (with a capacity of ca 300 MW electricity and 100 MW hot water). Silica precipitation takes place over a period of ca. 2 months at approximately 120°C and a flow rate around 1 m/s. The growth produces asymmetric ca. 1mm high dendritic structures ';leaning' towards the incoming fluid flow. A novel phase-field model combined with the lattice Boltzmann method is introduced to study how the growth morphologies vary under different hydrodynamic conditions, including non-laminar systems with turbulent mixing. The model accurately predicts the observed morphologies and is directly relevant for understanding the more general problem of precipitation influenced by turbulent mixing during flow in channels with rough walls and even for porous flow. Reference: Hawkins, C., Angheluta, L., Hammer, Ø., and Jamtveit, B., Precipitation dendrites in channel flow. Europhysics Letters, 102, 54001

  10. Experimental Configuration Effects on ICE Tumble Flow Evaluation

    NASA Astrophysics Data System (ADS)

    Santana, Bryan; Puzinauskas, Paulius

    2014-11-01

    The generation of ICE (Internal Combustion Engine) in-cylinder charge motions, such as swirl and tumble, have shown positive effects on reducing fuel consumption and exhaust emission levels at partial engine loads. Tumble flow is commonly measured utilizing a steady-flow rig and two-dimensional PIV (Particle Image Velocimetry) systems, among others. In order to optimize the tumble flow, it is important to retrieve accurate measurements. The tumble flow values could be affected by variations in the geometry and/or design of the steady-flow rig utilized during flow tests. In this research, a four-valve per cylinder head was tested on a steady flow bench, varying several aspects of the configuration to evaluate how they influence bulk momentum as well as PIV measurements. The configuration variations included symmetrical, asymmetrical and runner-fed configurations throughout testing. Volumetric flow rate and tumble strength flow measurements were retrieved at the selected L/D ratios. Additionally, several PIV seeding particles were characterized for size and shape. Corresponding PIV flow measurements using each type of seeding were made to evaluate how the particles influence the results. NSF ECE Grant #1358991 supported Bryan Santana Rivera as an REU student.

  11. Kilimanjaro ice cliff recession patterns derived from terrestrial photogrammetry

    NASA Astrophysics Data System (ADS)

    Winkler, Michael; Tad Pfeffer, W.; Hanke, Klaus; Cullen, Nicolas J.; Kaser, Georg

    2010-05-01

    Ice cliffs are intriguing features of glaciers around the world, but little is known about mechanisms of their formation and maintenance. Ice cliffs also characterize the plateau glaciers on Kilimanjaro, Tanzania (3° S, 37° E). Their heights range from 3 to more than 40 meters and they have at least persisted since the late 19th century when early explorers documented them. Snow accumulation is only possible on the flat parts of the plateau glaciers but not on the vertical or near-vertical cliffs. Dry calving due to ice dynamics is unlikely and ice ablation through sublimation and melt by far out weighs the negligible mass gain by deposition of water vapour. Consequently, as soon as the cliffs are established, they are forced to retreat and thus, the areal shrinkage of the glaciers on Africa's highest peak is closely linked to the existence of these cliffs. In order to extract climate change details from the glaciers on Kilimanjaro, the sensitivity of the ice cliffs to climate fluctuations must be understood. Strikingly, the cliffs are mainly either north- or south-facing which entails at this near-equatorial site that direct sunlight either always hits the cliff faces from dawn till dusk, or not at all. The examination of the annual insolation patterns at a 25m high, south-facing sample cliff shows that it is not hit by direct shortwave radiation from March to October. During this time not enough energy is available for melting and only sublimation occurs. From November to February the cliff is sunlit 12 hours a day and its surface temperature can reach 0° C. Melting sometimes occurs during some hours, although air temperature is almost always below freezing. Point measurements at the sample cliff reveal a 20-30 times faster retreat during the sunlit period because melting is a much more energy-efficient ablation process than sublimation. Repeat terrestrial photogrammetric surveys have been carried out at the transition dates from the shaded to the sunlit

  12. Modeling of Ice Flow and Internal Layers Along a Flow Line Through Swiss Camp in West Greenland

    NASA Technical Reports Server (NTRS)

    Wang, W. L.; Zwally, H. Jay; Abdalati, W.; Luo, S.; Koblinsky, Chester J. (Technical Monitor)

    2001-01-01

    An anisotropic ice flow line model is applied to a flow line through Swiss Camp (69.57 N, 49.28 W) in West Greenland to estimate the dates of internal layers detected by Radio-Echo Sounding measurements. The effect of an anisotropic ice fabric on ice flow is incorporated into the steady state flow line model. The stress-strain rate relationship for anisotropic ice is characterized by an enhancement factor based on the laboratory observations of ice deformation under combined compression and shear stresses. By using present-day data of accumulation rate, surface temperature, surface elevation and ice thickness along the flow line as model inputs, a very close agreement is found between the isochrones generated from the model and the observed internal layers with confirmed dates. The results indicate that this part of Greenland ice sheet is primarily in steady state.

  13. Ice and thermal cameras for stream flow observations

    NASA Astrophysics Data System (ADS)

    Tauro, Flavia; Petroselli, Andrea; Grimaldi, Salvatore

    2016-04-01

    Flow measurements are instrumental to establish discharge rating curves and to enable flood risk forecast. Further, they are crucial to study erosion dynamics and to comprehend the organization of drainage networks in natural catchments. Flow observations are typically executed with intrusive instrumentation, such as current meters or acoustic devices. Alternatively, non-intrusive instruments, such as radars and microwave sensors, are applied to estimate surface velocity. Both approaches enable flow measurements over areas of limited extent, and their implementation can be costly. Optical methods, such as large scale particle image velocimetry, have proved beneficial for non-intrusive and spatially-distributed environmental monitoring. In this work, a novel optical-based approach is utilized for surface flow velocity observations based on the combined use of a thermal camera and ice dices. Different from RGB imagery, thermal images are relatively unaffected by illumination conditions and water reflections. Therefore, such high-quality images allow to readily identify and track tracers against the background. Further, the optimal environmental compatibility of ice dices and their relative ease of preparation and storage suggest that the technique can be easily implemented to rapidly characterize surface flows. To demonstrate the validity of the approach, we present a set of experiments performed on the Brenta stream, Italy. In the experimental setup, the axis of the camera is maintained perpendicular with respect to the water surface to circumvent image orthorectification through ground reference points. Small amounts of ice dices are deployed onto the stream water surface during image acquisition. Particle tracers' trajectories are reconstructed off-line by analyzing thermal images with a particle tracking velocimetry (PTV) algorithm. Given the optimal visibility of the tracers and their low seeding density, PTV allows for efficiently following tracers' paths in

  14. GenePattern flow cytometry suite

    PubMed Central

    2013-01-01

    Background Traditional flow cytometry data analysis is largely based on interactive and time consuming analysis of series two dimensional representations of up to 20 dimensional data. Recent technological advances have increased the amount of data generated by the technology and outpaced the development of data analysis approaches. While there are advanced tools available, including many R/BioConductor packages, these are only accessible programmatically and therefore out of reach for most experimentalists. GenePattern is a powerful genomic analysis platform with over 200 tools for analysis of gene expression, proteomics, and other data. A web-based interface provides easy access to these tools and allows the creation of automated analysis pipelines enabling reproducible research. Results In order to bring advanced flow cytometry data analysis tools to experimentalists without programmatic skills, we developed the GenePattern Flow Cytometry Suite. It contains 34 open source GenePattern flow cytometry modules covering methods from basic processing of flow cytometry standard (i.e., FCS) files to advanced algorithms for automated identification of cell populations, normalization and quality assessment. Internally, these modules leverage from functionality developed in R/BioConductor. Using the GenePattern web-based interface, they can be connected to build analytical pipelines. Conclusions GenePattern Flow Cytometry Suite brings advanced flow cytometry data analysis capabilities to users with minimal computer skills. Functionality previously available only to skilled bioinformaticians is now easily accessible from a web browser. PMID:23822732

  15. Degradation of ground ice in a changing climate: the potential impact of groundwater flow

    NASA Astrophysics Data System (ADS)

    de Grandpré, I.; Fortier, D.; Stephani, E.

    2011-12-01

    Climate changes affecting the North West portion of Canada alter the thermal state of the permafrost and promote ground ice degradation. Melting of ground ice leads to greater water flow into the ground and to significant hydraulic changes (i.e. drainage of peatland and lakes, triggering of thermokarst and new groundwater flow patterns). Road infrastructures built on permafrost are particularly sensitive to permafrost degradation. Road construction and maintenance induce heat flux into the ground by the increase of solar radiation absorption (comparing to natural ground), the increase of snow cover on side slopes, the infiltration of water in embankment material and the migration of surface water in the active layer. The permafrost under the roads is therefore submitted to a warmer environment than in natural ground and his behavior reflects how the permafrost will act in the future with the global warming trend. The permafrost degradation dynamic under a road was studied at the Beaver Creek (Yukon) experimental site located on the Alaska Highway. Permafrost was characterized as near-zero Celcius and highly susceptible to differential thaw-settlement due to the ground ice spatial distribution. Ice-rich cryostructures typical of syngenetic permafrost (e.g. microlenticular) were abundant in the upper and lower cryostratigraphic units of fine-grained soils (Units 1, 2A, and 2C). The middle ice-poor silt layer (Unit 2B) characterized by porous cryostructure comprised the top of a buried ice-wedge network extending several meters in the underlying layers and susceptible to degradation by thermo-erosion. These particular features of the permafrost at the study site facilitated the formation of taliks (unfrozen zones) under the road which leaded to a greater water flow. We believe that water flow is promoting an acceleration of permafrost degradation by advective heat transfer. This process remains poorly studied and quantified in permafrost environment. Field data on

  16. Patterns in simulated turbulent channel flow

    NASA Technical Reports Server (NTRS)

    Stretch, D.

    1990-01-01

    The surface stress is a key diagnostic in wall bounded turbulent flows. Large fluctuations in the stress are believed to be associated with intermittent 'bursting' events during which a large proportion of the turbulence production takes place. If this is so, then a detailed investigation of the structure of the surface stress and its spatial relationship to events within the flow could have wide application in drag reduction and other aspects of flow control. The initial phase of this project, therefore, concentrated on the surface stress field. The first objective is to carry out a statistical analysis of the instantaneous surface stress in a simulated turbulent channel flow, including comparison with multipoint experimental data from a zero pressure gradient turbulent boundary layer. The second objective is to apply a simple pattern recognition procedure to educe the characteristic spatial structure of various flow diagnostics. The final objective is to extend the pattern recognition analysis to examine the whole three dimensional structure of the flow.

  17. Channelised Subglacial Hydrology Modulates West Antarctic Ice Stream Basal Conditions and Flow

    NASA Astrophysics Data System (ADS)

    Siegert, M. J.; Ross, N.; Schroeder, D. M.

    2014-12-01

    Ice-sheet models show a coincidence between ice flux and basal water-flow maxima, as water at the bed of an ice sheets acts generally to lubricate the basal interface. Hydrological flow paths support this view with ice and basal-water drainage basins being well-aligned. At the scale of an individual ice stream, however, we reveal a significant offset of this alignment. Airborne geophysical data across the trunk of the Institute Ice Stream reveal how subglacial hydrology acts to subdue ice flow in two ways: first, by removing basal sediment, which decreases opportunity for the deformation of basal material and increases basal roughness; and, second, by reducing basal water pressures. The macro flow of basal water beneath the ice stream is known well from high-resolution bed elevation data and satellite imagery, which reveal well-organised water flow along the Robin Subglacial Basin, terminating at the grounding line as a channel carving upwards into the adjacent ice shelf. The highest ice flow is offset from this channelized zone, however. Maximum velocities are located where the bed is very smooth and radio-echo returns are strong; consistent with a dilated weak sedimentary material at the ice stream bed. The geophysical evidence is consistent with the removal of basal sediment from the deepest regions of the Robin Subglacial Basin by the action of water and illustrates how accumulation of sedimentary material from ice streams is not necessary a precise locator for maximum ice-flow velocities at the scale of individual ice streams. The figure shows a radar section across the Institute Ice Stream, West Antarctica, revealing two modes of basal environment. One is flat and smooth, indicative of a soft wet bed. The other is rougher, as a consequence of the removal of basal material and water channelisation. This latter region is located in the deepest regions of the Robin Subglacial Basin. The former region is located beneath the highest ice flow speeds.

  18. Flow of ices in the Ammonia-Water System

    NASA Technical Reports Server (NTRS)

    Durham, W. B.; Kirby, S. H.; Stern, L. A.

    1993-01-01

    We have fabricated in the laboratory and subsequently deformed crystalline hydrates and partial melts of the water-rich end of the NH3-H2O system, with the aim of improving our understanding of physical processes occurring in icy moons of the outer solar system. Deformation experiments were carried out at constant strain rate. The range of experimental variables are given. Phase relationships in the NH3-H2O system indicate that water ice and ammonia dihydrate, NH3-2H2O, are the stable phases under our experiment conditions. X-ray diffraction of our samples usually revealed these as the dominant phases, but we have also observed an amorphous phase (in unpressurized samples only) and occasionally significant ammonia monohydrate, NH3-H2O. The onset of partial melting at the peritectic temperature at about 176 K appeared as a sharp transition in strength observed in samples of x(sub NH3) = 0.05 and 0.01, the effect of melt was less pronounced. For any given water ice + dihydrate alloy in the subsolidus region, we observed one rheological law over the entire temperature range from 175 K to about 140 K. Below 140 K, a shear instability similar to that occurring in pure water ice under the same conditions limited our ability to measure ductile flow. The rheological laws for the several alloys vary systematically from that of pure ice to that of dihydrate. Pure dihydrate is about 4 orders of magnitude less viscous than water ice just below the peritectic temperature, but because of a very pronounced temperature dependence in dihydrate (100 kJ/mol versus 43 kJ/mol for water ice) the viscosity of dihydrate equals or exceeds that of water ice at T less than 140 K. The large variation in viscosity of dihydrate with relatively small changes in temperature may be helpful in explaining the rich variety of tectonic and volcanic features seen on the surfaces of icy moons in the outer solar system.

  19. Flow Pattern Characterization for a Centrifugal Impeller

    NASA Astrophysics Data System (ADS)

    Benavides, Efrén M.

    2014-08-01

    This paper proposes a model for characterizing the flow pattern of a centrifugal impeller attending to the severity of the reverse flow. The model assumes 1) a definition of an escaping particle as the one that flows in every operational point from the trailing edge towards the leading edge of the impeller blades, and 2) a characterization of flow where an operational point is said to have a theoretical flow pattern if it is not possible to establish a fully-reversed escaping particle on it. Therefore, the first part of the article is focused on defining an escaping particle for a centrifugal compressor. The model locates over the map of a centrifugal impeller the line that splits the map in two regions: the region on the right hand side, where a theoretical flow pattern can exist, and the region on the left, where a theoretical flow pattern cannot exist. Therefore, the locus of this line marks a frontier where the expected performance of the impeller cannot be sustained as high as expected. The second part of the article uses a high-performance commercial centrifugal impeller wheel for contrasting the model. A qualitative characterization of the surge line, conclusions and discussions are presented.

  20. Reactivation of Kamb Ice Stream tributaries triggers century-scale reorganization of Siple Coast ice flow in West Antarctica

    DOE PAGESBeta

    Bougamont, M.; Christoffersen, P.; Price, S. F.; Fricker, H. A.; Tulaczyk, S.; Carter, S. P.

    2015-10-21

    Ongoing, centennial-scale flow variability within the Ross ice streams of West Antarctica suggests that the present-day positive mass balance in this region may reverse in the future. Here we use a three-dimensional ice sheet model to simulate ice flow in this region over 250 years. The flow responds to changing basal properties, as a subglacial till layer interacts with water transported in an active subglacial hydrological system. We show that a persistent weak bed beneath the tributaries of the dormant Kamb Ice Stream is a source of internal ice flow instability, which reorganizes all ice streams in this region, leadingmore » to a reduced (positive) mass balance within decades and a net loss of ice within two centuries. This hitherto unaccounted for flow variability could raise sea level by 5 mm this century. Furthermore, better constraints on future sea level change from this region will require improved estimates of geothermal heat flux and subglacial water transport.« less

  1. Flow, fracture and modelled present stabilities of the Larsen C and northernmost Larsen D ice shelves

    NASA Astrophysics Data System (ADS)

    Jansen, Daniela; Kulessa, Bernd; Sammonds, Peter; Luckman, Adrian; King, Edward; Glasser, Neil

    2010-05-01

    We modelled the flow of the Larsen C and northernmost Larsen D ice shelves using an adapted continuum-mechanical model, and applied a fracture criterion to the simulated velocities to investigate its present-day stability. Constraints come from satellite data and geophysical measurements in the 2008-09 and 2009-2010 austral summer. We obtained excellent agreements between modelled and measured ice-flow velocities, and inferred and observed distributions of rifts and crevasses. Ice-shelf thickness was derived from BEDMAP and ICESat data and depth-density inferred from our seismic data. Notable exceptions occur in regions of modelled basal accretion down flow of promontories, thus placing the first quantitative constraints on their mechanical effects. Anomalously soft marine ice, advected into the ice shelf in flow-parallel bands, controls rates of rift propagation downstream. Our model simulations confirm that the Larsen C ice shelf is stable in its current dynamic regime. Ice-mechanical heterogeneities in ice-stream suture zones, sustained by marine-ice production down flow of promontories, have significant stabilising effects on the ice shelf. Reduction in rates of marine-ice production could therefore lead to weakening of suture zones and possibly development of Larsen B-style dynamic conditions prior to its disintegration. First model studies with an extended continuum-mechanical flow model and fracture criterion allowing for ice-shelf mechanical heterogeneities show, that weakening of prominent marine ice-rich flow bands, inferred to be dominant in the north and south of Larsen C ice shelf would, promote Larsen B-style mechanical evolution. This emphasizes the importance of further research into the mechanics of suture zones and their dependency on marine ice provenance, together with thorough quantification of their modification of the ice-shelf stress regime and thus its stability.

  2. Sensitivity Analysis and Variational Data Assimilation for ice flow - Application to the Mertz ice-tongue

    NASA Astrophysics Data System (ADS)

    Martin, N.; Monnier, J.

    2012-12-01

    To be confident in the accuracy of the modelling of ice flows requires to con- front numerical experiments to actual observations. This type of flow is strongly sensitive to its input parameters such as rheological parameters and boundary conditions like the friction on the bedrock. Using optimal control theory, we build a global 4D-Var algorithm using direct and adjoint model of the variational problem thus providing local sensitivity analysis and data assimilation (see [1]). In order to compute approximation of these flows, one consider the non newtonian velocity- pressure Stokes system described using mixed finite element method. The treat- ment of the free surface is performed using an Arbitrary Lagrangian Eulerian de- scription with robus elastic deformation and the adjoint method is constructed by algorithmic differentiation of the direct code using Tapenade software (INRIA). We lean on prior developments of the software DassFlow (see [2]). One of the major question for inverse methods in glaciology is to infer the fric- tion coefficient at bottom through data assimilation because it cannot be measured. In other respect, our first results based on real data shows that the rheological expo- nent and/or the thermal coefficient of the constitutive law (distributed parameter) has the same type of influence (see Figure 1) and can be inferred as well. Another modeling issue lies in the dynamic of the grounding line when con- sidering the floating part of the ice domain. Then, sensitivity analysis of the model response with respect to this grounding line dynamic leads to a better understand- ing of this unstable process and its empirical modelling. We present a real data application on the Mertz ice-shelf (Antarctica). Topography and surface velocities data are being provided by B. Legrésy (see [3]). References [1] Martin, N. and Monnier, J. : A three fields finite elements solver for viscoplas- tic free surface flows and variational data assimilation. In

  3. The Flow of Buoyant Meltwater Next to Ice Shelves and Icebergs

    NASA Astrophysics Data System (ADS)

    Wells, A. J.; Worster, G.

    2008-12-01

    Melting at the base of an ice shelf can play a significant role in the polar oceans, contributing to the mass balance of the ice shelf and leading to the formation of Ice Shelf Water. Fresh meltwater is relatively buoyant compared to the surrounding ocean and can rise along the ice surface, with the strength of this flow depending critically on the heat and salt fluxes from the ocean to the ice. We justify a simplified theoretical model that describes the coupling of heat and salt fluxes with the buoyancy- driven flow of meltwater, next to both vertical and sloping ice surfaces. The flow develops with distance along the ice surface, and different flow regimes can be obtained depending on the length and the slope of the ice surface. Both the heat and salt fluxes differ between the two regimes. On moderate scales the flow is controlled by buoyancy in a narrow region close to the ice surface. This predicts that the melting rate is independent of distance along the ice surface, consistent with previous laboratory scale measurements of heat transfer. This regime may be important for ablation at the sides of tabular icebergs, and under some regions of ice shelves. Further downstream, the flow is dominated by buoyancy located further from the wall, and can be described by a model similar to those often used to model ice-shelf-water plumes. This predicts that the melting rate increases with distance along the ice surface. Simple analytic solutions are also derived for flow in an unstratified fluid, which indicate the possible sensitivity of the ablation rate to changes in ocean temperature. The predicted variation of the heat and salt fluxes with distance along the ice surface may have important consequences for more complex models of ice-shelf-water flow.

  4. A method of predicting flow rates required to achieve anti-icing performance with a porous leading edge ice protection system

    NASA Technical Reports Server (NTRS)

    Kohlman, D. L.; Albright, A. E.

    1983-01-01

    An analytical method was developed for predicting minimum flow rates required to provide anti-ice protection with a porous leading edge fluid ice protection system. The predicted flow rates compare with an average error of less than 10 percent to six experimentally determined flow rates from tests in the NASA Icing Research Tunnel on a general aviation wing section.

  5. Study of Cold Heat Energy Release Characteristics of Flowing Ice Water Slurry in a Pipe

    NASA Astrophysics Data System (ADS)

    Inaba, Hideo; Horibe, Akihiko; Ozaki, Koichi; Yokota, Maki

    This paper has dealt with melting heat transfer characteristics of ice water slurry in an inside tube of horizontal double tube heat exchanger in which a hot water circulated in an annular gap between the inside and outside tubes. Two kinds of heat exchangers were used; one is made of acrylic resin tube for flow visualization and the other is made of stainless steel tube for melting heat transfer measurement. The result of flow visualization revealed that ice particles flowed along the top of inside tube in the ranges of small ice packing factor and low ice water slurry velocity, while ice particles diffused into the whole of tube and flowed like a plug built up by ice particles for large ice packing factor and high velocity. Moreover, it was found that the flowing ice plug was separated into numbers of small ice clusters by melting phenomenon. Experiments of melting heat transfer were carried out under some parameters of ice packing factor, ice water slurry flow rate and hot water temperature. Consequently, the correlation equation of melting heat transfer was derived as a function of those experimental parameters.

  6. Graft compliance and anastomotic flow patterns.

    PubMed

    Wang, L C; Guo, G X; Tu, R; Hwang, N H

    1990-01-01

    The oscillatory flow patterns at the venous anastomosis of a hemodialysis angioaccess loop graft system were studied using two new compliant vascular prostheses: a longitudinally compliant polytetrafluoroethylene-composite (Baxter Ultraflex PTFE-Plus) graft (BA) and a radially compliant ultrafine polyester fiber (TORAY-UFPF) graft (TR). A non-compliant Gore-Tex polytetrafluoroethylene graft was used as the control. The experimental grafts were 8 mm inside diameter x 25 cm long. Flow experiments were done in a transparent, elastic bench-top flow model; fabrication was based on silicone rubber casts obtained from femoral-to-femoral arteriovenous loop grafts surgically implanted in dogs. The loop graft constructed in the dog model was made to mimic the branchial-to-cephalic angioaccess loop graft commonly used in hemodialysis patients. The flow model was connected to a pulse generator, an adjustable arterial afterload, and a venous afterload. Under identical input conditions, the pressure and flow waveforms were monitored simultaneously at the proximal and distal ends of both the arterial and venous anastomoses. For each graft studied, the anastomotic flow field was visualized using laser illuminated hydrogen bubbles as tracers. At pulse rates of 60 and 90 beats/min, graft flow rates were 2.2 and 2.5 L/min, respectively. Among the grafts studied, measurable differences in pressure and flow wave attenuation and their respective phase lags resulted in characteristically dissimilar flow patterns at the venous anastomosis. Growth of the separation zone at the toe of the anastomosis, and the pattern of retrograde flow in the distal vein are visibly different in all three grafts. PMID:2340213

  7. Overview of the Icing and Flow Quality Improvements Program for the NASA Glenn Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Irvine, Thomas B.; Kevdzija, Susan L.; Sheldon, David W.; Spera, David A.

    2001-01-01

    Major upgrades were made in 1999 to the 6- by 9-Foot (1.8- by 2.7-m) Icing Research Tunnel (IRT) at the NASA Glenn Research Center. These included replacement of the electronic controls for the variable-speed drive motor, replacement of the heat exchanger, complete replacement and enlargement of the leg of the tunnel containing the new heat-exchanger, the addition of flow-expanding and flow-contracting turning vanes upstream and downstream of the heat exchanger, respectively, and the addition of fan outlet guide vanes (OGV's). This paper describes the rationale behind this latest program of IRT upgrades and the program's requirements and goals. An overview is given of the scope of work undertaken by the design and construction contractors, the scale-model IRT (SMIRT) design verification program, the comprehensive reactivation test program initiated upon completion of construction, and the overall management approach followed.

  8. Flow Pattern Phenomena in Two-Phase Flow in Microchannels

    NASA Astrophysics Data System (ADS)

    Keska, Jerry K.; Simon, William E.

    2004-02-01

    Space transportation systems require high-performance thermal protection and fluid management techniques for systems ranging from cryogenic fluid management devices to primary structures and propulsion systems exposed to extremely high temperatures, as well as for other space systems such as cooling or environment control for advanced space suits and integrated circuits. Although considerable developmental effort is being expended to bring potentially applicable technologies to a readiness level for practical use, new and innovative methods are still needed. One such method is the concept of Advanced Micro Cooling Modules (AMCMs), which are essentially compact two-phase heat exchangers constructed of microchannels and designed to remove large amounts of heat rapidly from critical systems by incorporating phase transition. The development of AMCMs requires fundamental technological advancement in many areas, including: (1) development of measurement methods/systems for flow-pattern measurement/identification for two-phase mixtures in microchannels; (2) development of a phenomenological model for two-phase flow which includes the quantitative measure of flow patterns; and (3) database development for multiphase heat transfer/fluid dynamics flows in microchannels. This paper focuses on the results of experimental research in the phenomena of two-phase flow in microchannels. The work encompasses both an experimental and an analytical approach to incorporating flow patterns for air-water mixtures flowing in a microchannel, which are necessary tools for the optimal design of AMCMs. Specifically, the following topics are addressed: (1) design and construction of a sensitive test system for two-phase flow in microchannels, one which measures ac and dc components of in-situ physical mixture parameters including spatial concentration using concomitant methods; (2) data acquisition and analysis in the amplitude, time, and frequency domains; and (3) analysis of results

  9. Geographical Patterns of Sea-Ice Retreat in the Transition to a Seasonally Ice-Free Arctic

    NASA Astrophysics Data System (ADS)

    DeRepentigny, P.; Tremblay, B.; Newton, R.; Pfirman, S. L.

    2015-12-01

    The September sea-ice extent minimum is influenced by summertime processes, primarily thermodynamic, as well as dynamic processes during the previous winter. In this paper, we focus on the effect of the large-scale winter mean sea-ice circulation on the following September minimum sea-ice extent and, in particular, how coastal divergence in the western and eastern Arctic dictates the geographical pattern of retreat. We compare the Community Climate System Model 4 (CCSM4) and the Community Earth System Model 1 Large Ensemble (CESM-LE) with sea-ice motion vectors from NOAA/NSIDC for the past three decades. We find that the large-scale mean winter atmospheric circulation in CCSM4 is characterized by a positive Arctic Oscillation (AO) index with a broad Transpolar Drift Stream, sea-ice divergence in the western Arctic and a large negative bias in its Arctic mean sea-level pressure (around -7 mb). On the other hand, CESM-LE has a mean winter sea-ice circulation more similar to observations in its late 20th century climate and no bias in its mean sea-level pressure, although there are some spatial differences.We use a Lagrangian ice trajectory model to quantify the amount of ice divergence along the Alaskan and Eurasian coastlines by backtracking the September sea-ice extent minimum ice edge to its position throughout the previous year. We find that the sea-ice retreat in CCSM4 occurs mostly on the Pacific side of the Arctic Ocean with more coastal divergence in the Chukchi and Beaufort seas - in line with the more positive AO. On the other hand, the sea-ice retreat is found to be more symmetric around the North Pole in CESM-LE. Given that a positive trend in the AO index is a robust feature of Global Climate Models participating in CMIP5, our results suggest that sea ice will continue to retreat preferentially from the Pacific sector, as has been observed in the last decade.

  10. Spatial patterns in backscatter strength across the Greenland Ice Sheet

    NASA Technical Reports Server (NTRS)

    Jezek, K. C.

    1993-01-01

    The relationship between the physical properties of the Greenland ice sheet and Synthetic Aperture Radar (SAR) data collected from aircraft and from ERS-1 is addressed. Limited aircraft data are combined with a description of the glacier surface to predict qualitatively the spatial and seasonal variation in backscatter strength across the ice sheet. In particular the model predicts relatively low backscatter near the ice edge where scattering is dominated by rough surface effects. Backscatter increases through the lake zone as volume scattering becomes important. Strongest backscatter is found in the percolation facies where volume scatter from snow grains and volume scatter from large, buried ice bodies becomes important. Backscatter weakens in the interior ice sheet where fine grained snow is the only mechanism producing backscatter.

  11. Flow-separation patterns on symmetric forebodies

    NASA Technical Reports Server (NTRS)

    Keener, Earl R.

    1986-01-01

    Flow-visualization studies of ogival, parabolic, and conical forebodies were made in a comprehensive investigation of the various types of flow patterns. Schlieren, vapor-screen, oil-flow, and sublimation flow-visualization tests were conducted over an angle-of-attack range from 0 deg. to 88 deg., over a Reynolds-number range from 0.3X10(6) to 2.0X10(6) (based on base diameter), and over a Mach number range from 0.1 to 2. The principal effects of angle of attack, Reynolds number, and Mach number on the occurrence of vortices, the position of vortex shedding, the principal surface-flow-separation patterns, the magnitude of surface-flow angles, and the extent of laminar and turbulent flow for symmetric, asymmetric, and wake-like flow-separation regimes are presented. It was found that the two-dimensional cylinder analogy was helpful in a qualitative sense in analyzing both the surface-flow patterns and the external flow field. The oil-flow studies showed three types of primary separation patterns at the higher Reynolds numbers owing to the influence of boundary-layer transition. The effect of angle of attack and Reynolds number is to change the axial location of the onset and extent of the primary transitional and turbulent separation regions. Crossflow inflectional-instability vortices were observed on the windward surface at angles of attack from 5 deg. to 55 deg. Their effect is to promote early transition. At low angles of attack, near 10 deg., an unexpected laminar-separation bubble occurs over the forward half of the forebody. At high angles of attack, at which vortex asymmetry occurs, the results support the proposition that the principal cause of vortex asymmetry is the hydrodynamic instability of the inviscid flow field. On the other hand, boundary-layer asymmetries also occur, especially at transitional Reynolds numbers. The position of asymmetric vortex shedding moves forward with increasing angle of attack and with increasing Reynolds number, and moves

  12. Synoptic Patterns Associated with Northeast and Southeast Ice Storms

    NASA Astrophysics Data System (ADS)

    Vargas, R., Jr.; Booth, J. F.

    2014-12-01

    Wintertime storms that produce precipitation events such as snow, freezing rain, and ice pellets cause significant damage to utility services and disrupt travel. These synoptic systems involve deep isothermal regions where warm, moist air over-runs surface sub-freezing air. However, little else is known about the synoptic evolution of the storms. Therefore this study analyzes the dynamic and thermodynamic conditions of ice events along the east coast. The National Climatic Data Center (NCDC) Storm Events Database is used to pull the dates of ice events from the Northeast and Southeast climate regions for 1996-2013. We find that Southeast ice storms often cover a large geographical region, while Northeast ice storms tend to be much smaller but more frequent. We utilize Geographic Information Systems (GIS) to relate the spatial coverage of our ice events to population density in order to compare the impacts of the events in the two regions. Next, we analyze the synoptic control of ice storms from both regions in an effort to explain what causes the size differences. For the ice storms gathered from the Storm Events Database, composites are generated for sea level pressure, 2-meter temperatures, 850-hPa temperature and 850-500 hPa thickness, and vorticity parameters, from reanalysis data. A comparison of the composites for the Southeast and Northeast storms suggests that the size differences relate in part to the thermal structure produced by cold air damming. The ice events are also associated with objectively identified cyclone tracks, and we find that cyclone forward speed is inversely proportional to the size of the ice storm produced.

  13. A Theoretical and Experimental Investigation of Ice-Shelf Flow Dynamics

    NASA Astrophysics Data System (ADS)

    Wearing, M.; Worster, G.; Hindmarsh, R. C. A.

    2015-12-01

    Ice-shelf buttressing is a major control on the rate of ice discharged from fast-flowing ice streams that drain the Antarctic Ice Sheet. The collapse of an ice shelf can lead to dramatic acceleration and thinning of the ice streams and glaciers that flowed into the former shelf. The magnitude of the buttressing force depends on the shelf geometry and confinement. This geometry is determined by the ice-shelf extent, resulting from retreat due to iceberg calving and shelf advance due to flow. In contrast to large-scale ice-sheet models, which require high resolution datasets, we aim to gain insight using simple idealized models, focusing on the transition from lateral confinement to non-confinement. By considering a confined shelf with lateral shear stresses controlling the flow, steady-state analytical solutions can be calculated. These solutions are then compared to a numerical model for a confined flow, which incorporates both shear and extensional stresses. A boundary layer close to the calving front is identified, where both extensional and shear stresses control the dynamics. We test these idealized models against fluid-mechanical laboratory experiments, designed to simulate the flow of an ice shelf in a narrow channel. From these experiments velocity fields and altimetry for the ice-shelf are collected, allowing for comparison with the theoretical models and geophysical data.

  14. Bimodal pattern of seismicity detected at the ocean margin of an Antarctic ice shelf

    NASA Astrophysics Data System (ADS)

    Lombardi, Denis; Benoit, Lionel; Camelbeeck, Thierry; Martin, Olivier; Meynard, Christophe; Thom, Christian

    2016-06-01

    In Antarctica, locally grounded ice, such as ice rises bordering floating ice shelves, plays a major role in the ice mass-balance as it stabilizes the ice sheet flow from the hinterland. When in direct contact with the ocean, the ice rise buttressing effect may be altered in response of changing ocean forcing. To investigate this vulnerable zone, four sites near the boundary of an ice shelf with an ice rise promontory in Dronning Maud Land, East-Antarctica were monitored for a month in early 2014 with new instruments that include both seismic and GPS sensors. Our study indicated that this transition zone experiences periodic seismic activity resulting from surface crevassing during oceanic tide-induced flexure of the ice shelf. The most significant finding is the observation of apparent fortnightly tide-modulated low frequency, long duration seismic events at the seaward front of the ice rise promontory. A basal origin of these events is postulated with the ocean water surge at each new spring tide triggering basal crevassing or basal slip on a local bedrock asperity. Detection and monitoring of such seismicity may help identifying ice rise zones vulnerable to intensified ocean forcing.

  15. Bimodal pattern of seismicity detected at the ocean margin of an Antarctic ice shelf

    NASA Astrophysics Data System (ADS)

    Lombardi, Denis; Benoit, Lionel; Camelbeeck, Thierry; Martin, Olivier; Meynard, Christophe; Thom, Christian

    2016-08-01

    In Antarctica, locally grounded ice, such as ice rises bordering floating ice shelves, plays a major role in the ice mass balance as it stabilizes the ice sheet flow from the hinterland. When in direct contact with the ocean, the ice rise buttressing effect may be altered in response of changing ocean forcing. To investigate this vulnerable zone, four sites near the boundary of an ice shelf with an ice rise promontory in Dronning Maud Land, East-Antarctica were monitored for a month in early 2014 with new instruments that include both seismic and GPS sensors. Our study indicated that this transition zone experiences periodic seismic activity resulting from surface crevassing during oceanic tide-induced flexure of the ice shelf. The most significant finding is the observation of apparent fortnightly tide-modulated low-frequency, long-duration seismic events at the seaward front of the ice rise promontory. A basal origin of these events is postulated with the ocean water surge at each new spring tide triggering basal crevassing or basal slip on a local bedrock asperity. Detection and monitoring of such seismicity may help identifying ice rise zones vulnerable to intensified ocean forcing.

  16. Bedform signature of a West Antarctic palaeo-ice stream reveals a multi-temporal record of flow and substrate control

    NASA Astrophysics Data System (ADS)

    Graham, Alastair G. C.; Larter, Robert D.; Gohl, Karsten; Hillenbrand, Claus-Dieter; Smith, James A.; Kuhn, Gerhard

    2009-12-01

    The presence of a complex bedform arrangement on the sea floor of the continental shelf in the western Amundsen Sea Embayment, West Antarctica, indicates a multi-temporal record of flow related to the activity of one or more ice streams in the past. Mapping and division of the bedforms into distinct landform assemblages reveals their time-transgressive history, which implies that bedforms can neither be considered part of a single downflow continuum nor a direct proxy for palaeo-ice velocity, as suggested previously. A main control on the bedform imprint is the geology of the shelf, which is divided broadly between rough bedrock on the inner shelf, and smooth, dipping sedimentary strata on the middle to outer shelf. Inner shelf bedform variability is well preserved, revealing information about local, complex basal ice conditions, meltwater flow, and ice dynamics over time. These details, which are not apparent at the scale of regional morphological studies, indicate that past ice streams flowed across the entire shelf at times, and often had onset zones that lay within the interior of the Antarctic Ice Sheet today. In contrast, highly elongated subglacial bedforms on sedimentary strata of the middle to outer shelf represent a timeslice snapshot of the last activity of ice stream flow, and may be a truer representation of fast palaeo-ice flow in these locations. A revised model for ice streams on the shelf captures complicated multi-temporal bedform patterns associated with an Antarctic palaeo-ice stream for the first time, and confirms a strong substrate control on a major ice stream system that drained the West Antarctic Ice Sheet during the Late Quaternary.

  17. Trends in ice formation at Lake Neusiedl since 1931 and large-scale oscillation patterns

    NASA Astrophysics Data System (ADS)

    Soja, Anna-Maria; Maracek, Karl; Soja, Gerhard

    2013-04-01

    Ice formation at Lake Neusiedl (Neusiedler See, Fertitó), a shallow steppe lake (area 320 km2, mean depth 1.2 m) at the border of Austria/Hungary, is of ecological and economic importance. Ice sailing and skating help to keep a touristic off-season alive. Reed harvest to maintain the ecological function of the reed belt (178 km2) is facilitated when lake surface is frozen. Changes in ice formation were analysed in the frame of the EULAKES-project (European Lakes under Environmental Stressors, www.eulakes.eu), financed by the Central Europe Programme of the EU. Data records of ice-on, ice duration and ice-off at Lake Neusiedl starting with the year 1931, and air temperature (nearby monitoring station Eisenstadt - Sopron (HISTALP database and ZAMG)) were used to investigate nearly 80 winters. Additionally, influences of 8 teleconnection patterns, i.e. the Atlantic Multidecadal Oscillation (AMO), the East Atlantic pattern (EAP), the East Atlantic/West Russia pattern (EA/WR), the Eastern Mediterranean Pattern (EMP), the Mediterranean Oscillation (MO) for Algiers and Cairo, and for Israel and Gibraltar, resp., the North Atlantic Oscillation (NAO) and the Scandinavia pattern (SCA) were assessed. Ice cover of Lake Neusiedl showed a high variability between the years (mean duration 71±27 days). Significant trends for later ice-on (p=0.02), shorter ice duration (p=0.07) and earlier ice-off (p=0.02) for the period 1931-2011 were found by regression analysis and trend analysis tests. On an average, freezing of Lake Neusiedl started 2 days later per decade and ice melting began 2 days earlier per decade. Close relationships between mean air temperature and ice formation could be found: ice-on showed a dependency on summer (R=+0.28) and autumn air temperatures (R=+0.51), ice duration and ice off was related to autumn (R=-0.36 and -0.24), winter (R=-0.73 and -0.61) and concurrent spring air temperatures (R=-0.44). Increases of air temperature by 1° C caused an 8.4 days later

  18. Spatial and temporal patterns in Arctic river ice breakup revealed by automated ice detection from MODIS imagery

    NASA Astrophysics Data System (ADS)

    Cooley, Sarah; Pavelsky, Tamlin

    2016-04-01

    The annual spring breakup of river ice has important consequences for northern ecosystems and significant economic implications for Arctic industry and transportation. River ice breakup research is restricted by the sparse distribution of hydrological stations in the Arctic, where limited available data suggests a trend towards earlier ice breakup. The specific climatic mechanisms driving this trend, however, are complex and can vary both regionally and within river systems. Consequently, understanding the response of river ice processes to a warming Arctic requires simultaneous examination of spatial and temporal patterns in breakup timing. Here we present an automated algorithm for river ice breakup detection using MODIS satellite imagery that enables identification of spatial and temporal breakup patterns at large scales. We examine breakup timing on the Mackenzie, Lena, Ob' and Yenisey rivers for the period 2000-2014. First, we split each river into 10 km segments. Next, for each day of the breakup season, we classify each river pixel as snow/ice, mixed ice/water or open water based on MODIS reflectance values and remove all cloud-covered segments using the MODIS cloud product. We then define the breakup date as the first day where the segment is 75% open water. Using this method, we are able to determine breakup dates with a mean uncertainty of +/-1.3 days. We find our remotely sensed breakup dates to be highly correlated to ground breakup dates and the timing of peak discharge. All statistically significant temporal trends in breakup timing are negative, indicating an overall shift towards earlier breakup. Considerable variability in the statistical significance and magnitude of trends along each river suggests that different climatic and physiographic drivers are impacting spatial patterns in breakup. Trends detected on the lower Mackenzie corroborate recent studies indicating weakening ice resistance and earlier breakup timing near the Mackenzie Delta. In

  19. Shifting Arctic Sea-ice Formation and Melt Patterns in a Warming World

    NASA Astrophysics Data System (ADS)

    Newton, R.; Fowler, C.; Tremblay, B.; Pfirman, S. L.

    2011-12-01

    As the Arctic warms, sea-ice formation and melt regions are shifting. Ice retreats earlier, open water extends farther north, and fall freeze-up comes later. The changes are already having an impact on important features of the aquatic Arctic system such as surface productivity, water-column stratification, sea-ice velocities, and the export of freshwater (and buoyancy) to the Nordic Seas. These changes are likely to amplify as the trend toward warmer conditions continues. In this contribution we present ice formation and melt patterns over the duration of the polar satellite observation period, from 1979 to the current. The changes are complex, reflecting latitudinal and temporal shifts with warming of the Northern Hemisphere as well as dynamical trends, such as changes in the prevailing surface wind stress patterns and reduction of internal ice stress. We analyze the satellite-derived sea-ice formation and melt dataset with an eye on: the potential impacts on melt/deposition regions (nutrient delivery, water column stratification, contaminant release); the timing of ice formation anddeposition; changes in bathymetric regimes of the formatino and deposition (which imply changes in sea-ice rafted material transport); shifting freshwater transport patterns; and the underlying dynamical mechanisms driving the observed changes.

  20. Lagrangian analysis of ICESat altimetry reveals patterns of ice shelf basal melting

    NASA Astrophysics Data System (ADS)

    Moholdt, G.; Fricker, H. A.; Padman, L.

    2012-12-01

    Iceberg calving and ice shelf basal melting are normal mass-loss processes that over time roughly balance the outflow of ice from the Antarctic Ice Sheet. Most basal melting is thus compensated by ice advection and is not detected by the traditional methods of analyzing surface elevation changes in a fixed geographic coordinate system (Eulerian). Here we present a new method that derive elevation changes in a "Lagrangian" sense from repeat-track ICESat laser altimetry, where specific locations are followed on the advancing ice shelf surface. We use a published ice shelf velocity field to correct for ice advection between consecutive repeats, and then convert the Lagrangian dh/dt estimates into ice thickness changes based on a model of the firn layer. In some locations, the derived ice thickness changes are much larger the Eulerian approach. The Lagrangian approach reduces the noise level of the derived ice thickness changes and reveals clear spatial patterns that we interpret as variations in basal melting. For the largest Antarctic ice shelves (Ross and Filchner-Ronne), we find that the Lagrangian thinning rates increase progressively towards the fronts, which is consistent with oceanographic models that suggest higher basal melt rates in the frontal zone. There are few examples of localized Lagrangian thickening, suggesting that basal melting is likely dominating over basal freezing in the interior of most ice shelves. Combined with data on surface mass balance and firn compaction, our Lagrangian approach can provide new insights into the magnitude and extent of basal melting, as well as being an important validation for models of ice-ocean interaction.

  1. Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet

    PubMed Central

    Bons, Paul D.; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C.; Binder, Tobias; Eisen, Olaf; Jessell, Mark W.; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka

    2016-01-01

    The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier. PMID:27126274

  2. Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet

    NASA Astrophysics Data System (ADS)

    Bons, Paul D.; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C.; Binder, Tobias; Eisen, Olaf; Jessell, Mark W.; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka

    2016-04-01

    The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier.

  3. Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet.

    PubMed

    Bons, Paul D; Jansen, Daniela; Mundel, Felicitas; Bauer, Catherine C; Binder, Tobias; Eisen, Olaf; Jessell, Mark W; Llorens, Maria-Gema; Steinbach, Florian; Steinhage, Daniel; Weikusat, Ilka

    2016-01-01

    The increasing catalogue of high-quality ice-penetrating radar data provides a unique insight in the internal layering architecture of the Greenland ice sheet. The stratigraphy, an indicator of past deformation, highlights irregularities in ice flow and reveals large perturbations without obvious links to bedrock shape. In this work, to establish a new conceptual model for the formation process, we analysed the radar data at the onset of the Petermann Glacier, North Greenland, and created a three-dimensional model of several distinct stratigraphic layers. We demonstrate that the dominant structures are cylindrical folds sub-parallel to the ice flow. By numerical modelling, we show that these folds can be formed by lateral compression of mechanically anisotropic ice, while a general viscosity contrast between layers would not lead to folding for the same boundary conditions. We conclude that the folds primarily form by converging flow as the mechanically anisotropic ice is channelled towards the glacier. PMID:27126274

  4. Determination of temperature and pressure patterns associated to sea ice fields in Antarctica, with modern tools of pattern recognition

    NASA Astrophysics Data System (ADS)

    Orquera, F. J.; Torchio, M. A.; Barreira, S.

    2012-12-01

    Monthly sea ice anomalies derived from passive microwave satellite data for Antarctica spanning the period 1979-2010 are classified into 16 different patterns (6 for summer and autumn and 10 for winter and spring). Each of these patterns has an atmospheric temperature and pressure structure associated with it (i.e., a specific mode of climate variability). These results were obtained using principal component analysis (PCA) in T-Mode. Here we attempt to identify the sea ice pattern for 2011 without using the passive microwave data, and instead using what can be inferred from the temperature and pressure fields associated with the patterns. We approach this issue with a multilayer Perceptron (neuronal network) with supervised learning and a back-propagation algorithm. The Perceptron is the most common Artificial Neural Network topology dedicated to image pattern recognition. It was implemented through the use of temperature and pressure anomalies field images that were associated with a group of sea ice anomaly patterns. The variables analyzed included only composites of surface air temperature and pressure to simplify the density of input data and avoid a non-converging solution (monthly input data for the period 1979-2010). The results of this analysis can be used to identify the sea ice patterns without the need of a new PCA analysis of the sea ice data. The anticipated outcome of this study is to obtain an accurate prediction of sea ice and perform a forecast. The findings may be vital to a more accurate planning of future missions to coastal Antarctic bases.

  5. Pattern and timing of retreat of the last British-Irish Ice Sheet

    NASA Astrophysics Data System (ADS)

    Clark, Chris D.; Hughes, Anna L. C.; Greenwood, Sarah L.; Jordan, Colm; Sejrup, Hans Petter

    2012-06-01

    During the last glacial the ice sheet that subsumed most of Britain, Ireland and the North Sea attained its maximum extent by 27 ka BP and with an ice volume sufficient to raise global sea level by ca 2.5 m when it melted. We reconstruct the demise of this British-Irish Ice Sheet (BIIS) and present palaeo-glaciological maps of retreat stages between 27 and 15 ka BP. The whole land area was investigated using remote sensing data and we present maps of moraines, meltwater channels, eskers, and drumlins and a methodology of how to interpret and bring them together. For the continental shelf, numerous large moraines were discovered recording an extensive pattern of retreat stretching from SW Ireland to the Shetland Isles. From an integration of this new mapping of glacial geomorphology (>26,000 landforms) with previously published evidence, compiled in the BRITICE database, we derive a pattern of retreat for the whole BIIS. We review and compile relevant dates (881 examples) that constrain the timing of retreat. All data are held within a Geographic Information System (GIS), and are deciphered to produce a best-estimate of the combined pattern and timing of retreat. Pattern information reveals an ice sheet mainly comprised of a shelf-parallel configuration from SW Ireland to NE Scotland but it spread far enough to the south to incorporate outlying ice domes over Wales, the Lake District and Kerry. Final disintegration was into a number of separate ice caps, rather than reduction as a single mass, and paradoxically, retreat was not always back to high ground. By 23 ka BP ice withdrew along its northern boundaries at the same time as the southern margins were expanding, including transient ice streaming down the Irish Sea and advances of lobes in the Cheshire Basin, Vale of York and east coast of England. Ice divides migrated south. By 19 ka the ice sheet was in crisis with widespread marine-based ice losses, particularly in the northern North Sea and the Irish Sea

  6. Shallow flows over surfaces of patterned wettability

    NASA Astrophysics Data System (ADS)

    Grivel, Morgane; Jeon, David; Gharib, Morteza

    2014-11-01

    Our previous work showed that surfaces with spatially patterned wetting properties induce passive displacements of shallow flows. Polycarbonate plates were patterned with hydrophobic and hydrophilic stripes, and a thin, rectangular water jet impinged on the patterned surface. We reported development of intriguing roller structures at the hydrophobic-hydrophilic interfaces. In our present work, we study the effect of varying the stripes' width, spacing, and orientation on the dynamics of these roller structures. Specifically, we are interested in the vortex generation and air entrainment by the rollers. We report quantitative results to this effect. We will also discuss potential uses of this technique for modifying contact line dynamics and bow waves near ships. This work is supported by the Office of Naval Research (Grant # ONR-N00014-11-1-0031) and by NSF-GRFP.

  7. Accuracy improvement of the ice flow rate measurements on Antarctic ice sheet by DInSAR method

    NASA Astrophysics Data System (ADS)

    Shiramizu, Kaoru; Doi, Koichiro; Aoyama, Yuichi

    2015-04-01

    DInSAR (Differential Interferometric Synthetic Aperture Radar) is an effective tool to measure the flow rate of slow flowing ice streams on Antarctic ice sheet with high resolution. In the flow rate measurement by DInSAR method, we use Digital Elevation Model (DEM) at two times in the estimating process. At first, we use it to remove topographic fringes from InSAR images. And then, it is used to project obtained displacements along Line-Of-Sight (LOS) direction to the actual flow direction. ASTER-GDEM widely-used for InSAR prosessing of the data of polar region has a lot of errors especially in the inland ice sheet area. Thus the errors yield irregular flow rates and directions. Therefore, quality of DEM has a substantial influence on the ice flow rate measurement. In this study, we created a new DEM (resolution 10m; hereinafter referred to as PRISM-DEM) based on ALOS/PRISM images, and compared PRISM-DEM and ASTER-GDEM. The study area is around Skallen, 90km south from Syowa Station, in the southern part of Sôya Coast, East Antarctica. For making DInSAR images, we used ALOS/PALSAR data of 13 pairs (Path633, Row 571-572), observed during the period from November 23, 2007 through January 16, 2011. PRISM-DEM covering the PALSAR scene was created from nadir and backward view images of ALOS/PRISM (Observation date: 2009/1/18) by applying stereo processing with a digital mapping equipment, and then the automatically created a primary DEM was corrected manually to make a final DEM. The number of irregular values of actual ice flow rate was reduced by applying PRISM-DEM compared with that by applying ASTER-GDEM. Additionally, an averaged displacement of approximately 0.5cm was obtained by applying PRISM-DEM over outcrop area, where no crustal displacement considered to occur during the recurrence period of ALOS/PALSAR (46days), while an averaged displacement of approximately 1.65 cm was observed by applying ASTER-GDEM. Since displacements over outcrop area are considered

  8. Will ice flow in land-terminating regions of the Greenland ice sheet accelerate under future climate warming?

    NASA Astrophysics Data System (ADS)

    Doyle, S. H.; Hubbard, A.

    2015-12-01

    Recent observations and modelling studies investigating the dynamic response of land-terminating regions of the Greenland ice sheet to a warmer climate remain at best unreconciled and at worst equivocal and contradictory. Some studies suggest that ice flow will be regulated over annual time scales by the development of efficient subglacial drainage. Others suggest that such self-regulation processes may not be effective at higher elevations and that the recent and projected expansion of supraglacial lakes further into the ice sheet interior has lead to increased ice flow at high elevations. On the other hand, the observation that rapid in situ supraglacial lake drainage events may be triggered by precursory basal motion have led to the argument that, by inference, such lake drainage in the interior may be impossible, or at least hindered, by reduced strain rates and lack of surface crevasses in these regions. The response of the Greenland ice sheet to a warmer, wetter climate, in which late summer and autumnal cyclonic weather events drive widespread melt, rainfall and transient accelerations may also need to be accounted for in assessments of future Greenland ice mass loss if predicted changes in Greenland's climate are realised. This talk will critically assess recent insights gained into this topic, attempt to resolve some of them, and suggest directions for future research.

  9. Ice-flow structure and ice dynamic changes in the Weddell Sea sector of West Antarctica from radar-imaged internal layering

    NASA Astrophysics Data System (ADS)

    Bingham, Robert G.; Rippin, David M.; Karlsson, Nanna B.; Corr, Hugh F. J.; Ferraccioli, Fausto; Jordan, Tom A.; Le Brocq, Anne M.; Rose, Kathryn C.; Ross, Neil; Siegert, Martin J.

    2015-04-01

    Recent studies have aroused concerns over the potential for ice draining the Weddell Sea sector of West Antarctica to figure more prominently in sea level contributions should buttressing from the Filchner-Ronne Ice Shelf diminish. To improve understanding of how ice stream dynamics there evolved through the Holocene, we interrogate radio echo sounding (RES) data from across the catchments of Institute and Möller Ice Streams (IIS and MIS), focusing especially on the use of internal layering to investigate ice-flow change. As an important component of this work, we investigate the influence that the orientation of the RES acquisition track with respect to ice flow exerts on internal layering and find that this influence is minimal unless a RES flight track parallels ice flow. We also investigate potential changes to internal layering characteristics with depth to search for important temporal transitions in ice-flow regime. Our findings suggest that ice in northern IIS, draining the Ellsworth Subglacial Highlands, has retained its present ice-flow configuration throughout the Holocene. This contrasts with less topographically constrained ice in southern IIS and much of MIS, whose internal layering evinces spatial changes to the configuration of ice flow over the past ~10,000 years. Our findings confirm Siegert et al.'s (2013) inference that fast flow was diverted from Bungenstock Ice Rise during the Late Holocene and suggest that this may have represented just one component of wider regional changes to ice flow occurring across the IIS and MIS catchments as the West Antarctic Ice Sheet has thinned since the Last Glacial Maximum.

  10. ICEd-ALE Treatment of 3-D Fluid Flow.

    Energy Science and Technology Software Center (ESTSC)

    1999-09-13

    Version: 00 SALE3D calculates three-dimensional fluid flow at all speeds, from the incompressible limit to highly supersonic. An implicit treatment of the pressure calculation similar to that in the Implicit Continuous-fluid Eulerian (ICE) technique provides this flow speed flexibility. In addition, the computing mesh may move with the fluid in a typical Lagrangian fashion, be held in an Eulerian manner, or move in some arbitrarily specified way to provide a continuous rezoning capability. This latitudemore » results from use of an Arbitrary Lagrangian-Eulerian (ALE) treatment of the mesh. The partial differential equations solved are the Navier-Stokes equations and the mass and internal energy equations. The fluid pressure is determined from an equation of state and supplemented with an artificial viscous pressure for the computation of shock waves. The computing mesh consists of a three-dimensional network of arbitrarily shaped, six-sided deformable cells, and a variety of user-selectable boundary conditions are provided in the program.« less

  11. Flow patterns measurements with PIV laser method

    NASA Astrophysics Data System (ADS)

    Podlinski, Janusz; Kocik, Marek; Dors, Miroslaw; Metel, Emilia; Mizeraczyk, Jerzy

    2007-03-01

    In this paper a Particle Image Velocimetry (PIV) measurement technique and it's application for the flow patterns measurements in our experiments is presented. Present PIV system consist of double Nd:YAG laser with pulse energy of 50 mJ, optics for transmission and formation a laser beam, two CCD cameras (Kodak MegaPlus ES-1.0 and FlowSense M2), Dantec processor PIV 1100 and PC computer with FlowManager software. The maximum measured area is 0.5 m2 and flow velocity in the range of 0-300 m/s. So far, the PIV measurements were carried out in hydrodynamic and transonic ducts, corona discharge reactors, electrostatic precipitator models and a microwave torch discharge reactor in The Szewalski Institute of Fluid Flow Machinery, Polish Academy of Sciences in Gdansk. The PIV system was used also for the measurements of the velocity fields round the hull of the ship model in The Ship Design and Research Centre in Gdansk.

  12. Characteristic flow patterns generated by macrozoobenthic structures

    NASA Astrophysics Data System (ADS)

    Friedrichs, M.; Graf, G.

    2009-02-01

    A laboratory flume channel, equipped with an acoustic Doppler flow sensor and a bottom scanning laser, was used for detailed, non-intrusive flow measurements (at 2 cm s - 1 and 10 cm s - 1 ) around solitary biogenic structures, combined with high-resolution mapping of the structure shape and position. The structures were replicates of typical macrozoobenthic species commonly found in the Mecklenburg Bight and with a presumed influence on both, the near-bed current regime and sediment transport dynamics: a worm tube, a snail shell, a mussel, a sand mound, a pit, and a cross-stream track furrow. The flow was considerably altered locally by the different protruding structures (worm tube, snail, mussel and mound). They reduced the horizontal approach velocity by 72% to 79% in the wake zone at about 1-2 cm height, and the flow was deflected around the structures with vertical and lateral velocities of up to 10% and 20% of the free-stream velocity respectively in a region adjacent to the structures. The resulting flow separation (at flow Reynolds number of about 4000 and 20,000 respectively) divided an outer deflection region from an inner region with characteristic vortices and the wake region. All protruding structures showed this general pattern, but also produced individual characteristics. Conversely, the depressions (track and pit) only had a weak influence on the local boundary layer flow, combined with a considerable flow reduction within their cavities (between 29% and 53% of the free-stream velocity). A longitudinal vortex formed, below which a stagnant space was found. The average height affected by the structure-related mass flow rate deficit for the two velocities was 1.6 cm and 1.3 cm respectively (80% of height and 64%) for the protruding structures and 0.6 cm and 0.9 cm (90% and 127% of depth) for the depressions. Marine benthic soft-bottom macrozoobenthos species are expected to benefit from the flow modifications they induce, particularly in terms of

  13. A Theoretical and Experimental Investigation of Ice-Shelf Flow Dynamics

    NASA Astrophysics Data System (ADS)

    Wearing, Martin; Worster, Grae; Hindmarsh, Richard

    2015-11-01

    Ice-shelf buttressing is a major control on the rate of ice discharged from fast-flowing ice streams that drain the Antarctic Ice Sheet. The magnitude of the buttressing force depends on the shelf geometry and confinement. This geometry is determined by the ice-shelf extent, resulting from retreat due to iceberg calving and shelf advance due to flow. In contrast to large-scale ice-sheet models, which require high resolution datasets, we aim to gain insight using simple idealized models, focusing on the transition from lateral confinement to non-confinement. By considering a confined shelf with lateral shear stresses controlling the flow, steady-state analytical solutions can be calculated. These solutions are then compared to a numerical model for a confined flow, which incorporates both shear and extensional stresses. A boundary layer close to the calving front is identified, where both extensional and shear stresses control the dynamics. We test these idealized models against fluid-mechanical laboratory experiments, designed to simulate the flow of an ice shelf in a narrow channel. From these experiments velocity fields and altimetry for the ice-shelf are collected, allowing for comparison with the theoretical models and geophysical data.

  14. Organization of ice flow by localized regions of elevated geothermal heat flux

    NASA Astrophysics Data System (ADS)

    Pittard, M. L.; Galton-Fenzi, B. K.; Roberts, J. L.; Watson, C. S.

    2016-04-01

    The impact of localized regions of elevated geothermal heat flux on ice sheet dynamics is largely unknown. Simulations of ice dynamics are produced using poorly resolved and low-resolution estimates of geothermal heat flux. Observations of crustal heat production within the continental crust underneath the Lambert-Amery glacial system in East Antarctica indicate that high heat flux regions of at least 120 mW m-2 exist. Here we investigate the influence of simulated but plausible, localized regions of elevated geothermal heat flux on ice dynamics using a numerical ice sheet model of the Lambert-Amery glacial system. We find that high heat flux regions have a significant effect across areas of slow-moving ice with the influence extending both upstream and downstream of the geothermal anomaly, while fast-moving ice is relatively unaffected. Our results suggest that localized regions of elevated geothermal heat flux may play an important role in the organization of ice sheet flow.

  15. A method of predicting flow rates required to achieve anti-icing performance with a porous leading edge ice protection system

    NASA Technical Reports Server (NTRS)

    Kohlman, D. L.

    1983-01-01

    A proposed method of analytically predicting the minimum fluid flow rate required to provide anti-ice protection with a porous leading edge system on a wing under a given set of flight conditions is presented. Results of the proposed method are compared with the actual results of an icing test of a real wing section in the NASA Lewis Icing Research Tunnel.

  16. Detection and Analysis of Complex Patterns of Ice Dynamics in Antarctica from ICESat Laser Altimetry

    NASA Astrophysics Data System (ADS)

    Babonis, Gregory Scott

    There remains much uncertainty in estimating the amount of Antarctic ice mass change, its dynamic component, and its spatial and temporal patterns. This work remedies the limitations of previous studies by generating the first detailed reconstruction of total and dynamic ice thickness and mass changes across Antarctica, from ICESat satellite altimetry observations in 2003-2009 using the Surface Elevation Reconstruction and Change Detection (SERAC) method. Ice sheet thickness changes are calculated with quantified error estimates for each time when ICESat flew over a ground-track crossover region, at approximately 110,000 locations across the Antarctic Ice Sheet. The time series are partitioned into changes due to surficial processes and ice dynamics. The new results markedly improve the spatial and temporal resolution of surface elevation, volume, and mass change rates for the AIS, and can be sampled at annual temporal resolutions. The results indicate a complex spatiotemporal pattern of dynamic mass loss in Antarctica, especially along individual outlet glaciers, and allow for the quantification of the annual contribution of Antarctic ice loss to sea level rise. Over 5000 individual locations exhibit either strong dynamic ice thickness change patterns, accounting for approximately 500 unique spatial clusters that identify regions likely influenced by subglacial hydrology. The spatial distribution and temporal behavior of these regions reveal the complexity and short-time scale variability in the subglacial hydrological system. From the 500 unique spatial clusters, over 370 represent newly identified, and not previously published, potential subglacial water bodies indicating an active subglacial hydrological system over a much larger region than previously observed. These numerous new observations of dynamic changes provide more than simply a larger set of data. Examination of both regional and local scale dynamic change patterns across Antarctica shows newly

  17. Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

    NASA Astrophysics Data System (ADS)

    Doyle, Samuel H.; Hubbard, Alun; van de Wal, Roderik S. W.; Box, Jason E.; van As, Dirk; Scharrer, Kilian; Meierbachtol, Toby W.; Smeets, Paul C. J. P.; Harper, Joel T.; Johansson, Emma; Mottram, Ruth H.; Mikkelsen, Andreas B.; Wilhelms, Frank; Patton, Henry; Christoffersen, Poul; Hubbard, Bryn

    2015-08-01

    Intense rainfall events significantly affect Alpine and Alaskan glaciers through enhanced melting, ice-flow acceleration and subglacial sediment erosion, yet their impact on the Greenland ice sheet has not been assessed. Here we present measurements of ice velocity, subglacial water pressure and meteorological variables from the western margin of the Greenland ice sheet during a week of warm, wet cyclonic weather in late August and early September 2011. We find that extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior. We suggest that the late-season timing was critical in promoting rapid runoff across an extensive bare ice surface that overwhelmed a subglacial hydrological system in transition to a less-efficient winter mode. Reanalysis data reveal that similar cyclonic weather conditions prevailed across southern and western Greenland during this time, and we observe a corresponding ice-flow response at all land- and marine-terminating glaciers in these regions for which data are available. Given that the advection of warm, moist air masses and rainfall over Greenland is expected to become more frequent in the coming decades, our findings portend a previously unforeseen vulnerability of the Greenland ice sheet to climate change.

  18. The role of ice dynamics in shaping vegetation in flowing waters.

    PubMed

    Lind, Lovisa; Nilsson, Christer; Polvi, Lina E; Weber, Christine

    2014-11-01

    Ice dynamics is an important factor affecting vegetation in high-altitude and high-latitude streams and rivers. During the last few decades, knowledge about ice in streams and rivers has increased significantly and a respectable body of literature is now available. Here we review the literature on how ice dynamics influence riparian and aquatic vegetation. Traditionally, plant ecologists have focused their studies on the summer period, largely ignoring the fact that processes during winter also impact vegetation dynamics. For example, the freeze-up period in early winter may result in extensive formation of underwater ice that can restructure the channel, obstruct flow, and cause flooding and thus formation of more ice. In midwinter, slow-flowing reaches develop a surface-ice cover that accumulates snow, protecting habitats under the ice from formation of underwater ice but also reducing underwater light, thus suppressing photosynthesis. Towards the end of winter, ice breaks up and moves downstream. During this transport, ice floes can jam up and cause floods and major erosion. The magnitudes of the floods and their erosive power mainly depend on the size of the watercourse, also resulting in different degrees of disturbance to the vegetation. Vegetation responds both physically and physiologically to ice dynamics. Physical action involves the erosive force of moving ice and damage caused by ground frost, whereas physiological effects - mostly cell damage - happen as a result of plants freezing into the ice. On a community level, large magnitudes of ice dynamics seem to favour species richness, but can be detrimental for individual plants. Human impacts, such as flow regulation, channelisation, agriculturalisation and water pollution have modified ice dynamics; further changes are expected as a result of current and predicted future climate change. Human impacts and climate change can both favour and disfavour riverine vegetation dynamics. Restoration of streams

  19. Surface micro-grooves for near-wall exergy and flow control: application to aircraft intake de-icing

    NASA Astrophysics Data System (ADS)

    Naterer, G. F.; Glockner, P. S.; Thiele, D.; Chomokovski, S.; Venn, G.; Richardson, G.

    2005-03-01

    This paper develops a new surface micro-profiling technique for reducing exergy losses and controlling near-wall flow processes, particularly for anti-icing of a helicopter surface. Fabrication of embedded surface microchannels entails surface etching with KOH and XeF2 gas, so that the interspersed microchannels can be assembled into a surface layer of silicon. Testing of the micro-profiled surfaces is performed with particle image velocimetry in a water tunnel. Experimental data indicate that converging open microchannels lead to certain differences of flow patterns on the downstream side of an engine cooling bay. Furthermore, exergy losses for external flow past the parallel embedded microchannels are shown to be lower than previous benchmark results without microchannels. Analytical results are presented for these losses of available energy and exergy destruction. Reduced drag of slip-flow conditions within each microchannel offsets the added friction irreversibility of larger surface area. By altering the near-wall flow patterns, it is anticipated that embedded surface microchannels can provide a useful new approach for dealing with flow-related problems of aircraft icing.

  20. Generation of pyroclastic flows by explosive interaction of lava flows with ice/water-saturated substrate

    NASA Astrophysics Data System (ADS)

    Belousov, Alexander; Behncke, Boris; Belousova, Marina

    2011-04-01

    We describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes Klyuchevskoy (Russia) and Etna (Italy). The explosions occurred at considerable (up to 5 km) distances from primary volcanic vents, generally at steep (15-35°) slopes, and in places where incandescent basaltic or basaltic-andesitic lava propagated over ice/water-saturated substrate. The explosions produced high (up to 7 km) vertical ash/steam-laden clouds as well as pyroclastic flows that traveled up to 2 km downslope. Individual lobes of the pyroclastic flow deposits were up to 2 m thick, had steep lateral margins, and were composed of angular to subrounded bomb-size clasts in a poorly sorted ash-lapilli matrix. Character of the juvenile rock clasts in the pyroclastic flows (poorly vesiculated with chilled and fractured cauliflower outer surfaces) indicated their origin by explosive fragmentation of lava due to contact with external water. Non-juvenile rocks derived from the substrate of the lava flows comprised up to 75% in some of the pyroclastic flow deposits. We suggest a model where gradual heating of a water-saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction (in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava). On steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water-saturated substrate. The sliding lava and substrate disintegrate and intermix, triggering explosive "fuel-coolant" type interaction that produces large volume of fine-grained clastic material. Relatively cold steam-laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material, thus part of it descends downslope in the form of pyroclastic flow. Similar explosive events were described for active lava flows of Llaima (Chile), Pavlof (Alaska), and Hekla (Iceland

  1. Historical Dates of Ice-Affected Flows for 18 Rivers in New England

    USGS Publications Warehouse

    Hodgkins, Glenn A.; Caldwell, James M.; Dudley, Robert W.

    2003-01-01

    Historical dates of ice-affected flows for 18 rivers in New England were compiled and are presented in this report. The length of this record for the rivers ranges from 48 to 71 years, with an average of 62 years. The minimum number of days of ice-affected flow in a water year (October 1 to September 30) ranged from zero on three rivers in south-coastal Maine and coastal New Hampshire to 110 on the Allagash River in northern Maine. The maximum number of days of ice-affected flow in a water year ranged from 106 on the Royal River in south-coastal Maine to 171 on the Allagash River in northern Maine. Six streamflow-< gaging stations in Maine, New Hampshire, and Vermont had their latest days of ice-affected flow in the spring of 1939.

  2. Characteristics and distribution patterns of snow and meteoric ice in the Weddell Sea and their contribution to the mass balance of sea ice

    NASA Astrophysics Data System (ADS)

    Eicken, Hajo; Lange, Manfred A.; Wadhams, Peter

    1994-01-01

    Based on snow- and ice-thickness measurements at >11 000 points augmented by snow- and icecore studies during 4 expeditions from 1986 - 92 in the Weddell Sea, we describe characteristics and distribution patterns of snow and meteoric ice and assess their importance for the mass balance of sea ice. For first-year ice (FY) in the central and eastern Weddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker snow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepage into the snow pack, snow salinities averaged 4‰. Through 18O measurements the distribution of meteoric ice (i.e. precipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean density of 290 kg/m3, the snow cover itself contributes 8% to total ice mass (7% FY, 11% SY). Analysis of 18O in snow indicates a local maximum in accumulation in the 65 to 75°S latitude zone. Hydrogen peroxide in the snow has proven useful as a temporal tracer and for identification of second-year floes. Drawing on accumulation data from stations at the Weddell Sea coast, it becomes clear that the onset of ice growth is important for the evolution of ice thickness and the interaction between ice and snow. Loss of snow to leads due to wind drift may be considerable, yet is reduced owing to metamorphic processes in the snow column. This is confirmed by a comparison of accumulation data from coastal stations and from snow depths over sea ice. Temporal and spatial accumulation patterns of snow are shown to be important in controlling the sea-ice cover evolution.

  3. Analysing subglacial geology hidden beneath the ice streams flowing into the Weddell Sea (West Antarctica)

    NASA Astrophysics Data System (ADS)

    Ferraccioli, F.; King, O.; Jordan, T. A.; Ross, N.; Bingham, R. G.; Le Brocq, A. M.; Smith, A.; Hindmarsh, R. C. A.; Siegert, M. J.

    2014-12-01

    Subglacial geology provides important controls on the onset and maintenance of fast glacial flow in the West Antarctic Ice Sheet (WAIS). Widespread subglacial sediments deposited within deep rift basins, thinner drapes of marine sediments within the West Antarctic Rift System (WARS) and high geothermal heat flux associated with Cenozoic magmatism have been previously identified as key geological controls that can modulate ice sheet dynamics. Here, we compile a suite of new and vintage aeromagnetic and airborne gravity observations to examine the large-scale geological setting of several major ice streams flowing into the Weddell Sea Embayment and assess the role of geological controls on subglacial topography and WAIS flow regimes. We focus on the subglacial geology beneath the Institute and Moeller ice streams, the Rutford ice stream and the Evans ice stream. We show that the Moeller ice stream is underlain by a major strike-slip fault system, which is part of the tectonic boundary between East and West Antarctica. A set of en-echelon subglacial basins formed along the strike-slip fault and these basins appear to steer enhanced flow far inland. Deep sedimentary basins are not present along this fault system, however, suggesting that subglacial sediments are not necessarily a geological template for the onset of fast glacial flow. The recently identified Robin Subglacial Basin that underlies the fast flowing coastal region of the Institute ice stream contains 1-3 km of sedimentary infill and smooth bedrock topography. Enhanced flow in the tributaries of the Institute ice stream cuts across the Ellsworth Mountains and is controlled by basement faults displacing metasedimentary and metavolcanic rocks. Prominent magnetic anomalies overlie outcrops of Jurassic granitic intrusions and enable us to trace their subglacial extent beneath the catchments of Institute, Moeller and Rutford ice streams. These large granitoid bodies form topographic highs that appear to divert

  4. Self-regulation of ice flow varies across the ablation area in South-West Greenland

    NASA Astrophysics Data System (ADS)

    van de Wal, R. S. W.; Smeets, C. J. P. P.; Boot, W.; Stoffelen, M.; van Kampen, R.; Doyle, S.; Wilhelms, F.; van den Broeke, M. R.; Reijmer, C. H.; Oerlemans, J.; Hubbard, A.

    2014-09-01

    The concept of a positive feedback between ice flow and enhanced melt rates in a warmer climate fuelled the debate regarding the temporal and spatial controls on seasonal ice acceleration. Here we combine melt, basal water pressure, and ice velocity data. We show using twenty years of data covering the whole ablation area that there is no strong feedback between annual ice velocities and melt rates. Annual velocities even slightly decreased with increasing melt. Results also indicate that melt variations are most important for velocity variations in the upper ablation zone up to the equilibrium line altitude. During the extreme melt in 2012 a large velocity response near the equilibrium line was observed, highlighting the possibility of rapidly changing bed conditions in this part of the ice sheet that may lead to a doubling of the annual ice velocity.

  5. Self-regulation of ice flow varies across the ablation area in south-west Greenland

    NASA Astrophysics Data System (ADS)

    van de Wal, R. S. W.; Smeets, C. J. P. P.; Boot, W.; Stoffelen, M.; van Kampen, R.; Doyle, S. H.; Wilhelms, F.; van den Broeke, M. R.; Reijmer, C. H.; Oerlemans, J.; Hubbard, A.

    2015-04-01

    The concept of a positive feedback between ice flow and enhanced melt rates in a warmer climate fuelled the debate regarding the temporal and spatial controls on seasonal ice acceleration. Here we combine melt, basal water pressure and ice velocity data. Using 20 years of data covering the whole ablation area, we show that there is not a strong positive correlation between annual ice velocities and melt rates. Annual velocities even slightly decreased with increasing melt. Results also indicate that melt variations are most important for velocity variations in the upper ablation zone up to the equilibrium line altitude. During the extreme melt in 2012, a large velocity response near the equilibrium line was observed, highlighting the possibility of meltwater to have an impact even high on the ice sheet. This may lead to an increase of the annual ice velocity in the region above S9 and requires further monitoring.

  6. The Contribution of Englacial Latent Heat Transfer to Seaward Ice Flux from Regions of Convergent and Divergent Ice Flow in Western Greenland

    NASA Astrophysics Data System (ADS)

    Poinar, K.; Joughin, I. R.

    2014-12-01

    Glacial meltwater can refreeze within firn and crevasses, warming the ice through latent heat transfer. The consequent softening of the ice has been identified as a potential destabilization mechanism for the Greenland Ice Sheet, which would flow more quickly seaward with lower viscosity. We calculate the effect of meltwater refreezing within firn and englacial features on ice temperature and viscosity in two contrasting areas of western Greenland: Jakobshavn Isbrae, a convergent, fast-flowing outlet glacier, and the Pakitsoq area (Swiss Camp) directly to its north, a "dead zone" experiencing slow, divergent flow because of its location between two outlet glaciers. We explore how much refreezing affects the seaward velocity of ice in each location by comparing our modeled temperature profiles to borehole data. Pakitsoq ice shows significant englacial latent heat transfer, or cryo-hydrologic warming, while the ice in Jakobshavn has warmed largely due to percolation within the firn. We find that the Pakitsoq region is rather unique in western Greenland because of the long residence time of the ice in the ablation zone (800 years) there; ice flowing through Jakobshavn, by contrast, spends only 20 years in the ablation zone, not enough time for deep, diffusive englacial warming to occur. Examination of the velocity field of the ice sheet indicates that 70% of the ice flux through western Greenland spends insufficient time (200 years or less) in the ablation zone to produce significant englacial warming. Thus, the effects of englacial latent heat transfer may be fairly limited to regions of divergent flow such as Pakitsoq. Ice loss in these regions, which tend to be land-terminating, is dominated by surface melt rather than seaward ice motion, further suggesting that englacial heat transfer may have a lesser effect on the stability of the ice sheet than previously supposed.

  7. Ice flow dynamics and mass loss of Totten Glacier, East Antarctica, from 1989 to 2015

    NASA Astrophysics Data System (ADS)

    Li, Xin; Rignot, Eric; Mouginot, Jeremie; Scheuchl, Bernd

    2016-06-01

    Totten Glacier has the largest ice discharge in East Antarctica and a basin grounded mostly below sea level. Satellite altimetry data have revealed ice thinning in areas of fast flow. Here we present a time series of ice velocity measurements spanning from 1989 to 2015 using Landsat and interferometric synthetic-aperture radar data, combined with ice thickness from Operation IceBridge, and surface mass balance from Regional Atmospheric Climate Model. We find that the glacier speed exceeded its balance speed in 1989-1996, slowed down by 11 ± 12% in 2000 to bring its ice flux in balance with accumulation (65 ± 4 Gt/yr), then accelerated by 18 ± 3% until 2007, and remained constant thereafter. The average ice mass loss (7 ± 2 Gt/yr) is dominated by ice dynamics (73%). Its acceleration (0.6 ± 0.3 Gt/yr2) is dominated by surface mass balance (80%). Ice velocity apparently increased when ocean temperature was warmer, which suggests a linkage between ice dynamics and ocean temperature.

  8. Paleo-Ice Sheet/Stream Flow Directions of the Northern Antarctic Peninsula Ice Sheet Based Upon New Synthesis of Multibeam Seabed Imagery

    NASA Astrophysics Data System (ADS)

    Domack, E. W.; Lavoie, C.; Scambos, T. A.; Pettit, E. C.; Schenke, H. W.; Yoo, K. C.; Larter, R. D.; Gutt, J.; Wellner, J.; Canals, M.; Anderson, J. B.; Amblas, D.

    2014-12-01

    We provide a new map of swath bathymetry for the northern Antarctic Peninsula, including data sets from five national programs. Our map allows for the compilation and examination of Late Glacial Maximum (LGM) paleo-ice sheet/stream flow directions developed upon the seafloor from the preservation of: mega-scale glacial lineations, drumlinized features, and selective linear erosion. We combine this with terrestrial observations of flow direction to place constraints on ice divides and accumulation centers (ice domes). The results show a flow divergence in Larsen B embayment, between flow emanating off the Seal Nunataks (including Robertson Island) that directed ice in a southeast direction, then easterly as the flow transits toward the Robertson Trough. A second, stronger "streaming flow" directed ice southeasterly then southward, as ice overflowed the Jason Peninsula to reach the Jason Trough, the southern perimeter of the embayment. This reconstruction is far more detailed than other recent compilations because we followed specific flow indicators and have kept tributary flow paths parallel. Our reconstitution also refines the extent of at least five other distinct paleo-ice stream systems which in turn serve to delineate seven broad regions where ice domes must have been centered across the continental shelf during the LGM.

  9. Flow variability and ongoing margin shifts on Bindschadler and MacAyeal Ice Streams, West Antarctica

    NASA Astrophysics Data System (ADS)

    Hulbe, C. L.; Scambos, T. A.; Klinger, M.; Fahnestock, M. A.

    2016-02-01

    Ice streams on the Ross Sea side of the West Antarctic Ice Sheet are known to experience flow variability on hourly, annual, and multicentury time scales. We report here on observations of flow variability at the decade scale on the Bindschadler and MacAyeal Ice Streams (BIS and MacIS). Our analysis makes use of archived ice velocity data and new mappings from composited Landsat 7 and Landsat 8 imagery that together span the interval from 1985 to 2014. Both ice streams speedup and slowdown in a range of about ±5 m a-2 over our various comparison intervals. The rates of change are variable in both time and space, and there is no evidence of external forcing at work across the two streams. Widespread changes are most likely linked to instability in the subglacial till and/or subglacial water flow. Sticky spots near the confluence of the two ice streams are loci for speed changes. These relatively young and slow-flowing features appear to be forcing shifts in margin position near the outlets of both streams. The margin jumps reduce the effective outlet widths of the streams by 20% and 30% on BIS and MacIS, respectively. Those magnitudes are similar to the outlet narrowing experienced by Kamb Ice Stream prior to its stagnation.

  10. Investigation of the flow in the diffuser section of the NASA Lewis icing research tunnel

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.; Keith, Theo G., Jr.

    1989-01-01

    The flow in the diffuser section of the Icing Research Wind Tunnel at NASA Lewis Research Center is investigated using both tunnel calibration measurements and numerical simulation techniques. Local pressure and temperature measurements are made to establish velocity and temperature profiles in the diffuser of the tunnel. These profiles are compared with similar measurements made prior to renovating the equipment which generates the tunnel's icing cloud. This comparison indicates the manner in which this change affected the flow. The measured data were also compared with a numerical simulation of the flow to help understand how such changes may favorably alter the tunnel flow.

  11. A study of grout flow pattern analysis

    SciTech Connect

    Lee, S. Y.; Hyun, S.

    2013-01-10

    A new disposal unit, designated as Salt Disposal Unit no. 6 (SDU6), is being designed for support of site accelerated closure goals and salt nuclear waste projections identified in the new Liquid Waste System plan. The unit is cylindrical disposal vault of 380 ft diameter and 43 ft in height, and it has about 30 million gallons of capacity. Primary objective was to develop the computational model and to perform the evaluations for the flow patterns of grout material in SDU6 as function of elevation of grout discharge port, and slurry rheology. A Bingham plastic model was basically used to represent the grout flow behavior. A two-phase modeling approach was taken to achieve the objective. This approach assumes that the air-grout interface determines the shape of the accumulation mound. The results of this study were used to develop the design guidelines for the discharge ports of the Saltstone feed materials in the SDU6 facility. The focusing areas of the modeling study are to estimate the domain size of the grout materials radially spread on the facility floor under the baseline modeling conditions, to perform the sensitivity analysis with respect to the baseline design and operating conditions such as elevation of discharge port, discharge pipe diameter, and grout properties, and to determine the changes in grout density as it is related to grout drop height. An axi-symmetric two-phase modeling method was used for computational efficiency. Based on the nominal design and operating conditions, a transient computational approach was taken to compute flow fields mainly driven by pumping inertia and natural gravity. Detailed solution methodology and analysis results are discussed here.

  12. A Numerical Evaluation of Icing Effects on a Natural Laminar Flow Airfoil

    NASA Technical Reports Server (NTRS)

    Chung, James J.; Addy, Harold E., Jr.

    2000-01-01

    As a part of CFD code validation efforts within the Icing Branch of NASA Glenn Research Center, computations were performed for natural laminar flow (NLF) airfoil, NLF-0414. with 6 and 22.5 minute ice accretions. Both 3-D ice castings and 2-D machine-generated ice shapes were used in wind tunnel tests to study the effects of natural ice is well as simulated ice. They were mounted in the test section of the Low Turbulence Pressure Tunnel (LTPT) at NASA Langley that the 2-dimensionality of the flow can be maintained. Aerodynamic properties predicted by computations were compared to data obtained through the experiment by the authors at the LTPT. Computations were performed only in 2-D and in the case of 3-D ice, the digitized ice shape obtained at one spanwise location was used. The comparisons were mainly concentrated on the lift characteristics over Reynolds numbers ranging from 3 to 10 million and Mach numbers ranging from 0.12 to 0.29. WIND code computations indicated that the predicted stall angles were in agreement with experiment within one or two degrees. The maximum lift values obtained by computations were in good agreement with those of the experiment for the 6 minute ice shapes and the minute 3-D ice, but were somewhat lower in the case of the 22.5 minute 2-D ice. In general, the Reynolds number variation did not cause much change in the lift values while the variation of Mach number showed more change in the lift. The Spalart-Allmaras (S-A) turbulence model was the best performing model for the airfoil with the 22.5 minute ice and the Shear Stress Turbulence (SST) turbulence model was the best for the airfoil with the 6 minute ice and also for the clean airfoil. The pressure distribution on the surface of the iced airfoil showed good agreement for the 6 minute ice. However, relatively poor agreement of the pressure distribution on the upper surface aft of the leading edge horn for the 22.5 minute ice suggests that improvements are needed in the grid or

  13. Radiocarbon deglaciation chronology of the Thunder Bay, Ontario area and implications for ice sheet retreat patterns

    NASA Astrophysics Data System (ADS)

    Lowell, Thomas V.; Fisher, Timothy G.; Hajdas, I.; Glover, K.; Loope, H.; Henry, T.

    2009-08-01

    The sensitivity of ice sheets to climate change influences the return of meltwater to the oceans. Here we track the Laurentide Ice Sheet along a ˜400 km long transect spanning about 6000 yr of retreat during the major climate oscillations of the lateglacial. Thunder Bay, Ontario is near a major topographic drainage divide, thus terrestrial ablation processes are the primary forcers of ice margin recession in the study area. During deglaciation three major moraine sets were produced, and have been assigned minimum ages of 13.9 ± 0.2, 12.3 ± 0.2-12.1 ± 0.1, and 11.2 ± 0.2 cal ka BP from south to north. These define a slow retreat (˜10-50 m/a) prior to major climate oscillations which was then followed by a factor of ˜2 increase during the Bölling-Alleröd, and an additional increase during the early Holocene. When compared to retreat rates in other terrestrial settings of the ice sheet, nearly identical patterns emerge. However this becomes problematic because a key control on retreat rates is the surface slope of the ice sheet and this should vary considerably over areas of so-called hard and soft beds. Further these ice margin reconstructions would not allow meltwater sourced in the Hudson Basin to drain into the Atlantic basin until after Younger Dryas time.

  14. Evolution of crystal fabric: Ice-Age ice versus Holocene ice

    NASA Astrophysics Data System (ADS)

    Kennedy, J. H.; Pettit, E. C.

    2009-12-01

    Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007

  15. Unsaturated Zone Flow Patterns and Analysis

    SciTech Connect

    C. Ahlers

    2001-10-17

    This Analysis/Model Report (AMR) documents the development of an expected-case model for unsaturated zone (UZ) flow and transport that will be described in terms of the representativeness of models of the natural system. The expected-case model will provide an evaluation of the effectiveness of the natural barriers, assess the impact of conservatism in the Total System Performance Assessment (TSPA), and support the development of further models and analyses for public confidence building. The present models used in ''Total System Performance Assessment for the Site Recommendation'' (Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) 2000 [1532461]) underestimate the natural-barrier performance because of conservative assumptions and parameters and do not adequately address uncertainty and alternative models. The development of an expected case model for the UZ natural barrier addresses issues regarding flow-pattern analysis and modeling that had previously been treated conservatively. This is in line with the Repository Safety Strategy (RSS) philosophy of treating conservatively those aspects of the UZ flow and transport system that are not important for achieving regulatory dose (CRWMS M&O 2000 [153246], Section 1.1.1). The development of an expected case model for the UZ also provides defense-in-depth in areas requiring further analysis of uncertainty and alternative models. In general, the value of the conservative case is to provide a more easily defensible TSPA for behavior of UZ flow and transport processes at Yucca Mountain. This AMR has been prepared in accordance with the ''Technical Work Plan for Unsaturated Zone (UZ) Flow and Transport Process Model Report'' (Bechtel SAIC Company (BSC) 2001 [155051], Section 1.3 - Work Package 4301213UMG). The work scope is to examine the data and current models of flow and transport in the Yucca Mountain UZ to identify models and analyses where conservatism may be reduced and

  16. Pattern and timing of retreat of the last British-Irish Ice Sheet

    NASA Astrophysics Data System (ADS)

    Clark, C. D.; Hughes, A. L.; Greenwood, S. L.

    2009-12-01

    Ice sheets leave behind a fragmentary record of their activity, which is then incompletely sampled by geoscientists, and a small fraction of this evidence is subjected to geochronometric dating, some of which yields useful timing constraints on the ice sheet. We thus have an incomplete knowledge of the time-space envelope of ice sheet extent and yet we possess a strong desire to link any changes to known or posited climate fluctuations. If we are to reduce conjecture, speculation and wishful event-matching (‘my moraine records a Heinrich event but your doesn’t!’), clearly the magnitude of the task demands a systematic and cautious approach. For Britain and Ireland there is a wealth of published evidence, maps and dates, that have never been systematically assembled to yield a dated retreat pattern for the ice sheet. In this paper we summarise new mapping of glacial landforms (especially moraines and meltwater channels), merge it with published work, and together, use the data (including drumlins, eskers and ice dammed lakes) to derive a pattern of retreat. We review and compile all known relevant dates for the region (> 400 examples) that constrain the timing of retreat. All data is held within a GIS, and is then manipulated to produce a best-estimate of the combined pattern and timing of retreat of the ice sheet. The data, method and results will be presented and it is emphasised that this is almost certainly not the complete picture, but provides a useful framework of what is known.

  17. Measurement of flow under ice covers in North America

    USGS Publications Warehouse

    Walker, J.F.; Wang, D.

    1997-01-01

    A substantial proportion of natural streams in the United States and Canada are affected by ice cover during the winter. To substantiate the currently used procedures for measuring streamflow during the winter, the U.S. Geological Survey (USGS) and Water Survey of Canada (WSC) began independent, coordinated programs for research and development related to the measurement of streamflow under an ice cover. Detailed measurements of vertical velocity profiles under ice covers in field settings were collected by each agency in accordance with standardized guidelines. The data were then compiled into a joint database. This paper presents a description of the two measurement programs, describes the structure and format of the joint database, and provides preliminary summaries of the data. Ongoing research efforts by the USGS and WSC are described briefly to give examples of the use of the joint database.

  18. The Annual Glaciohydrology Cycle in the Ablation Zone of the Greenland Ice Sheet: Part 2. Observed and Modeled Ice Flow

    NASA Technical Reports Server (NTRS)

    Colgan, William Terence; Rajaram, Harihar; Anderson, Robert S.; Steffen, Konrad; Zwally, H. Jay; Phillips, Thomas; Abdalati, Waleed

    2012-01-01

    Ice velocities observed in 2005/06 at three GPS stations along the Sermeq Avannarleq flowline, West Greenland, are used to characterize an observed annual velocity cycle. We attempt to reproduce this annual ice velocity cycle using a 1-D ice-flow model with longitudinal stresses coupled to a 1-D hydrology model that governs an empirical basal sliding rule. Seasonal basal sliding velocity is parameterized as a perturbation of prescribed winter sliding velocity that is proportional to the rate of change of glacier water storage. The coupled model reproduces the broad features of the annual basal sliding cycle observed along this flowline, namely a summer speed-up event followed by a fall slowdown event. We also evaluate the hypothesis that the observed annual velocity cycle is due to the annual calving cycle at the terminus. We demonstrate that the ice acceleration due to a catastrophic calving event takes an order of magnitude longer to reach CU/ETH ('Swiss') Camp (46km upstream of the terminus) than is observed. The seasonal acceleration observed at Swiss Camp is therefore unlikely to be the result of velocity perturbations propagated upstream via longitudinal coupling. Instead we interpret this velocity cycle to reflect the local history of glacier water balance.

  19. Modulating patterns of two-phase flow with electric fields

    PubMed Central

    Liu, Dingsheng; Hakimi, Bejan; Volny, Michael; Rolfs, Joelle; Anand, Robbyn K.; Turecek, Frantisek; Chiu, Daniel T.

    2014-01-01

    This paper describes the use of electro-hydrodynamic actuation to control the transition between three major flow patterns of an aqueous-oil Newtonian flow in a microchannel: droplets, beads-on-a-string (BOAS), and multi-stream laminar flow. We observed interesting transitional flow patterns between droplets and BOAS as the electric field was modulated. The ability to control flow patterns of a two-phase fluid in a microchannel adds to the microfluidic tool box and improves our understanding of this interesting fluid behavior. PMID:25379091

  20. Regulation of ice stream flow through subglacial formation of gas hydrates

    NASA Astrophysics Data System (ADS)

    Winsborrow, Monica; Andreassen, Karin; Hubbard, Alun; Plaza-Faverola, Andreia; Gudlaugsson, Eythor; Patton, Henry

    2016-05-01

    Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice-bed interface remains elusive. Basal resistance is critical, especially sticky spots--localized zones of high basal traction--for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea-Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ~250 km2 sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction--a sticky spot--that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon.

  1. Geothermal Heating, Convective Flow and Ice Thickness on Mars

    NASA Technical Reports Server (NTRS)

    Rosenberg, N. D.; Travis, B. J.; Cuzzi, J.

    2001-01-01

    Our 3D calculations suggest that hydrothermal circulation may occur in the martian regolith and may significantly thin the surface ice layer on Mars at some locations due to the upwelling of warm convecting fluids driven solely by background geothermal heating. Additional information is contained in the original extended abstract.

  2. Numerical study of the effects of icing on viscous flow over wings

    NASA Technical Reports Server (NTRS)

    Sankar, L. N.

    1993-01-01

    The progress made during the period 1 Jan. - 30 Jun. 1993 on the numerical study of the effects of icing on viscous flow over wings is summarized. The tasks performed were development of 3-D boundary layer methods for accurate estimates of the velocity field and surface heat transfer rates in the vicinity of the leading edge ice shape; studies of the effects of icing on 3-D highlift system performance; and continued improvement and validation of the 3-D Navier-Stokes solver. Results are discussed.

  3. Morphometry and pattern of a large sample (>20,000) of Canadian eskers and implications for subglacial drainage beneath ice sheets

    NASA Astrophysics Data System (ADS)

    Storrar, Robert D.; Stokes, Chris R.; Evans, David J. A.

    2014-12-01

    Ice sheet flow is strongly influenced by the nature and quantity of meltwater entering the subglacial system. Accessing and monitoring contemporary drainage systems beneath ice sheets is notoriously difficult, but it is possible to utilise the exposed beds of palaeo-ice sheets. In particular, eskers record deposition in glacial drainage channels and are widespread on the exposed beds of former ice sheets. However, unlike some other common glacial landforms (e.g. drumlins) there have been relatively few attempts to investigate and quantify their characteristics at the ice sheet scale. This paper presents data on the distribution, pattern, and morphometry of a large (>20,000) sample of eskers in Canada, formed under the Laurentide Ice Sheet, including quantification of their length, fragmentation, sinuosity, lateral spacing, number of tributaries, and downstream elevation changes. Results indicate that eskers are typically very long (hundreds of km) and often very straight (mean sinuosity approximates 1). We interpret these long esker systems to reflect time-transgressive formation in long, stable conduits under hydrostatic pressure. The longest eskers (in the Keewatin sector) are also the least fragmented, which we interpret to reflect formation at an ice margin experiencing stable and gradual retreat. In many locations, the lateral distance between neighbouring eskers is remarkably consistent and results indicate a preferred spacing of around 12 km, consistent with numerical models which predict esker spacing of 8-25 km. In other locations, typically over soft sediments, eskers are rarer and their patterns are more chaotic, reflecting fewer large R-channels and rapidly changing ice sheet dynamics. Comparison of esker patterns with an existing ice margin chronology reveals that the meltwater drainage system evolved during deglaciation: eskers became more closely spaced with fewer tributaries as deglaciation progressed, which has been interpreted to reflect increased

  4. Detached-Eddy Simulations of Separated Flow Around Wings With Ice Accretions: Year One Report

    NASA Technical Reports Server (NTRS)

    Choo, Yung K. (Technical Monitor); Thompson, David; Mogili, Prasad

    2004-01-01

    A computational investigation was performed to assess the effectiveness of Detached-Eddy Simulation (DES) as a tool for predicting icing effects. The AVUS code, a public domain flow solver, was employed to compute solutions for an iced wing configuration using DES and steady Reynolds Averaged Navier-Stokes (RANS) equation methodologies. The configuration was an extruded GLC305/944-ice shape section with a rectangular planform. The model was mounted between two walls so no tip effects were considered. The numerical results were validated by comparison with experimental data for the same configuration. The time-averaged DES computations showed some improvement in lift and drag results near stall when compared to steady RANS results. However, comparisons of the flow field details did not show the level of agreement suggested by the integrated quantities. Based on our results, we believe that DES may prove useful in a limited sense to provide analysis of iced wing configurations when there is significant flow separation, e.g., near stall, where steady RANS computations are demonstrably ineffective. However, more validation is needed to determine what role DES can play as part of an overall icing effects prediction strategy. We conclude the report with an assessment of existing computational tools for application to the iced wing problem and a discussion of issues that merit further study.

  5. Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland

    NASA Astrophysics Data System (ADS)

    Hughes, T.; Sargent, A.; Fastook, J.; Purdon, K.; Li, J.; Yan, J.-B.; Gogineni, S.

    2015-08-01

    The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier-Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

  6. Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica and Jakobshavn Isbrae, Greenland

    NASA Astrophysics Data System (ADS)

    Hughes, T.; Sargent, A.; Fastook, J.; Purdon, K.; Li, J.; Yan, J.-B.; Gogineni, S.

    2016-01-01

    The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling along flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier-Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

  7. Patterns and rates of riverbank erosion involving ice-rich permafrost (yedoma) in northern Alaska

    NASA Astrophysics Data System (ADS)

    Kanevskiy, Mikhail; Shur, Yuri; Strauss, Jens; Jorgenson, Torre; Fortier, Daniel; Stephani, Eva; Vasiliev, Alexander

    2016-01-01

    Yedoma, a suite of syngenetically frozen silty ice- and organic-rich deposits with large ice wedges that accumulated during the late Pleistocene, is vulnerable to thermal degradation and erosion because of the extremely high ice contents. This degradation can result in significant surface subsidence and retreat of coastal bluffs and riverbanks with large consequences to landscape evolution, infrastructure damage, and water quality. We used remote sensing and field observations to assess patterns and rates of riverbank erosion at a 35-m-high active yedoma bluff along the Itkillik River in northern Alaska. The total volumetric ground-ice content-including wedge, segregated, and pore ice-was estimated to be ~ 86%. The process of riverbank erosion and stabilization include three main stages typical of the areas with ice-rich permafrost: (1) thermal erosion combined with thermal denudation, (2) thermal denudation, and (3) slope stabilization. Active riverbank erosion at the main study site started in July 1995, when the Itkillik River changed its channel. The total retreat of the riverbank during 1995-2010 within different segments of the bluff varied from 180 to 280 m; the average retreat rate for the most actively eroded part of the riverbank was almost 19 m/y. From August 2007 to August 2011, the total retreat varied from 10 to almost 100 m. The average retreat rate for the whole 680-m-long bluff was 11 m/y. For the most actively eroded central part of the bluff (150 m long) it was 20 m/y, ranging from 16 to 24 m/y. More than 180,000 m3 of ground ice and organic-rich frozen soil, or almost 70,000 metric tons (t) of soil solids including 880 t of organic carbon, were transported to the river from the retreating bank annually. This study reports the highest long-term rates of riverbank erosion ever observed in permafrost regions of Eurasia and North America.

  8. Martian Polar Caps: Folding, Faulting, Flowing Glaciers of Multiple Interbedded Ices

    NASA Astrophysics Data System (ADS)

    Kargel, J. S.

    2001-12-01

    The Martian south polar cap (permanent CO2 cap and polar layered deposits), exhibit abundant, varied, and widespread deformational phenomena. Folding and boudinage are very common. Strike-slip or normal faults are rarer. Common in the vicinity of major troughs and scarps are signs of convergent flow tectonics manifested as wrinkle-ridge-like surface folds, thrust faults, and viscous forebulges with thin-skinned extensional crevasses and wrinkle-ridge folds. Such flow convergence is predicted by theory. Boudinage and folding at the 300-m wavelength scale, indicating rheologically contrasting materials, is widely exposed at deep levels along erosional scarps. Independent morphologic evidence indicates south polar materials of contrasting volatility. Hence, the south polar cap appears to be a multiphase structure of interbedded ices. The north polar cap locally also exhibits flow indicators, though they are neither as common nor as varied as in the south. The large-scale quasi-spiral structure of the polar caps could be a manifestation of large-scale boudinage. According to this scenario, deep-level boudinage continuously originates under the glacial divide (the polar cap summit). Rod-like boudin structures are oriented transverse to flow and migrate outward with the large-scale flow field. Troughs develop over areas between major boudins. A dynamic competition, and possibly a rough balance, develops between the local flow field in the vicinity of a trough (which tends to close the trough by lateral closure and upwelling flow) and sublimation erosion (which tends to widen and deepen them). Over time, the troughs flow to the margins of the polar cap where they, along with other polar structures, are destroyed by sublimation. Major ice types contributing to rheological and volatility layering may include, in order of highest to lowest mechanical strength, CO2 clathrate hydrate, water ice containing inert/insoluble dust, pure water ice, water ice containing traces of

  9. The Effect of Break Edge Configuration on the Aerodynamics of Anti-Ice Jet Flow

    NASA Astrophysics Data System (ADS)

    Tatar, V.; Yildizay, H.; Aras, H.

    2015-05-01

    One of the components of a turboprop gas turbine engine is the Front Bearing Structure (FBS) which leads air into the compressor. FBS directly encounters with ambient air, as a consequence ice accretion may occur on its static vanes. There are several aerodynamic parameters which should be considered in the design of anti-icing system of FBS, such as diameter, position, exit angle of discharge holes, etc. This research focuses on the effects of break edge configuration over anti-ice jet flow. Break edge operation is a process which is applied to the hole in order to avoid sharp edges which cause high stress concentration. Numerical analyses and flow visualization test have been conducted. Four different break edge configurations were used for this investigation; without break edge, 0.35xD, 74xD, 0.87xD. Three mainstream flow conditions at the inlet of the channel are defined; 10m/s, 20 m/s and 40 m/s. Shear stresses are extracted from numerical analyses near the trailing edge of pressure surface where ice may occur under icing conditions. A specific flow visualization method was used for the experimental study. Vane surface near the trailing edge was dyed and thinner was injected into anti-ice jet flow in order to remove dye from the vane surface. Hence, film effect on the surface could be computed for each testing condition. Thickness of the dye removal area of each case was examined. The results show noticeable effects of break edge operation on jet flow, and the air film effectiveness decreases when mainstream inlet velocity decreases.

  10. ICESat measurements reveal complex pattern of elevation changes on Siple Coast ice streams, Antarctica

    NASA Astrophysics Data System (ADS)

    Csatho, B.; Ahn, Y.; Yoon, T.; van der Veen, C. J.; Vogel, S.; Hamilton, G.; Morse, D.; Smith, B.; Spikes, V. B.

    2005-12-01

    We compare ICESat data (2003-2004) to airborne laser altimetry data (1997-98 and 1999-2000) to monitor surface changes over portions of Van der Veen (VdVIS), Whillans (WIS) and Kamb ice streams (KIS) in the Ross Embayment of the West Antarctic Ice Sheet. The spatial pattern of detected surface changes is generally consistent with earlier observations. However, important changes have occurred during the past decade. For example, areas on the VdVIS and WIS, where large thinning was detected by the airborne surveys, are now closer to being in balance. The upper trunk of KIS continues to build up with thickening rates reaching 0.4 m/year. Our results provide new evidence that the overall mass balance of the region is becoming more positive, but a significant spatial variability exists. They also demonstrate the potential of ICESat data for detecting spatial patterns of surface elevation change in Antarctica.

  11. Pattern of CsICE1 expression under cold or drought treatment and functional verification through analysis of transgenic Arabidopsis.

    PubMed

    Ding, Z T; Li, C; Shi, H; Wang, H; Wang, Y

    2015-01-01

    CsICE1 is thought to be involved in hardiness resistance of tea plants. Using seedling cuttings of biennial Wuniuzao in this study, the pattern of CsICE1 expression under cold temperature (4°, -5°C), drought [20% polyethylene glycol 6000 (PEG-6000)], and plant hormone [200 mg/L abscisic acid (ABA), 1 mg/L brassinolide (BR)] treatment was studied by real-time quantitative PCR. Additionally, stress resistance, such as the freezing resistance of CsICE1, was studied using Arabidopsis lines transformed with sense or anti-sense CsICE1 via Agrobacterium tumefaciens infection. Our results showed that CsICE1 mRNA could be induced under -5°C, PEG, ABA, or BR treatment, although the pattern of expression differed for all treatments. Compared to wild type (WT) and anti-sense ICE1 transgenic lines, sense lines displayed higher relative germination rates under salt and drought stress. After freezing treatment, the sense transgenic lines over-expressing CsICE1 showed a higher survival rate, increased levels of proline, and decreased levels of malonaldehyde. Conversely, compared with WT, anti-sense ICE1 transgenic lines had lower proline levels and higher malonaldehyde levels under freezing conditions. Our study indicates that CsICE1 is an important anti-freezing gene and that over-expression of CsICE1 can improve cold resistance and enhance salt and drought tolerance of transgenic lines. PMID:26400357

  12. Glacial geomorphology and past ice flows in the Larsen A embayment, Antarctica

    NASA Astrophysics Data System (ADS)

    Campo, J.; Wellner, J. S.; Lavoie, C.

    2012-12-01

    During the Last Glacial Maximum (LGM), the expanded Antarctic Peninsula Ice Sheet was grounded on the continental shelf in the Northwestern Weddell Sea at least 10 km past the modern grounding line. The grounded ice of the Antarctic Peninsula Ice Sheet sculpted a suite of characteristic geomorphic features onto the shelf - features that were uncovered upon the retreat of the ice sheet, indicating flow direction and style. The break up of the Larsen A Ice Shelf in recent decades has continued to expose more areas of the inner shelf. A US. Antarctic Program cruise aboard the NB Palmer, completed in April of this year as part of the LARISSA program, collected multibeam swath bathymetric data and 3.5 kHz chirp sub-bottom sediment profiler data in the Larsen A embayment. New multibeam data close to the shoreline, particularly in Drygalski Trough and Bombardier Bay, has been merged with existing swath data from the U.S. and British programs to permit mapping and interpretation of ice flow from the tributaries and across the shelf. Initial observations of chirp data suggest little marine or glaciomarine sediment has accumulated in these tributary fjords, hinting that glacial retreat there occurred relatively recently. All sediment volumes for which profiles were collected occur above the glacial unconformity carved by the post-glacial retreat. Interpretation of chirp data is ongoing for volume calculations and mapping of discrete units. Ongoing work is currently being completed to measure volumes of sediment accumulation, which will then be correlated to sediment cores studied by project collaborators. The multibeam data is being analyzed in ArcGIS to determine the changes in length/width scales of the geomorphic features. As expected, the subglacial features on the outer shelf are elongated compared to the linear features on the inner shelf. Based on Evans, et al. [2005] combined with data collected this year, we have mapped ice flow form the tributaries and out through

  13. Continuum-mechanical, Anisotropic Flow model for polar ice masses, based on an anisotropic Flow Enhancement factor

    NASA Astrophysics Data System (ADS)

    Placidi, Luca; Greve, Ralf; Seddik, Hakime; Faria, Sérgio H.

    2010-03-01

    A complete theoretical presentation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor (CAFFE model) is given. The CAFFE model is an application of the theory of mixtures with continuous diversity for the case of large polar ice masses in which induced anisotropy occurs. The anisotropic response of the polycrystalline ice is described by a generalization of Glen’s flow law, based on a scalar anisotropic enhancement factor. The enhancement factor depends on the orientation mass density, which is closely related to the orientation distribution function and describes the distribution of grain orientations (fabric). Fabric evolution is governed by the orientation mass balance, which depends on four distinct effects, interpreted as local rigid body rotation, grain rotation, rotation recrystallization (polygonization) and grain boundary migration (migration recrystallization), respectively. It is proven that the flow law of the CAFFE model is truly anisotropic despite the collinearity between the stress deviator and stretching tensors.

  14. Subglacial lake and meltwater flow predictions of the last North American and European Ice Sheets

    NASA Astrophysics Data System (ADS)

    Livingstone, S. J.; Clark, C. D.; Tarasov, L.

    2012-04-01

    There is increasing recognition that subglacial lakes act as key components within the ice sheet system, capable of influencing ice-sheet topography, ice volume and ice flow. The subglacial water systems themselves are recognised as being both active and dynamic, with large discharges of meltwater capable of flowing down hydrological pathways both between lakes and to the ice-sheet margins. At present, much glaciological research is concerned with the role of modern subglacial lake systems in Antarctica. Another approach to the exploration of subglacial lakes involves identification of the geological record of subglacial lakes that once existed beneath ice sheets of the last glaciation. Investigation of such palaeo-subglacial lakes offers significant advantages because we have comprehensive information about the bed properties, they are much more accessible and we can examine and sample the sediments with ease. If we can find palaeo-subglacial lakes then we have the potential to advance understanding with regard to the topographic context and hydrological pathways that the phenomena form a part of; essentially we gain spatial and sedimentological information in relation to investigations of contemporary subglacial lakes and lose out on the short-time dynamics. In this work we present predictions of palaeo-subglacial lakes and meltwater drainage pathways under the former European and North American ice sheets during the last glaciation. We utilise data on the current topography and seafloor bathymetry, and elevation models of the ice and ground surface topography (interpolated to a 5 km grid) to calculate the hydraulic potential surface at the ice-sheet bed. Meltwater routing algorithms and the flooding of local hydraulic minima allow us to predict subglacial channels and lakes respectively. Given that specific ice-surface and bed topographies are only known from modelled outputs, and thus contain significant uncertainty, we utilise many such outputs to examine

  15. Nanoscale Fluid Flows in the Vicinity of Patterned Surfaces

    NASA Astrophysics Data System (ADS)

    Cieplak, Marek; Koplik, Joel; Banavar, Jayanth R.

    2006-03-01

    Molecular dynamics simulations of dense and rarefied fluids comprising small chain molecules in chemically patterned nanochannels predict a novel switching from Poiseuille to plug flow along the channel. We also demonstrate behavior akin to the lotus effect for a nanodrop on a chemically patterned substrate. Our results show that one can control and exploit the behavior of fluids at the nanoscale using chemical patterning.

  16. Numerical simulation of the motion of an ice keel in a stratified flow

    NASA Astrophysics Data System (ADS)

    Mortikov, E. V.

    2016-01-01

    The results of the three-dimensional numerical simulation for the study of the stratification effect and wave processes associated with it on the drag of the underwater part of the hummocked ice are considered. The numerical model is based on the sampling of equations on a rectangular grid using the immersed boundary method that makes it possible to explicitly describe the interaction of moving ice with a stratified flow. The dependence of the drag force on the Froude number was established based on these calculations. This dependence has expressed points of maximum and minimum. The form of this dependence is common for the considered models of ice keels. The obtained estimations of drag force consistent with the known results of laboratory experiments show the need for the construction of parametrizations of the drag coefficient on the ice-ocean boundary, taking into account wave effects.

  17. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars

    USGS Publications Warehouse

    Head, J.W.; Neukum, G.; Jaumann, R.; Hiesinger, H.; Hauber, E.; Carr, M.; Masson, P.; Foing, B.; Hoffmann, H.; Kreslavsky, M.; Werner, S.; Milkovich, S.; Van Gasselt, S.

    2005-01-01

    Images from the Mars Express HRSC (High-Resolution Stereo Camera) of debris aprons at the base of massifs in eastern Hellas reveal numerous concentrically ridged lobate and pitted features and related evidence of extremely ice-rich glacier-like viscous flow and sublimation. Together with new evidence for recent ice-rich rock glaciers at the base of the Olympus Mons scarp superposed on larger Late Amazonian debris-covered piedmont glaciers, we interpret these deposits as evidence for geologically recent and recurring glacial activity in tropical and mid-latitude regions of Mars during periods of increased spin-axis obliquity when polar ice was mobilized and redeposited in microenvironments at lower latitudes. The data indicate that abundant residual ice probably remains in these deposits and that these records of geologically recent climate changes are accessible to future automated and human surface exploration.

  18. Timing and regional patterns of snowmelt on Antarctic sea ice from passive microwave satellite observations

    NASA Astrophysics Data System (ADS)

    Arndt, Stefanie; Willmes, Sascha; Dierking, Wolfgang; Nicolaus, Marcel

    2016-04-01

    The better understanding of temporal variability and regional distribution of surface melt on Antarctic sea ice is crucial for the understanding of atmosphere-ocean interactions and the determination of mass and energy budgets of sea ice. Since large regions of Antarctic sea ice are covered with snow during most of the year, observed inter-annual and regional variations of surface melt mainly represents melt processes in the snow. It is therefore important to understand the mechanisms that drive snowmelt, both at different times of the year and in different regions around Antarctica. In this study we combine two approaches for observing both surface and volume snowmelt by means of passive microwave satellite data. The former is achieved by measuring diurnal differences of the brightness temperature TB at 37 GHz, the latter by analyzing the ratio TB(19GHz)/TB(37GHz). Moreover, we use both melt onset proxies to divide the Antarctic sea ice cover into characteristic surface melt patterns from 1988/89 to 2014/15. Our results indicate four characteristic melt types. On average, 43% of the ice-covered ocean shows diurnal freeze-thaw cycles in the surface snow layer, resulting in temporary melt (Type A), less than 1% shows continuous snowmelt throughout the snowpack, resulting in strong melt over a period of several days (Type B), 19% shows Type A and B taking place consecutively (Type C), and for 37% no melt is observed at all (Type D). Continuous melt is primarily observed in the outflow of the Weddell Gyre and in the northern Ross Sea, usually 20 days after the onset of temporary melt. Considering the entire data set, snowmelt processes and onset do not show significant temporal trends. Instead, areas of increasing (decreasing) sea-ice extent have longer (shorter) periods of continuous snowmelt.

  19. Pattern formation in flowing electrorheological fluids.

    PubMed

    von Pfeil, Karl; Graham, Michael D; Klingenberg, Daniel J; Morris, Jeffrey F

    2002-05-01

    A two-fluid continuum model is developed to describe mass transport in electro- and magnetorheological suspensions. The particle flux is related to the field-induced stresses. Solutions of the resulting mass balance show column formation in the absence of flow, and stripe formation when a suspension is subjected simultaneously to an applied electric field and shear flow. PMID:12005727

  20. The transition of flow patterns through critical stagnation points in two-dimensional groundwater flow

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A flow pattern is characterized by aquifer features and the number, type, and distribution of stagnation points (locations where the discharge is zero). This article identifies a condition for transition of flow patterns in two-dimensional groundwater flow obeying Darcy's law by examining changes in...

  1. Basal ice flow regime influenced by glacial lake formation in Rhonegletscher, Switzerland

    NASA Astrophysics Data System (ADS)

    Nishimura, D.; Tsutaki, S.; Sugiyama, S.

    2010-12-01

    After the retreat of glacier terminus over a bedrock bump, a glacial lake has formed in front of Rhonegletscher, Switzerland. It is suspected that ice flow regime is now significantly influenced by the lake water. To investigate the impact of lake formation on glacier dynamics, we carried out surface and borehole observations in the terminus region of Rhonegletscher. In 2008 and 2009 summer seasons, we drilled more than 20 boreholes to measure borehole deformation by repeated inclinometry. Ice surface speed was measured by surveying stakes installed nearby the boreholes. We used a borehole televiewer to measure basal sliding speed by tracking stones and markers at the bottom of the boreholes. We also measured basal sediment layer thickness by hammering a penetrometer at the bottom of the boreholes. Our measurements showed clear decrease in the ice deformation rate near the lake (Fig. 1). Ice deformation accounted for 60-80% in the upper part of our study site (e.g. boreholes 1 and 5), whereas it is less than 10% near the lake (e.g. boreholes 7, 10 and 11). This result suggests that the basal ice flow near the lake is enhanced by the lake water. According to the basal sliding speed measurement in borehole 2, sliding accounted for less than 10% of basal flow speed from 2 to 31 August 2009. Deformation of a subglacial sediment layer is thus important in this region. The penetrometer measurement confirmed that the study site is underlain by a subglacial sediment layer whose thickness was in a range of 0-70 m. Fig.1 Terminus of Rhonegletscher and proglacial lakes indicated by the shaded areas. The columns show ice surface and deformation speeds measured at each borehole site from 9 July to 5 September in 2009. Ice deformation speed was negligibly small at boreholes 7, 10, and 11. Surface contour spacing is 20 m.

  2. Tide-modulated ice flow variations drive seismicity near the calving front of Bowdoin Glacier, Greenland

    NASA Astrophysics Data System (ADS)

    Podolskiy, Evgeny A.; Sugiyama, Shin; Funk, Martin; Walter, Fabian; Genco, Riccardo; Tsutaki, Shun; Minowa, Masahiro; Ripepe, Maurizio

    2016-03-01

    Glacier microseismicity is a promising tool to study glacier dynamics. However, physical processes connecting seismic signals and ice dynamics are not clearly understood at present. Particularly, the relationship between tide-modulated seismicity and dynamics of calving glaciers remains elusive. Here we analyze records from an on-ice seismometer placed 250 m from the calving front of Bowdoin Glacier, Greenland. Using high-frequency glacier flow speed measurements, we show that the microseismic activity is related to strain rate variations. The seismic activity correlates with longitudinal stretching measured at the glacier surface. Both higher melt rates and falling tides accelerate glacier motion and increase longitudinal stretching. Long-term microseismic monitoring could therefore provide insights on how a calving glacier's force balance and flow regime react to changes at the ice-ocean interface.

  3. Turbulent jet patterns in accelerating flows

    NASA Technical Reports Server (NTRS)

    Lipshitz, A.; Greber, I.

    1981-01-01

    Results of flow visualization experiments, and a semi-empirical model of a single turbulent jet injected perpendicularly to a different density cross flow are presented. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flow. It uses an entrainment correlation obtained from previous experiments of a jet in a cross stream. The results show trajectories and spreading rates, and are typified by a set of three parameters: momentum ratio, Froude number and density ratio. Agreement between test and calculated results is encouraging, but tend to be poorer with increasing momentum ratio.

  4. Patterns and instability of grannular flow

    SciTech Connect

    Ecke, Robert E; Borzsonyi, Tamas; Mcelwaine, Jim N

    2009-01-01

    Dense granular flows are often observed to become unstable and form inhomogeneous structures in nature or industry. Although recently significant advances have been made in understanding simple flows, instabilities are often not understood in detail. We present experimental and numerical results that show the formation of longitudinal stripes. These arise from instability of the uniform flowing state of granular media on a rough inclined plane. The form of the stripes depends critically on the mean density of the flow with a robust form of stripes at high density that consists of fast sliding plug-like regions (stripes) on top of highly agitated boiling material -- a configuration reminiscent of the Leidenfrost effect when a droplet of liquid lifted by its vapor is hovering above a hot surface.

  5. The ability to survive intracellular freezing in nematodes is related to the pattern and distribution of ice formed.

    PubMed

    Raymond, Méliane R; Wharton, David A

    2016-07-01

    A few species of nematodes can survive extensive intracellular freezing throughout all their tissues, an event that is usually thought to be fatal to cells. How are they able to survive in this remarkable way? The pattern and distribution of ice formed, after freezing at -10°C, can be observed using freeze substitution and transmission electron microscopy, which preserves the former position of ice as white spaces. We compared the pattern and distribution of ice formed in a nematode that survives intracellular freezing well (Panagrolaimus sp. DAW1), one that survives poorly (Panagrellus redivivus) and one with intermediate levels of survival (Plectus murrayi). We also examined Panagrolaimus sp. in which the survival of freezing had been compromised by starvation. Levels of survival were as expected and the use of vital dyes indicated cellular damage in those that survived poorly (starved Panagrolaimus sp. and P. murrayi). In fed Panagrolaimus sp. the intracellular ice spaces were small and uniform, whereas in P. redivivus and starved Panagrolaimus sp. there were some large spaces that may be causing cellular damage. The pattern and distribution of ice formed was different in P. murrayi, with a greater number of individuals having no ice or only small intracellular ice spaces. Control of the size of the ice formed is thus important for the survival of intracellular freezing in nematodes. PMID:27143749

  6. Flow Quality Surveys in the Settling Chamber of the NASA Glenn Icing Research Tunnel (2011 Tests)

    NASA Technical Reports Server (NTRS)

    Steen, Laura E.; VanZante, Judith Foss; Broeren, Andy P.; Kubiak, Mark J.

    2014-01-01

    In 2011, the heat exchanger and refrigeration plant for NASA Glenn Research Centers Icing Research Tunnel (IRT) were upgraded. Flow quality surveys were performed in the settling chamber of the IRT in order to understand the effect that the new heat exchanger had on the flow quality upstream of the spray bars. Measurements were made of the total pressure, static pressure, total temperature, airspeed, and flow angle (pitch and yaw). These measurements were directly compared to measurements taken in 2000, after the previous heat exchanger was installed. In general, the flow quality appears to have improved with the new heat exchanger.

  7. Flow Quality Surveys in the Settling Chamber of the NASA Glenn Icing Research Tunnel (2011 Tests)

    NASA Technical Reports Server (NTRS)

    Steen, Laura E.; VanZante, Judith Foss; Broeren, Andy P.; Kubiak, Mark J.

    2012-01-01

    In 2011, the heat exchanger and refrigeration plant for NASA Glenn Research Center's Icing Research Tunnel (IRT) were upgraded. Flow quality surveys were performed in the settling chamber of the IRT in order to understand the effect that the new heat exchanger had on the flow quality upstream of the spray bars. Measurements were made of the total pressure, static pressure, total temperature, airspeed, and flow angle (pitch and yaw). These measurements were directly compared to measurements taken in 2000, after the previous heat exchanger was installed. In general, the flow quality appears to have improved with the new heat exchanger.

  8. Development of a flow visualization apparatus. [to study convection flow patterns

    NASA Technical Reports Server (NTRS)

    Spradley, L. W.

    1975-01-01

    The use of an optical flow visualization device for studying convection flow patterns was investigated. The investigation considered use of a shadowgraph, schlieren and other means for visualizing the flow. A laboratory model was set up to provide data on the proper optics and photography procedures to best visualize the flow. A preliminary design of a flow visualization system is provided as a result of the study. Recommendations are given for a flight test program utilizing the flow visualization apparatus.

  9. Flow-like features in Valles Marineris, Mars: Possible ice-driven creep processes

    NASA Astrophysics Data System (ADS)

    Rossi, A. P.; Komatsu, G.; Kargel, J. S.

    1999-09-01

    Recent high resolution MOC images have revealed the presence of deformed impact craters on flow-like features characterized by narrow bands of alternating light and dark material on the walls of Valles Marineris. The maximum crater elongations are consistent with the flow directions. Moreover the directions of these flows follow the topography downslope. In some cases, the flows emanate from cirque-like depressions, and the flows are divided by sharp ridges similar to arête. These landforms have resemblance to (1) alpine-type glacier morphology, including cirques, arêtes, and glaciers containing medial moraines; and (2) Grand Canyon-type sapping and mass wasting features. Certain aspects of the features in Valles Marineris seem more consistent with the first hypothesis involving a viscous rheology of the flows driven by ice-assisted creep processes. This hypothesis includes direct analogies to glaciers and rock glaciers. In the case of rock glaciers, flow is produced by freeze-thaw and by internal deformation of ice cores or lenses, whereas in the case of glaciers, movement occurs by internal deformation plus basal sliding in some cases where the glacier is melted at its bed. The amounts and roles of ice in the genesis of the Martian glacier-type landforms in Valles Marineris are not clear at this point. The population density of undeformed fresh impact craters on these flows appears to be low compared with the surrounding plateau areas. This may indicate relatively recent ages of the flow processes. Despite the limited coverage of the MOC images, the occurrence of the flow-like features associated by the deformed impact craters is common in most areas of Valles Marineris that have been imaged. We currently are working on the systematic survey of these flow-like features. We are also in the process of analyzing MOLA data in order to constrain the geometry of these landforms.

  10. The Extent of Channelized Basal Water Flow Under the Greenland Ice Sheet

    NASA Astrophysics Data System (ADS)

    Downs, J.; Johnson, J. V.; Harper, J. T.

    2015-12-01

    Glacial ice flows due to a combination of deformation and basal sliding, with sliding accounting for most of the fastest ice flow. Basal sliding is controlled by the transport of water at the glacier's bed, which can be accomplished through both high pressure, low discharge, distributed flow, or low pressure, high discharge, channelized flow. Higher pressures are generally associated with more complete decoupling of a glacier from its bed and faster flow. As the intensity of summer melt in Greenland has increased, our poor understanding of the drainage network's discharge capacity and its coupling to sliding has generated fundamental questions, such as: will larger fluxes of liquid water promote or inhibit basal sliding? To investigate this question we have implemented a model of distributed and channelized flow developed by Werder et. al 2013. The sensitivity of the modeled channel network to basal and surface geometry, melt rate, boundary conditions, and other parameters is examined in a sequence of experiments using synthetic geometries. Expanding on these experiments, we run the model with realistic surface and bedrock data from Issunguata Sermia in Western Central Greenland. These experiments benefit from a wealth of in-situ data, including observations of basal water pressure. Our results suggest that the development of large channels is limited to the margins of the ice sheet, and that higher pressures continue to prevail in the interior.

  11. Flow properties of ice cream mix prepared from palm oil: anhydrous milk fat blends.

    PubMed

    Rosnani, A I Wan; Aini, I Nor; Yazid, A M M; Dzulkifly, M H

    2007-05-15

    Ice cream mixes containing 33.4% total solids including 10% fat, 11.1% milk solid-non fat (MSNF), 12% sugar, 0.35% commercial blend of emulsifier/ stabiliser and water were produced. The blending of PO with AMF were conducted at three different ratios 30: 70, 50: 50 and 70: 30, respectively. The experimental ice cream mixes were compared with a control ice cream mix prepared from AMF. The flow properties were measured after ageing at 0, 1, 1.5, 2 and 24 h and determined using a controlled stress rheometer (Haake RS 100). The Power Law and Casson equation was employed to estimate the yield stress of an ice cream mixes. The regression coefficients (r) was represented well by the Casson model (r > 0.99) for all the samples, indicating goodness of fit. The profiles of the consistency coefficients (K(c)) were quite similar for all experimental samples, which could be attributed to the fact that all the samples exhibited similar viscoelastic behaviour. The flow behaviour index (n) of an ice cream mix prepared from PO and their blends with AMF were less then 1.0 (range 0.04-0.08) indicating that they were psuedoplastic fluid. The eta(o) at shear rate 20(-1) indicated higher degree of viscosity in AMF. PMID:19086519

  12. Deriving Process-Driven Collaborative Editing Pattern from Collaborative Learning Flow Patterns

    ERIC Educational Resources Information Center

    Marjanovic, Olivera; Skaf-Molli, Hala; Molli, Pascal; Godart, Claude

    2007-01-01

    Collaborative Learning Flow Patterns (CLFPs) have recently emerged as a new method to formulate best practices in structuring the flow of activities within various collaborative learning scenarios. The term "learning flow" is used to describe coordination and sequencing of learning tasks. This paper adopts the existing concept of CLFP and argues…

  13. Melting of ice stuck on cylinders placed horizontally in a water flowing duct

    NASA Astrophysics Data System (ADS)

    Sugawara, M.; Komatsu, Y.; Beer, H.

    2016-04-01

    Melting of ice stuck on seven in-lined cooling cylinders placed horizontally in a water flowing duct is investigated by means of a numerical analysis on the PHOENICS Code. The numerical results are validated compared with the experiment of an ice sphere melting. Parameters for calculations are inlet temperature, inlet velocity and clearance between the cylinders. The most concern of the melting is a finding of a curious behavior that is the melting in small inlet velocity on the long clearance between the cylinders.

  14. Flow quality studies of the NASA Lewis Research Center Icing Research Tunnel diffuser

    NASA Technical Reports Server (NTRS)

    Arrington, E. Allen; Pickett, Mark T.; Sheldon, David W.

    1994-01-01

    The purpose was to document the airflow characteristics in the diffuser of the NASA Lewis Research Center Icing Research Tunnel and to determine the effects of vortex generators on the flow quality in the diffuser. The results were used to determine how to improve the flow in this portion of the tunnel so that it can be more effectively used as an icing test section and such that overall tunnel efficiency can be improved. The demand for tunnel test time and the desire to test models that are too large for the test section were two of the drivers behind this diffuser study. For all vortex generator configurations tested, the flow quality was improved.

  15. Study of flow patterns in fume hood enclosures

    SciTech Connect

    Pathanjali, C.; Rahman, M.M.

    1996-12-31

    A three-dimensional model for flow inside a fume hood enclosure was developed and numerical computations were carried out to explore the flow pattern and possible path of contaminant transport under different operating conditions of the hood. Equations for the conservation of mass and momentum were solved for different flow rate and opening conditions in the hood. The face velocity was maintained constant at its rated value of 0.4 m/s. The flow was assumed to enter through the front window opening (positive x-direction) and leave the cupboard through an opening on the top of the hood (positive z-direction). The flow was assumed to be fully turbulent. The {kappa}-{var_epsilon} model was used for the prediction of turbulence. The flow pattern for different sash openings were studied. The flow patterns around an object located at the bottom of the hood was studied for different locations of the object. In addition, the effect of a person standing in front of the hood on the flow pattern was investigated. It was found that air entering the hood proceeds directly to the back wall, impinges it and turns upward toward the top wall and exits through the outlet. The flow finds its way around any object forming a recirculating region at its trailing surface. With an increase in the sash opening, the velocity becomes higher and the fluid traces the path to the outlet more quickly. The volume occupied by recirculating flow decreases with increase in sash opening. The computed flow patterns will be very useful to design experiments with optimum sash opening providing adequate disposal of contaminants with minimum use of conditioned air from inside the room.

  16. Flow Interference between a Circular (Upstream) and a Square Cylinder: Flow Pattern Identification

    NASA Astrophysics Data System (ADS)

    Mohan, Jayalakshmi; R, Ajith Kumar; Kumar, Nithin S.

    2014-11-01

    In this paper, flow interference between an upstream circular cylinder and a square cylinder of equal size is studied in tandem arrangement. The main objective of this invesigation is to identify the possible flow patterns at different spacing ratios, L/B where L is the centre-to-centre distance between the cylinders and B is the characteristic dimension of the bodies. All the experiments are conducted in a water channel and the test Reynolds number is 2100 (based on B). L/B is varied from 1.0 to 5.0. The flow visualization experiments are videographed and then analyzed frame-by-frame to capture the finer details of the flow patterns. Flow over single square and circular cylinders is analyzed first. Then, flow interference between two circular cylinders is investigated. Subsequently, flow over a circular-square configuration is investigated. No such studies are reported so far. Different flow patterns are observed for the circular-square configuration. Additionally, the time of persistence of each flow pattern have been recorded over a sufficiently long period of time to see the most dominant flow pattern. The schedule of occurrence of flow patterns have also been studied during this investigation. This study is very much relevant in the context of possible interference effects occuring in engineering structures such as buildings, heat exchanger tubes etc.

  17. Flow Interference between a Square (Upstream) and a Circular Cylinder: Flow Pattern Identification

    NASA Astrophysics Data System (ADS)

    Kumar, Nithin S.; R, Ajith Kumar; Mohan, Jayalakshmi

    2014-11-01

    In this paper, flow interference between an upstream square cylinder and a circular cylinder of equal size is studied in tandem arrangement. The main objective of this invesigation is to identify the possible flow patterns at different spacing ratios, L/B where L is the centre-to-centre distance between the cylinders and B is the characteristic dimension of the bodies. All the experiments are conducted in a water channel and the test Reynolds number is 2100 (based on B). L/B is varied from 1.0 to 5.0. The flow visualization experiments are videographed and then analyzed frame-by-frame to capture the finer details of the flow patterns. Flow over single square and circular cylinders is analyzed first. Then, flow interference between two square cylinders is investigated. Subsequently, flow over a square-circular configuration is investigated. No such systematic studies are reported so far. Different flow patterns are observed for the square-circular configuration. Additionally, the time of persistence of each flow pattern have been recorded over a sufficiently long period of time to see the most dominant flow pattern. The schedule of occurrence of flow patterns have also been studied during this investigation. This study bears considerable practical relevance in the context of possible interference effects occurring in engineering structures such as buildings, bridges etc.

  18. Investigating the Flow Dynamics of Ice Shelves using Laboratory Experiments, Simple Theoretical Models and Geophysical Data Analysis

    NASA Astrophysics Data System (ADS)

    Wearing, M.; Hindmarsh, R. C. A.; Worster, G.

    2014-12-01

    Ice-shelf calving-rates and the buttressing ice shelves provide to grounded ice are both difficult to model and quantify. An increased understanding of the mechanics of this process is imperative in determining the dynamics of marine ice sheets and consequently predicting their future extent and thickness. Alley et al. (2008) proposed an empirically derived calving law, relating the calving rate to the strain rate at the calving front. However, Hindmarsh (2012) showed that a similar relationship could be deduced by considering the viscous flow of the ice shelf. We investigate the relationship between the ice shelf flow field and the strain rate field in the area close to the calving front. Analysis is undertaken of ice surface velocity data for a range of large Antarctic ice shelves (data from Rignot et al., 2011) and an inferred strain rate field produced from that data. These geophysical results are compared with a series of simple mathematical models from which thickness profiles and velocity fields can be obtained for a range of geometries and flow regimes. Fluid mechanical laboratory experiments simulating the flow of an ice shelf in an idealized channel geometry provide a further comparison to the theoretical models and geophysical data, and allow a wider range of parameters to be tested. We show some results from these laboratory experiments aimed at exploring the success of the mathematical models.

  19. MEANS FOR VISUALIZING FLUID FLOW PATTERNS

    DOEpatents

    Lynch, F.E.; Palmer, L.D.; Poppendick, H.F.; Winn, G.M.

    1961-05-16

    An apparatus is given for determining both the absolute and relative velocities of a phosphorescent fluid flowing through a transparent conduit. The apparatus includes a source for exciting a narrow trsnsverse band of the fluid to phosphorescence, detecting means such as a camera located downstream from the exciting source to record the shape of the phosphorescent band as it passes, and a timer to measure the time elapsed between operation of the exciting source and operation of the camera.

  20. Flow Patterns Around a Complex Building

    SciTech Connect

    Calhoun, R; Chan, S; Lee, R; Leone, J, Shinn, J; Stevens, D

    1999-09-24

    The authors compare the results of a computer simulated flow field around building 170 (B170) at Lawrence Livermore National Laboratory (LLNL) with field measurements. In order to aid in the setup of the field experiments, the simulations were performed first. B170 was chosen because of its architectural complexity and because a relatively simple fetch exists upwind (a field lies southwest of the site). Figure 1 shows a computational model of the building which retains the major architectural features of the real building (e.g., courtyard, alcoves, and a multi-level roof). Several important characteristics of the cases presented here are: (1) the flow was assumed neutral and no heat flux was imposed at the ground, representing cloudy or morning conditions, (2) a simple canopy parameterization was used to model the effect of a large row of eucalyptus trees which is located to the northeast of the building, (3) the wind directions studied were 200, 225, 250 degrees measured clockwise from true north (the prevailing winds at LLNL are from the southwest in the summer), (4) the incoming wind profile was modeled as logarithmic with a maximum of about 3 meters per second. In addition, note that the building is rotated counterclockwise by 25 degrees with respect to the east/west axis. For convenience, the flow is modeled in a coordinate system that has been rotated with the building.

  1. Flow and fracture of ices, with application to icy satellites (Invited)

    NASA Astrophysics Data System (ADS)

    Durham, W. B.; Stern, L. A.; Pathare, A.; Golding, N.

    2013-12-01

    Exploration of the outer planets and their satellites by spacecraft over the past 4 decades has revealed that the prevailing low temperatures in the outer solar system have not produced "dead" cryoworlds of generic appearance. Rather, there is an extraordinary diversity in average densities, presence/absence and compositions of atmospheres and planetary rings, average albedos and their seasonal changes, near-surface compositions, and surface records of impact cratering and endogenic tectonic and igneous processes. One reason for this diversity is that the icy minerals present in abundance on many of these worlds are now or once were at significant fractions of their melting temperatures. Hence, a host of thermally activated processes related to endogenic activity (such as crystal defect migration, mass diffusion, surface transport, solid-solid changes of state, and partial melting) may occur that can enable inelastic flow on the surfaces and in the interiors of these bodies. Planetary manifestations include viscous crater relaxation in ice-rich terrain, cryovolcanism, the presence of a stable subsurface ocean, and the effects of solid-ice convection in deep interiors. We make the connection between theoretical mechanisms of deformation and planetary geology through laboratory experiment. Specifically, we develop quantitative constitutive flow laws (strain rate vs. stress) that describe the effects of relevant environmental variables (hydrostatic pressure, temperature, phase composition, chemical impurities). Our findings speak to topics including (1) the behavior of an outer ice I layer, its thickness, the depth to which a stagnant lid might extend, and possibility of wholesale overturn; (2) softening effects of dissolved species such as ammonia and perchlorate; (3) hardening effects of enclathration and of rock dust; and (4) effects of grain size on strength and factors affecting grain size. Other applications of lab data include dynamics of the deep interiors of

  2. Pattern formation induced by a differential Poiseuille flow

    NASA Astrophysics Data System (ADS)

    Stucchi, L.; Vasquez, D. A.

    2014-12-01

    Differential advection, where a reactant is advected while another one is immobilized, leads to instabilities in reaction-advection-diffusion systems. In particular, a homogeneous steady state looses stability for strong enough flows, leading to chemical patterns moving in the direction of the flow. In this paper we study the effects of differential advection due to a two-dimensional Poiseuille flow. We carry out a linear stability analysis on a homogeneous state using an activator-inhibitor reaction. We find that shear dispersion induced by the Poiseuille flow may lead to instabilities at slower flow rates. We find that contrary to the one-dimensional system, the instability depends on which substance is advected. We find a critical average flow speed for instability depending on tube size. Numerical solutions of the nonlinear reaction-advection-diffusion result in patterns of constant shape propagating along the tube.

  3. Thermal runaway instabilities: A possible mechanism for fast-flow in surging glaciers and ice streams

    NASA Astrophysics Data System (ADS)

    Fastook, J.

    2011-12-01

    Thermal runaway is the process whereby increased temperature due to strain heating produced by deformation of a viscous material affects its mechanical properties in a way that softens the material, allowing greater strain rates, which in turn produce more strain heating and further increased temperatures. Such positive feedback has been shown to lead to catastrophic failure of viscoelastic materials such as polymers, metallic glasses, rocks under high pressure, and rapidly deforming crystalline solids. Such processes often result in rather narrow shear bands in which much of the deformation occurs. Such narrow shear bands are characteristic of the edges of ice streams, which show an almost square velocity profile, and may also mimic the mostly uniform vertical velocity profiles often invoked in models of sliding where considerable movement is allowed to occur at the bed of the glacier. We examine a simplified analytic model of such thermal runaway leading to the collapse of a shearing material (Braeck et al., Phys. Rev. E, 80(4), 2009). A definite singularity point in the applied stress In this treatment is evident, beyond which thermal runaway leads to rapidly increasing temperature and rate of deformation. While quite limited in the analytic sense, the results point to the possibility that such thermal runaway could exist in ice sheets, and could possibly be responsible for surges in glaciers as well as the steady fast flow of ice streams, even without invoking of the "basal lubrication" usually associated with such sliding situations. Using a simple 1D model of heat flow through a slab of ice whose surface is held at a defined temperature, whose bed receives a specific geothermal heat flux, and whose material properties (the ice hardness parameter in the Flow Law) are given by an Arrhenius exponential function of temperature, we present a parameter-space examination of the dependence of such a process on driving stress (ie. ice thickness and surface slope

  4. Flow pattern and heat transfer behavior of boiling two-phase flow in inclined pipes

    NASA Astrophysics Data System (ADS)

    Liu, Dezhang; Ning, Ouyang

    1992-09-01

    Movable Electrical Conducting Probe (MECP), a kind of simple and reliable measuring transducer, used for predicting full-flow-path flow pattern in a boiling vapor/liquid two-phase flow is introduced in this paper. When the test pipe is set at different inclination angles, several kinds of flow patterns, such as bubble, slug, churn, intermittent, and annular flows, may be observed in accordance with the locations of MECP. By means of flow pattern analysis, flow field numerical calculations have been carried out, and heat transfer coefficient correlations along full-flow-path derived. The results show that heat transfer performance of boiling two-phase flow could be significantly augmented as expected in some flow pattern zones. The results of the investigation, measuring techniques and conclusions contained in this paper would be a useful reference in foundational research for prediction of flow pattern and heat transfer behavior in boiling two-phase flow, as well as for turbine vane liquid-cooling design.

  5. Application of a Third Order Upwind Scheme to Viscous Flow over Clean and Iced Wings

    NASA Technical Reports Server (NTRS)

    Bangalore, A.; Phaengsook, N.; Sankar, L. N.

    1994-01-01

    A 3-D compressible Navier-Stokes solver has been developed and applied to 3-D viscous flow over clean and iced wings. This method uses a third order accurate finite volume scheme with flux difference splitting to model the inviscid fluxes, and second order accurate symmetric differences to model the viscous terms. The effects of turbulence are modeled using a Kappa-epsilon model. In the vicinity of the sold walls the kappa and epsilon values are modeled using Gorski's algebraic model. Sampling results are presented for surface pressure distributions, for untapered swept clean and iced wings made of NACA 0012 airfoil sections. The leading edge of these sections is modified using a simulated ice shape. Comparisons with experimental data are given.

  6. The importance of particulate texture to the flow strength of ice + dust

    USGS Publications Warehouse

    W. B. Durham; N. Golding; Stern, Laura A.; A. Pathare; D. L. Goldsby; D. Prior

    2015-01-01

    Preliminary experimental surveys of the flow of dilute mixtures of ice plus hard particulates under planetary conditions indicate a strengthening effect with respect to pure ice, but with dependencies on environmental conditions (temperature, stress, grain size) that vary widely from study to study [1-4]. With the expectation that the textural character of the particulate fraction (size, shape, spatial distribution of particulates; relationship of particulates to ice grain boundaries, etc.) also influences rheological behavior, we have begun a more systematic investigation of the effect of particulates on strength. We rely extensively on cryogenic scanning electron microscopy (CSEM) and to maximize planetary relevance we focus on behavior at low stress and small grain size.

  7. Flow Quality Surveys in the Settling Chamber of the NASA Glenn Icing Research Tunnel (2011 Tests)

    NASA Technical Reports Server (NTRS)

    Steen, Laura E.; Van Zante, Judith Foss; Broeren, Andy P.; Kubiak, Mark J.

    2012-01-01

    In 2011, the heat exchanger and refrigeration plant for NASA Glenn Research Center's Icing Research Tunnel (IRT) were upgraded. Flow quality surveys were performed in the settling chamber of the IRT in order to understand the effect that the new heat exchanger had on the flow quality upstream of the spray bars. Measurements were made of the total pressure, static pressure, total temperature, airspeed, and ow angle (pitch and yaw). These measurements were directly compared to measurements taken in 2000, after the previous heat exchanger was installed. In general, the flow quality appears to have improved with the new heat exchanger.

  8. Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

    NASA Technical Reports Server (NTRS)

    Kerho, M.; Bragg, M.; Shin, J.

    1992-01-01

    Research was performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30 deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the three dimensional experiment compare well to the computational simulations.

  9. Helium bubble flow visualization of the spanwise separation on a NACA 0012 with simulated glaze ice

    NASA Technical Reports Server (NTRS)

    Kerho, M.; Bragg, M.; Shin, J.

    1992-01-01

    Research has been performed to experimentally visualize and document the flow separation due to simulated glaze ice accretion on a NACA 0012 semispan with 30-deg sweep using helium bubbles as flow tracers. Results are compared to Navier-Stokes computational simulations for different angles of attack. Prior to acquiring data for the semispan model, a two-dimensional experiment was conducted to determine the accuracy of using the helium bubbles as flow tracers. Results from the 3D experiment compare well to the computational simulations.

  10. Patterns of Flows in an Intermediate Prominence Observed by Hinode

    NASA Astrophysics Data System (ADS)

    Ahn, Kwangsu; Chae, Jongchul; Cao, Wenda; Goode, Philip R.

    2010-09-01

    The investigation of plasma flows in filaments/prominences gives us clues to understanding their magnetic structures. We studied the patterns of flows in an intermediate prominence observed by Hinode/SOT. By examining a time series of Hα images and Ca II H images, we have found horizontal flows in the spine and vertical flows in the barb. Both of these flows have a characteristic speed of 10-20 km s-1. The horizontal flows displayed counterstreaming. Our detailed investigation revealed that most of the moving fragments in fact reversed direction at the end point of the spine near a footpoint close to the associated active region. These returning flows may be one possible explanation of the well-known counterstreaming flows in prominences. In contrast, we have found vertical flows—downward and upward—in the barb. Most of the horizontal flows in the spine seem to switch into vertical flows when they approach the barb, and vice versa. We propose that the net force resulting from a small deviation from magnetohydrostatic equilibrium, where magnetic fields are predominantly horizontal, may drive these patterns of flow. In the prominence studied here, the supposed magnetohydrostatic configuration is characterized by magnetic field lines sagging with angles of 13° and 39° in the spine and the barb, respectively.

  11. Instability patterns in a miscible core annular flow

    NASA Astrophysics Data System (ADS)

    D'Olce, Marguerite; Martin, Jerome; Rakotomalala, Nicole; Salin, Dominique; Talon, Laurent

    2006-11-01

    Laboratoire FAST, batiment 502, campus universitaire, 91405 Orsay Cedex (France). Experiments are performed with two miscible fluids of equal density but different viscosities. The fluids are injected co-currently and concentrically into a cylindrical pipe. The so-obtained base state is an axisymmetric parallel flow, for which the ratio of the flow rates of the two fluids monitors the relative amount (and so the radius) of the fluids. Depending on this relative amount and on the total flow rate of the fluids, unstable axisymmetric patterns such as mushrooms and pearls are observed. We delineate the diagram of occurrence of the two patterns and characterize the instabilities.

  12. Using composite flow laws to extrapolate lab data on ice to nature

    NASA Astrophysics Data System (ADS)

    de Bresser, Hans; Diebold, Sabrina; Durham, William

    2013-04-01

    The progressive evolution of the grain size distribution of deforming and recrystallizing Earth materials directly affects their rheological behaviour in terms of composite grain-size-sensitive (GSS, diffusion/grain boundary sliding) and grain-size-insensitive (GSI, dislocation) creep. After time, such microstructural evolution might result in strain progressing at a steady-state balance of mechanisms of GSS and GSI creep. In order to come to a meaningful rheological description of materials deforming by combined GSS and GSI mechanisms, composite flow laws are required that bring together individual, laboratory derived GSS and GSI flow laws, and that include full grain size distributions rather than single mean values representing the grain size. A composite flow law approach including grain size distributions has proven to be very useful in solving discrepancies between microstructural observations in natural calcite mylonites and extrapolations of relatively simple laboratory flow laws (Herwegh et al., 2005, J. Struct Geol., 27, 503-521). In the current study, we used previous and new laboratory data on the creep behavior of water ice to investigate if a composite flow law approach also results in better extrapolation of lab data to nature for ice. The new lab data resulted from static grain-growth experiments and from deformation experiments performed on samples with a starting grain size of either < 2 microns ("fine grained ice") or of 180-250 microns ("coarse grained ice"). The deformation experiments were performed in a special cryogenic Heard-type deformation apparatus at temperatures 180-240 K, at confining pressures 30-100 MPa, and strain rates between 1E-08/s and 1E-04/s. After the experiments, all samples were studied using cryogenic SEM and image analysis techniques. We also investigated natural microstructures in EPICA drilling ice core samples of Dronning Maud Land in Antartica. The temperature of the core ranges from 228 K at the surface to 272 K

  13. Scale invariance of subsurface flow patterns and its limitation

    NASA Astrophysics Data System (ADS)

    Hergarten, S.; Winkler, G.; Birk, S.

    2016-05-01

    Preferential flow patterns in the subsurface are of great importance for the availability and the quality of water resources. However, knowledge of their spatial structure is still behind their importance, so that understanding the nature of preferential flow patterns is a major issue in subsurface hydrology. Comparing the statistics of river catchment sizes and spring discharges, we found that the morphology of preferential subsurface flow patterns is probably scale invariant and similar to that of dendritic river networks. This result is not limited to karstic aquifers where the occurrence of dendritic structures has been known at least qualitatively for a long time. The scale invariance even seems to be independent of the lithology of the aquifer. However, scale invariance of river patterns seems to be only limited by the continental scale, while scale invariance of subsurface flow patterns breaks down at much smaller scales. The upper limit of scale invariance in subsurface flow patterns is highly variable. We found a range from thousands of square kilometers for limestone aquifers down to less than 1 km2 in the weathered zone and debris accumulations of crystalline rocks.

  14. Influence of regional precipitation patterns on stable isotopes in ice cores from the central Himalayas

    NASA Astrophysics Data System (ADS)

    Pang, H.; Hou, S.; Kaspari, S.; Mayewski, P. A.

    2014-02-01

    Several ice cores have been recovered from the Dasuopu (DSP) Glacier and the East Rongbuk (ER) Glacier in the central Himalayas since the 1990s. Although the distance between the DSP and the ER ice core drilling sites is only ~ 125 km, the stable isotopic record (δ18O or δD) of the DSP core is interpreted in previous studies as a temperature proxy, while the ER core is interpreted as a precipitation proxy. Thus, the climatological significance of the stable isotopic records of these Himalayan ice cores remains a subject of debate. Based on analysis of regional precipitation patterns over the region, we find that remarkable discrepancy in precipitation seasonality between the two sites may account for their disparate isotopic interpretations. At the ER core site, the Indian summer monsoon (ISM) precipitation is dominating due to topographic blocking of the moisture from westerlies by the high ridges of Mt. Qomolangma (Everest), which results in a negative correlation between the ER Δ18O or δD record and precipitation amount along the southern slope of the central Himalayas in response to the "amount effect". At the DSP core site, in comparison with the ISM precipitation, the wintertime precipitation associated with the westerlies is likely more important owing to its local favorable topographic conditions for interacting with the western disturbances. Therefore, the DSP stable isotopic record may be primarily controlled by the westerlies. Our results have important implications for interpreting the stable isotopic ice core records recovered from different climatological regimes of the Himalayas.

  15. Hydraulic Transport of Ice-Water Mixtures

    NASA Astrophysics Data System (ADS)

    Fujita, Toshihiko

    When an ice thermal storage system is introduced into a district cooling system,the hydraulic ice transport system must have an advantage over a conventional water transport system in saving pipe sizes and pumping powers. Referring to the literature providing direct information on the hydraulic transport of ice-water mixtures,the author comments on the following subjects : •Definitions of an ice packing factor. • The capacity of heat transported with ice-water mixtures. • District distribution system. • Flow patterns in ice-water two-phase flow in straight pipes. • General expressions for pressure losses in solid-liquid two-phase flow. • The characteristics of pressure losses in ice-water two-phase flow. •Choking phenomena in channels.

  16. Measurements of natural ice nuclei with a continuous flow diffusion chamber

    NASA Technical Reports Server (NTRS)

    Rogers, D. C.

    1983-01-01

    A description is given of a continuous flow diffusion chamber technique for measuring the atmospheric concentrations of natural C-F nuclei. It is noted that the same device can also measure deposition nuclei; these two modes can thus be separated and compared. The laminar flow characteristics allow the temperature and supersaturation to be calculated with a high degree of precision and confidence. The method avoids the problems of a supporting substrate and of concentrating the sample into a small volume (as for membrane filters). The present measurements of natural ice nucleus concentrations at +1 percent water supersaturation are found to be comparable to research aircraft measurements of ice crystal concentrations in winter cap clouds over Elk Mountain, Wyoming (Vali et al., 1982).

  17. Flow Patterns During Friction Stir Welding

    NASA Technical Reports Server (NTRS)

    Guerra, M.; Schmidt, C.; McClure, J. C.; Murr, L. E.; Nunes, A. C.; Munafo, Paul M. (Technical Monitor)

    2002-01-01

    Friction Stir Welding is a relatively new technique for welding that uses a cylindrical pin or nib inserted along the weld seam. The nib (usually threaded) and the shoulder in which it is mounted are rapidly rotated and advanced along the seam. Extreme deformation takes place leaving a fine equiaxed structure in the weld region., The flow of metal during Friction Stir Welding is investigated using a faying surface tracer and a nib frozen in place during welding. It is shown that material is transported by two processes. The first is a wiping of material from the advancing front side of the nib onto a zone of material that rotates and advances with the nib. The material undergoes a helical motion within the rotational zone that both rotates and advances and descends in the wash of the threads on the nib and rises on the outer part of the rotational zone. After one or more rotations, this material is sloughed off in its wake of the nib, primarily on the advancing side. The second process is an entrainment of material from the front retreating side of the nib that fills in between the sloughed off pieces from the advancing side.

  18. Flow Quality Studies of the NASA Glenn Research Center Icing Research Tunnel Circuit (1995 Tests)

    NASA Technical Reports Server (NTRS)

    Arrington, E. Allen; Kee-Bowling, Bonnie A.; Gonsalez, Jose C.

    2000-01-01

    The purpose of conducting the flow-field surveys described in this report was to more fully document the flow quality in several areas of the tunnel circuit in the NASA Glenn Research Center Icing Research Tunnel. The results from these surveys provide insight into areas of the tunnel that were known to exhibit poor flow quality characteristics and provide data that will be useful to the design of flow quality improvements and a new heat exchanger for the facility. An instrumented traversing mechanism was used to survey the flow field at several large cross sections of the tunnel loop over the entire speed range of the facility. Flow-field data were collected at five stations in the tunnel loop, including downstream of the fan drive motor housing, upstream and downstream of the heat exchanger, and upstream and downstream of the spraybars located in the settling chamber upstream of the test section. The data collected during these surveys greatly expanded the data base describing the flow quality in each of these areas. The new data matched closely the flow quality trends recorded from earlier tests. Data collected downstream of the heat exchanger and in the settling chamber showed how the configuration of the folded heat exchanger affected the pressure, velocity, and flow angle distributions in these areas. Smoke flow visualization was also used to qualitatively study the flow field in an area downstream of the drive fan and in the settling chamber/contraction section.

  19. Flow Quality Measurements in an Aerodynamic Model of NASA Lewis' Icing Research Tunnel

    NASA Technical Reports Server (NTRS)

    Canacci, Victor A.; Gonsalez, Jose C.

    1999-01-01

    As part of an ongoing effort to improve the aerodynamic flow characteristics of the Icing Research Tunnel (IRT), a modular scale model of the facility was fabricated. This 1/10th-scale model was used to gain further understanding of the flow characteristics in the IRT. The model was outfitted with instrumentation and data acquisition systems to determine pressures, velocities, and flow angles in the settling chamber and test section. Parametric flow quality studies involving the insertion and removal of a model of the IRT's distinctive heat exchanger (cooler) and/or of a honeycomb in the settling chamber were performed. These experiments illustrate the resulting improvement or degradation in flow quality.

  20. Flow patterns in free liquid film caused by thermocapillary effect

    NASA Astrophysics Data System (ADS)

    Ueno, Ichiro; Fei, Linhao; Kowata, Yosuke; Kaneko, Toshihiro; Pettit, Donald

    2015-11-01

    The basic flow patterns realized in a thin free liquid film driven by the thermocapillary effect are focused. Spetial attention is paied to the effect of the volume ratio of the liquid film to the hole sustaining the film on the flow patterns. We prepare a thin liquid film of less than 0 . 5 mm in thickness in order to stably realize the film under normal gravity. Liquid has in general negative temperature coefficient of it surface tension; that is, the fluid is driven to the colder to hotter regions by the non-uniform surface-tension distribution. In the case of thin free liquid film, however, it is found that a unique flow pattern is induced. One of the present authors, DRP, carried out a series of experiments under microgravity condition in the International Space Station (ISS) in 2003. He prepared a ring made of metal, and formed a thin film of water inside the ring. Once he added a non-uniform temperature distribution to the film by placing a heated iron at one end of the ring, a net flow toward the heated iron was realized. In order to understand flow patterns, we focus on the flow structures of the thermocapillary convection in a cross section normal to the end walls as well as the surface temperature distributions.

  1. Flow patterns and morphology of a prograding river delta

    NASA Astrophysics Data System (ADS)

    Shaw, John B.; Mohrig, David; Wagner, R. Wayne

    2016-02-01

    The transition of flow between laterally confined channels and the unchannelized delta front controls the morphodynamic evolution of river deltas but has rarely been measured at the field scale. We quantify flow patterns and bathymetry that define the evolution of the subaqueous delta front on the Wax Lake Delta, a rapidly prograding delta in coastal Louisiana. A significant portion of flow (˜59%) departs the channel network over lateral channel margins as opposed to the downstream channel tips. Bathymetric surveys and remotely sensed estimates of flow direction allow spatial changes in flow velocity to be quantified and patterns of erosion and deposition to be estimated. Shallowing along channel margins produces spatial acceleration and erosion. Lateral spreading, deceleration, and deposition occur within three to eight channel widths outside of the channel margins. In interdistributary bays, the shape of each flow path is constrained by "nourishment boundaries" that separate the outflows from neighboring channels. Deposit elevation decreases with a basinward slope of 2.4 × 10-4 with distance from a channel margin along any flow path, regardless of the channel or location that flow departed the network. Bathymetric depressions called "interdistributary troughs" form along nourishment boundaries where flow paths are the longest and deposit elevation is correspondingly low. We conclude that the deposit morphology exerts a strong control on bathymetric evolution and that interaction between neighboring channels and even neighboring deltas can influence delta front morphology.

  2. Optical Imaging of Flow Pattern and Phantom

    NASA Technical Reports Server (NTRS)

    Galland, Pierre A.; Liang, X.; Wang, L.; Ho, P. P.; Alfano, R. R.; Breisacher, K.

    1999-01-01

    Time-resolved optical imaging technique has been used to image the spatial distribution of small droplets and jet sprays in a highly scattering environment. The snake and ballistic components of the transmitted pulse are less scattered, and contain direct information about the sample to facilitate image formation as opposed to the diffusive components which are due to multiple collisions as a light pulse propagates through a scattering medium. In a time-gated imaging scheme, these early-arriving, image-bearing components of the incident pulse are selected by opening a gate for an ultrashort period of time and a shadowgram image is detected. Using a single shot cooled CCD camera system, the formation of water droplets is monitored as a function of time. Picosecond time-gated image of drop in scattering cells, spray droplets as a function of let speed and gas pressure, and model calcification samples consisted of calcium carbonate particles of irregular shapes ranging in size from 0. 1 to 1.5 mm affixed to a microscope slide have been measured. Formation produced by an impinging jet will be further monitored using a CCD with 1 kHz framing illuminated with pulsed light. The desired image resolution of the fuel droplets is on the 20 pm scale using early light through a highly scattering medium. A 10(exp -6)m displacement from a jet spray with a flow speed of 100 m/sec introduced by the ns grating pulse used in the imaging is negligible. Early ballistic/snake light imaging offers nondestructive and noninvasive method to observe the spatial distribution of hidden objects inside a highly scattering environment for space, biomedical, and materials applications. In this paper, the techniques we will present are time-resolved K-F transillumination imaging and time-gated scattered light imaging. With a large dynamic range and high resolution, time-gated early light imaging has the potential for improving rocket/aircraft design by determining jets shape and particle sizes

  3. Ice front configuration and torrential flow features of the Late Wisconsinan interlobate region of southcentral Michigan

    SciTech Connect

    Taylor, L.D. . Dept. of Geological Sciences)

    1994-04-01

    A large re-entrant, bordered on three sides by ice of the Michigan, Saginaw and Huron-Erie lobes, developed over a five-county area in southcentral Michigan during ice retreat of the Port Bruce Stade of the Woodfordian Substage. At this time, ice occupied positions marked by the Sturgies, Tekonsha, and Kalamazoo Moraines. The presence of numerous boulder beds within outwash deposits attests to frequent episodes of torrential flow. A major source of the discharge was the draining of short-lived proglacial and subglacial lakes identified by lacustrine deposits which occur at different altitudes within moraine belts. Tunnel valleys, meltwater channels, and narrow chutes carried the high discharges of water that were partly responsible for the Kankakee torrent of northeastern Illinois. The configuration of abandoned meltwater channels in eastern Calhoun and western jackson counties, between the Kalamazoo Moraine on the northeast and the Tekonsha Moraine to the southwest, indicates that a large ice-collapsed depression, 30 km long and 8 km to 16 km wide, developed within the Saginaw lobe just behind its margin. For a short period of time it contained intermittent glacial lakes one of which drained through the Kesler Lakes sluiceway. A large outwash plain, the Union City-Mendon sluiceway, heads at the Tekonsha Moraine in southcentral Calhoun County and extends southwest through northeastern Branch County to the Sturgis Moraine. Several abandoned narrow chutes, up to 1.6 km long and 60 m to 300 m wide, are incised in the outwash plain in the vicinity of Union City. Channel geometry indicates that flow exceeded 850 cms (30,000 cfs) during bankfull discharge and came from the overflow of a lake dammed by ice blocks in the ancient St. Joseph River floodplain.

  4. Development of Three-Dimensional Flow Code Package to Predict Performance and Stability of Aircraft with Leading Edge Ice Contamination

    NASA Technical Reports Server (NTRS)

    Strash, D. J.; Summa, J. M.

    1996-01-01

    In the work reported herein, a simplified, uncoupled, zonal procedure is utilized to assess the capability of numerically simulating icing effects on a Boeing 727-200 aircraft. The computational approach combines potential flow plus boundary layer simulations by VSAERO for the un-iced aircraft forces and moments with Navier-Stokes simulations by NPARC for the incremental forces and moments due to iced components. These are compared with wind tunnel force and moment data, supplied by the Boeing Company, examining longitudinal flight characteristics. Grid refinement improved the local flow features over previously reported work with no appreciable difference in the incremental ice effect. The computed lift curve slope with and without empennage ice matches the experimental value to within 1%, and the zero lift angle agrees to within 0.2 of a degree. The computed slope of the un-iced and iced aircraft longitudinal stability curve is within about 2% of the test data. This work demonstrates the feasibility of a zonal method for the icing analysis of complete aircraft or isolated components within the linear angle of attack range. In fact, this zonal technique has allowed for the viscous analysis of a complete aircraft with ice which is currently not otherwise considered tractable.

  5. An Observationally-Validated Theory of Viscous Flow Dynamics at the Ice-Shelf Calving-Front

    NASA Astrophysics Data System (ADS)

    Hindmarsh, R. C.

    2011-12-01

    Calving of floating ice shelves exerts a fundamental control on their geometry, which directly determines the forces acting on grounded ice that control ice-sheet stability. At the calving front, the viscous supply of ice is balanced by calving. I show that a boundary layer in viscous ice flow exists at the calving front with simple quantitative characteristics matching one set of empirically-derived calving relationships [1]. This relationship is consequently likely to be related to viscous supply rather than fracturing. This explanation has a deeper significance, since the boundary layer is dynamically analogous to one posited to control the stability of ice flow at the grounding line. The observational validation of the properties of the calving front boundary layer shown here is consequently significant confirmation of the boundary layer theory of grounding-line dynamics [2] and the likelihood of a marine ice-sheet instability. [1] Alley, R.B. and 7 others. (2008). A simple law for ice-shelf calving. Science, 322(5906), 1344. (10.1126/science.1162543.) [2] Ice sheet grounding line dynamics: Steady states, stability and hysteresis. J. Geophys. Res., 112, F03S28, doi:10.1029/2006JF000664.

  6. Patterns in the sky: Natural visualization of aircraft flow fields

    NASA Technical Reports Server (NTRS)

    Campbell, James F.; Chambers, Joseph R.

    1994-01-01

    The objective of the current publication is to present the collection of flight photographs to illustrate the types of flow patterns that were visualized and to present qualitative correlations with computational and wind tunnel results. Initially in section 2, the condensation process is discussed, including a review of relative humidity, vapor pressure, and factors which determine the presence of visible condensate. Next, outputs from computer code calculations are postprocessed by using water-vapor relationships to determine if computed values of relative humidity in the local flow field correlate with the qualitative features of the in-flight condensation patterns. The photographs are then presented in section 3 by flow type and subsequently in section 4 by aircraft type to demonstrate the variety of condensed flow fields that was visualized for a wide range of aircraft and flight maneuvers.

  7. The North Polar Layered Deposits on Mars: The Internal Layering of Gemina Lingula and Implications for Ice Flow

    NASA Astrophysics Data System (ADS)

    Karlsson, Nanna B.; Holt, John W.; Hindmarsh, Richard C. A.; Choudhary, Prateek

    2010-05-01

    horizons in the lower part. The upper horizons also generally achieve a better fit in the western part of GL while the fit for the lower horizons has a less distinct geographical variation. These differences could indicate a time gap in the deposition of the layers and may be explained by the existence of an angular unconformity previously identified within GL (Holt and Safaeinili, 2009). It is possible that the lower layers experienced a significantly different history than the upper, and/or that the geometry of the upper layers is primarily the result of draping the unconformity surface which is an elongated dome. Only taking into account individual layer geometry, our comparison between modelled and observed internal layering indicates that it is possible that ice flow has influenced the shape of NPLD. However, if this is the case GL must have extended farther to the southeast, or alternatively the accumulation pattern must have been significantly different to what is assumed in the model. Fishbaugh and Hvidberg. Journal of Geophysical Research, 111, 2006. Greve et al. Planetary and Space Science, 52, p. 775-787, 2004. Greve and Mahajan. Icarus, 174, p. 475-485, 2005. Hindmarsh et al. Annals of Glaciology, 50, 130140, 2009. Holt and Safaeinili. LPSC XXXX, # 1721, 2009. Phillips et al. Science, 320, 1182, 2008. Putzig et al. Icarus, 204, p. 443-457, 2009. Seu et al. Journal of Geophysical Research, 112, 2007. Winebrenner et al. Icarus, 195, p. 90-105, 2008.

  8. Patterns of 3D flow in a rotating cylinder array

    NASA Astrophysics Data System (ADS)

    Craig, Anna; Dabiri, John; Koseff, Jeffrey

    2015-11-01

    Experimental data are presented for large arrays of rotating, finite-height cylinders, which show that the three-dimensional flows are strongly dependent on the geometric and rotational configurations of the array. Two geometric configurations of the cylinders, each with two rotational configurations, were examined for a total of four arrays. 2D PIV was conducted in multiple intersecting horizontal and vertical sheets at a location far downstream of the leading edge of the array in order to build up a picture of the 3D developed flow patterns. It was found that the rotation of the cylinders drives the formation of streamwise and transverse flow patterns between cylinders. These horizontal flow patterns, by conservation of mass, drive vertical flows through the top of the array. As the array of rotating cylinders may provide insight into the flow kinematics of an array of vertical axis wind turbines, this planform flux is of particular interest as it would bring down into the array high kinetic energy fluid from above the array, thus increasing the energy resource available to turbines far downstream of the leading edge of the array.

  9. Experimental studies of ice grain ejection by massive gas flow from ice and implications to Comets, Triton and Mars

    NASA Astrophysics Data System (ADS)

    Laufer, Diana; Bar-Nun, Akiva; Pat-El, Igal; Jacovi, Ronen

    2013-01-01

    This is an experimental study of ice grain ejection when trapped gases are released from water ice. When ice is formed by adherence of water molecules at low temperatures, it forms an amorphous structure with many pores, where gas molecules can reside. When further ice layers are formed, the gases are trapped in the ice. Upon its warming-up, the ice structure changes, releasing fractions of the trapped gas. If they do not encounter obstacles, they are released quiescently by dynamic percolation. In a non-dense ice a huge flux of ice grains emanates from the ice, propelled by gas jets and covering its entire surface. When the overlying ice is denser, due to back-migration of water vapor during its sublimation, gas trying to escape from below cannot penetrate the dense ice and breaks it, producing non-circular craters and a chaotic terrain, as observed experimentally and in close encounters with Comets Wild 2, Tempel 1 and Hartley 2. These experimental findings explain several observations of Solar System bodies: ice grain ejection from Comets Temple 1 and Hartley 2. Also explained are the dark jets observed on Triton, where their ejection speed suggests a deep source. On Mars, dark streaks are observed in the southern pole in spring, most likely by plumes carrying dark dust, carried by winds and falling on the surface. As found by us experimentally, only frozen CO2 covered by water ice or mixed with it will work to form jets, whereas pure frozen CO2 will sublimate quiescently.

  10. Assessment of East Antarctic ice flow directions, ice grounding events, and glacial thermal regime across the middle Miocene climate transition from the ANDRILL-SMS and CRP drill holes

    NASA Astrophysics Data System (ADS)

    Passchier, S.; Hauptvogel, D.; Hansen, M.; Falk, C.; Martin, L.

    2010-12-01

    Here we present a synthesis of early and middle Miocene ice sheet development based on facies analyses and multiple compositional studies on the AND-2A and CRP drillcores from the Ross Sea, ca. 10 km off the coast of East Antarctica. The middle Miocene is characterized by one of the three largest shifts in deep-sea oxygen isotope records. During this time the East Antarctic ice sheet became dry-based at high elevation in the Transantarctic Mountains and advanced across the Ross Sea continental shelf to create widespread glacial unconformities. However, detailed proxy records also indicate that ice development was complex and may have occurred in a stepwise fashion, instead of one major episode. Our analyses of “grounded ice” diamictites from both the CRP and AND-2A cores show a significant change in composition across the middle Miocene transition. More detailed analyses of the stratigraphic distribution of facies, heavy mineral provenance, particle size, and major and trace element geochemistry in AND-2A show that relatively large polythermal ice-sheets similar in size to the modern were already present between 17.6 and 17.1 Ma. These results are in agreement with proxy records suggesting that Antarctic ice volumes were larger than today’s volume during the Mi-1b glaciation. Between 17.1 and 15.6-14.9 Ma, a predominance of iceberg debris sourced from the Ferrar Group in the Transantarctic Mountains suggests vigorous glacial erosion and fjord incision by East Antarctic outlet glaciers. The facies characteristics and comparison with compositional data from Neogene tills in the Transantarctic Mountains further suggest that the East Antarctic ice sheet may have been smaller than today during the Miocene climatic optimum (~17-15 Ma) with ice possibly reaching sea level only near the central Transantarctic Mountains. Advance of the grounding line and the development of glacial flow patterns compatible with a larger ice sheet than the modern commenced between 15

  11. Analysis of spatial flow patterns across the Indian subcontinent via multi-basin hydrological modelling

    NASA Astrophysics Data System (ADS)

    Pechlivanidis, Ilias; Arheimer, Berit

    2016-04-01

    In here, we use examples from the recent HYPE hydrological model set-up across 6010 subbasins for the Indian subcontinent, named India-HYPE v1.0 (Pechlivanidis and Arheimer, 2015), and demonstrate the potential of multi-basin modelling for process understanding and comparative hydrology. We analyse the flow characteristics in all modelled 6010 subbasins and group them based on similarities in 12 flow signatures to gain insights in spatial patterns of flow generating processes. We applied a k-means clustering approach within the 12-dimensional space (consisting of the 12 calculated flow signatures) to categorise the subbasins based on their combined similarity in flow signatures. To highlight the hydrological insights gained during model identification, we conducted the clustering analysis on two different steps of the model calibration and explored the sensitivity of calibration on the spatial patterns of flow signatures. Analysis resulted into six different classes of varying size with different distribution in signatures. Although the classes are geographically distinct, their flow response is dependent on the physiographic and climatic characteristics at the regional scale. Factors including for instance the dominance of snow/ice processes, volume in precipitation and evaporation rates affect the catchment functioning and hence drive the clustering. Catchments in the Himalayan region and the Western Ghats respond similarly and are characterised by high mean annual specific runoff values and variable flow regime. Response of the catchments in the tropical zone is characterised by high peaks, while catchments in the dry regions show very strong flow variability and respond quickly to rainfall. Finally, model parameterisation can affect the spatial pattern of clusters in terms of catchment functioning. In particular, clusters after calibration seem to have a consistent spatial structure; this also justifies the validity of parameter regionalisation approaches based

  12. Radar-based observatiions of variable thickness debris cover on martian ice masses: evidence of debris transfer by flowing ice on Mars

    NASA Astrophysics Data System (ADS)

    Souness, Colin; Brough, Stephen; Woodward, John; Hubbard, Bryn; Davis, Joel; Grindrod, Peter

    2016-04-01

    The mid-latitudes of Mars host a wide range of ice-based landforms, many of which display surface morphologies indicative of viscous flow of that ice. Despite being shrouded beneath a layer of rocky debris, these viscous flow features (VFFs) are thought to have similarities with terrestrial glaciers. Until recently most studies that focussed on the origin, structure and role of these martian VFFs were restricted to observations made from satellite imagery. Little data have been available to gain a clearer picture of VFF internal structure, which has impeded our collective ability to infer many particulars of VFF growth and flow, including the extent to which these ice flows have interacted with, and potentially helped shape, the martian landscape. However, the Shallow Radar (SHARAD) system mounted on the Mars Reconnaissance Orbiter (MRO) can, in some cases, provide a valuable insight into what lies beneath the surface of these ice masses. We present a SHARAD-based study of glacial systems on Mars which reveals pronounced heterogeneity in the thickness of their observed superficial debris covers. The surface debris layers in question appear to thicken in a down-slope direction. Radar data indicates that in the lower reaches of each studied glacial catchment, ice surface debris cover exceeds 10 m in thickness. The observed flow-parallel a-symmetry in debris thickness atop these martian glaciers is similar to that recorded on many terrestrial glaciers, indicating that cumulative down-flow debris mass transfer such as occurs within glacierised catchments on Earth may also currently operate, or have operated, on Mars. This suggests that glaciers on Mars have played a substantial role in redistributing lithic material from mountainous catchments to lower-lying areas, potentially throughout the glacial regions of Mars' mid-latitudes, thus making an important processual contribution to the evolution of Mars' contemporary landscape.

  13. Aeromagnetic and gravity imaging of subglacial geology beneath major ice streams flowing in the Weddell Sea Embayment

    NASA Astrophysics Data System (ADS)

    Ferraccioli, Fausto; King, Owen; Jordan, Tom; Ross, Neil; Bingham, Rob; Rippin, David; LeBrocq, Anne; Siegert, Martin; Smith, Andy; Hindmarsh, Richard

    2014-05-01

    Extensive airborne geophysical research has helped unveil subglacial geology beneath the West Antarctic Ice Sheet (WAIS) in particular over the Ross Sea Embayment. Three key geological controls on the onset and maintenance of fast glacial flow for the WAIS have emerged including the presence of widespread subglacial sediments deposited within deep rift basins, thinner drapes of marine sediments within the low lying topography of the West Antarctic Rift System (WARS) and high geothermal heat flux associated with Cenozoic rift-related magmatism. Here, we compile a suite of new and vintage aerogeophysical observations over the catchments of several major ice streams flowing into the Weddell Sea Embayment to examine their large-scale geological setting and assess the role of regional geological controls on subglacial topography and WAIS flow regimes. Specifically, we examine the subglacial geology beneath the catchments of the Institute and Moeller ice streams, the Rutford ice stream and the Evans ice stream using a combination of airborne radar, aeromagnetic and airborne gravity imaging. We show that the Moeller ice stream is underlain by the largest strike-slip fault system recognised so far along the tectonic boundary between East and West Antarctica. This fault system controls the location of a set of en-echelon subglacial basins that steer enhanced flow inland. We find no evidence, however, for deep sedimentary basins along this fault system, suggesting that subglacial sediments are not necessarily a geological template for the onset of fast flow. However, the newly identified Robin Subglacial Basin that underlies the fast flowing coastal region of the Institute ice stream contains 1-3 km of sedimentary infill and remarkably smooth bedrock topography. Enhanced flow in the tributaries of the Institute ice stream that cut through the Ellsworth Mountains are controlled by major basement faults likely active in Cambrian and Permian times and perhaps reactivated during

  14. Effect of the mitral valve on diastolic flow patterns

    NASA Astrophysics Data System (ADS)

    Seo, Jung Hee; Vedula, Vijay; Abraham, Theodore; Lardo, Albert C.; Dawoud, Fady; Luo, Hongchang; Mittal, Rajat

    2014-12-01

    The leaflets of the mitral valve interact with the mitral jet and significantly impact diastolic flow patterns, but the effect of mitral valve morphology and kinematics on diastolic flow and its implications for left ventricular function have not been clearly delineated. In the present study, we employ computational hemodynamic simulations to understand the effect of mitral valve leaflets on diastolic flow. A computational model of the left ventricle is constructed based on a high-resolution contrast computed-tomography scan, and a physiological inspired model of the mitral valve leaflets is synthesized from morphological and echocardiographic data. Simulations are performed with a diode type valve model as well as the physiological mitral valve model in order to delineate the effect of mitral-valve leaflets on the intraventricular flow. The study suggests that a normal physiological mitral valve promotes the formation of a circulatory (or "looped") flow pattern in the ventricle. The mitral valve leaflets also increase the strength of the apical flow, thereby enhancing apical washout and mixing of ventricular blood. The implications of these findings on ventricular function as well as ventricular flow models are discussed.

  15. Effect of the mitral valve on diastolic flow patterns

    SciTech Connect

    Seo, Jung Hee; Vedula, Vijay; Mittal, Rajat; Abraham, Theodore; Dawoud, Fady; Luo, Hongchang; Lardo, Albert C.

    2014-12-15

    The leaflets of the mitral valve interact with the mitral jet and significantly impact diastolic flow patterns, but the effect of mitral valve morphology and kinematics on diastolic flow and its implications for left ventricular function have not been clearly delineated. In the present study, we employ computational hemodynamic simulations to understand the effect of mitral valve leaflets on diastolic flow. A computational model of the left ventricle is constructed based on a high-resolution contrast computed-tomography scan, and a physiological inspired model of the mitral valve leaflets is synthesized from morphological and echocardiographic data. Simulations are performed with a diode type valve model as well as the physiological mitral valve model in order to delineate the effect of mitral-valve leaflets on the intraventricular flow. The study suggests that a normal physiological mitral valve promotes the formation of a circulatory (or “looped”) flow pattern in the ventricle. The mitral valve leaflets also increase the strength of the apical flow, thereby enhancing apical washout and mixing of ventricular blood. The implications of these findings on ventricular function as well as ventricular flow models are discussed.

  16. Subaqueous ice-contact fans: Depositional systems characterised by highly aggradational supercritical flow conditions

    NASA Astrophysics Data System (ADS)

    Lang, Joerg; Winsemann, Jutta

    2015-04-01

    Subaqueous ice-contact fans are deposited by high-energy plane-wall jets from subglacial conduits into standing water bodies. Highly aggradational conditions during flow expansion and deceleration allow for the preservation of bedforms related to supercritical flows, which are commonly considered rare in the depositional record. We present field examples from gravelly and sandy subaqueous ice-contact fan successions, which indicate that deposition by supercritical flows might be considered as a characteristic feature of these depositional systems. The studied successions were deposited in deep ice-dammed lakes, which formed along the margins of the Middle Pleistocene Scandinavian ice sheets across Northern Germany. The gravel-rich subaqueous fan deposits are dominated by large scour-fills (up to 25 m wide and 3 m) deep and deposits of turbulent hyperconcentrated flows, which are partly attributed to supercritical flow conditions (Winsemann et al., 2009). Scours (up to 4.5 m wide and 0.9 m deep) infilled by gravelly backsets are observed above laterally extensive erosional surfaces and are interpreted as deposits of cyclic steps. Laterally discontinuous beds of low-angle cross-stratified gravel are interpreted as antidune deposits. Downflow and up-section the gravel-rich deposits pass into sand-rich successions, which include deposits of chutes-and-pools, breaking antidunes, stationary antidunes and humpback dunes (Lang and Winsemann, 2013). Deposits of chutes-and-pools and breaking antidunes are characterised by scour-fills (up to 4 m wide and 1.2 m deep) comprising backsets or gently dipping sigmoidal foresets. Stationary antidune deposits consist of laterally extensive sinusoidal waveforms with long wavelengths (1-12 m) and low amplitudes (0.1-0.5 m), which formed under quasi-steady flows at the lower limit of the supercritical flow stage and high rates of sedimentation. Humpback dunes are characterised by divergent sigmoidal foresets and are interpreted as

  17. Urban Infrastructure, Channel-Floodplain Morphology and Flood Flow Patterns

    NASA Astrophysics Data System (ADS)

    Miller, A. J.; Smith, J. A.; Nelson, C. B.

    2006-12-01

    The relationship between the channel and the floodplain in urban settings is heavily influenced by (1) altered watershed hydrologic response and frequency distribution of flows, (2) channel enlargement resulting from altered hydrology under conditions of limited sediment supply, (3) direct modification of channels and floodplains for purposes of erosion mitigation, flood protection, commercial development and creation of public amenities, (4) valley constrictions and flow obstructions associated with bridges, culverts, road embankments and other types of floodplain encroachment causing fragmentation or longitudinal segmentation of the riparian corridor. Field observation of inundation patterns associated with recurring floods in the Baltimore metropolitan area is used in combination with 2-dimensional hydraulic modeling to simulate patterns of floodplain inundation and to explore the relationships between magnitude and shape of the flood hydrograph, morphology of the urban channel-floodplain system, and the frequency and extent of floodplain inundation. Case studies include a July 2004 flood associated with a 300-year 2-hour rainfall in a small (14.2 km2) urban watershed, as well as several other events caused by summer thunderstorms with shorter recurrence intervals that generated an extraordinary flood response. The influence of urban infrastructure on flood inundation and flow patterns is expressed in terms of altered (and hysteretic) stage-discharge relationships, stepped flood profiles, rapid longitudinal attenuation of flood waves, and transient flow reversals at confluences and constrictions. Given the current level of interest in restoration measures these patterns merit consideration in planning future development and mitigation efforts.

  18. Observations on traffic flow patterns and traffic engineering practice

    NASA Astrophysics Data System (ADS)

    Wang, Feng; Gao, Lixin

    2002-07-01

    Border Gateway Protocol allows ASs to apply diverse routing policies for selecting routes and propagating reachability information to other ASs. This enables network operators to configure routing policies so as to control traffic flows between ASs. However, BGP is not designed for the inter-AS traffic engineering. This makes it difficult to implement effective routing policies to address network performance and utilization problems. Network operators usually tweak routing policies to influence the inter-domain traffic among the available links. This can lead to undesirable traffic flow patterns across the Internet and degrade the Internet traffic performance. In this paper, we show several observations on Internet traffic flow patterns and derive routing policies that give rise to the traffic flow patterns. Our results show that an AS can reach as much as 20% of the prefixes via a peer link even though there is a path via a customer link. In addition, an AS can reach as much as 80% of the prefixes via a provider link even though there is a path via a peer link. Second, we analyze the cause of the prevalence of these traffic patterns. Our analysis shows that an AS typically does not receive the potential route from its customers or peers. Third, we find that alternate routes have with lower propagation delay than the chosen routes for some prefixes. This shows that some traffic engineering practices might adversely affect Internet performance.

  19. Anisotropic Peridotite Rheology and Regional Upper Mantle Flow Patterns

    NASA Astrophysics Data System (ADS)

    Blackman, D. K.; Boyce, D.; Dawson, P.; Castelnau, O.

    2014-12-01

    We investigate the rheologic impact of strong lattice preferred orientation (LPO), such as develops due to plate-driven shear, on the pattern of upper mantle flow near plate boundaries. We use finite element models to simulate a regional system of mantle flow, that includes LPO evolution in olivine polycrystal aggregates tracked along flow paths and anisotropic viscosity tensors based on the LPO. Our first, loosely coupled approach begins with a flow field based on a scalar viscosity. The results are postprocessed to compute LPO by integration along streamlines, and an anisotropic viscosity tensor field is derived from LPO. A new flow field is then computed based on the viscosity tensor field. For this case, the predicted flow field differed in a modest but geologically relevant way from the isotropic case. In preparation for incorporating the LPO and effective viscosity calculation directly into the flow code, we have been testing this step separately to assess the sensitivity of the computed tensor to specified deformation parameters. New work explores a power law stress:strain rate relation for the LPO development, upon which the aggregate's effective viscosity tensor depends. The pattern and amplitude of predicted deviation from isotropic viscosity are stronger than for the previously assumed linear stress:strain rate case, as expected. Initial runs that employ the power law viscosity tensor in updated flow calculations are underway at the time of this writing. In addition to the stress exponent for LPO and the resulting viscosity tensor, flow model parameters that notably impact the predictions include the specified stiffening as asthenosphere cools to lithospheric temperatures and mesh resolution within the axial and the base of lithosphere regions. We will present results for subaxial oceanic spreading center flow and report the outcomes of model parameter testing.

  20. Flow-driven instabilities during pattern formation of Dictyostelium discoideum

    NASA Astrophysics Data System (ADS)

    Gholami, A.; Steinbock, O.; Zykov, V.; Bodenschatz, E.

    2015-06-01

    The slime mold Dictyostelium discoideum is a well known model system for the study of biological pattern formation. In the natural environment, aggregating populations of starving Dictyostelium discoideum cells may experience fluid flows that can profoundly change the underlying wave generation process. Here we study the effect of advection on the pattern formation in a colony of homogeneously distributed Dictyostelium discoideum cells described by the standard Martiel-Goldbeter model. The external flow advects the signaling molecule cyclic adenosine monophosphate (cAMP) downstream, while the chemotactic cells attached to the solid substrate are not transported with the flow. The evolution of small perturbations in cAMP concentrations is studied analytically in the linear regime and by corresponding numerical simulations. We show that flow can significantly influence the dynamics of the system and lead to a flow-driven instability that initiate downstream traveling cAMP waves. We also show that boundary conditions have a significant effect on the observed patterns and can lead to a new kind of instability.

  1. A full Stokes ice flow model for the vicinity of Dome Fuji, Antarctica, with induced anisotropy and fabric evolution

    NASA Astrophysics Data System (ADS)

    Seddik, H.; Greve, R.; Zwinger, T.; Placidi, L.

    2011-06-01

    A three-dimensional, thermo-mechanically coupled ice flow model with induced anisotropy has been applied to a ~200 × 200 km domain around the Dome Fuji drill site, Antarctica. The model ("Elmer/Ice") is based on the open-source multi-physics package Elmer (http://www.csc.fi/elmer/) and solves the full Stokes equations. Flow-induced anisotropy in ice is accounted for by an implementation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor ("CAFFE model"). Steady-state simulations for present-day climate conditions are conducted. The main findings are: (i) the flow regime at Dome Fuji is a complex superposition of vertical compression, horizontal extension and bed-parallel shear; (ii) for an assumed geothermal heat flux of 60 mW m-2 the basal temperature at Dome Fuji reaches the pressure melting point and the basal melting rate is ~0.35 mm a-1; (iii) in agreement with observational data, the fabric shows a strong single maximum at Dome Fuji, and the age of the ice is decreased compared to an isotropic scenario; (iv) as a consequence of spatially variable basal melting conditions, the basal age tends to be smaller where the ice is thicker and larger where the ice is thinner. The latter result is of great relevance for the consideration of a future drill site in the area.

  2. A full-Stokes ice flow model for the vicinity of Dome Fuji, Antarctica, with induced anisotropy and fabric evolution

    NASA Astrophysics Data System (ADS)

    Seddik, H.; Greve, R.; Zwinger, T.; Placidi, L.

    2009-01-01

    A three-dimensional, thermo-mechanically coupled ice flow model with induced aniso-tropy has been applied to a ~200×200 km domain around the Dome Fuji drill site, Antarctica. The model ("Elmer/Ice") is based on the open-source multi-physics package Elmer (http://www.csc.fi/elmer/) and solves the full-Stokes equations. Flow-induced anisotropy in ice is accounted for by an implementation of the Continuum-mechanical, Anisotropic Flow model, based on an anisotropic Flow Enhancement factor ("CAFFE model"). Steady-state simulations for present-day climate conditions are conducted. The main findings are: (i) the flow regime at Dome Fuji is a complex superposition of vertical compression, horizontal extension and bed-parallel shear; (ii) for a geothermal heat flux of 60 mW m-2 the basal temperature at Dome Fuji reaches the pressure melting point and the basal melting rate is ~1 mm a-1; (iii) the fabric shows a weak single maximum at Dome Fuji, which increases the age of the ice compared to an isotropic scenario; (iv) as a consequence of spatially variable basal melting conditions, and contrary to intuition, the basal age is smaller where the ice is thicker and larger where the ice is thinner. The latter result is of great relevance for the consideration of a future drill site in the area.

  3. Subcutaneous blood flow in early male pattern baldness

    SciTech Connect

    Klemp, P.; Peters, K.; Hansted, B.

    1989-05-01

    The subcutaneous blood flow (SBF) was measured by the /sup 133/Xe washout method in the scalp of 14 patients with early male pattern baldness. Control experiments were performed in 14 normal haired men matched for age. The SBF in the scalp of the normal individuals was about 10 times higher than previously reported SBF values in other anatomical regions. In patients with early male pattern baldness, SBF was 2.6 times lower than the values found in the normal individuals (13.7 +/- 9.6 vs 35.7 +/- 10.5 ml/100 g/min-1). This difference was statistically significant (p much less than 0.001). A reduced nutritive blood flow to the hair follicles might be a significant event in the pathogenesis of early male pattern baldness.

  4. Signature of recent ice flow acceleration in the radar attenuation and temperature structure of Thwaites Glacier, West Antarctica

    NASA Astrophysics Data System (ADS)

    Schroeder, Dustin; Seroussi, Helene; Chu, Winnie; Young, Duncan

    2016-04-01

    Englacial temperature structure exerts significant control on the rheology and flow of glaciers and ice sheets. It is however logistically prohibitive to directly measure at the glacier-catchment scale. As a result, numerical ice sheet models often make broad assumptions about englacial temperatures based on contemporary ice surface velocities. However, this assumption might break down in regions - like the Amundsen Sea Embayment - that have experienced recent acceleration since temperature and rheology do not respond instantaneously to changes in ice flow regime. To address this challenge, we present a new technique for estimating englacial attenuation rates using bed echoes from radar sounding data. We apply this technique to an airborne survey of Thwaites Glacier and compare the results to temperature and attenuation structures modeled using the numerical Ice Sheet System Model (ISSM) for three surface velocity scenarios. These include contemporary surface velocities, surface velocities from the early 1970s, and ice-sheet balance velocities. We find that the observed attenuation structure is much closer to those modeled with pre-acceleration surface velocities. This suggests that ice sheet models initialized with contemporary surface velocities are likely overestimating the temperature and underestimating the rheology of the fast-flowing trunk and grounding zone of Thwaites Glacier.

  5. Divergent patterns of recent sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region

    NASA Astrophysics Data System (ADS)

    Frey, Karen E.; Moore, G. W. K.; Cooper, Lee W.; Grebmeier, Jacqueline M.

    2015-08-01

    Over the past three decades of the observed satellite record, there have been significant changes in sea ice cover across the Bering, Chukchi, and Beaufort seas of the Pacific Arctic Region (PAR). Satellite data reveal that patterns in sea ice cover have been spatially heterogeneous, with significant declines in the Chukchi and Beaufort seas, yet more complex multi-year variability in the Bering Sea south of St. Lawrence Island. These patterns in the Chukchi and Beaufort seas have intensified since 2000, indicating a regime shift in sea ice cover across the northern portion of the PAR. In particular, satellite data over 1979-2012 reveal localized decreases in sea ice presence of up to -1.64 days/year (Canada Basin) and -1.24 days/year (Beaufort Sea), which accelerated to up to -6.57 days/year (Canada Basin) and -12.84 days/year (Beaufort Sea) over the 2000-2012 time period. In contrast, sea ice in the Bering Sea shows more complex multi-year variability with localized increases in sea ice presence of up to +8.41 days/year since 2000. The observed increases in sea ice cover since 2000 in the southern Bering Sea shelf region are observed in wintertime, whereas sea ice losses in the Canada Basin and Beaufort Sea have occurred during summer. We further compare sea ice variability across the region with the National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs. wind-driven processes. Results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover, those in the Beaufort Sea are primarily wind driven, those offshore in the Canada Basin are primarily thermally driven, and those in the Bering Sea are influenced by elements of both. Sea ice variability (and its drivers) across the PAR provides critical insight into the forcing effects of recent shifts in climate and its likely

  6. Rapid Sediment Erosion and Drumlin Formation Observed Beneath a Fast-Flowing Antarctic Ice Stream

    NASA Astrophysics Data System (ADS)

    Smith, A. M.; Murray, T.; Nicholls, K. W.; Makinson, K.; Adalgeirsdottir, G.; Behar, A. E.

    2005-12-01

    What happens beneath a glacier affects both the way it flows and the landforms left behind when it retreats. Unfortunately, although the subglacial environment is one of the most critical to understanding ice flow and the processes of bedform formation, it is also the most difficult to study. As part of the RABID project on Rutford Ice Stream, West Antarctica in 2004/05, seismic reflection data were acquired at the same geographic location as identical surveys conducted 7 and 13 years previously. Analysis of the data from all 3 seismic surveys gives both the bed topography and an indication of the bed material and basal conditions. In particular, we can distinguish between places where the bed is soft, water-saturated sediments, probably deforming pervasively with the motion of the overlying ice, and those where the bed, whilst still sedimentary, is harder and the ice flow is probably dominated by basal sliding. Over the six years between the first and second surveys, 6 m of sediment was eroded from a region of the bed approximately 500 m wide. This occurs in one of the basal sliding areas. Typical interpreted and modelled subglacial erosion rates from all glacial environments are normally of the order of 0.1-100 mm/a. Our minimum observed rate of 1 m/a is remarkably high, particularly for a glacier which appears to have been in overall steady-state for at least many hundreds of years, and probably much longer. Over the seven years between the second and third surveys, further major changes occurred at the ice stream bed. The previous erosion ceased. Subsequently, a large mound of deforming sediment over-rode this same area of the glacier bed. This mound is 10 m high, 100 m wide and at least a few hundred metres long. This is a very short time for the formation of such a large feature, only 7 years previously nothing of its kind existed at this location. We interpret these dimensions and sediment characteristics as an actively-forming drumlin. Our results are the

  7. The Influence of the Zonal Wave Three on Antarctic Sea Ice during Ice Advance Season

    NASA Astrophysics Data System (ADS)

    Khan, H. M.; Raphael, M. N.

    2015-12-01

    Previous works have looked at the influence of key atmospheric circulation patterns on sea ice in the Antarctic in terms of the atmosphere's seasonal cycle. This study examines the influence of one of these atmospheric patterns, the zonal wave three (ZW3), in terms of the sea ice's seasons from 1979-2009 in order to better understand the response of the sea ice. An index to represent the amplitude of the ZW3 was calculated using zonal anomalies of 850 hPa geopotential heights taken from the ERA-Interim data set. Sea ice concentrations (SIC), taken from the Hadley Center sea ice and sea surface temperature data set, were found to be significantly positively correlated with the ZW3 index during the ice advance season (March to August) in the Ross and Weddell Seas and off the Amery ice shelf. These regions align with where cold, southerly flow associated with the ZW3 are found. In the Amundsen-Bellingshausen Seas region, SIC was found to be negatively correlated with the ZW3 index, which coincides with where the warm, northerly flow of the wave is found in this region. Regression analysis showed SIC to be significantly dependent upon the ZW3 in parts of the Ross Sea, the ice edge in the Amundsen-Bellingshausen Seas and off the Amery ice shelf during ice advance season. The results suggest that the ZW3 plays a role in the occurrence of the observed sea ice trends in the Ross Sea, Amundsen-Bellingshausen Seas, Weddell Sea and off the Amery ice shelf regions during the ice advance season, the critical period for sea ice growth. The results also demonstrate that re-examining the influence of relevant atmospheric patterns on sea ice in terms of the ice's seasonal cycles could allow firmer connections to be established between sea ice trends and atmospheric patterns.

  8. MODFLOW 2. 0: A program for predicting moderator flow patterns

    SciTech Connect

    Peterson, P.F. . Dept. of Nuclear Engineering); Paik, I.K. )

    1991-07-01

    Sudden changes in the temperature of flowing liquids can result in transient buoyancy forces which strongly impact the flow hydrodynamics via flow stratification. These effects have been studied for the case of potential flow of stratified liquids to line sinks, but not for moderator flow in SRS reactors. Standard codes, such as TRAC and COMMIX, do not have the capability to capture the stratification effect, due to strong numerical diffusion which smears away the hot/cold fluid interface. A related problem with standard codes is the inability to track plumes injected into the liquid flow, again due to numerical diffusion. The combined effects of buoyant stratification and plume dispersion have been identified as being important in operation the Supplementary Safety System which injects neutron-poison ink into SRS reactors to provide safe shutdown in the event of safety rod failure. The MODFLOW code discussed here provides transient moderator flow pattern information with stratification effects, and tracks the location of ink plumes in the reactor. The code, written in Fortran, is compiled for Macintosh II computers, and includes subroutines for interactive control and graphical output. Removing the graphics capabilities, the code can also be compiled on other computers. With graphics, in addition to the capability to perform safety related computations, MODFLOW also provides an easy tool for becoming familiar with flow distributions in SRS reactors.

  9. Lineations on the ``White'' Accumulation Areas of the Residual Northern Ice Cap of Mars: Their Relation to the ``Accublation'' and Ice Flow Hypothesis

    NASA Astrophysics Data System (ADS)

    Fisher, David A.; Winebrenner, Dale P.; Stern, Harry

    2002-09-01

    Mars Orbiter Camera (MOC) images of the whiter areas of the residual North Polar Cap (P. C. Thomas et al. 2000, Nature404, 161-164) show a gentle hummocky pitted surface that has been popularly called "cottage cheese" terrain. The pits are 1 or 2 m deep and tens of meters across. They are typically joined in roughly linear strings or long depressions and these features are referred to here as "lineations." The lineations tend to have one or occasionally two preferred directions. We have examined the MOC imagery for the North Cap and using high-resolution images that have good wide-angle context images were able to determine the lineation angles for 31 sites scattered over most of the ice cap. We propose a process that will produce linear features in the white areas, then relate the orientation of the lineations over much of the North Cap to these processes and the inferred ice flow direction. There is first-order agreement between the measured sign of the lineation angles and those predicted assuming ice flow. Higher accumulations and velocities are predicted in the catchment for ice that flows into Chasma Boreale. This comes from the indications that katabatic winds are concentrated in this catchment.

  10. Modelling ice layer formation using a preferential flow formulation in the physics based multi-layer SNOWPACK model

    NASA Astrophysics Data System (ADS)

    Wever, Nander; Würzer, Sebastian; Fierz, Charles; Lehning, Michael

    2016-04-01

    For physics based snow cover models, simulating the formation of dense ice layers inside the snowpack has been a long time challenge. In spite of their small vertical extend, the presence of ice lenses inside the snowpack can have a profound impact on vapor, heat and liquid water flow. These effects may ultimately influence processes on larger scales when, for example, looking at hydrological processes or wet snow avalanche formation. Also microwave emission signals from the snowpack are strongly influenced by the presence of ice layers. Recent laboratory experiments and modelling techniques of liquid water flow in snow have advanced the understanding of liquid water flow in snow, in particular the formation of preferential flow paths. We present a modelling approach in the one-dimensional, multi-layer snow cover model SNOWPACK for preferential flow that is based on a dual-domain approach (i.e., separation into a matrix flow and a preferential flow domain) and solving Richards equation for both. In recently published laboratory experiments, water ponding inside the snowpack has been identified to initiate preferential flow. Those studies also quantified the part of the snowpack involved in preferential flow as a function of grain size. By combining these concepts with an empirical function to determine refreezing of preferential flow water inside the snowpack, we are able to simulate preferential water flow in the model. We found that preferential flow paths arriving at a layer transition in the snowpack may lead to ponding conditions. Subsequent refreezing then may form dense ice layers (>700 kg/m3). We compare the simulations to 14 years of biweekly snow profiles made at the Weissfluhjoch study plot at 2540m altitude in the Eastern Swiss Alps. We show that we are able to reproduce several ice lenses that were observed in the field, whereas some profiles remain challenging to simulate.