bluuebunny/crossref_metadata_2025 huggingface dataset:
A Systematic Review and Meta-Analysis of Cyber-Victimization and Educational Outcomes for Adolescents
Authors: Gardella Joseph H. , Fisher Benjamin W. , Teurbe-Tolon Abbie R.
Published: September 2017

Adolescents’ Internet use is increasingly mobile, private, and unsupervised, which raises concerns given that the Internet increasingly serves as a medium for experiencing victimization. Although it is widely recognized that in-person victimization has a deleterious effect on adolescents’ educational outcomes, the extent to which cyber-victimization has similar effects is less well known. This systematic review and meta-analysis offers a synthesis of the relationship between cyber-victimization and educational outcomes of adolescents aged 12 to 17, including 25 effect sizes from 12 studies drawn from a variety of disciplines. A series of random-effects meta-analyses using robust variance estimation revealed associations between cyber-victimization and higher school attendance problems (r = .20) and academic achievement problems (r = .14). Results did not differ by provided definition, publication status, reporting time frame, gender, race/ethnicity, or average age. Implications for future research are discussed within context of theoretical, critical, and applied discussions.
Mechanical Properties of Dye 3 Greenland Deep Ice Cores
Authors: Azuma Nobuhiko , Higashi Akira
Published: September 2017

Uniaxial compression tests were carried out with specimens cut from several deep ice cores obtained at Dye 3, Greenland, in 1980 and 1981. The power law relationship of = Αση was obtained between the uniaxial strain-rate and the uniaxial stress σ. In a range of strain-rates between 10−8 and 10−7 s−1, the value of the power n for samples with strong single maximum fabric was approximately 4, significantly larger than the value of 3 which has been generally accepted from experiments using artificial polycrystalline ice. A work-hardening effect was found in the ice-core samples taken from a depth of 1900 m, which had a smaller grain size than the others. Recrystallization occurred when the temperature of the specimen was raised during the test and this ultimately caused the formation of the so-called diamond pattern ice fabric.
An Atmospherically Driven Sea-Ice Drift Model for the Bering Sea
Authors: Pease C. H. , Overland J. E.
Published: September 2017

A free-drift sea-ice model for advection is described which includes an interactive wind-driven ocean for closure. A reduced system of equations is solved economically by a simple iteration on the water stress. The performance of the model is examined through a sensitivity study considering ice thickness, Ekman-layer scaling, wind speed, and drag coefficients. A case study is also presented where the model is driven by measured winds and the resulting drift rate compared to measured ice-drift rate for a three-day period during March 1981 at about 80 km inside the boundary of the open pack ice in the Bering Sea.

The advective model is shown to be sensitive to certain assumptions. Increasing the scaling parameter A for the Ekman depth in the ocean model from 0.3 to 0.4 causes a 10 to 15% reduction in ice speed but only a slight decrease in rotation angle (α) with respect to the wind. Modeled α is strongly a function of ice thickness, while speed is not very sensitive to thickness. Ice speed is sensitive to assumptions about drag coefficients for the upper (CA) and lower (CW) surfaces of the ice. Specifying CA and the ratio of CA to CW are important to the calculations.
A Model Simulation of 20 Years of Northern Hemisphere Sea-Ice Fluctuations
Authors: Walsh John E. , Hibler William D. , Ross Becky
Published: September 2017

A dynamic-thermodynamic sea-ice model (Hibler 1979) is used to simulate northern hemisphere sea ice for a 20-year period, 1961 to 1980. The model is driven by daily atmospheric grids of sea-level pressure (geo-strophic wind) and by temperatures derived from the Russian surface temperature data set. Among the modifications to earlier formulations are the inclusion of snow cover and a multilevel ice-thickness distribution in the thermodynamic computations.

The time series of the simulated anomalies show relatively large amounts of ice during the early 1960s and middle 1970s, and relatively small amounts during the late 1960s and early 1970s. The fluctuations of ice mass, both in the entire domain and in individual regions, are more persistent than are the fluctuations of ice-covered area. The ice dynamics tend to introduce more high-frequency variability into the regional (and total) amounts of ice mass. The simulated annual ice export from the Arctic Basin into the East Greenland Sea varies interannually by factors of 3 to 4.
Observing Polar-Ice Variability
Authors: Zwally H. Jay
Published: September 2017

The repetitive synoptic ice data obtainable by satellite sensing provide a means of studying the time-dependent behavior of both sea ice and ice sheets on climatic time scales. Examples of sea-ice parameters which may be measured are extent, concentration, and multiyear fraction; and examples of ice-sheet/ice-shelf parameters are surface elevation, ice-front position, extent and duration of summer melting, and ice accumulation rates. Desired snow-cover parameters include extent and snow depth or water-equivalent depth. The unique ability of satellites to measure such ice parameters and the characteristics of the consequent data sets significantly influence the structure of ice models that can be successfully used with the data. Ice data sets recently acquired by satellite sensing are described. The past decade of sea-ice data provides a detailed description of the interannual variability of sea ice on a regional and seasonal basis. Because of the longer time scales involved in ice-sheet variations, a comparable record of ongoing ice-sheet variations has not yet been established, but important baseline data sets are being developed.
Statistical-Dynamical Model of Accumulation on the Greenland Ice Sheet
Authors: Keen Richard A.
Published: September 2017

A relatively simple, three-parameter model is used to simulate the annual precipitation (accumulation) distribution for the Greenland ice sheet and surrounding regions. The three parameters are (1) the flux of relative vorticity at the 500 mbar level (a measure of cyclonic activity), (2) atmospheric moisture content, and (3) surface terrain. The climatological (1946–79) precipitation distribution predicted by the model displays major features of the observed distribution derived from pit studies. However, the model suggests that, due to changes in storm tracks during this period of 33 a, accumulation distribution maps based on pit studies for varying periods of record may not be representative of a true mean for a uniform period of record. The model is then applied to reconstructed ice-age conditions. Compared to present conditions, accumulation reductions of 60¾ or more are indicated for much of the southern half of Greenland; only slight reductions are noted for northern Greenland.
Sea-Ice and Snow-Cover Data Availability, Needs and Problems
Authors: Barry R. G. , Crane R. G. , Weaver R. L. , Anderson M. A.
Published: September 2017

Various types of sea-ice and snow-cover data are required for operational purposes in real time, for engineering assessments of associated hazards and for regional to global-scale modeling of the climate system. Data on the primary characteristics of ice and snow (extent, depth or thickness, and ice concentration) are becoming available to meet many present types of modeling requirement but secondary properties such as snow-water content, ridging intensity, open-water fraction and ice drift are less readily available.

Data for these major variables of snow and ice cover are considered with respect to problems encountered in obtaining and using digital information necessary for modern computer analyses. Such problems include the limitations of the basic observations (observational or sensor accuracy), the spatial and temporal resolution of different data sets, varying national practices of observing and reporting, and the problems of meshing data collected by different means and having spatial differences and temporal changes of observation time, site location, sensor system and resolution, etc. The relative reliability and climatic “information content” of some historical data sets are briefly examined and available digital data sets on modern global ice- and snow-cover conditions are described.
Annual Salt and Energy Budget Beneath an Antarctic Fast Ice Cover
Authors: Allison Ian , Tivendale C. M. , Copson G. R.
Published: September 2017

Water temperature and salinity profiles were measured to a depth of 300 m below a fast ice cover near Mawson, Antarctica over a full annual cycle. Together with measurements of ice thickness and salinity, they are used to determine the heat and salt balance of the ice/ocean system at this site. The energy balance of the ocean is related to measured energy fluxes at the surface.

Throughout the winter there is a net advection of salty water to the site which enhances the salinity increase in the water due to brine ejected from ice. After the ice reaches its maximum thickness there is considerable advection of warmer water which both raises the water temperature at the site and provides heat for the large oceanic heat flux previously reported for Mawson. The rate of this heat advection increases as the ice extent around Antarctica decreases. The ice partially melts in situ and breaks out in mid January. This effective removal of fresh water is balanced by a large influx of melt water from the continental ice sheet. The fresh water, initially near the surface, becomes well mixed to depths of greater than 200 m by strong storms in the ice free period from mid January to early April.
The Effect of Snow Distribution on Gamma-Ray Survey of Snow Cover
Authors: Johnsrud Morten
Published: September 2017

Topography and snowdrifts may cause large variations in the snow cover as well as in snow depth from one year to another. A simple model is developed to study the influence of different snow distributions and the importance of this as a source of error. The ground surface “seen” from the detector will appear as a disc that can be divided into a number of small elements where it is possible to place the wanted snow distribution. Calculations of the gamma radiation field with different snow distributions show how small changes in the snow cover and distribution will influence the measurements as a function of the average snow water equivalent.
Salination of Snow on Sea Ice and Formation of Snow Ice
Authors: Takizawa Takatoshi
Published: September 2017

Field experiments were carried out to investigate a change in salinity of the snow cover on sea ice and of the snow ice. Snow which covered thin sea ice was flooded with the brine that was pushed out onto the sea ice surface, resulting in a rise in salinity to more than 32‰, which was higher than that of sea water. On the day after the salination of the snow, the flooded snow was found to have been either frozen into snow ice or kept unfrozen. In either case the brine was excluded in turn from the flooded snow. As a result, the wet snow or snow ice had a salinity somewhat above 20‰. It is suggested that subsequently the wet snow keeps the salinity at more than 20‰, while the salinity of the snow ice decreases gradually with time.
Experiments on Thermal Convection in Snow
Authors: Powers D. , Colbeck S.C. , O'Neill K.
Published: September 2017

Thermal convection is observed in snow and in a compact of water-saturated glass beads. While uncertainty in the permeability of the snow limits our ability to compare the observed and calculated onset of convection, agreement between the observed and calculated effects of convection on heat transfer in snow is good. Experimental results with glass beads agree with both the calculated onset of and heat transfer by convection. Attempts are made to assess the effects of convection on snow metamorphism. While much is still uncertain about the significance of thermal convection in snow, it is clear that the phenomenon does occur.
Ocean-atmosphere energy exchange over thin, variable concentration Antarctic pack ice
Authors: Worby A. P. , Allison Ian
Published: September 2017

Several recent studies have suggested that much of the winter-time Antarctic ice is thin (<0.3m). The presence of extensive areas of thin ice has a significant effect on ocean-atmosphere energy exchange. This is investigated using the Maykut (1978) thin-ice energy-budget model in a study for typical September Antarctic ice and climatic conditions. To study the sensitivity of turbulent heat loss to ice concentrations, the Maykut model is combined with an empirical parameterization for the turbulent fluxes from leads (Andreas, 1980) which takes account of the non-linear relationship between heat loss and lead width (or ice concentration). In this one-dimensional sensitivity study, a constant floe-size is assumed, and ice-concentration variations are simulated by changing the width of the leads between floes. The modelled results, for the floe size considered, indicate that at 80% ice concentration the turbulent heat loss through the thin ice component can be greater than that from leads. As concentration decreases, however, the fractional loss through the ice, and, hence, the ice-thickness distribution, becomes less significant. For the concentrations lower than 50%, there is little change in turbulent loss with further decrease in ice cover, as the atmosphere effectively “sees” open ocean.
Numerical simulations of a compact convergent system of ice floes
Authors: Hopkins M.A. , Hibler W.D.
Published: September 2017

The granular nature of the Arctic pack ice, and the plastic nature of the deformation of the pack due to ridging, has long been recognised. However, because of a lack of experimental data, assumptions must be made to define the shape of the yield curve and the associated flow rule which characterize the aggregate rheology of the ice pack. In this work, the results of numerical experiments with a simulated granular viscous-plastic material are presented. The experiments model the granular texture of the ice pack as a dense assembly of non-uniform diameter disks in a rectangular control area. Deformation of the control area is driven by constant strain rates. In the experiments, the ratio of the principal strain rates is varied from isotropic convergence through uniaxial divergence. The stresses computed in the experiments, at the various strain-rate ratios, define a yield curve in principal-stress space. The effects of different coefficients of friction and viscous damping on the shape of the yield curve are explored.
An evaluation of scale-dependent effects of atmosphere-glacier interactions on heat supply to glaciers
Authors: Ohata Tetsuo
Published: September 2017

Scale-dependent atmosphere-glacier interactions operate over a glacier surface as the surface has different thermal and radiative characteristics from those of the surrounding ground. In order to evaluate heat supply to the glacier surface in the main ablation period, three main interaction processes are considered: advection, glacier wind, and multiple reflection of solar radiation. The amount of heat supply was calculated for the equilibrium line altitude (ELA) by assuming a simple rectangular-shaped glacier, and by applying meteorological and glaciological data for four different glaciated regions (Tien Shan, Patagonia, west Kunlun and Nepal Himalaya). The total heat supply due to the above three processes had the common tendency of being smallest for glaciers of 1 to several kilometres in length, and largest at 16 km, which was the maximum length considered in this study. Among the cases, the Tien Shan showed a daytime heat supply higher by 2.3 MJ m−2 for a 16km-long glacier compared with a small glacier 2 km in length. Relating this difference directly to ELA, an ELA approximately 300 m higher might be expected for a long glacier than a short one, assuming the same amount of solid precipitation. Glacier inventory data for China support this tendency, but the calculated value is slightly larger than that observed. The results show that there is a possibility that responses in glacier variation to climate change may be modified considerably through scale-dependent atmosphere-glacier interactions.
Reactions of a calving glacier to large changes in water level
Authors: Laumann Tron , Wold Bjørn
Published: September 2017

Austdalsvatn in western Norway was regulated in 1988 as a reservoir for a hydropower development. From a pre-1988 water level of 1157 m a.s.l. the new water level will vary more or less annually from 1170 to 1200 m a.s.l. The outlet glacier Austdalsbreen calves into this reservoir. About 1600 m up-valley from its terminus the glacier flows over a bedrock riegel that is, at its lowest point, ∼ 15 m above the projected maximum lake level of 1200 m. As a result of the increase in water level, the surface velocity near the front has increased from about 0.07 to 0.13 m d−1.

Calculations suggest that the glacier terminus will retreat about 750 m in 50 years. The measured response of the glacier terminus for the first three years is in good agreement with the simulations.
The mechanical properties of saline ice under uniaxial compression
Authors: Kuehn Gary A. , Schulson Erland M.
Published: September 2017

Understanding the mechanical properties of saline ice is important for engineering design as well as for operations in polar regions. In order to gain understanding of the basic mechanisms of deformation and fracture, laboratory-grown columnar saline ice, representative of first-year sea ice, was tested in uniaxial compression under a variety of conditions of Strain rate (10−7 to 10−1 s−1), temper-aiure (−40°, −20°, −10° and −5°C) and orientation (loading vertically or horizontally: i.e. parallel or perpendicular to the growth direction). The range of strain rate spanned the ductile-to-brittle transition for every combination of temperature and specimen orientation. The results of over 250 tests are reported. Mechanical properties, failure mode and ice structure are analyzed with respect to the testing conditons. The results show that strength is dependent upon the ice structure, orientation, strain rate and temperature. During loading in the ductile regime the structure is altered (e.g. by recrystallization), whereas in the brittle regime the majority of the structural change is through cracking. The results are compared to results from the literature on both natural sea ice and laboratory-grown saline ice. Where possible, they are interpreted in terms of micromechanica] models.
A constant-speed penetrometer for high-resolution snow stratigraphy
Authors: Schneebeli Martin , Johnson Jerome B.
Published: September 2017

A new constant-speed penetrometer for field and laboratory measurement has been developed. The initially independent work of SFISAR and CRREL has been brought together, and a portable field device is now in an advanced stage of testing. The new penetrometer has high rigidity and a high-resolution large dynamic range force sensor. It uses a much smaller sensing head (5 mm) than previous designs and has a constant-speed drive. With this construction, the penetration resistance of very fine layers and the influence of the bonding strength between snow grains can be more accurately determined than is possible with the rammsonde or Pandalp. Artificial foam layers as thin as 2 mm and thin layers in snow have been detected by the penetrometer. Thin snow layers detected from penetration-resistance profiles have been correlated to fine layering as determined from plane-section microphotographs of samples taken adjacent to the profile. The instrument’s measurements are highly repeatable and the lack of subjective decisions when operating the penetrometer makes the penetration resistance a quantitative measure of snow stratigraphy.
The interaction between drifting snow and atmospheric turbulence
Authors: Bintanja Richard
Published: September 2017

This paper presents a modelling study of the influence of suspended snow on turbulence in the atmospheric surface layer. Turbulence is diminished in drifting and blowing snow, since part of the turbulent energy is used to keep the particles in suspension. This decrease in turbulence directly affects the vertical turbulent fluxes of momentum and snow particles (and other scalars), and can effectively be simulated by introducing an appropriate Richardson number to account for the stability effects of the stably stratified air-snow mixture. We use a one-dimensional model of the atmospheric surface layer in which the Reynolds stress and turbulent suspended snow flux are parameterized in terms of their mean vertical gradients (first-order closure). The model calculates steady-state vertical profiles of mean wind speed, suspended snow mass in 16 size classes and stability parameters. Using the model, the influence of snowdrifting on the wind-speed profile is quantified for various values of the initial friction Velocity (which determines the steepness of the initial wind-speed profile). It will be demonstrated why the roughness length appears to increase when snowdrifting occurs. Finally, we present a parameterization of the effects of snowdrifting on atmospheric stability which can be used in data analyses as a first-order approximation.
Drifting-snow acoustic detector: experimental tests in La Molina, Spanish Pyrenees
Authors: Font D. , Naaim-Bouvet F. , Roussel M.
Published: September 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.
Comparison of the Surface Conditions of the Inland Ice Sheet, Dronning Maud Land. Antarctica. Derived from Noaa AVHRR Data with Ground Observation
Authors: Fujii Yoshiyuki , Yamanouchi Takashi , Suzuki Kazuya , Tanaka Shinya
Published: September 2017

The surface conditions of the inland ice sheet in east Dronning Maud Land, Antarctica, are derived from the NOAA-7 AVHRR data received at Syowa Station and then compared with the ground observations which were collected in November 1984 along a 243 km long traverse route at altitudes ranging from 2700 to 3400 m a.s.l. The variations in the AVHRR data are well related to the distribution of glazed surfaces. The areas with lower albedo, higher surface temperature, lower ratio of channel 2/channel 1, and lower T4-T5 coincide with the areas where a glazed surface has developed. This result is attributed to the fact that the glazed surface is composed of a multi-layered ice crust and that its radiative and thermal properties are closer to ice than to snow. The present study shows that the NOAA AVHRR data are useful for distinguishing bare ice, glazed surfaces, and snow surfaces of the Antarctic ice sheet.
Comparison of Observed and Modeled Ice Motion in the Arctic Ocean
Authors: Zwally H. Jay , Walsh John E.
Published: September 2017

Daily maps of multiyear ice concentration, derived from Nimbus-7 SMMR passive microwave data, are analyzed to obtain the displacement of the multiyear ice edge and information on the convergence/divergence within the pack. The dynamic—thermodynamic sea-ice model of Hibler (1979) is run with daily time steps and with forcing by the interannually varying fields of geostrophic wind and temperature-derived thermodynamic fluxes. Model-data comparisons are made for the net drift during the months of November through January of the 1978—79, 1979—80, and 1980—81 seasons, and for the shorter-term drift during a 52 day period. Both the model and the data-based drifts for the 25 November 1978 to 28 January 1979 period differ from the classical Beaufort-gyre pattern exhibited in the other two winters. For the 52 day period of November—December 1978, both the model and the data show an eastward drift followed by a westward drift of the ice edges in the Laptev Sea, and for the 25 November 1978 to 28 January 1979 period, a net westward drift of about 250 km. Overall, the model and the data exhibit the same patterns of ice movement with marked month-to-month and large interannual variations in the drift. Good agreement is found in most regions of the central Arctic, but pronounced discrepancies occur near the edge of the total ice pack in the East Greenland Sea. During a short period of large changes in multiyear ice concentration in the central Arctic around 2 December 1980, the divergence implied by the changes in multiyear concentration is qualitatively compared with the divergence computed from the modeled velocity fields. Both the microwave data and the model results indicate similar temporal characteristics of pack-ice response during this major deformation event.
Remote Sensing of Sea-Ice Growth and Melt-Pool Evolution, Milne Ice Shelf, Ellesmere Island, Canada
Authors: Jeffries Martin O. , Sackinger William M. , Serson Harold V.
Published: September 2017

Periodically since 1950, air photographs and SLAR images have been taken of the Arctic ice shelves. The study of air photographs and SLAR images of the outer part of Milne Ice Shelf had three aims: (1) to map losses and ice re-growth at the shelf front, (2) to map the evolution of melt pools on shelf ice and multi-year land-fast sea ice, and (3) to assess the usefulness of air photographs and SLAR for these purposes. For mapping of ice calvings and subsequent sea-ice growth, both air photographs and radar images have been used sucessfully. However, air photographs are better than radar for mapping ice-surface features. The ridge-and-trough systems that characterize the surface of the ice shelf and old sea ice are clearly visible on each type of imagery but, because of their larger scale, air photographs proved to be most useful for a study of melt-pool evolution. The orientation of the melt pools is parallel to the prevailing winds which drive water along the troughs. The drainage system evolves by a process of elongation and coalesence.
Imaging Subglacial Topography by a Synthetic Aperture Radar Technique
Authors: Musil G.J. , Doake C.S.M.
Published: September 2017

A synthetic aperture radar (SAR) technique has been used to image part of the grounding-line region of Bach Ice Shelf in the Antarctic Peninsula. The radar was sledge-mounted and operated in a pulsed mode with a carrier frequency of 120 MHz. The coherently detected output was recorded photographically as in-phase and quadrature components. Because the system was essentially stationary for each measurement, there was no doppler information about the reflecting points as in the more commonly used airborne and satellite-based SARs. Instead, the phase history was used directly to identify point targets by a correlation method.

Three sounding runs were carried out over the grounding line to give views of the area from separate directions. An aperture length of 104 m was necessary to achieve 8 m resolution in the along-track direction for an ice thickness of 290 m. The mapped swath was 88 m wide. Corrections to the data were made to allow for density variations and absorption in the ice. The back-scatter coefficient showed greater variations in echo strength over grounded ice compared with floating ice and texture analysis of the radar image revealed a statistically significant difference between these two regimes.
Satellite Snow-Cover Monitoring in the Qilian Mountains and an Analysis for Characteristics of Stream Snow-Melt Run-Off in the Hexi Region, Gansu, China
Authors: Qunzhi Zeng , Shunying Zhang , Xianzhang Chen , Jian Wang
Published: September 2017

The images of NOAA/TIROS-N APT, AVHRR and a few Landsat MSS obtained from 1980 to 1985 are analysed in this paper. It is found that the snow-cover distribution in Qilian Mountains is above 3700 m a.s.l. during winter to spring every year. There are two concentrations of snow cover. One is on Mount Leng Longling in the upper reaches of the Shiyang River and the other is located between Hala Lake and Mount Danghe Nanshan.

Based on preliminary investigations, it is known that the surface water resource in the Hexi region is 68 8 × 108 m3, of which about 24.8% is from glaciers and melting, and the snow-melt run-off is 7.63 × 108 m3, equal to 62.6% of the total amount of spring run-off.

The average value of Cv for spring run-off in the Shiyang River, Heihe River, and Shule River is 0 32 and the Cv value of snow-melt run-off in spring is 0.41, about three times as much as that of the annual run-off in the Hexi, region. A prediction model of spring snow-melt run-off at the Ying Louxia Hydrometric station in the Heihe River area can be constructed by using hydrometeorological data and snow-cover percentage for the Heihe River basin obtained from NOAA/TIROS-N APT, and AVHRR images. The prediction models (2) and (3) have been tested by the Water Resources Management Office of the Heihe River basin in the Zhangye and Flood Prevention Office of Gansu Province. The prediction accuracy is suitable for demands.
The Timing of Initial Spring Melt in the Arctic from Nimbus-7 SMMR Data (Abstract)
Authors: Anderson Mark R.
Published: September 2017

The ablation of sea ice is an important feature in the global climate system. During the melt season in the Arctic, rapid changes occur in sea-ice surface conditions and areal extent of ice. These changes alter the albedo and vary the energy budgets. Understanding the spatial and temporal variations of melt is critical in the polar regions. This study investigates the spring onset of melt in the seasonal sea-ice zone of the Arctic Basin through the use of a melt signature derived by Anderson and others from the Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) data. The signature is recognized in the “gradient ratio” of the 18 and 37 GHz vertical brightness temperatures used to distinguish multi-year ice. A spuriously high fraction of multi-year ice appears rapidly during the initial melt of sea ice, when the snow-pack on the ice surface has started to melt. The brightness-temperature changes are a result of either enlarged snow crystals or incipient puddles forming at the snow/ice interface.

The timing of these melt events varies geographically and with time. Within the Arctic Basin, the melt signatures are observed first in the Chukchi and Kara/Barents Seas. As the melt progresses, the location of the melt signature moves westward from the Chukchi Sea and eastward from the Kara/Barents Seas to the Laptev Sea region. The timing of the melt signal also varies with year. For example, the melt signature occurred first in the Chukchi Sea in 1979, while in 1980 the signature was first observed in the Kara Sea.

There are also differences in the timing of melt for specific geographic locations between years. The melt signature varied almost 25 days in the Chukchi Sea region between 1979 and 1980. The other areas had changes in the 7–10 day range.

The occurrence of these melt signatures can be used as an indicator of climate variability in the seasonal sea-ice zones of the Arctic. The timing of the microwave melt signature has also been examined in relation to melt observed on short-wave imagery. The melt events derived from the SMMR data are also related to the large-scale climate conditions.
Microwave Snow-Water Equivalent Mapping of the Upper Colorado River Basin, U.S.A. (Abstract)
Authors: Campbell W.J. , Josberger E.G. , Gloersen P. , Chang A.T.C.
Published: September 2017

During spring 1984, a joint agency research effort was made to explore the use of satellite passive microwave techniques to measure snow-water equivalents in the upper Colorado River basin. This study involved the near real-time acquisition of microwave radiances from the Scanning Multichannel Microwave Radiometer (SMMR) aboard the Nimbus-7 satellite, coupled with quasi-simultaneous surface measurements of snow-pack depth and profiles of temperature, density, and crystal size within the basin. A key idea in this study was to compare, for the same space and time-scales, the SMMR synoptic physics data taken in the basin. Such a snow-measurement program was logistically difficult, but two field teams took detailed snow-pit measurements at 18 sites in Colorado, Utah, and Wyoming during the last 2 weeks of March, when the snow-pack is normally at its maximum extent and depth. These observations were coupled with snow-water-equivalent measurements from Soil Conservation Service SNOTEL sites. Microwave- gradient ratio, Gr (Gr is the difference of the vertically polarized radiances at 8 mm and 17 mm divided by the sum), maps of the basin were derived in a near real-time mode every 6 days from SMMR observations. The sequential Gr maps showed anomalously low values in the Wyoming snow-pack when compared to the other states. This near real-time information then directed the field teams to Wyoming to carry out an extensive survey, which showed that these values were due to the presence of depth hoar; the average crystal sizes were more than twice as large as in the other areas. SMMR can be used to monitor the spatial distribution and temporal evolution of crystal size in snow-packs. Also, scatter diagrams of snow-water equivalents from the combined snow-pit and SNOTEL observations versus Gr from the Wyoming part, and the Colorado and Utah part, of the basin can be used to estimate snow-water equivalents for various parts of the basin.
Spectral Response Patterns of Snow and Ice Surfaces for the Landsat Multispectral Scanner (Abstract)
Authors: Kristensen M. , McIntyre N.F.
Published: September 2017

The high-resolution imagery recorded by systems such as the multi-spectral scanners (MSSs) of the Landsat satellites has revolutionized the study of all types of surface in the polar regions. Visible and near-infra-red imagery has found a wide range of glaciological uses. There is, however, a lack of comparability within and between MSS data which may be a contributary factor to some current problems in interpretation of remotely sensed glaciological data.

With the expected continuity of MSS coverage for the forseeable future, it is highly desirable to extend use of the data beyond the basic mapping and feature identification which has made it such a valuable resource. One of the most obvious developments is to investigate characteristics of the reflecting surfaces and to achieve absolute identification of snow and ice surfaces. Although conversion of digital MSS grey tones to radiances enables direct comparison with other sources, automatic identification requires detailed and extensive knowledge of the spectral and reflecting characteristics of surfaces which are to be monitored. This is often best achieved through ground-based observation.

In order to provide a base line against which corrected radiances from Landsat MSS data can be compared, a spectrally gated photometer has been used to measure albedo at MSS wave bands in a wide range of conditions. The surfaces monitored in several parts of Norway include sea ice, lake ice, snow, firn and glacier ice, permafrost, and reference surfaces. A range of supporting measurements (including grain-size, surface irregularity, density, level, and free-water content) allows accurate characterization of each surface. This enables identification of spectral-response patterns for each surface category and hence the classification of their reflectances as recorded by the MSS. Examples are given of the application of such classifications to imagery of the polar regions.
Comparison of Surface Characteristics of the Antarctic Ice Sheet with Satellite Observations (Abstract)
Authors: Young N. , Goodwin I.
Published: September 2017

Ground surveys of the ice sheet in Wilkes Land, Antarctica, have been made on oversnow traverses operating out of Casey. Data collected include surface elevation, accumulation rate, snow temperature, and physical characteristics of the snow cover. By the nature of the surveys, the data are mostly restricted to line profiles. In some regions, aerial surveys of surface topography have been made over a grid network.

Satellite imagery and remote sensing are two means of extrapolating the results from measurements along lines to an areal presentation. They are also the only source of data over large areas of the continent. Landsat images in the visible and near infra-red wavelengths clearly depict many of the large- and small scale features of the surface. The intensity of the reflected radiation varies with the aspect and magnitude of the surface slope to reveal the surface topography. The multi-channel nature of the Landsat data is exploited to distinguish between different surface types through their different spectral signatures, e.g. bare ice, glaze, snow, etc. Additional information on surface type can be gained at a coarser scale from other satellite-borne sensors such as ESMR, SMMR, etc. Textural enhancement of the Landsat images reveals the surface micro-relief.

Features in the enhanced images are compared to ground-truth data from the traverse surveys to produce a classification of surface types across the images and to determine the magnitude of the surface topography and micro-relief observed. The images can then be used to monitor changes over time.
High-Precision Distance Measurement with an unmanned, Moving Target
Authors: Ito H. , Schroff K. , Frei Hans-jörg
Published: September 2017

A device was developed, which rotates a marker for the distance measurement in the desired direction, without an operator at the spot. This is also possible with a moving object, on which the marker is set up. The device, together with adequate distance-measuring instruments, yields a precise distance measurement by a single observer at a single station. Examples of measurements using it during sea-ice studies in the Greenland Sea are described. It is shown that the application of the instrument provides a satisfactory basis for precise glacier surveying with limited personnel, cost, and time.
Recent Changes of Nordbogletscher and Nordgletscher, Johan Dahl Land, South Greenland
Authors: Knudsen N.Tvis
Published: September 2017

Generally, outlet glaciers from the Inland Ice in South Greenland have retreated and thinned considerably since the 19th century. A sector in Johan Dahl Land, comprising the glaciers Nordbogletscher, Nordgletscher, and Eqalorutsit kangigdlît sermiat, has no trim-line zones. These glaciers have probably reached their most advanced position in historical time and are advancing further.

Marginal and surface changes of the glaciers, over the last 30 years, are determined, using topographic maps based on aerial photographs taken in 1953, 1977, and 1981 and compared with ablation and surface movement of ice measured at stakes, established in 1978 at Nordbogletscher.

The conclusion, made on the basis of the observations, is that the advance is the result of a higher transport rate of ice from the accumulation area than can ablate during the summers in the ablation area, under prevailing climatic conditions.
Using Sequential Photography to Estimate Ice Velocity at the Terminus of Columbia Glacier, Alaska
Authors: Krimmel R.M. , Rasmussen L.A.
Published: September 2017

The terminus of Columbia Glacier, Alaska, was observed with a single automatic 35 mm camera to determine velocity with a time resolution in the order of a day. The photographic coordinates of the image of a target were then transformed linearly into the direction numbers of the line of sight from the camera to the target. The camera orientation was determined from the film-plane locations of known landmark points by using an adaption of vertical photogrammetry techniques. The line of sight, when intersected with some mathematically-defined glacier surface, defines the true space coordinates of a target, The time sequence of a target’s position was smoothed, first in horizontal x, y space to a straight line, then in y (the principal direction of ice flow) and time with a smoothing cubic spline, and then the x-component was computed from the y-component by considering the inclination of the straight line. This allows daily velocities (about 8 m/day) to be measured at a distance of 5 km, using a 105 mm lens. Errors in daily displacements were estimated to be 1 m. The terminus configuration was also measured using the same photo set.
Analysis and Simulation of Altimeter Performance for the Production of Ice Sheet Topographic Maps
Authors: Partington K.C. , Rapley C.G.
Published: September 2017

Satellite-borne, radar altimeters have already demonstrated an ability to produce high-precision, topographic maps of the ice sheets. Seasat operated in a tracking mode, designed for use over oceans, but successfully tracked much of the flatter regions of the ice sheet to ± 72° latitude. ERS-1 will extend coverage to ± 82° latitude and will be equipped with an ocean mode similar to that of Seasat and an ice mode designed to permit tracking of the steeper, peripheral regions. The ocean mode will be used over the flatter regions, because of its greater precision.

Altimeter performance over the ice sheets has been investigated through a study of Seasat tracking behaviour and the use of an altimeter performance simulator, with a view to assessing the likely performance of ERS-1 and the design of improved tracking systems. Analysis of Seasat data shows that lock was frequently lost, as a result of possessing a non-linear height error signal over the width of the range window. Having lost lock, the tracker frequently failed to transfer rapidly and effectively to track mode. Use of the altimeter performance simulator confirms many of the findings from Seasat data and it is being used to facilitate data interpretation and mapping, through the modelling of waveform sequence.
Velocity Measurements On Daugaard-Jensen Gletscher, Scoresby Sund, East Greenland
Authors: Reeh Niels , Olesen Ole B.
Published: September 2017

The surface movement of Daugaard-Jensen Gletscher, East Greenland, a fast-moving outlet glacier from the Greenland ice sheet, was determined by means of theodolite measurements, using intersections from observation stations on bedrock, once or twice a day, during a ten-day period. With a gap of about three weeks, the observation programme was resumed for another three days which allowed “long term” mean velocities to be calculated, as references for a study of velocity fluctuations on time scales in the range 2–10 days. Various methods of analysing non-synchronous theodolite measurements on fast-moving glaciers are discussed, and previously-reported large velocity fluctuations are critically reviewed. It is concluded that, on the time scales studied, velocities in the frontal region of Daugaard-Jensen Gletscher fluctuate by up to 15%. However, on one occasion, a velocity increase of more than 50% was observed, lasting for about 7.5 hours. This event is inferred to be the result of a sudden increase in the water pressure of the subglacial drainage system, caused by the tapping of an ice-dammed lake behind the glacier front. The more moderate velocity fluctuations are most likely also due to changes of the subglacial hydraulic system.
Results from the Radio Echo-Sounding on Parts of the Jostedalsbreen Ice Cap, Norway
Authors: Saetrang Arne Chr. , Wold Bjørn
Published: September 2017

The paper describes instrumentation, navigation methods, and interpretation problems from radio echo-sounding on parts of Jostedalsbreen. A map of the subglacial topography is presented. Ice thickness ranges from 60 m to 600 m with most sections between 150 m and 300 m.
Surface Features of Ice Stream B, Marie Byrd Land, West Antarctica
Authors: Vornberger P.L. , Whillans I.M.
Published: September 2017

Aerial photographs have been obtained of Ice Stream B, one of the active ice streams draining the West Antarctic Ice Sheet. A sketch map made from these photographs shows two tributaries. The margin of the active ice is marked by curved crevasses and intense crevassing occurs just inward of them. Transverse crevasses dominate the center of the ice streams and diagonal types appear at the lower end. A “suture zone” originates at the tributary convergence and longitudinal surface ridges occur at the downglacier end. The causes of these surface features are discussed and the relative importance of four stresses in resisting the driving stress is assessed. We conclude that basal drag may be important, longitudinal compression is probably important at the lower end, and longitudinal tension is probably most important near the head of the ice stream. Side drag leads to shearing at the margins, but does not restrain much of the ice stream.
Topographic Characteristics in the Ablation Area of the Khumbu Glacier, Nepal Himalaya
Authors: Watanabe O. , Iwata S. , Fushimi H.
Published: September 2017

Topographic sketch mapping of the whole ablation area of the Khumbu Glacier, East Nepal Himalaya, is performed, using a simple, stereo-photogrammetric method. This map shows that the surface morphology can be classified into 11 morphologic characteristics. Depending on their distribution and combination, the ablation area can be divided into four morphologic areas. Detailed maps, on a scale of 1:1000–2500, of these four areas indicate that the distribution and combination of these 11 morphologic characteristics result from thickness of the debris cover, supraglacial streams and ponds, and glacier dynamics. The irregularity in the ablation area of the Khumbu Glacier can be considered to be a consequence of the mass balance between rate of ice charge from upstream and irregular distribution of ablation rate, depending on debris-cover characteristics in situ.
Glacier Inventories of Iceland: Evaluation and Use of Sources of Data
Authors: Williams R.S.
Published: September 2017

All sources of cartographic, aerial photographic, satellite image, and related data, from the 18th century to the present, for the eight geographic groups of Iceland’s glaciers, were evaluated for use in preparing a preliminary inventory of Iceland’s glaciers, based on information requirements of the Temporary Technical Secretariat for World Glacier Inventory. On the basis of an evaluation of all sources of historic and modern data for the Langjökull Group, the 1:50 000 scale U.S. Army Map Service Series C762 maps of Iceland were determined to be the best maps from which to derive information for a preliminary inventory, as long as the limitations of these maps are considered and accommodated. The fluctuations of Langjökull’s principal outlet glaciers on maps and Landsat images were found to be consistent with field observations at the International Hydrological Decade monitoring stations. Accumulation area ratios were calculated from late summer snow lines on 1973 Landsat images of Vatnajökull (0.70), Langjökull (0.78), and Mýrdalsjökull (0.35), Measurements of the area of the now stagnant glacier on Ok showed a rapid reduction in area (68 per cent) between 1910 and 1960, but a decline in rate of wastage since 1960 (73 per cent between 1910 and 1978). From 1910 and 1945 topographic maps, the volume of the glacier on Ok was found to be reduced by 0.62 km3.