bluuebunny/crossref_metadata_2025 huggingface dataset:
Mapping of glacial motion and surface topography of Hielo Patagónico Norte, Chile, using satellite SAR L-band interferometry data
Authors: Rignot Eric , Forster Rick , Isacks Bryan
Published: February 2017

The first topographic and ice-motion maps of the northwestern flank of Hielo Patagónico Norte (HPN, northern Patagonia Icefield), in Chile, were produced using satellite synthetic-aperture interferometric radar data acquired by NASA’s Spaceborne Imaging Radar C instrument in October 1994. The topographic map has a 10 m vertical precision with a 30 m horizontal spacing, which should be sufficient to serve as a reference for monitoring future mass changes of the icefield. The ice-motion map is accurate to within 4 mm d−1 (or 1 m a−1). The radar-derived surface topography and ice velocity are used to estimate the ice discharge from the accumulation area of four outlet glaciers, and the calving flux and mass balance of Glaciar San Rafael. The results demonstrate the use of SAR interferometry for monitoring glaciological parameters on a spatial and temporal scale unattainable by any other means.
The relative strengths of debris-laden basal ice and clean glacier ice: some evidence from Taylor Glacier, Antarctica
Authors: Lawson Wendy
Published: February 2017

An understanding of the mechanical behaviour of the basal zone of an ice mass is fundamental to understanding the overall dynamics of that ice mass. Despite the fact that debris-laden ice is found in the basal zones of many glaciers and ice sheets, its mechanical behaviour is only poorly understood. This paper attempts to expand our knowledge of the mechanical behaviour of debris-laden ice by examining the uniaxial compressive strength of debris-laden basal ice sampled from the snout of the Taylor Glacier, Antarctica.

The mechanical behaviour of debris-laden ice (debris content 5–20% by volume) under uniaxial compression, and the relationship between the behaviours of debris-laden basal ice and ‘clean’ glacier ice, is complex and variable. At the relatively warm temperatures at which uniaxial compressive strength tests were conducted in the field, debris-laden ice was generally weaker than clean glacier ice. At these temperatures, between 0° and −5°C, pressure melting was the dominant deformation mechanism in the debris-laden ice and cracking the dominant deformation mechanism in clean ice. At −25°C, however, debris-laden ice reached higher strengths than lite clean glacier ice and cracking was the dominant deformation mechanism in both ice types. The change in relationship between the strengths of debris-laden and clean ice with temperature is inferred to be attributable to the temperature dependence of the rate of pressure melting.

These results suggest that the dynamic effects and significance of the presence of a debris-laden ice layer in the basal zone of an ice mass are likely to be highly variable in space and time.
A comparison of different ways of dealing with isostasy: examples from modelling the Antarctic ice sheet during the last glacial cycle
Authors: Le Meur Emmanuel , Huybrechts Philippe
Published: February 2017

The bedrock isostatic response exerts a strong control on ice-sheet dynamics and is therefore always taken into account in ice-sheet models. This paper reviews the various methods normally used in the ice-sheet modelling community to deal with the bedrock response and compares these with a more sophisticated full-Earth model. Each of these bedrock treatments, five in total, is coupled with a three-dimensional thermomechanical ice-sheet model under the same forcing conditions to simulate the Antarctic ice sheet during the last glacial cycle. The outputs of the simulations are compared on the basis of the time-dependent behaviour for the total ice volume and the mean bedrock elevation during the cycle and of the present rate of uplift over Antarctica. This comparison confirms the necessity of accounting for the elastic bending of the lithosphere in order to yield realistic bedrock patterns. It furthermore demonstrates the deficiencies inherent to the diffusion equation in modelling the complex deformation within the mantle. Nevertheless, when characteristic parameters are varied within their range of uncertainty, differences within one single method are often of the same order as those between the various methods. This overview finally attempts to point out the main advantages and drawbacks of each of these methods and to determine which one is most appropriate depending on the specific modelling requirements.
Parameterization of fluxes over heterogeneous snow cover for GCMs
Authors: Essery Richard
Published: February 2017

Fluxes of heat and moisture over heterogeneous snow cover are studied using a boundary-layer model. The performance of a “tile” model, suitable for calculating gridbox-average surface fluxes in a GCM, is assessed in comparison with the boundary-layer model. The impact of using a tile representation for heterogeneous snow cover in a single-column version of the Hadley Centre GCM is discussed.
On the role of sea-ice transport in modifying arctic responses to global climate change
Authors: Maslanik James , Dunn Jeremy
Published: February 2017

The role of dynamics in modifying the response of the Arctic ice pack to inter-annually varying forcings and to climate perturbations is investigated using simulations from a two-dimensional ice model and a global climate model (GCM). Inter-annual variability in ice-covered area for 1985-93 is dominated by ice transport, and different transport regimes affect substantially the response of the ice pack to climate perturbations. The thermodynamic-only simulations are more sensitive to initial ice conditions, and respond less than the dynamk-thermodynamic model to small perturbations, but with a greater response to larger perturbations. Comparisons of GCM simulations that use different ice treatments highlights the importance of considering the distribution of ice thickness and extent in assessing climate-change responses.
Simulation of sea ice in the NCAR Climate System Model
Authors: Weatherly John W. , Bettge Thomas W. , Briegleb Bruce P.
Published: February 2017

The Climate System Model (CSM) developed at the National Center for Atmospheric Research (NCAR) consists of atmosphere, land and ocean models, as well as a dynamic-thermodynamic sea-ice model. The results of sea-ice simulation using the first coupled climate simulation with the CSM is presented. It was found that the simulated total-ice areas in both hemispheres compared well with observations for winter, but were too large for summer. The numerical solution of the cavitating fluid dynamics was found to allow excessive ridging of ice, and an ad hoc correction was implemented. The ice velocities were realistic for the Antarctic, but for the Arctic were turned toward Alaska and Siberia by modeled winds and currents. This ice-drift pattern was reflected by ice thickness, which lacks the observed ridging near Greenland. The results illustrate the sensitivity of sea ice to the simulation of polar climate and the challenge of modeling the entire climate system.
Investigating the interactions among river flow, salinity and sea ice using a global coupled atmosphere—ocean—ice model
Authors: Miller James R. , Russell Gary L.
Published: February 2017

A global coupled atmosphere-ocean-ice model is used to examine the interdependence among several components of the hydrologic cycle in the Arctic Ocean, including river discharge, sea-ice cover, and the flow of sea ice through Fram Strait. Since the ocean model has a free surface, fresh-water inflow from rivers is added directly to the ocean. The timing of the peak spring river flow depends on snowmelt runoff and its subsequent routing through the river system. Thermodynamic sea ice is included, and a new sea-iee advection scheme is described. The model’s river discharge affects salinity at the mouth of large rivers. The effect of the river discharge on sea-ice cover is not clear, either locally or at the basin scale. There is significant inter-annual variability of ice flow through Fram Strait, but the model’s flow is about half of that observed. The anomalous ice flow through Fram Strait is most highly correlated with the meridional wind stress. Potential implications for the “great salinity” anomaly are discussed.
On the improvement of sea-ice models for climate simulations: the sea ice model intercomparison project
Authors: Lemke Peter , Hibler W.D. , Flato G. , Harder M. , Kreyscher M.
Published: February 2017

Experiments with dynamic thermodynamic sea-ice models indicate a strong dependence of the net freezing rate, sea-ice transport and variability on dynamic model parameters. Although current dynamic—thermodynamic sea-ice models show relatively good agreement with observations, an optimization seems to be necessary, especially for the parameterizations of dynamic processes.

Presently, only a few coupled climate models use dynamic-thermodynamic sea-ice models. In order to promote, by means of coordinated numerical experiments, the development of an optimal sea-ice model for climate research, the Sea Ice Ocean Modelling Panel of the Arctic Climate System Study (ACSYS, a project of the World Climate Research Programme has initiated the Sea Ice Model Intercomparison Project (SIMIP). The first results from this model hierarchy approach are presented.
Application of a Conceptual Precipitation-Runoff Model (HYGYMODEL) in a Debris-Covered Glacierized Basin in the Langtang Valley, Nepal Himalaya
Authors: Rana Birbal , Nakawo Masayoshi , Fukushima Yoshihiro , Agkta Yutaka
Published: February 2017

A conceptual precipitation runoff model (HYCYMODEL) is used to simulate the daily runoff from the 67% glacierized Lirung basin (16% of which is covered by debris). The average thermal resistance of the debris cover of the Lrung Glacier has been estimated from the surface temperature of the debris, which was obtained from Landsat 5 (TM Band 6) images. This enabled calculation of the melt rate of the debris-covered area of the glacier using meteorological data collected at a nearby weather station. The calculated discharge results are roughly compatible with the observed daily discharges.
Rapid changes in snow cover at low elevations in the Sierra Nevada, California, U.S.A.
Authors: Kattelmann Richard
Published: February 2017

Snow cover in the intermittent snow zone of the Sierra Nevada can occupy more than 10 000 km2of the mountain range, but it has received relatively little attention in river forecasting. Snow is deposited at lower elevations only during the cold storms of winter, and remains there only for a few days or weeks. When cold storms have created a thin snow cover at low elevations, a subsequent warm storm can melt this snow in just a few hours and increase the runoff response dramatically. Operational hydrological models and river-forecasting procedures have tended to overlook contributions from the intermittent-snow zone, focusing instead on rainfall-runoff or melt from the snowpack zone at higher elevations. Data-collection efforts are minimal in this zone, too. Ideally, spatially distributed models of snowmelt and runoff generation are needed to account for the typically large differences in snow cover on different aspects in the intermittent snow zone. Although aircraft and satellite imagery would be most desirable to monitor the distribution of snow cover in the intermittent-snow zone, even a few climate stations that report precipitation type and snow presence would be a major improvement over the present situation in the Sierra Nevada.
Arctic precipitation as represented in the NCEP/NCAR reanalysis
Authors: Serreze Mark C. , Maslanik James A.
Published: February 2017

Arctic precipitation as depicted in the National Center for Environmental Prediction (NGEP) and the National Center for Atmospheric Research (NCAR) reanalysis effort is evaluated using 6 hourly model output for the period 1986–93 in conjunction with gauge-corrected climatologies. Climatological fields from the model agree favorably with observations in terms of general spatio-temporal patterns, but with some notable differences. In particular, the precipitation maximum over the central Arctic (the region north of 70°N) is depicted in July, one month too early. Values are too low from August through December, resulting in underestimates of annual precipitation of about 40 mm. Despite these shortcomings, the modeled precipitation fields appear to be sufficiently realistic to represent a base for blending with other data to provide gridded fields suitable for use in climate studies and sea-ice models.
Dependence of new-snow density on slope angle
Authors: Endo Yasoichi , Kominami Yuji , Niwano Shouji
Published: February 2017

The mass per unit horizontal area, vertical height and density of new snow accumulated on various slopes of 0° to 75° were measured. Although the mass of new snow on these slopes was nearly the same, vertical height increased and density decreased with increase of slope angle. Differences in heights and densities of new snow due to slope angle were explained by considering both accumulation and densification processes on the slopes.
A portable calorimeter for measuring liquid-water content of wet snow
Authors: Kawashima Katsuhisa , Endo Toru , Takeuchi Yukari
Published: February 2017

In order to facilitate the measurement of liquid-water content of snow in high mountains, a portable calorimeter named “Endo-type snow-water content meter” was developed. It is composed of a metal-coated container made of insulating materials and a lid of the container with a small-thermistor thermometer. Its strong points are its light weight, small size and easy fabrication with cheap materials. The total weight of the device is as light as 250 g, which is less than 10% of the snow-water content meter widely used in Japan (Akitaya-type snow-water content meter). The results of experiments have revealed that the device is capable of measuring the liquid-water content within 2 minutes with an accuracy of 2% by weight.
Drifting-snow acoustic detector: experimental tests in La Molina, Spanish Pyrenees
Authors: Font D. , Naaim-Bouvet F. , Roussel M.
Published: February 2017

A new gauge to detect drifting snow has been tested at an experimental site at La Molina, eastern Spanish Pyrenees during the 1996 winter.

Based on an acoustic principle, it consiste of a miniature microphone located at the base of an aluminium pole of a Variable length (depending on the average height of the snow accumulated in a season). While snowdrifting occurs and the pole is exposed to the flux (wind + snow particles), the snow grains impact on the pole and the sound produced by these collisions is recorded as an electrical signal.

30 m away from the snowdrifting detector, there is an anemometric station. The comparison of both records allows determination of thresholds and deposit wind velocities. In addition, this gauge allows users to know, during a wind episode, the exact amount of time during which snowdrifting occurs without being in the field. The interpretation of the values obtained using the acoustic detector is not yet an easy subject to discuss. We slill do not know what the drift-density equivalents for tile recorded noise levels are. However, these are only preliminary results and we expect to complete the calibration of the gauge during the coming months.
Short-term numerical avalanche forecast used operationally at Météo-France over the Alps and Pyrenees
Authors: Durand Yves , Giraud Gérald , Mérindol Laurent
Published: February 2017

Avalanche-hazard estimation for the present and the following days is one of the main tasks of the avalanche forecaster. For 4 years, some have used the results of a series of automatic numerical models in the Alpine massifs of France. Thee programs describe in real time the main meteorological conditions(SAFRAN),the evolution of the snow cover(Crocus)and the resulting avalanche risks[MÉPRA)at different elevations, slopes and aspects of the massifs considered.

This paper presents the latest evolution of this automatic tool. With the new version it is now possible to provide 1 day forecasts of the state of the snow cover over the massifs of both the Alps and Pyrenees, including the main characteristics of the snowpack and an assessment of the corresponding avalanche hazards.

To achieve this result, the main changes were with SAFRAN. Two combined methods are used within the same package: adaptations of larger-scale meteorological forecasts and use of observations of analogous weather situations from the past. These two approaches are complementary especially for evaluating precipitation where the second solution has important fine-scale information while the first exhibits important local biases.

Validation of this new application was done carefully and proved the quality of the method, now used in real-time by local forecasters. We present some validation results, concerned both with forecasted precipitation fields at the scale of the massif and forecasted avalanche risks deduced fromMÉPRA.
Sediment-mass exchange between turbid meltwater streams and proglacial deposits of storglaciären, northern Sweden
Authors: Holmlund Per , Burman Helene , Rost Torbjörn
Published: February 2017

Detailed changes in surface elevation of a recently deglaciated area have been mapped using a high-resolution photogrammetric method, with a view to estimating the contribution of debris from the proglacial area to the meltwater streams draining Storglaciären, northern Sweden, over the period 1980-90. The net contribution of sediments originating from the deglaciated area immediately in front of the glacier was of the order of 50% of the suspended silt load transported by meltwater at the flume Rännan downstream from the glacier, but at the same time, a similar amount of sediment accumulated along the streams. Though there is a significant exchange of mass, the net change is close to zero. Moreover, the survey provides detailed information about morphological changes in the landscape. Different processes, such as melting of permafrost, fluvial erosion and sedimentation, have been active.

Erosion and sedimentation rates were calculated from the difference between digital terrain models based on aerial photographs taken in 1980 and 1990. The result shows erosion in the central part of the proglacial area and accumulation of coarser sediments along the braided streams. In places, the ground is sinking, possibly due to melting of permafrost.

Where the ice is thinner, in the marginal zone, the thermal regime of ice in the tongue of Storglaciären corresponds well with the proglacial geomorphology. At present, the glacier has a 30-40 m thick cold surface layer which at the thinner marginal zone corresponds to a 100-200 m wide frozen rim. The temperature distribution within the ice was mapped using high-resolution radar.
Regional-scale meltwater erosion and deposition patterns, northern Quebec, Canada
Authors: Brennand T. A. , Shaw J. , Sharpe D. R.
Published: February 2017

Glaciofluvial ridges, several hundred kilometres long, are commonly referred to as interlobate moraines because they appear to have formed at the convergence of two distinct ice lobes. Flow convergence is indicated by patterns of striations, streamlined forms and eskers. The so-called interlobate moraines are also thought to have formed asynchronously as the ice margin retreated. By contrast, we argue that the Harricana moraine of northern Quebec, Canada, formed following flow convergence in a regional-scale subglacial outburst flood. Flowlines constructed from streamlined bedforms mapped on the glacial map of Canada, reinterpretation of these streamlined forms as products of meltwater erosion, and field records of erosional marks (S-forms) in bedrock and glaciofluvial deposits to the lee of bedrock highs support this model. The effects of this flow convergence on the ice-sheet topography and drainage controlled the location of the broad conduit in which the Harricana moraine was deposited. Continued flow in this conduit and melting of the conduit walls explain the local patterns of striae, the supply of debris to the conduit, and the morphological and sedimentary characteristics of the moraine itself. From these characteristics, we conclude that the moraine was formed synchronously. This conclusion, if correct, is instructive regarding the deglacial hydrological organization of a large sector of the Laurentide ice sheet.
A 1200 year record of accumulation from northern Greenland
Authors: Friedmann Arne , Moore John C. , Thorsteinsson Thorsteinn , Kipfstuhl Josef , Fischer Hubertus
Published: February 2017

We present the first detailed study of regional and secular changes in accumulation rate from northern Greenland. Four 100–150 m ice cores from this previously little investigated region have been dielectrically profiled and a good chronology for all four ice cores established by modelling the density profiles and identifying volcanic peaks in the records. This made it possible to calculate the accumulation rates of each core. The current accumulation rates show that there is a large region of low accumulation rate to the northeast of central Greenland with drops in accumulation rate of 25% 150 km, and 50% 300 km from Summit.

Relatively large variations in accumulation rate over time are seen in all the cores. We have compared the resulting accumulation-rate record, which should be related to changes in local air temperature over northern Greenland, with Scandinavian tree-ring records and have interpreted the data as showing an early Medieval Warm Epoch, but no pronounced “Little Ice Age” and no unequivocal greenhouse warming effect as yet in northern Greenland.
1000 years of climatic change in China: ice-core δ18O evidence
Authors: Lin P. N. , Thompson L.G. , Davis M.E. , Mosley-Thompson E.
Published: February 2017

Since 1987, ice cores have been drilled from the Dunde and Guliya ice caps on the Tibetan Plateau, western China. Here, the oxygen isotopic (δ18O) records for the last 1000 years from both these cores are compiled and compared. Using surface temperature observations since the mid-1960s from meteorological stations on the plateau and δ18O measured on precipitation collected contemporaneously, the empirical relationship: δ18O = 0.6 T
s – 12 is established. δ18O appears to serve as a reasonable proxy for regional surface temperatures and a reasonable basis for reconstructing 1000a proxy temperature records from Dunde and Guliya. The reconstructed temperature histories for Dunde (on the eastern Tibetan Plateau) and Guliya (on the western Tibetan Plateau) show some centennial-scale similarities, but reveal quite different histories for higher-frequency variability over the last millennium. The ice-core δ18O histories from Dunde and Guliya are compared with a tree-ring index from western China and the dust-fall record from eastern China, but show no consistent relationship. The most prominent similarity between the reconstructed temperature histories for Dunde and Guliya is the marked warming of the last few decades. From the 1000a perspective provided be these ice-core records, the recent warming on Dunde is unique in its strength and persistence; however, the warming on Guliya (inferred from 18O enrichment) is more recent (since 1985) and not unprecedented. This recent warming over the Tibetan Plateau is evident in the limited meteorological records.
Velocities of Pine Island Glacier, West Antarctica, from ERS-1 SAR images
Authors: Lucchitta B. K. , Rosanova C. E. , Mullins K. F.
Published: February 2017

Pine Island Glacier is one of the major ice streams draining West Antarctica. We calculated average velocities for both its grounded and floating parts by tracking crevasses and other patterns moving with the ice on two sequential images acquired in February and December 1992 by ERS-1 SAR (European Remote-Sensing Satellite, Synthetic Aperture Radar). Velocities in the fast-moving central parts of the glacier range from about 1.3 km a−1 on the grounded part to about 2.6 km a−1 on the floating part. Velocity increases rapidly just below the grounding line. For the floating part, velocities are approximately 0.3 km a−1 faster than previously established from Landsat images by other workers. This observation suggests that the discharge is larger and, therefore, the mass balance less positive than previously thought; however, our study also shows that current information is insufficient to allow for precise mass-balance calculations. Images of the glacier front show that a calving event released an iceberg about 5 km wide between February and December 1992. The position of the glacier front has not changed substantially between 1973 (Landsat image) and 1992 (ERS-1 images).
Studies on microparticles contained in medium-depth ice cores retrieved from east Dronning Maud Land, Antarctica
Authors: Higashi Akira , Fujii Yoshiyuki
Published: February 2017

SEM observations of microparticles in ice-core samples retrieved by the Japanese Antarctic Research Expedition in east Dronning Maud Land have been carried out since 1987. Morphology and elemental composition by EDS of many microparticles taken from various depths of the 700 m Mizuho ice core were compared with each other and with those of stratospheric microparticles in NASA Cosmic Dust Catalogs and microparticles hitherto found in deep ice cores retrieved in Antarctica. Number concentrations of microparticles were measured on all samples throughout the 700 m Mizuho ice core. Remarkable fluctuations found in the depth profile of the concentration seem to coincide with cold climates indicated by δ18O of the same core. Compositional analysis of volcanic ash at a depth of 500.7 m in the Mizuho ice core, dated at approximately 6000 years BP, indicates that the ash originated from the South Sandwich Islands.
Characteristics of bubble volumes in firn-ice transition layers of ice cores from polar ice sheets
Authors: Kameda Takao , Naruse Renji
Published: February 2017

The air-bubble formation process has been studied experimentally by using five ice cores from the Greenland and Antarctic ice sheets. Bubble volumes in firn-ice samples were measured by a classical method based on Boyle Mariotte's law for an ideal gas. It was found that the bubble volume varies with depth as a function of bulk density in the firn-ice transition layer, which is represented by an exponential function of firn density. Air bubbles start to form rapidly at a bulk density of 0.763–0.797 Mg m-3. This density (ρib) seems to be correlated with the ice temperature in the ice sheets; ρibincreases with a decrease in the ice temperature. Vbshows the maximum value in the density range 0.819–0.832 Mg m-3. The corresponding porosity of the density ranges between 0.110 and 0.097. This porosity does not seem to correlate with ice temperature or accumulation rate at the coring site. These characteristics of firn densities probably affect the amount of entrapped air in glacier ice (total air content) in polar ice sheets.
First access to the ocean beneath Ekströmisen, Antarctica, by means of hot-water drilling
Authors: Nixdorf U. , Oerter H. , Miller H.
Published: February 2017

A hot-water drill developed during the past 2 years at Alfred-Wegener- Institut was used to penetrate Ekströmisen several times near the German wintering-over base, Neumayer (70°39´S, 08° 15´W). The drilling operation was very successful and the initial large diameter (≥ 35 cm) allowed easy access to the ocean. One hole was used to install an ultrasonic echo-sounder which recorded the ablation at the ice-shelf bottom continuously. Another hole was destined for emplacement of a thermistor string throughout the 237 m thick ice shelf for ice-temperature measurements. Several CTD profiles in the 175 m deep water column and the analysis of water samples provided valuable data for the understanding of ice-shelf-ocean interactions.
Analysis of satellite radar-altimeter return wave forms over the East Antarctic ice Sheet
Authors: Yi D. , Bentley C.R.
Published: February 2017

The precision of satellite-radar altimetry over the Antarctic ice sheet can be improved by using a physically based retracking algorithm on the altimeter returns ("wave forms"). Ridley and Partington (1988) have shown that both surface and volume-scattering affect the shape of the return. Here, we develop a model that is based on a variable combination of surface- and volume-scattering and determine the model parameters through least-square fitting to the observed wave forms. The model parameters include surface roughness, proportion of volume-scattering, extinction coefficient and an amplitude coefficient. Geosat data collected over a test sector of the East Antarctic ice sheet have been analyzed to find quantitative estimates of seasonal and geographic variations of the several parameters. Our results show that the effect of volume-scattering can change the elevation measurement over the inland part of the East Antarctic ice sheet by more than I m and that there are both spatial and temporal variations; temporal variations are less significant than spatial variations.
An 80 year record of retreat of the Koettlitz Ice Tongue, McMurdo Sound, Antarctica
Authors: Gow Anthony J. , Govoni John W.
Published: February 2017

A survey of ice-front changes since 1910–13 shows that the Koettlitz Ice Tongue, located along the western shore of McMurdo Sound, Antarctica, has undergone significant retreat during the past 80 years. The ice front in 1910–13 was located 5 km in front of the Dailey Islands. Today, only two of the six Dailey Islands remain connected to the Koettlitz Ice Tongue. The most recent break-out of ice is believed to have occurred in 1979 or 1980, resulting in an estimated loss of 80 km2 of ice. Based on the current position of the ice front, it is estimated that a minimum of 300 km of ice has called off the Koettlitz Ice Tongue during the 80 year period that has elapsed since the ice front was first mapped in 1910–13.
Decay of surface topography on the Ross Ice Shelf, Antarctica
Authors: Casassa Gino , Whillans Ian M.
Published: February 2017

The time decay of surface undulations is modeled analytically. The particular application is the decay of flow stripes on the Ross Ice Shelf that emanate from Byrd Glacier. The model predicts two extreme undulation types. One extreme, which we term the buckle solution, has a decay time of only 13 years. The other, the pinch-and-swell case, can persist much longer (700 years), because each surface ridge is underlain by deep roots. Flow stripes may originate as a combination of both the buckle and pinch-and-swell extremes, but only the pinch-and-swell aspect is predicted to survive in the ice shelf The predicted decay time and that measured from satellite imagery are in close agreement.
Simulations of anisotropy and fabric development in polar ices
Authors: Castelnau O. , Duval P.
Published: February 2017

The preferred orientation of ice crystals in polar ice sheets developsas a result of intracrystalline slip. Polycrystalline plasticity theory has been successfully used to simulate development of fabrics in rocks. In this study, we present a simpletheory for plastic deformation and fabric evolution. Each crystal within the aggregateis assumed to deform only by basal glide, and recrystallization processes are not directly taken into account. We have adopted the uniform stress bound, that is, stress is supposed to be homogeneous in the polycrystal. Simulated fabrics in uniaxial compression and tension are similar to those observed in ice sheets. In simple shear,simulations show thatcaxes rotate toward the direction of the maximal compression,in contradiction to the intuitive conclusion that stable orientations correspond to the easy glide position. But, these results are in agreement with predictions of Taylor theory and self-consistent approaches. We suggest that effects of vertical compression and/or rotation recrystallization are of great importance for fabric evolution in polarice sheets. The proposed model can reproduce viscosities of anisotropic ice samples tested in compression or tension but it is not able to reproduce the low viscosity of ices with a single-maximum fabric when tested in simple shear
Surface-velocity field of the northern Larsen Ice Shelf, Antarctica
Authors: Bindschadler R. A. , Fahnestock M. A. , Skvarca P. , Scambos T. A.
Published: February 2017

Three satellite images of the northern Larsen Ice Shelf arc used to derive velocity fields for the periods 1975–86 and 1986 89. Substantial increases in the speed of the ice between these periods are detected to a high degree of confidence. Ice which entered the ice shelf between Fothergill Point and Cape Worsley and ice from Drygalski Glacier has accelerated by approximately 15% over the measurement period. Ice from Bombardier and Dinsmoor Glaciers also exhibits acceleration but by a lesser amount. These accelerations may be the result of either significant retreat experienced by the ice shelf during this period or warming in the Antarctic Peninsula region. Velocities measured by surface survey over a 15 d period in 1991 indicate a slower velocity than the image-derived velocities in the limited region of overlap. These differences appear to be systematic and may be the result of uncontrolled errors in the surface survey. Limited control of one image could also contribute to some of these differences.
Sea-bed depths at the mouth of Rutford Ice Stream, Antarctica
Authors: Smith A. M. , Doake C. S. M.
Published: February 2017

Seismic measurements of ice- and water column thickness have been made on Rudard Ice Stream where it joins the Ronne Ice Shelf. Assuming that the ice is in hydrostatic equilibrium, these values have been used to calculate sea-bed elevations. A sea-bed trough more than 2 km below sea level along the western margin continues downstream from the grounded to the floating ice.
The central part of the Filchner-Ronne Ice Shelf, Antarctica: internal structures revealed by 40MHz monopulse RES
Authors: Blindow N.
Published: February 2017

About 1200 km of surface-based radio-echo sounding (RES) profiles were measured during the German Antarctic field season 1989-90 on the Filchner Ronne Ice Shelf (FRIS), Antarctica, with a 40 MHz monopulse sounder developed in Münster. In the area investigated, downstream of Doake Ice Rumples and Henry Ice Rise, a basal layer of marine ice up to 400 m thick was found below the meteoric ice, which is less than 100 m thick in some places. High absorption losses and low bottom reflectivity of the basal layer prevented sounding of the total ice thickness, except for areas near the ice edge with strong melting.

From common mid-point (CMP) measurements, the velocities of electromagnetic waves in the ice shelf were determined, to obtain precise depths from travel times for airborne and surface-based soundings.

The continuous profiling yielded the total ice thickness in the northern part and a variety of internal structures, including lavers in the meteoric and the marine ice, remnants of crevasses, varying reflections of the meteoric-marine interface reflection (MMR). From these data, it is shown that the most-disturbed MMR signatures originate at grounding zones at Doake lee Rumples and at both sides of Henry Ice Rise. The status of the meteoric ice bottom is preserved by the formation of marine ice. Hence, structures remain widely unchanged over 400 km of flow. Internal features that can be correlated on parallel profiles perpendicular to the flow provide an independent means for the construction of flow lines. Even in areas with a smooth MMR, reflection amplitudes show variations by a factor of 2. Their spatial frequency is maximal on profiles prependicular to the now direction. A possible explanation for the amplitude variations is the varying salinity of the top of the marine ice.
Numerical flow simulation at local parts of Filchner-Ronne Ice Shelf, Antarctica
Authors: Jonas M. , Grosfeld K. , Thyssen F.
Published: February 2017

The Munster radio-echo-sounding (RES) work in the central part of Filchner-Ronne Ice Shelf has revealed new information. Different signatures are discernible in the airborne RES data. Local model calculations in the area between Henry Ice Rise and Berkner Island are used to interpret these signatures in terms of thermal and dynamic parameters. From our airborne measurements, the shapes of the meteoric and marine-ice layers were prepared as input data for dynamic-model calculations. A general increase in the temperature-dependent flow parameter is compared vvith a spatially variable flow parameter that is derived from model calculations concerning freezing and melting processes. Velocity and strain fields were calculated by a finite-difierence method on a local data base between Henry Ice Rise and Berkner Island.
Formation of high-power, high-voltage rectangular pulses with the controlled stabilization of the pulse peak
Authors: Petrov A.V. , Pavlov S.K. , Usov Y.P.
Published: February 2017

The pulse shaper based on a capacitive storage device with an active switch operating on a resistive load is considered. The electrical circuit includes a capacitor with a reference voltage for the stabilization of peak of the pulse. The capacitor connected in parallel with a load via the unilateral conductive switch. A general analysis of the shaping circuit was carried out. Analytical expressions for determination of the stabilization accuracy and the stabilization duration have been obtained. The results of computer simulation of dependence of these characteristics as function of pulse parameters and shaper features are presented. The influence of short-term and abrupt change of the resistance load on the stabilization process of peak of the pulse is considered. The possibility of obtaining of pulses with a controlled stability of pulse peaks <1% for pulses with duration to 100 µs at voltages up to 20 kV and energy stored in a capacitor to 3.4 kJ is shown in prototype of the shaper.
Low Drag Aerofoils
Authors: Whitehead L. G.
Published: February 2017

During the past few years a new series of low drag aerofoils has been developed which represents a radical departure from earlier practice. The changes envisaged are much greater than those which accompanied the general change-over from the biplane to the monoplane, and give rise to many problems whose solution requires considerable theoretical and experimental work. An important feature of the new sections is the precision in design and manufacture which is essential for their success. This has given renewed interest to the investigation of many of the detailed problems of air flow and calls for parallel improvements in manufacturing technique so as to achieve the high standard of surface finish required.

The purpose of this paper is to give a brief account of the theoretical basis of the design and application of the modified profiles as aircraft wing sections. It deals with the design of aerofoils for the subsonic range only, or, to be more precise, for flight at speeds below the critical Mach Number at which shock waves are first formed. The critical value usually lies in the range 0.6 to 0.8, depending on the wing shape and incidence, as will be described in more detail later.
The Derivation and Use of Aerodynamic Transfer Functions of Airframes
Authors: Spearman F. R. J.
Published: February 2017

The aerodynamic characteristics of airframes are expressed as aerodynamic transfer functions, giving the relationships between input and output for each of the three separate planes of motion, roll, pitch, and yaw. By assuming no cross-coupling between planes and linear aerodynamics, and by making certain other assumptions, which apply particularly to conventional airframes with fixed wings and rear controls, relatively simple approximate algebraic transfer functions giving the relationships between the control surface deflection (the input) and any airframe motion (the output), are obtained.

The open loop aerodynamic transfer functions thus obtained are used as part of the auto-pilot block diagram, in which the performance of other components, such as actuators, instruments and electrical networks, are also expressed in transfer function form. The aerodynamic transfer functions are useful in auto-pilot evolution and synthesis in that they aid selection of the airframe motions to be measured, modified, and fed back to close the auto-pilot loop.

For mathematical assessment of closed loop performance and stability, open loop transient and frequency responses are used, and curves of airframe responses are plotted in linear, logarithmic and polar form by standard methods from the aerodynamic transfer functions. Some methods of using these curves, which follow the general lines adopted in servo-mechanism and electronic amplifier design, are explained briefly.

Analogue computers are frequently used when the computations to be made are so complicated as to need the use of a computing machine. The aerodynamic transfer functions then form one block of the simulator set-up, and on larger computers the more exact form, including any non-linearities and cross-coupling effects, can be used.
The Effect of Excess Scavenge Air on the Pressure Drop in the Cylinder of a Two-Stroke Cycle Engine During Exhaust Blow down
Authors: Benson R. S.
Published: February 2017

The laws of reflection of pressure waves at temperature discontinuities are well known. Of particular interest is the effect of temperature discontinuities on the pressure conditions in the exhaust pipes and cylinders of two-stroke cycle engines, both models and running engines. Model experiments are usually performed at low temperatures with the cylinder release temperature and exhaust pipe temperatures of the same order; under these conditions the reverse type of temperature phenomenon occurs to that in running engines with excess scavenge air. In the case of a model during the exhaust blowdown the gas from the cylinder reaches the exhaust pipe with a greater density than that of the gas initially in the exhaust pipe.
Steels Used in Aero Work
Authors: Hatfield W. H.
Published: February 2017

Before proceeding, I wish to say that I much appreciate the invitation to present this paper to your Society. The science of aeronautics has evolved at a great pace, and typifies what can be done with applied science, and the tangible results are so apparent that it would be superfluous to discuss them. It would appear to me that the rapidity with which the efficiency has increased is due to the whole-hearted collaboration of the different branches of applied science and engineering, the honours being shared after giving first place 10 the sportinginstinct of the early flyer, by the physicist, the engineer, and the metallurgist. You will notice that my modesty places the metallurgist last. It is quite a confession to make, but it is a fact, nevertheless, that I accepted with pleasure your invitation to give this paper, principally because I have always taken a keen interest in the metallurgical side of aeronautics.
The Flight of Birds
Authors: Fullerton Colonel
Published: February 2017

1. The object of this paper is to explain the principles upon which the flapping flight of birds depend and to show how the velocities, power expended and gliding angles can be approximately calculated. The birds are considered to be flying on a horizontal course with constant velocity. The calculations have been made for five birds, the Teal, the Grouse, the Common Swift, the Starling and the Stork, but the formulae given can of course be used for any bird.

2. The results obtained seem to show that:—

1st.—As regards velocities, the very high speeds given by some writers are by no means so impossible as is generally supposed.

2nd.—The power expended at these high speeds is much less than the estimates usually made.
Further Notes on Aviation in Canada
Authors: Stedman C. W.
Published: February 2017

In the Aeronautical Journal of September, 1922, the writer published an article setting out a brief description of the work that is being undertaken by aircraft in Canada, and describing more fully the details of the problems that were peculiar to the country, more particularly the technical work in connection with winter flying, and, in order to avoid repetition as much as possible, it is necessary to refer occasionally to that previous paper.
A Detailed Consideration of the Effect of Meteorological Conditions on Airships
Authors: Scott G. H. , Richmond V. C.
Published: February 2017

In presenting this paper the authors are conscious of the fact that it contains very little information which is actually new. They feel, however, that the collection and co-relation of items of theory and experience which may not be widely known will prove useful to those who may have to consider the employment of airships on long journeys through necessarily varying meteorological conditions.
Reliability of Aircraft Engines
Authors: Siddeley J. D.
Published: February 2017

The progress of mechanical flight to the present stable position occupied by aircraft as a means of transport has been so closely related with the problems associated with the development of the power unit, that an examination of such an important factor as its “ reliability ” appears justified.

In searching for possible means to produce power, it was natural that the use of steam as a motive power should have been considered. First Langley and then Maxim in 1895 produced a steam plant designed for aircraft. No practical success was attained by these early efforts, and a considerable period elapsed before the successful power unit for aircraft was evolved.
Meteorology In Relation To Aeronautics
Authors: Dines W. H.
Published: February 2017

I have been asked by your Council to address you to-night on one or more of the many points where aviation and meteorology come into contact. I cannot lay claim to much knowledge of aviation and my excuse must be the rapid increase of such knowledge during the last few years and the fact that under our present conditions much of it must be of a confidential nature; but the importance of meteorological conditions for the practical business of flying is so obvious and so great that I think it may be of use and interest to point out the effect that the more prominent meteorological phenomena have upon aviation.
From Qumran to Qur’ān: the Religious Worlds of Ancient Christianity
Authors: Stroumsa Guy G.
Published: February 2017

This essay seeks to present, in a nutshell, a number of reflections on the long trajectory of ancient Christianity, particularly in the East, from its beginnings until the coming of Islam. As is well known, the Islamic conquests transformed the Christian self-understanding in the East, on both sides of the border between Byzantium and the Caliphate. In the West, too, the consciousness of the new, powerful challenge to the Christian empire was never very far away. Hence the advent of Islam constitutes the first real challenge to the belief in the ecumenical destiny of Christianity.
Justin’s Christian Philosophy: New Possibilities for Relations between Jews, Graeco-Romans and Christians
Authors: Hayes A. D. R.
Published: February 2017

Identity is always a complicated and negotiated reality, whether personal or communal, and this is certainly true for Christian identity in the second century CE. This century was the setting for many complicated changes that gave birth to Christianity as it is commonly understood. Naming, and the use of the terms ‘outsiders’ and ‘followers of Christ’ to define those we would call ‘Christians’, were important parts of this process. Examining how early Christians presented themselves can help us to understand the development of both Christianity and Judaism, and also to appreciate better how the early Christians saw themselves. Justin Martyr (100-65) is a central figure in this task. This essay will analyse his presentation, at a crucial point in history, of what it meant to be a follower of Christ.