bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential Consequences Of “Dirty” Arctic Sea Ice
Authors: Pfirman Stephanie , Lange Manfred A. , Ledley Tamara S.
Published: September 2017

Observations of high particulate loads on Eurasian Basin sea ice in 1987 raise questions of consequence for sediment budgets, ice melting, ice modeling and remote sensing. Biogenic and lithogenic particles were observed in concentrations high enough to color the ice surface brown over large area (greater than 15 × 15 km2) within the Siberian branch of the Transpolar Drift stream. The sediment is most likely incorporated when ice forms on the Siberian shelf seas, and is concentrated at the ice surface after several years of summer surface melting and biological growth within the Arctic basin. Much of the particle-laden multi-year ice appears to leave the Arctic basin via Fram Strait, depositing its sediment load along the axis of the East Greenland Current.

To date, variation in sea-ice particle load has not been taken into consideration when modeling ice thickness or distribution for past or future environmental scenarios, with the exception of soot deposited from nuclear war. Naturally elevated surface-particle concentration may occur if there is increased deposition from long-range or coastal transport of aeolian material, increased sediment input into sea ice which is then exposed to surface melting, and/or increased biogenic productivity on the ice surface. Such conditions may have prevailed during the Younger Dryas. If particle loads become high enough to cause extensive sea-ice melting, changes may be expected in sea-ice concentration and distribution, sea-floor sedimentation rates, and oceanic productivity.
Increased Accumulation On The Antarctic Ice Sheet Due To Climatic Warming
Authors: Warren Stephen , Frankenstein Susan
Published: September 2017

Climatic warming due to increased greenhouse gases is expected to cause increased precipitation in the next century because of the increased water content of the air, assuming constant relative humidity. Since temperatures over most of Antarctica are far below freezing even in the warmest month of the year, the increase in melting is probably negligible compared to the increase in precipitation.

Oerlemans (1982) showed that this increase of precipitation would cause a growth of the ice sheet, tending to lower sea level. This would partially counteract the rise of sea level due to increased melting on mountain glaciers and Greenland, and to a possible (and more difficult to predict) surge of ice from West Antarctica.

Oerlemans may have underestimated the increase in accumulation. He used results of General Circulation Models (GCMs) which indicated an increase of precipitation by only 12% for a temperature change ΔΤ = 3 Κ and 30% for ΔΤ = 8 K. In contrast, the change in accumulation rate at Dome C (Lorius and others, 1979) accompanying the warming from the recent ice age to the present was in accord with the simple assumption that accumulation is proportional to saturation vapor pressure at the temperature of the inversion layer, i.e. a 30% increase for ΔΤ = 3 K.

The experimental results are to be preferred to the climate model results because GCMs do not represent ice-sheet accumulation processes well. Most of the accumulation is not snow falling from clouds but instead results from clear-sky ice-crystal formation in near-surface air, or hoarfrost deposition on the surface. GCMs lack sufficient vertical resolution to represent the strong temperature inversion on which these accumulation mechanisms depend.

The figure shows that the increase of vapor pressure due to ΔΤ = 5 Κ varies from a factor of 1.9 at Τ = −60°C to a factor of 1.6 at Τ = −20°C. A climatic warming of 5 K. over Antarctica, which is possible during the next century, could thus increase the Antarctic accumulation from its present 17g cm−2 yr−1 to 30 g cm−2 yr−1, leading to a 50 cm drop in sea level in 100 years. This assumes that the simple proportionality of precipitation rate to saturation vapor pressure applies as well to the coastal regions, which is doubtful because the accumulation processes are not the same as on the plateau.

The potential importance of Antarctic accumulation changes in contributing to changes of sea level argues for further study of the mechanisms of Antarctic precipitation and for their improved representation in climate models.
Bidirectional Reflectance of Polar and Alpine Snow Surfaces
Authors: Kuhn M.
Published: September 2017

The reflectance distribution of polar and alpine snow was measured under various conditions at 450, 514, 750 and 1000 nm wavelength. A reflectance peak appears in the azimuth directions up to 60° to both sides of the solar azimuth, is more prominent at high zenith angles of incidence and of reflectance and is better developed in coarse than in fine-grained snow. Under natural conditions, when only hemispherical-directional reflectivity can be determined, the anisotropy is spread in the blue part of the spectrum where the diffuse component dominates global irradiance. Bidirectional reflectance of a laser beam at 514 nm over alpine snow is comparable to that at 1000 nm over polar snow.
Simulation of a destructive avalanche at Maseguchi, Japan
Authors: Mcclung D.M. , Kobayashi S. , Izumi K.
Published: September 2017

In 1986, a large avalanche destroyed 11 houses and killed 13 people at Maseguchi, Japan. Previous attempts to model the avalanche were based on the assumption that it was a powder avalanche consisting of snow particles suspended by air turbulence. In this paper, the avalanche is modelled as a dry flowing avalanche with a dense core of flowing material at the base. It is suggested that for a comprehensive explanation of the observed damage and the characteristics of the avalanche deposit, the assumption that the avalanche was a flowing avalanche is more appropriate. The comparison of model results from a flowing versus a powder avalanche is of general interest for avalanche zoning and design of structures in avalanche-threatened areas.
Energy budget comparison of snowmelt rates in a deciduous forest and an open site
Authors: Ohta T. , Hashimoto T. , Ishibashi H.
Published: September 2017

Daily snowmelt rates at a leafless deciduous forest site were 40–85% of those at an open site. Reduced snowmelt rates were caused by a difference in meteorological conditions at the forested site. Solar radiation, net radiation and wind speed were especially reduced in the forest, and relationships between them at the two sites were represented by linear functions. Snowmelt rates at the two sites could be predicted by an energy budget method, and net radiation was the major component in the snowmelt energy at both sites. Differences between snowmelt rates at the two sites were due to net radiation differences over many days, but dependency on net radiation at both sites was reduced under particular meteorological conditions. Parameteric analysis under fixed meteorological conditions indicates that this dependency is changed by wind speed, temperature and humidity, because wind speed is reduced in the forest and decrease of turbulent heat exchange in the forest will be notable under strong wind conditions.
Analysis of powder-snow avalanches using three-dimensional topographic data
Authors: Fukushima Yusuke , Hayakawa Norio
Published: September 2017

A fluid-dynamical model of powder-snow avalanches is developed which takes into account three-dimensional topography and can compute an avalanche’s running course. The model also predicts the variations of height, speed and concentration of snow particles in the avalanche, as well as the level of turbulence. Application of the model to the Maseguchi avalanche, which occurred in 1986 at Niigata, Japan, shows it can provide reasonable prediction of the running course, height and speed of an avalanche.
Development of a meteorological forecast for snow accumulation on transmission lines
Authors: Ito Tatsuhito , Yamaoka Masaru , Ohura Hisayuki , Taniguchi Takashi , Wakahama Gorow
Published: September 2017

In Hokkaido we have often experienced hazardous accidents, such as tower collapses and conductor breakage, caused by wet-snow accretion on transmission lines, and over many years have developed countermeasures for wet-snow accretion. Recently we have been developing a system to forecast areas where snow accretion may occur. We used the southern part of Hokkaido, divided into 5 km × 5 km meshes, as a forecast area; our predictions were hourly, 3–24 hours in advance. A method of predicting meteorological data which forms an important part of the system predicts three elements which influence wet-snow accretion: air temperature, precipitation, and wind direction and speed. We used an interpolation for predicting temperature and precipitation and a one-level, mesoscale model for diagnosing surface winds for wind direction and speed. By applying the method to many examples of wet-snow accretion, we checked the prediction of weather elements.
A case study of snowstorm gusts and blowing/drifting snow
Authors: Maki Masayuki , Nakai Sento , Yagi Tsuruhei , Nakamura Hideomi
Published: September 2017

The mechanisms of strong winds associated with snow clouds, and the relationship between strong winds and blowing/drifting snow, were investigated. A snowstorm occurred with a typical L-mode snow band which was generated and organized longitudinally during a continental cold-air outbreak over the Sea of Japan. Doppler radar observations revealed that the snow band consisted of small echo cells arranged along the direction of the snow band. When one of the echo cells passed, blowing/drifting snow was generated and intensified by a snow cloud-induced gust, and the horizontal visibility near the ground surface was significantly decreased. Doppler radar and radiosonde data showed that the gust was due to the cold air outflow (CAO) from the snow clouds. The leading edge of the CAO was about 9 km ahead of the center of the snow cloud and the depth of the CAO was about 600 m near the forward flank of the snow cloud. The CAO was caused by a downdraft at the center of the snow cloud, which was initiated at a height of about 1.3 km and with a velocity in excess of 1 ms−1. The observed CAO speed was explained by the theory of the gravity current.
Areal investigation of drifting snow on Tsugaru Plain, Japan
Authors: Higashiura Masao , Sato Takeshi , Sato Atsushi , Kimura Tadashi , Maki Masayuki , Nakai Sento , Nakamura Hideomi , Yagi Tsuruhei
Published: September 2017

This research investigates mechanisms of drifting snow accumulation, and of strong wind associated with snow clouds (developed cumulus). Detailed structure of snow drifting close to the ground was observed at several sites by use of snow particle counters (SPC), visibility meters and other meteorological instruments, simultaneously with observations of wind structure in the lower atmosphere using Doppler radar and radiosonde. Areal distributions of drifting snow were also observed as a function of time. Primary results include the following. (1) The intensity of drifting snow was found to have a strong correlation with fetch distance. Of obstacles to windward of the observation point, a river interfered with drifting snow more effectively than did a hamlet. (2) The areal distribution of drifting snow is explained fully. (3) Visibility, reflectivity and wind velocity at ground level are strongly related to drifting snow patterns.
Some numerical experiments on firn ventilation with heat transfer
Authors: Albert M.R.
Published: September 2017

Preliminary estimates of the thermal signature of ventilation in polar firn are obtained from two-dimensional numerical calculations. The simulations show that spatially varying surface pressure can induce airflow velocities of 10−5 m s−1 at 1.5 m depth in uniform firn, and higher velocities closer to the surface. The two-dimensional heat-transfer results generally agree with our earlier one-dimensional conclusions that the thermal effects of ventilation tend to decrease the temperature gradient in the top portions of the pack. Field observations of ventilation through temperature measurements are most likely to be observed when the firn temperature at depths on the order of 10 m is close to the air temperature, since steep temperature gradients can mask the thermal effects of ventilation. Preliminary indications are that, as long as surface-pressure amplitude is sufficient to move the air about in the top tens of centimeters in the snow, the resulting temperature profile during ventilation is fairly insensitive to the frequency of the surface-pressure forcing for pressure frequencies in the range 0.1–10.0 Hz.
Evaluation of the snow-removal options in an urban area based on the preferences of inhabitants
Authors: Miyakoshi Kazuhiro , Matsumoto Shoji
Published: September 2017

Basically there are three kinds of snow removal: mechanical snow removal (MSR), snow-thawing pipe systems (STP) and snow-conveying open channels (SCOC). This paper identifies inhabitants’ attitudes toward snow-removal options and quantitatively evaluates their preferences by applying the Analytical Hierarchy Process (ΑΗΡ) method. A hierarchy is specified separately for the road in front of a house and the site of a house. A case study carried out for citizens living in the city of Ojiya in Niigata reveals that the space available for walking is an important factor, and hence STP scores considerably higher than SCOC and MSR. For the evaluation of a house site, the frequency per season of removing snow from a roof is the most important factor. House designs for overcoming snow accumulation are also evaluated.
Estimating the weight of a snow cover using only meteorological factors
Authors: Shinojima Kenji , Harada Hiroshi
Published: September 2017

We compute the weight of the snow cover as a function of the daily quantity of precipitation and daily melting using only data from the Automated Meteorological Data Acquisition System (AMeDAS), which is used widely in Japan. The correlation between long-term measurements and meteorological data in AMeDAS factors was computed by statistical methods from the Forestry and Forest Product Research Institute, Tokamachi Experiment Station, in Niigata Prefecture, using data for 11 winter seasons (1977–87).

The daily quantity of melting is expressed with a three-day moving average of degree days. The coefficient of correlation between the daily groups of each value of the 1323 days during the 11 winter seasons was 0.986 with a standard deviation of ±590 Ν m−2. Thus, if air temperature and precipitation can be obtained for an area, the weight of the snow cover can be estimated with confidence.
Transformation process observations of polar firn to ice
Authors: Langway Chester C. , Shoji Hitoshi , Mitani Atau , Clausen Henrik B.
Published: September 2017

The transformation of snow to ice under compressive stress is a very slow process unless meltwater is present. A qualitative measure of permeability variation with depth was continuously determined for various shallow-ice cores from the dry-snow zones in both Greenland and Antarctica to investigate this transformation process. Results of the study provide insight into snow densification mechanisms and generally characterize the pore close-off phenomena. Measurements show that bulk densities may be expressed as a function of overburden; pore close-off takes place when the overburden is approximately 3.0–4.5 bar.
On the initiation of ice sheets
Authors: Abe-Ouchi Ayako , Blatter Heinz
Published: September 2017

The initiation and evolution of ice sheets are investigated using a two-dimensional thermo-mechanical ice-sheet model. The importance of the amount of snow accumulation on the ice sheet initiation is summarised in the following three points: (1) an ice sheet can grow from an initial area of less than 50 km diameter with a positive but large-enough accumulation rate; (2) the pattern of multiple steady-state solution branches critically depends on the surface mass balance; and (3) snow accumulation strongly controls the growth rate of the ice mass, which is crucial for ice sheets evolving in the limited time available during Milankovitch cycles.
Model project for establishing an avalanche warning and evacuation system
Authors: Terada Hideki , Fujisawa Kazunori , Nakamura Yoshimitsu , Minami Noriyuki
Published: September 2017

A project was started in 1990 to rationalize the avalanche warning and evacuation system. The major items in the model project were: (1) zoning methods for dangerous areas; (2) establishment of a surveillance system; and (3) methods of determining a warning and evacuation standard. Since the scale of a snow avalanche cannot be predicted, areas with more than 30 KN m2 of impact are identified. Equipment for conducting automatic surveillance and data processing was developed to telemeter snow and weather data. Issuing warning or evacuation advice is the focus of the discussion. Judgment is based on information on current conditions obtained from a telemeter and from residents, and on information provided by forecasts of snowfall and temperatures until the following morning. Two methods of judgment are under consideration: one is to set out a standard value based on meteorological data obtained by observation, the other is based on a discriminant of danger level.
Application of a mixture theory to stress waves in snow
Authors: Austiguy George E. , Brown Robert L.
Published: September 2017

A continuum theory of mixtures is applied to model snow as a mixture of an elastic solid and an elastic fluid. Three wave types, two dilational and one rotational, are shown to exist. Numerical evaluation shows velocity and attenuation increasing with frequency for all three waves. Wave velocity increases with increasing density while attenuation decreases with increasing density for all three waves. The first dilational wave is associated with the pore fluid, has a slow wave speed and is highly attenuated. This wave exhibits diffusive behavior at low frequencies and nondispersive behavior at high frequencies. The second dilation wave is associated with the solid ice material. It is the fastest of the three wave types and does not appreciably attenuate. Nondispersive wave behavior characterizes this wave at low and high frequencies. The rotational wave occurs only in the solid, is the least attenuated of all three waves, and propagates at velocities greater than that of the first, but less than that of the second, dilational wave. The rotational wave exhibits nondispersive behavior at low and high frequencies. Wave velocities and attenuation show behavior that is in agreement with existing experimental data.
A statistical model for maximum avalanche run-out distances in southwest Montana
Authors: McKittrick L.R. , Brown R.L.
Published: September 2017

An extreme value (Gumbel) distribution was evaluated as a model of maximum run-out distances of avalanches in southwest Montana defined in terms of dimensionless ratios. The run-out ratios are defined relative to an arbitrarily defined reference point. The development and analysis of the statistical model were based on data taken from surveys of 24 avalanche paths. The technique bears promise as a user-friendly tool; however, due to the small vertical drop of avalanches in southwest Montana, the model appears to be quite sensitive to measurement errors in the field. This sensitivity also seems to depend on the definition of the reference point. Comparison with models developed for other mountain ranges indicates that models developed for one range cannot be used to estimate accurately maximum avalanche run-out distances in other mountain ranges until influencing factors are better understood.
Model for effective thermal conductivity of a dry snow cover composed of uniform ice spheres
Authors: Adams Edward E. , Sato Atsushi
Published: September 2017

The effective thermal conductivity of a snow cover is estimated assuming an idealized collection of uniformly packed ice spheres. An effective thermal conductivity is calculated based on the thermal resistance due to ice-grain contacts or bonds, the pore space/ice acting in series and the unobstructed pore. It is shown to depend very strongly on the snow density and intergranular bonding and, to some extent, on temperature. Conductivity tends to increase as density and the ratio of the contact radius to ice-sphere radius increase. The ice network is generally determined to be the most influential in determining the effective thermal conductitivity. Calculated results fall within the range of empirically determined values.
Passive-microwave remote sensing of snow
Authors: Koike Tosio , Suhama Tomoyuki
Published: September 2017

The radiative-transfer theory and the Rayleigh scattering model were used to obtain the microwave brightness temperatures from dry snowpacks on the ground, which was modelled by a scattering dielectric layer and an underlying homogeneous half-space. The total radio brightness at the radiometer was the sum of the direct and diffuse radiation field intensities. The result of the model application was in good agreement with the observational data, which were obtained through the airborne experiments for the MOS-1 Verification Program around Asahikawa, Hokkaido, Japan, in February 1988.
Accurate mapping of Arctic glaciers over 50 years ago
Authors: Wright John
Published: September 2017

This paper will describe what it was like to map Arctic glaciers starling 62 years ago in Iceland; then in Nordaustland, Svalbard, in 1935–36; and finally in northwest Greenland and Ellesmere Island, Northwest Territories, Canada, in 1937–38. The glacier in Iceland was resurveyed by a party including me in 1992; and I made a less successful attempt to resurvey the Greenland glacier in 1993.
Sediment deformation and basal dynamics beneath a glacier surge front: Bakaninbreen, Svalbard
Authors: Porter Philip R. , Murray Tavi , Dowdeswell Julian A.
Published: September 2017

Bakaninbreen is a 17 km long surge-type glacier in southern Spitsbergen, Svalbard, which began surging between the springs of 1985 and 1986, forming a surge front where fast-moving surge ice meets non-surging ice. This surge front has propagated 6 km down-glacier over the period to 1995. Instruments known as “ploughmeters” were installed into the deformable sedimentary bed close to the surge front to assess mechanical conditions year-round. Forces experienced by ploughmeters located down-glacier of the surge front are generally lower than those recorded by a ploughmeter up-glacier of the surge front. Ploughmeters installed at the bed down-glacier of the surge front show initially low applied forces, followed by increasing applied forces. We interpret this increase in applied forcing as a late-active-phase motion event. Analysis of ploughmeter data allows calculation of the yield strength of basal sediments. Yield-strength estimates at Bakaninbreen are in the range 16.6–87.5 kPa. Comparison with estimates of basal shear stress suggests that sediments up-glacier of the surge front will be actively deforming, whereas there will be only limited deformation down-glacier of the surge front. Immediately down-glacier of the surge front, calculations indicate negligible basal shear stresses. Together with the deformation of sediment from up-glacier, this implies a build-up of sediment at the surge front, offering a potential explanation for the sediment-filled thrust faults outcropping on the surge front.
Comparison of satellite-derived with ground-based measurements of the fluctuations of the margins of Vatnajökull, Iceland, 1973–92
Authors: Williams Richard S. , Hall Dorothy K. , Sigurðsson Oddur , Chien Janet Y. L.
Published: September 2017

Vatnajökull, Iceland, is the Earth’s most studied ice cap and represents a classical glaciological field site on the basis of S. Pálsson’s seminal glaciological field research in the late 18th century. Since the 19th century, Vatnajökull has been the focus of an array of glaciological studies by scientists from many nations, including many remote-sensing investigations since 1951. Landsat-derived positions of the termini of 11 outlet glaciers of Vatnajökull were compared with frontal positions of six of these 11 outlet glaciers determined by field observations during the period 1973–92. The largest changes during the 19 year period (1973–92) occurred in the large lobate, surge-type outlet glaciers along the southwestern, western, and northern margins of Vatnajökull. Tungnaárjökull receded −1413 ± 112 m (−1380 ± 1 m from ground observations), and Brúarjökull receded −1975 ± 191 m (−2096 ± 5 m from extrapolated ground observations) between 1973 and 1992. Satellite images can be used to delineate glacier margin changes on a time-lapse basis, if the glacier margin can be spectrally discriminated from terminal moraines and sandur deposits and if the advance/recession is larger than maximum image pixel size. “Local knowledge” of glaciers is critically important, however, in the accurate delineation of glacier margins on Landsat images.
Spatial, temporal and kinematic characteristics of surges of Variegated Glacier, Alaska
Authors: Lawson Wendy
Published: September 2017

Analysis of five surges of Variegated Glacier, Alaska, indicates that they all terminated with their surge fronts in the terminal lobe of the glacier, and that different surges penetrated into the terminal lobe by different amounts. Of the five surges, the one that occurred in 1905–06 penetrated furthest into the terminal lobe. The 1964–65 surge affected a greater proportion of the glacier than either the 1947–48 or the 1982–83 surge, caused greater total ice displacements than the 1982–83 surge and appears to have resulted in larger total displacements down-glacier than the 1982–83 surge. Overall, the 1964–65 surge was a significantly larger event than either the 1947–48 or the 1982–83 surge.
Glacier geomorphometry — an approach for analyzing long-term glacier surface changes using grid-based digital elevation models
Authors: Etzelmüller Bernd , Ludvig Sollid Johan
Published: September 2017

This paper presents an approach to long-term glacier monitoring. Mathematical surface descriptors, such as altitude, slope and curvature (surface form) are used to classify and quantify glacier surface developments. The analysis is based on photogrammetically derived grid-based digital elevation models over a period of decades. This paper outlines the concept and applies it to five valley glaciers in Spitsbergen, Svalbard, which differ with respect to size, thermal regime and dynamics. The results reflect differences between the glaciers investigated which are attributable to glacier dynamics, in particular concerning the glacier’s possible surge behaviour during a period with retreat and mass losses.
Use of the total input and output of ions to measure meltwater runoff time through a glacier’s accumulation area
Authors: Raben Peter , Theakstone Wilfred H.
Published: September 2017

Ionic analyses of snow samples collected from snow pits and cores, and samples of meltwater collected from the only river draining the Norwegian glacier Austre Okstindbreen during the 1995 summer, showed that the input/output relations of sodium and chloride were nearly identical. Sampling at the pits revealed that some 72% of the Na+ and Cl– ions which accumulated in winter drained from the snowpack in early June with the first 12% of the meltwater. Concentrations and loads of the two ions in the first meltwater draining from the glacier in late May were relatively high. There then followed a slight decrease in both the concentrations and the loads of the two ions in samples of the river water, and more-or-less steady levels were present for a long period. In late July, concentrations decreased. Loads decreased in early August, indicating that most of the winter-accumulated ions had drained from the catchment. Input and output calculations for Na+ and C1– indicate a total drainage time for the first meltwater from the uppermost part of the accumulation area of 6–7 weeks, equivalent to an average drainage velocity of 100 md–1.
Eastern Alpine glacier activity and climatic records since 1860
Authors: Kuhn M. , Schlosser E. , Span N.
Published: September 2017

We have analyzed records of glacier-front variations, mass-balance reconstructions, temperature and precipitation data of Alpine stations, and found that the difference between summer and winter temperature in connection with winter precipitation is a useful indicator of glacier activity. Application of this parameter to the records of six stations since 1860 indicated the advance around 1920 had been preceded by a decade with frequent positive mass balances, while the period 1928–64 was characterized by increased climatic continentality and strong, uniform glacier retreats.
Experimental studies on the transformation from firn to ice in the wet-snow zone of temperate glaciers
Authors: Kawashima Katsuhisa , Yamada Tomomi
Published: September 2017

The densification of water-saturated firn, which had formed just above the firn-ice transition in the wet-snow zone of temperate glaciers, was investigated by compression tests under pressures ranging from 0.036 to 0.173 MPa, with special reference to the relationship between densification rate, time and pressure. At each test, the logarithm of the densification rate was proportional to the logarithm of the time, and its proportionality constant increased exponentially with increasing pressure. The time necessary for ice formation in the firn aquifer was calculated using the empirical formula obtained from the tests. Consequently, the necessary time decreased exponentially as the pressure increased, which shows that the transformation from firn in ice can be completed within the period when the firn aquifer exists, if the overburden pressure acting on the water-saturated firn is above 0.12–0.14 MPa. This critical value of pressure was in good agreement with the overburden pressure obtained from depth–density curves of temperate glaciers. It was concluded that the depth of firn–ice transition was self-balanced by the overburden pressure to result in the concentration between 20 and 30 m.
Flow simulation of a firn-covered cold glacier
Authors: Gagliardini Olivier , Meyssonnier Jacques
Published: September 2017

A numerical simulation of the flow of the cold glacier of Dôme du Goûter (4304 m, Mont Blanc, France) is presented. Owing to the large thickness of the firn layer, the simulation was done by using a rheological model for porous ice derived from a model for ceramic sintering and adapted to fit available data on in situ measured density profiles and firn mechanical behaviour. The flow calculation was made under the assumptions of axisymmetric geometry and stationary conditions, by solving a coupled problem. For a given density field, the velocities were obtained by the finite-element method. Then the integration of the mass-conservation equation along the streamlines derived from this velocity field gave the corresponding stationary densities. The results of the numerical simulation, besides the velocity and density fields, are the age of the ice along the streamlines. They are compared with observation and field data.
Borehole video observation of englacial and basal ice conditions in a temperate valley glacier
Authors: Copland Luke , Harbor Jon , Sharp Martin
Published: September 2017

As part of a study of ice dynamics, 25 boreholes were drilled with high-pressure hot water to the base of Haut Glacier d’Arolla, Switzerland. The boreholes were distributed across a half-section of the glacier, with closest spacing towards the glacier margin. The interior structure of the glacier was investigated by lowering a miniature color video camera down 11 boreholes, and the glacier bed was observed in 3 boreholes.

The video showed distinct changes in ice conditions with depth in the glacier, including ice foliations and changes in ice-bubble content and color. A basal ice layer of varying thickness was recorded in two of the three boreholes in which the glacier bed was observed. This basal ice layer was characterized by relatively sediment-rich, coarse-clear ice, and was thickest in a zone of high water-pressure fluctuations. The available evidence suggests that localized freezing at the glacier bed caused by variations in water pressure is the primary source of this basal ice layer. The near-surface transition between finegrained and coarse-bubbly ice, and between coarse-bubbly and coarse-clear ice, appeared to correlate with the depths of influence of diurnal and annual cold waves, respectively. Two types of ice foliation were identified, consisting of distinct planar coarse-clear ice, or more pervasive coarse-bubbly or fine-grained ice. An origin from crevasse closure or the transposition of sedimentary stratification provides the most likely explanation for these.
Airborne measurement of glacier surface elevation by scanning laser altimeter
Authors: Kennett Michael , Eiken Trond
Published: September 2017

Airborne scanning laser altimetry is a relatively new technique for remote sensing of ground elevation. A laser ranger is scanned across a swath beneath the aircraft, producing a two-dimensional distribution of elevations when combined with data on aircraft position and orientation. Smooth snow-covered glaciers are ideal surfaces for laser scanning since they are highly reflective. A new prototype laser system is described together with results from Hardangerjökulen, Norway. An analysis of the data shows that noise levels are very low at around 2 cm, and that repeatability between overlapping swaths is approximately ± 10 cm. This is consistent with an absolute accuracy of 15 cm or better from manufacturer’s and other measurements. Swath widths of over 1 km are attainable, at lowing complete coverage of small to medium-sized glaciers using parallel flight tracks. The high accuracy and dense, even coverage (about 20 000 points per km2) gives good-quality derived products such as DEMs and enables reliable measurement of glacier volume change. Scanning laser altimetry has many advantages over photogrammetry, which was previously the only remote-sensing method of measuring elevations over large areas but which performs poorly over snow-covered glaciers.
Advances in ice radar studies of a temperate alpine glacier, South Cascade Glacier, Washington, U.S.A.
Authors: Fountain Andrew G. , Jacobel Robert W.
Published: September 2017

South Cascade Glacier, Washington, U.S.A., is one of the most extensively studied glaciers in the Western Hemisphere. In addition to mass-balance measurements, which date to 1958, numerous hydrological investigations have been carried out during the last three decades, and repeated ice-thickness determinations have been made using a variety of techniques. In the late 1960s, the basal topography was initially determined by gravitimetric methods. In the mid-1970s some of the fist depth measurements using radar on temperate ice were made. The basal topography was remapped soon after from a series of point radar measurements and boreholes drilled to the glacier bottom. During the 1990s, the ice thickness was remapped using digital recording of continuous profiles that obtained over 5000 ice-thickness measurements. Profiles have been corrected for the finite beamwidth of the antenna radiation pattern and reflections in steep terrain, resulting in a significantly improved depiction of the basal surface and internal structures. The map based on our recent radar profiles confirms the large-scale features of the basal topography previously depicted and reveals more structural detail. A bright reflector was detected at the base of the glacier and could be traced in adjacent profiles. Comparison with results from water-level measurements in boreholes drilled to the bed indicates that the reflector is a subglacial conduit.
Interpretation of borehole impulse tests at Haut Glacier d’Arolla, Switzerland
Authors: Kulessa Bernd , Hubbard Bryn
Published: September 2017

One hundred and sixteen impulse tests were conducted in a dense borehole array at Haut Glacier d’Arolla, Switzerland, during July and August 1995. Impulse-test response pressure oscillations reveal marked variations in three parameters: relative amplitude decay, oscillation frequency and net water-level displacement. Analysis of response signals from water-filled boreholes indicates that (i) responses from individual boreholes are reproducible over some tens of minutes; (ii) responses are similar, but not identical, for slug insertion (“slug tests”) and removal (“bail tests”); (iii) signal amplitude decay varies with the depth at which the recording pressure transducer is located in a borehole; and (iv) coherent minima in all three response parameters coincide with the location of a known preferential, subglacial water-flow pathway. This correspondence suggests, first, that water-filled and non-fluctuating boreholes have established a link to the subglacial aquifer at Haut Glacier d’Arolla and, secondly, that locally transmissive basal sediments may be identified by relatively low response-signal frequencies, response-signal decays and net water-level displacements. Impulse testing water-filled boreholes therefore has the capacity to provide information relating to the local hydrogeological properties of subglacial aquifers.

In 43 cases, water levels in boreholes adjacent to those being tested were recorded in order to identify possible subglacial linkages. No such connections were detected.
Undulating topography on the Antarctic ice sheet revealed by NOAA AVHRR images
Authors: Seko Katsumoto , Furukawa Teruo , Nishio Fumihiko , Watanabe Okitsugu
Published: September 2017

Undulating topography on the East Antarctic ice sheet was clearly revealed by NOAA AVHRR. The following three patterns of undulating topography were detected by using high-pass filtered images from the visible to thermal infrared channels. In coastal regions (below 2000 m a.s.l.), undulation can be clearly detected by the fluctuation of reflectance in visible channel. It has wavy structure with spacing less than 10 km and alignment at a right angle to the ice-flow lines. In the katabatic zone (from 2000 m a.s.l. to 3000 m a.s.l) well defined fluctuations of albedo stpectrum can be seen with spacing from 10 km to 20 km, aligned at right angles to the ice-flow lines or prevailing katabatic wind direction. Ground-survey data show that the undulating topography is associated with large variations of net accumulation rate. On the inland plateau (above 3000 m a.s.l.), undulation can be clearly seen in the fluctuation of thermal infrared channel in winter. Ground-survey data show that the signal corresponds to the undulating topography. The alignment of the undulation is at a right angle to the ice-flow lines and the spacing is longer than 20 km. The characteristics of these undulations represent the ice-flow dynamics and accumulation anomaly.
Use of snow cover derived from satellite passive microwave data as an indicator of climate change
Authors: Goodison B.E. , Walker A.E.
Published: September 2017

To assess future global change, monitoring of the climate system through observation and analysis of seasonal and interannual fluctuations of climate variables is necessary. Cryospheric elements such as snow cover are often seen as sensitive indicators and integrators of basic climate conditions and hence an indicator of regional and global change. Snow-cover elements which may serve as signals of variability and change are discussed with respect to the effective use of conventional and remotely sensed information. Conventional data are shown to be effective for assessing questions of temporal variability, but are limited for spatial variability. Passive microwave satellite data make an important contribution by providing spatial and temporal information on snow water equivalent (SWE) and the regional distribution of snowpack extent and state. Use of NIMBUS-7 SMMR (Scanning Multichannel Microwave Radiometer) data to develop a time series of SWE is assessed as a complement to conventional data. Limitations of SMMR coverage compared to DMSP SSM/I (Special Sensor Microwave/Imager) coverage for production of SWE maps for climate change analysis are discussed. Although there are limitations during early season snow cover, information derived from passive microwave data is shown to be able to map and compute the areal coverage of SWE allowing interannual comparison of the amount of water available, the date of peak accumulation and the associated spatial distribution. However, the satellite data record is still too short to establish any definitive trend in snow-cover variability.
Satellite passive microwave observations and analysis of Arctic and Antarctic sea ice, 1978–1987
Authors: Gloersen Per , Campbell William J. , Cavalieri Donald J. , Comiso Josefino C. , Parkinson Claire L. , Jay Zwally H.
Published: September 2017

We have recently completed an analysis that examines in detail the spatial and temporal variations in global sea-ice coverage from 26 October 1978, through 20 August 1987. The sea-icemeasurements we analyzed are derived from data collected by a multispectral, dual-polarized, constant incidence-angle microwave imager, the Scanning Multichannel Microwave Radiometer (SMMR) on board the NASA Nimbus 7 satellite. The characteristics of the SMMR have permitted a more accurate calculation of total sea-ice concentrations (fraction of ocean area covered by sea ice) than earlier single-channel instruments and, for the first time, a determination of both multiyear sea-ice concentrations and physical temperatures of the sea-ice pack. An estimate of the SMMR wintertime total ice concentration accuracy of ± 7% in both hemispheres has been obtained. As this is an improvement over the estimated accuracies of previous microwave sensors, we are able to present improved calculations of the sea-ice extents (areas enclosed by the 15% ice concentration boundaries), sea-ice concentrations, and open-water areas within the ice margins. This analysis will be published in a book, Arctic and Antarctic sea ice, 1978–1987: satellite passive microwave observations and analysis, due for publication in1992. Some highlights from the analysis are presented in this paper.
Snow depths and grain-size relationships with relevance for passive microwave studies
Authors: Armstrong Richard L. , Chang Alfred , Rango Albert , Josberger Edward
Published: September 2017

The application of passive microwave radiometry to the remote sensing of snow properties is based on the ratio of emitted to scattered portions of the upwelling radiation. Increased scattering is indicative of increased snow amount, i.e. the number of snow grains present. However, scattering is also directly proportional to snow grain-size for a given snow amount. Current snow cover retrieval algorithms produce inaccurate results when snow grain-sizes are unusually large. Therefore, it is necessary to characterize snow grain-size on a regional scale (and perhaps local scale in extreme situations) in order to adjust passive microwave algorithms. Preliminary analysis indicates that: (1) algorithms are not as sensitive to the presence of large grain-sizes as the initial theory had indicated; (2) standard deviation of grain-size diameters throughout the total snow cover may often be less than 0.5 mm, thus average grain-size data may often serve to characterize the detailed stratigraphy of the total snow cover; (3) conditions in subfreezing snow which produce grain-sizes that greatly exceed a mean diameter value of 1–2 mm result from snow cover/climate relationships which can be modelled/monitored on a regional scale. A preliminary method is investigated for selecting snow retrieval algorithms according to prevailing regional-scale grain-size.
Characterization of a hoar-development episode using SSM/I brightness temperatures in the vicinity of the GISP2 site, Greenland
Authors: Shuman Christopher A. , Alley Richard B. , Anandakrishnan Sridhar
Published: September 2017

Formation of a surface-hoar/depth-hoar complex at the GISP2 site in central Greenland was correlated with large changes in Special Sensor Microwave/Imager (SSM/I) brightness-temperature data. Pass-averaged SSM/I brightness-temperature data over a 1/2° latitude by 1° longitude cell for the 19 and 37 GHz, vertically (V) and horizontally (Η) polarized bands were manipulated to yield differential (V-Η) trends which clearly show a gradual decline as the hoar formation caused a progressively rougher surface with progressively lower density. The hoar episode ended as snowfall, and high winds buried and destroyed the surface-hoar layer and caused rapid V-Η increases in ≈ 1 day. Comparison of the different trends with changes in the field-monitored variables and theoretical values suggest that the V-Η trends are sensitive primarily to changes in surface roughness, and secondarily to near-surface density changes. Consistent expression of trends in microwave brightness temperature over 35 adjacent study cells indicates that this technique may provide a remote-sensing signature capable of defining the timing and spatial extent of surface- and depth-hoar formation in central Greenland.
Relation between ice sheet internal radio-echo reflections and ice fabric at Mizuho Station, Antarctica
Authors: Fujita Shuji , Mae Shinji
Published: September 2017

The relationship between ice fabric and the internal radio-echo reflections was investigated using observation data collected at Mizuho Station, Antarctica. The data were obtained by 179 MHz radio-echo sounding and the ice fabric was measured from 700 m Mizuho ice core. The dielectric permittivity tensor at given depths in the ice sheet was calculated from the ice fabric.

The calculated dielectric permittivity tensor showed that the ice sheet at Mizuho Station is a uniaxially birefringent medium. The symmetrical axis of rotation was the same as the flow line. In such a medium, theory predicts that the electric field vectors are allowed only in the two directions parallel and perpendicular to the flow line. The prediction coincided well with the observation: a strong signal was observed only when the transmitting antenna and the receiving antenna, kept parallel to one another, were oriented parallel or perpendicular to the flow line. However, the observed signal strength in these two directions differed from one another at each depth.

It is also shown that the power reflection coefficient due to the variation of ice fabric with depth is of approximately the same order as that due to the density change and is large enough to produce the predominant internal radio-echo reflections.
Seasonal variations in brightness temperature for central Antarctica
Authors: Van Der Veen C.J. , Jezek K. C.
Published: September 2017

The radiative-transfer model developed by Zwally (1977) is modified and coupled to a one-dimensional time-dependent temperature model, to calculate the seasonal variation in brightness temperature. By comparing this with observed records, the radiative properties of firn can be determined. By retaining scattering as a source term in the radiative transfer function, agreement between model-derived scattering and absorption coefficients and those calculated from the Mie/Rayleigh scattering theory can be obtained. The horizontal brightness temperature is not linked to the vertical one through a constant power reflection coefficient.