bluuebunny/crossref_metadata_2025_split huggingface dataset:
Using Linear Discriminant Analysis to Classify Snowfall Situations into Avalanching and Non-Avalanching Ones
Authors: Drozdovskaya N.F. 
Published: September 2017

AbstractThe existing methods of predicting avalanche danger often do not meet users’ demands because of the empiric character of the insufficient volume of information used. In such forecasts the contribution of each individual parameter into the prognostic information is unknown, and this is very important when studying such an event as avalanche formation, which is conditioned by a complex interaction of numerous factors, including snow accumulation, snow thickness, and the conditions of its development. It is obvious that such problems can be successfully solved by statistical methods, and that explains the growing interest in numerical methods of avalanche forecasting. Problems of multi-dimensional observations arises in many scientific fields. The method suited for this problem is discriminant analysis, the purpose of which is to divide a multi-dimensional observation vector into predetermined classes.This study considers the prognostic (diagnostic) problems of fresh-snow avalanches released during snowfall or in the two days after it has ceased. The theoretical basis is a complex of statistical methods: correlation and dispersion analysis, “sifting” for the choice of predictors’ informative groups, construction of linear parametric discriminant functions, predictions based on training sample, and verification of discriminant functions based on independent material.The archive used in the study consisted of 500 avalanching cases and 1 300 non-avalanching ones. All situations were grouped according to geomorphological characteristics. Each situation is described by eight meteorological characteristics. The results of classification of snowfall situations into avalanching and non-avalanching ones are as follows: reliability of p is from 75% to 91%, H from 0.15 to 0.51; based on independent material the reliability of p is from 63% to 85%, H from 0. 10 to 0.56.
Fracture Toughness of Fresh-Water Ice
Authors: Liu H. W. , Miller K. J. 
Published: September 2017

AbstractThe plane-strain fracture toughness of fresh-water ice was measured at various loading rates and temperatures. The fracture toughness of ice decreases as loading rate increases and as the test temperature approaches the melting point. The presence of liquid water seems to reduce the fracture toughness. The fracture toughness for crack arrest is slightly lower than the static fracture toughness.
Dielectric Behaviour of Ice Microcrystals: A Study Versus Temperature
Authors: Boned Christian , Lagourette Bernard , Clausse Marc 
Published: September 2017

AbstractDispersions of ice microcrystals were obtained from the breakdown of supercooling of water-in-oil type emulsions whose disperse phase was either resin-exchanged water or aqueous solutions of NH4Cl. Their complex permittivity ε⋆ = ε´–jε˝ was studied versus temperature T, up to the melting point of ice microcrystals, by means of an automatically balancing admittance bridge (General Radio 1680 A) working at 400 Hz and 1 kHz, The plots ε´(T), ε˝(T) and ε˝(ε´) reveal that these systems exhibit two distinct dielectric relaxations located on either side of a temperature Tm which was found to be equal to about — 20°C in the case of water and lower than — 20°C in the case of aqueous solutions of NH4Cl. The relaxation located in the lower temperature range arises from the Debye dipolar absorption of ice while the other one could be related to structural changes occurring within the lattice of ice as T approaches its melting point. These results are consistent with those obtained by investigating versus frequency the dielectric behaviour of ice monocrystals at discrete sub-zero temperatures close to their melting point.
Enthalpy Relaxation Phenomenon of Heavy Ice
Authors: Haida Osamu , Suga Hiroshi , Seki Syūzō 
Published: September 2017

AbstractThe heat capacities of quenched and annealed heavy ice Ih were measured in the temperature range 14 to 300 K by an adiabatic calorimeter. A relaxational thermal anomaly was found at around 115K and this phenomenon was ascribed to the onset of deuteron ordering in the crystal. The average activation enthalpy of the relaxational process was determined to be (26±5) kJ mol–1. Residual entropies of the crystal were recalculated on the basis of the present heat-capacity data combined with the revised values for enthalpy of vapourization, saturated vapour pressure, and spectroscopic entropy. They are (3.47±0.41) J K–1 mol–1 for the quenched crystal and (3.44±0.41) J K–1 mol–1 for the crystal annealed at 102–106 K for 264 h. The characteristics and the origin of the anomaly are discussed in comparison with that of ordinary ice.
Determination of a-Axis Orientations of Polycrystalline Ice
Authors: Matsuda Masuyoshi 
Published: September 2017

AbstractTwo new methods have been devised for measurement of crystallographic lattice orientations of individual crystals in polycrystalline ice. The first uses edge-length ratios of etch pits. The second uses a combination of optical measurement on a thin section and etch-pit technique. Although the second method does not work for crystals with their c-axis oriented parallel to the thin section, it is much simpler and more practical than the first method. When used on polycrystalline glacier ice, this method gave the three a-axes orientations as well as c-axis orientation for each crystal with an accuracy of 5°.
Evaluation of Jet-Roof Geometry for Snow-Cornice Control
Authors: Dawson K. L. , Lang T. E. 
Published: September 2017

AbstractNumerical hydrodynamic simulation of the jet-roof geometry for control of snow deposition to prevent cornice formation at mountain ridges is reported. Different jet-roof geometries are evaluated based upon the extent and size of the ground-surface stagnation region and the recirculation region to the lee of the roof. Results show that jet-roof length should be of the same order as nominal height of the roof from the ground surface. Efficient placement of the roof is shown to be that with the leading edge directly above the mountain ridge, and roof angle approximately equal to lee slope angle. In numerical simulation of flow-field start-up, near steady-state flow is approached in less than 1.0 s real time, indicating short transient-flow duration.
Time-Series Modelling of Avalanche Activity from Meteorological Data
Authors: Salway A. A. 
Published: September 2017

AbstractAvalanche-hazard evaluation by field analysts is largely achieved along causal intuitive lines, depending for its success upon the experience of the analyst in his particular area. Several attempts have been made in the past to quantify such procedures by means of statistical models based upon meteorological measurements. Modified forms of a multivariate technique known as linear discriminant analysis have been tried with only partial success. Intercorrelated variables and autocorrelated data, omission of time-lagged terms, insufficient variation in the dependent variable, and sampling difficulties may have combined to weaken the discriminant approach. These problems and the nature of the phenomenon suggest that a stochastic transfer-function time-series approach may be a useful alternative method.A numerical weighting scheme has been devised for the representation of avalanche activity for the Rogers Pass area of British Columbia in terms of terminus, size, and moisture-content codes for each event. From various types of correlation analysis performed on data for the period 1965–73, models were developed using the “best” weighting scheme for avalanche activity representation and the most promising meteorological variables, as indicated by the results of the correlation analysis.These relatively simple models demonstrate a good fit to the actual data, in both a descriptive and a simulated-forecasting situation.
Forces on Structures Impacted and Enveloped by Avalanches
Authors: Pedersen R. R. , Dent J. D. , Lang T. E. 
Published: September 2017

AbstractA computer code is reported that models two-dimensional flow of a snow-avalanche cross-section over a down-slope structure of arbitrary cross-sectional shape. Impact forces and pressure are predicted, and the flow pattern past the structure may be arrayed pictorially. The model is applied to the prediction of forces on rectangular obstacles which are of fractional height to the nominal avalanche flow depth for avalanche flow speeds up to 20 m/s. The program is applied to modeling an experiment by Salm of impact of snow blocks upon a slope-normal wall in order to demonstrate the accuracy of the code in comparison to impact-force histories measured by Salm. Difference between the experimental results and the computer simulation is less than 21%, and supporting discussion is given on factors that may account for the difference.
Radiation measurement at Lewis Glacier, Mount Kenya, Kenya
Authors: Hastenrath Stefan , Patnaik J. K. 
Published: September 2017

AbstractShort- and long-wave radiation on variously oriented vertical surfaces, direct solar radiation, global radiation, and long–wave radiation on a horizontal surface were measured on Lewis Glacier, Mount Kenya, at 4800 m. For the orientation of vertical surfaces, the following azimuths were selected: 45°, facing the steep slope of the upper glacier; 135°, facing a rock ridge and some glacier surface in the foreground; 225°, facing down–glacier towards the Teleki valley with open sky occupying much of the view; and 315°, directed towards the steep south-east face of the Nelion peak.The horizontal components of diffuse short-wave radiation reach a magnitude comparable to those of direct radiation. As a result of contrastingly different albedos of natural surfaces, the horizontal component of diffuse short–wave radiation is particularly large from the direction of the upper glacier, with values around 330–500 W m−2, and smallest from the direction of the rock face of Nelion peak, where values are around 150–330 W m−2. Long–wave radiation seems enhanced from the direction of the Nelion face, and reduced from the azimuth of the upper glacier, thus apparently reflecting differences in emissivity and temperature.
Laboratory Studies of the Optical Properties of Young Sea Ice
Authors: Perovich Donald K. , Grenfell Thomas C. 
Published: September 2017

AbstractLaboratory experiments were performed to determine the optical properties of young salt ice and to examine correlations between the optical properties and the state of the ice. Ice was grown at different temperatures (–10, –20, –30, and –37°C) from water of different salinities (0, 16, and 31‰). The experiments were conducted in a cylindrical tank 1 m in diameter designed to approximate natural ice growth and to permit in situ optical measurements. Observed incident, reflected, and transmitted irradiances were used in conjunction with a modified Dunkle and Bevans photometric model to determine spectral albedos and extinction coefficients. Cold ice only 0.25 m thick had albedos which were comparable to the values for 2 to 3 m multi-year ice examined by previous researchers during the summer melt season; extinction coefficients were 1.5 to 15 times greater. As the ice temperature and hence brine volume decreased, both albedo and extinction coefficient increased; when the ice temperature dropped below the eutectic point, they increased sharply. In addition, ice grown at lower air temperatures had greater albedos and extinction coefficients even when ice temperatures were the same. Variations in the optical properties of the ice are determined by changes in the amount of brine and its distribution; thus the optical properties of salt ice depend not only on ice temperature but on initial growth rate. Variations in ice salinity over the range 4‰ to 14‰ produced no detectable changes in the optical properties.
Neoglacial to Recent Glacier Fluctuations on the Volcano Popocatépetl, Mexico
Authors: White Sidney E. 
Published: September 2017

AbstractNeoglacial to historic and recent fluctuations of the firn field and one glacier on Popocatépetl, Mexico, include advance prior to 1519 to possible mid-Neoglaciation stadial position on gentle, north flanks at 4 150 m, then retreat up-valley to 4 335 m by 1906, and to 4 435 m by 1920 at 7 m/year. After volcanic eruptions and melting to about 4 800 m in 1921, growth of firn field and advance of a thin ice lobe before 1949 to 4 573 m by 1950, then retreat in next eight years at about 34 m/year, re-advance of the firn edge as an ice bulge to about 4 700 m by 1968, and as a thick double-lobed glacier to about 4 600 m by 1978 and 1979. A 37 year crevasse study shows continuous active firn-field movement on the north-west side of the cone.
Theory and Laboratory Observations of Naled Ice Growth
Authors: Schohl G. A. , Ettema R. 
Published: September 2017

AbstractBased on observations of naleds (also called aufeis or icings) grown in a refrigerated laboratory flume, a detailed, composite description of the processes associated with naled ice growth is presented. A spread length is derived that represents a mass balance between the water supplied to a naled’s surface and the ice that freezes on to the surface. Herein, this spread length is termed an equilibrium length. Guided by this concept of equilibrium length and the laboratory data, length- and time-scales applicable to the growth of two-dimensional naleds are proposed. These scales proved useful for normalizing the times and streamwise lengths that correspond to distinct phases of naled ice growth. It is observed that, even in a laboratory flume, naleds spread and thicken in a complex, layer-by-layer manner.To the best of the authors’ knowledge, this is the first reported laboratory study on naled ice growth. The descriptions and concepts presented herein should be useful to engineers concerned with the effects of naleds on engineering works, and of interest to those who are planning experiments on naleds.
Refraction Correction for Radio Echo-Sounding of Ice Overlain by Firn
Authors: Rasmussen L. A. 
Published: September 2017

AbstractRadio-echo signals travel faster in firn than in ice, which affects the analysis of ice-mass thickness. If this effect is neglected, then the calculated thickness of an ice mass may be in error by an amount of the order of one-tenth of the firn thickness. An exact formulation is derived for the path of the signal through the firn and the ice. Explicit solutions are given for constant, linear, and quadratic profiles of the refractive index in the firn layer.
Discharges of Turbid Water during Mini-Surges of Variegated Glacier, Alaska, U.S.A.
Authors: Humphrey Neil , Raymond Charles , Harrison Will 
Published: September 2017

AbstractDischarges of water, sediment, and dissolved impurities from Variegated Glacier, Alaska, were monitored in the early summers of 1980 and 1981 during the occurrence of mini-surges. Seasonal trends, weather-related events, and diurnal variations similar to behavior of other temperate glacier streams were found. The principal effect in the stream associated with mini-surge occurrence was a brief discharge of extremely turbid water. The turbidity is assumed to be introduced into the basal hydraulic system by initiation of the fast motion of a mini-surge at a time and location on the upper glacier known from other measurements. The mean water velocity in the hydraulic system over the intervening distance is thereby determined (0.3 ms−1). The mean water velocity, together with the water discharge (≈16 m3 s−1 at the terminus), places constraints on the distribution of water velocity u and total cross-sectional area AT of the flow paths along the glacier base. This leads to the conclusion that within the zone of mini-surge occurrence in its unperturbed state: u is about 0.1 ms−1 or possibly less; AT is about 102 m 2 or possibly more, and it must be divided into a very large number of small passageways, be blocked by constrictions, or both. The total water cross-section corresponds to a layer 0.1–0.2 m thick when spread uniformly over the glacier width. The water velocity is close to or less than the propagation velocity of the mini-surges. Between the zone affected by mini-surges and the stream, a dynamically less active lower section of the glacier is probably underlain by a small number of conduits, in which the water velocity may be very high (≥ 2 m s−1). Water discharge following the mini-surges puts an upper limit on water-storage changes associated with the anomalous ice motion.
Determination of Particle Paths using the Finite-Element Method
Authors: Stolle D. F. E. , Killeavy M. S. 
Published: September 2017

AbstractLarge ice masses contain a wealth of information regarding past climates and atmospheric chemistry. To interpret properly information from ice cores obtained from glaciers, a time-scale for the ice core must be established. A procedure based on the finite-element method, using velocity-pressure and stream-function formulations to establish particle paths and hence isochrones, is outlined. Examples are presented which demonstrate the ability of the procedure to predict particle paths and isochrones which can be used to determine the time-scale or to confirm dates established by other methods, of ice cores obtained from large ice masses.
Flow of the Brunt Ice Shelf, Antarctica, Derived from Landsat Images, 1974–85
Authors: Simmons D.A. 
Published: September 2017

AbstractSatellite images recorded in 1973, 1974, and 1985 of the Brunt Ice Shelf are compared. There are sufficient identifiable features moving with the ice shelf to show flow patterns over an area of ~10 000 km2. Velocities vary from 500 m a−1 in the west, near the Dawson-Lambton Ice Stream, to 1300 m a−1 in the east, within the Stancomb-Wills Ice Stream.
A topological approach to the strain-rate pattern of ice sheets
Authors: Nye J. F. 
Published: September 2017

AbstractThe pattern of horizontal strain rate in an ice sheet is discussed from a topological point of view. In a circularly symmetric ice sheet, the isotropic point for strain rate at its centre is degenerate and structurally unstable. On perturbation the degenerate point splits into two elementary isotropic points, each of which has the lemon pattern for the trajectories of principal strain rate. Contour maps of principal strain-rate values are presented which show the details of the splitting.
Mechanisms of fast flow in Jakobshavns Isbræ, West Greenland: Part I. Measurements of temperature and water level in deep boreholes
Authors: Iken A. , Echelmeyer Κ. , Harrison W. , Funk M. 
Published: September 2017

AbstractSeveral holes were drilled to depths of 1500–1630 m along a profile across Jakobshavns Isbræ, 50 km upstream from the calving front. Drilling was by hot water and required approximately 20 h. The holes were rapidly closed by refreezing, but it was possible to instrument them with thermistors and tilt sensors before this occurred.Near the margins of the ice stream the holes reached the bed and connected with the subglacial drainage system. Water-level changes recorded in these holes are discussed in terms of the basal hydraulic system. The temperature measurements show that the glacier is temperate-based. Moreover, extrapolation of a measured temperature profile and its curvature suggests that a temperate layer of substantial thickness may exist at the bed near the center of the ice stream. There is a striking difference in the shapes of temperature profiles measured at different locations: beneath the center line the temperature minimum is at a considerably smaller relative depth than near the margins, but it is nearly the same in magnitude (−22.1°C). This may indicate a disproportionately large vertical stretching of the basal ice in the center of the ice stream. Since the basal ice is warmer and much less viscous than the ice above, a thickening of that layer would cause a corresponding increase of surface velocity. We presume that this mechanism contributes to the fast flow of Jakobshavns Isbræ.
Consolidation of sediments by glaciers: relations between sediment geotechnics, soft-bed glacier dynamics and subglacial ground-water flow
Authors: Boulton G. S. , Dobbie K. E. 
Published: September 2017

AbstractA theory of subglacial consolidation is developed which shows how the meltwater flux beneath a glacier leaves a consolidation signature from which many important glacier-dynamic properties can be inferred. Conditions under which water is discharged through channels or in a thin film at the ice—bed interface or by ground-water flow are discussed, and it is concluded that glaciers flowing over aquifers of high transmissibility can induce deep circulation patterns quite different from non-glacial circulation. Examples of glacial pre-consolidation profiles in sediments from The Netherlands and England are used to illustrate how basal melting rates, subglacial ground-water flow patterns, ice overburden, basal shear stress, ice-surface profile and the amount of sediment removed by erosion can be inferred.
Glaciation and deglaciation mechanisms in a coupled two-dimensional climate—ice-sheet model
Authors: Berger André , Gallée Hubert , Tricot Christian 
Published: September 2017

AbstractA two-dimensional model which links the atmosphere, the mixed layer of the ocean, the sea ice, the continents, the ice sheets and their underlying bedrock has been used to test the Milankovitch theory over the last glacial—interglacial cycle. It was found that the orbital variations alone can induce, in such a system, feed-backs sufficient to generate the low-frequency part of the climatic variations over the last 122 kyear. These simulated variations at the astronomical time-scale are broadly in agreement with ice volume and sea-level reconstructions independently obtained from geological data. Imperfections in the simulated climate were the insufficient southward extent of the ice sheets and the too small hemispheric cooling during the last glacial maximum. These deficiencies were partly remedied in a further experiment (Gallée and others, in press) by using the time-dependent CO2 atmospheric concentration given by the Vostok ice core in addition to the astronomical forcing. For this second experiment, the main mechanisms and feedbacks responsible for the glaciation and the deglaciation in the model are discussed here.
Statistics of firn closure: a simulation study
Authors: Enting I. G. 
Published: September 2017

AbstractThe trapping of bubbles of air in polar ice has provided a unique record of past atmospheric composition. However, the interpretation of measured concentrations depends on the statistics of the trapping process. Measurements of trace atmospheric constituents whose concentrations are changing steadily can be interpreted in terms of an “effective age” of the gas which differs from the age of the ice by a delay which corresponds to the mean trapping time. The statistics of bubble trapping can be modelled as a percolation model which is one of a class of models whose transitions are characterized by large critical fluctuations. These critical fluctuations cause an intrinsic sample-to-sample variability in the delay time and thus in the effective age. Monte Carlo simulations using a lattice model of the firn are presented, showing the effect of finite sample size on the age distribution of trapped gas. For samples containing more than about 103–104 bubbles, the simulations indicate that the range of variability is small compared to the average duration of the trapping process.