bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of Surge-Type Glaciers (Abstract)
Authors: Clarke G.K.C. , Schmok J. , Ommanney C.S.L.
Published: September 2017

Glaciers can be separated into two classes according to their flow behaviour: normal (relatively steady, annually-averaged, flow rates) and surge-type (pronounced non-annual fluctuations in flow rates). Using glacier inventory data, we compared the population statistics of 1637 normal and surge-type glaciers in the St. Elias Mountains, Yukon Territory, Canada. Within the 38 drainage basins analysed, there is a pronounced spatial variation in the concentration of surge-type glaciers, but no obvious environmental control can be evinced. Analysis of the length distribution function for surge-type glaciers reveals that long glaciers (length exceeding 15 km) have a greater tendency to be surge-type than short glaciers.
Water Temperature Measurements in Turbulent Streams During Periods of Frazil-Ice Formation
Authors: Osterkamp T. E. , Gilfilian R. E. , Gosink J. P. , Benson C. S.
Published: September 2017

Field measurements of water temperatures in two turbulent streams in interior Alaska have been made during periods of frazil-ice production. The measured equilibrium temperature of the water Te-0.005°C agrees with the value calculated from the electrical conductivity of the water. Average cooling rates of the streams during the summer-to-fall stream cooling period were on the order of several tenths of a degree per day with average surface heat losses of -5 to -18 W m−2. Just prior to a frazil-ice event, the water-cooling rates were -1 to -3 mK min−1 with surface heat losses of -47 to -140 M m−2Supercooling at the water surface of a stream prior to and during frazil-ice production does not exceed 0.2°C as shown by measurements of air-water temperature profiles and by radiometer measurements. Mater supercooling at the time of frazil-ice nucleation was <10 mK. These measurements show that frazil-ice nuclei in streams must be other ice particles, cold organic materials, cold soil particles, or a combination of these, that may be introduced into the stream by mass exchange processes at the air-water interface.

The maximum observed supercooling was ΔTm 40 mK. Two measured values for the residual supercooling were 3 and 9 mK. Frazil growth rates calculated from the observed values of supercooling show that, unless the period of residual supercooling is very long, most of the frazil-ice production during one night of supercooling occurred in the transient thermal period from the time of nucleation to the time that the water became residually supercooled.
10Be in Polar Ice and Atmospheres
Authors: Raisbeck G.M. , Yiou F.
Published: September 2017

We briefly review the application of cosmogenic 10Be measurements in ice and polar atmospheres to: (i) the dating of ice cores, (ii) the deduction of past accumulation rates, (iii) information on the influx of stratospheric aerosols in polar regions, and the mechanism of incorporation of aerosols into the ice. We find that at high latitudes (>74°), the 10Be deposition rate in the ice is more constant than the 10Be concentration.
Ice-Shelf Topography and Structure Determined Using Satellite-Radar Altimetry and Landsat Imagery
Authors: Stephenson Simon N. , Jay Zwally H.
Published: September 2017

The glaciological structure and dynamics of West and Shackleton Ice Shelves, East Antarctica, are qualitatively determined using a combination of satellite remote-sensing techniques. Sketch maps traced from unenhanced imagery show the ice edge, grounding lines, flow lines, and rifts. Surface-elevation profiles and contour maps from radar altimetry provide free-board elevations of the floating ice and show flow-line undulations and rumples characteristic of grounded ice. West and Shackleton Ice Shelves consist of a combination of fast-moving ice tongues from outlet glaciers and slow-moving parts constrained by islands, ice rises, and ice rumples.
Numerical, Analytical, and Laboratory Experimental Studies of Granular Avalanche Flows
Authors: Hutter Kolumban , Savage Stuart B. , Nohguchi Yasuaki
Published: September 2017

Flow avalanches may be regarded as being composed of a granular fluid. When dislodged, the snow masses accelerate down a slope until the inclination of its bed tends towards the horizontal, at which stage bed friction eventually brings the snow to rest. We present a completely new analysis of the motion of a finite mass of granular material along an inclined base.

We regard a granular snow mass as an incompressible continuum to which a Coulomb-like basal friction law can be applied. Depth-averaged equations of motion are formulated in terms of a curvilinear coordinate system along a curved bed, and incorporate an averaged longitudinal velocity and a height distribution. A numerical finite-difference technique is employed to integrate these equations. We present numerical results obtained for motion along a curved bed and compare this with the solutions of the equations with results from laboratory observations. The experiments have been performed in order to monitor the motion of a finite mass of granules, either plastic particles or glass beads, along a chute consisting of both an inclined and a horizontal zone, the two zones being connected by a curved element. The particle spread along the chute and the mass distribution of the granules in the run-out zone, as obtained from these experiments, are compared with those derived from theoretical computations. The results show that the model used predicts the motion of a granular avalanche reasonably well.

Finally, it is indicated how the basal friction law may be extended or altered in order to reproduce the dynamic processes involved in causing the abrupt cessation of the snow mass-motion characteristic in the run-out zone.
Past and Forecast Fluctuations of Glacier Blanc (French Alps)
Authors: Letréguilly Anne , Reynaud Louis
Published: September 2017

In 1980 the new advance of Glacier Blanc covered a trail leading to a mountain hut and threatened the footbridge that crosses its melt-water stream. This event prompted the Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE) to undertake a new study of the glacier. With the old Eaux et Forêts measurements, and the more recent LGGE ones, it has been possible to forecast the probable fluctuations in glacier length by two different methods: a statistical method based on a correlation between the variations in length and mass balance, and a one-dimensional numerical ice-flow model. Both methods show that a substantial glacier retreat is unlikely during the 1985–90 period.
A Mathematical Model for Instability in Snow Gliding Motion
Authors: Nohguchi Yasuaki
Published: September 2017

In this paper a fundamental model is proposed to describe the time-dependent behaviour of uniform snow glide on an infinite slope. This model is composed both of a mechanical balance equation relating a driving force and a resistant force, and of a rate equation for a real contact area at the boundary. In the model, a steady motion of glide is described as a stable equilibrium of glide motion, and a non-steady motion is considered as a transient one not in equilibrium. Finally, the model is applied to a full-depth avalanche release caused by acceleration of snow glide. By comparing the model predictions with glide-velocity field data, a proper model of acceleration prior to full-depth avalanche release is determined. As a result, we can obtain the safety standards to be applied in the event of full-depth avalanches in terms of a glide velocity.
Recent Warming in Central Greenland?
Authors: Alley Richard B. , Koci Bruce R.
Published: September 2017

Recent warming has occurred in near-surface firn in central Greenland, as shown by analysis of a 217 m temperature profile from the GISP2 site. However, this warming falls within the range of natural variability and provides no clear evidence of a greenhouse signal.
Modeling Onset of Glaciation
Authors: Crowley Thomas J. , North Gerald R.
Published: September 2017

Numerous studies have shown that climate has varied between ice-free and glaciated states, with transitions often marked by abrupt steps. We summarize some modeling studies that have attempted to explain elements of the long-term trend and discuss a particular model for abrupt transitions that involves instabilities due to albedo discontinuities at the snow/ice edge.
Little Ice Age (Neoglacial) Paleoenvironmental Conditions At Siple Station, Antarctica
Authors: Mosley-Thompson Ellen , Thompson Lonnie G. , Grootes Pieter M. , Gundestrup N.
Published: September 2017

The 550-year records of δ18O and dust concentrations from Siple Station, Antarctica suggest warmer and less dusty atmospheric conditions from 1600 to 1830 A.D. which encompasses much of the northern hemisphere Little Ice Age (LIA). Dust and δ18O data from South Pole Station indicate that the opposite conditions (e.g. cooler and more dusty) were prevalent there during the LIA. Meteorological data from 1945–85 show that the LIA temperature opposition between Amundsen-Scott and Siple, inferred from δ18O, is consistent with the present spatial distribution of surface temperature. There is some observational evidence suggesting that under present conditions stronger zonal westerlies produce a temperature pattern similar to that of the LIA. These regional differences demonstrate that a suite of spatially distributed, high resolution ice-core records will be necessary to characterize the LIA in Antarctica
Glacier Recession and Lake Shrinkage Indicating a Climatic Warming and Drying Trend in Central Asia
Authors: Yafeng Shi , Jiawen Ren
Published: September 2017

Mass balance observations on Urumqi River No. 1 Glacier and Tuyuksu Glacier in Tianshan show a large deficit during the 1980s as compared to the decades before. The Qinghai Lake in northeastern Qinghai-Xizang (Tibet) Plateau and the Issyk-kul Lake in Soviet Tianshan have been continuously shrinking during the past few centuries. Since the maximum of the Little Ice Age which occurred mainly in the 18th century, glaciers have decreased in area by about 44% in the Urumqi valley. These data and other evidence from glaciers, lakes, etc. clearly indicate that the climatic warming and drying tendency grows stronger in this century and will possibly persist to the early decades of the next century. The growing greenhouse effect due to the increase of CO2 and other related gases will enhance this tendency in the near future. However, should the high temperature period of the early and middle Holocene reappear, the climate would become humid.
Annually-Averaged Polar Sea-Ice Extents During 1978–1987: Northern Extent Decrease and Southern Extent Oscillation
Authors: Gloersen Per , J. Campbell William
Published: September 2017

Recently reported observations of a nine-year decrease in global sea-ice extent, obtained from the Scanning Multichannel Microwave Radiometer onboard the Nimbus-7 satellite during 1978–87 and averaged with an annual running mean, have been separated into Arctic and Antarctic components. The annually-averaged global extent decrease was 2.5%. Here it is shown that the greater part of this decrease occurred in the Arctic where there was a decline of 3.5% with a goodness of fit of 0.54.

Superimposed on this decline was a small oscillation with a period of about four years and an amplitude of about 1%. A significantly smaller and statistically insignificant decrease of 1.2% with a goodness of fit of 0.03 is observed in the annually averaged Antarctic sea-ice extent. However, three large oscillations with amplitudes of about 4% and periods of about three years occurred in phase with three El Niño events.
26-Year High Resolution Profile Of Major Anions In Snow From Coats Land, Antarctica
Authors: Mulvaney R. , Peel D.A. , Reid A.P.
Published: September 2017

In January 1987, an 7.8 m core, with an age at the bottom of 26 years, was collected from a site approximately 150 km inland from Halley Station (77°02.2′S, 22°32′W; altitude 1862 m a.s.l.); 10 m temperature ≈ −30°C; accumulation rate ≈ 14 g cm−2 a−1). The site lies some 140 km from the coast of the Weddell Sea and within the area bounded in winter by the polar vortex.

The core has been analysed at a frequency of ≈28 samples per accumulation year for sulphate, nitrate and chloride, and has been dated stratigraphically from the clear seasonal cycles in non sea salt sulphate (Mulvaney and Peel, 1988). With this resolution it is possible to examine the seasonal pattern of deposition of chemical species and their phase relationships.

Of particular interest is the possibility that ice cores may preserve evidence for disturbances in tropospheric chemistry, associated with the recent spring-time depletion of stratospheric ozone. It has been proposed that this is accompanied by a denitrification of the stratosphere during the winter months, implying enhanced levels of NOX in the late winter/spring troposphere and in precipitation. Our data reveal a strong seasonal signal in nitrate deposition, apparently peaking in spring. Similar behaviour has been reported by Wagenbach and others (1988) for nitrate in the atmospheric aerosol, in a 3-year sequence (1983–86) from Georg von Neumayer Station (70°S, 8°W). There does not appear to be any evidence in our data of an increase in spring-time nitrate deposition since the appearance of the Antarctic ozone hole in 1978.
High Evaporation On Glaciers On The Northwestern Tibetan Plateau
Authors: Ohata Tetsuo , Takahashi Shuhei , Ohno Hiroyuki
Published: September 2017

Quite high amounts of evaporation observed on glaciers in dry Central Asia are one important component in the mass balance of glaciers. During glaciological research at West Kunlun Mountains on the northwestern Tibetan plateau in 1987, high evaporation of more than 2 mm of water per day was observed near the equilibrium line (5800–5900 m a.s.l.) in mid-summer due to dry and windy climate. Annual evaporation is estimated by a semi-empirical method using the full year meteorological data taken by an automatic meteorological station. This value shows that evaporation occupies quite a high percentage within the mass balance near the equilibrium line and on the whole glacier. Discussions will centre on comparison with evaporation data obtained on other glaciers and on the effect of such evaporation in the climate-glacier relation.
Impurity Distributions In Ice Under Different Environmental Conditions
Authors: Wolff Eric , Mulvaney Robert
Published: September 2017

We have shown previously (Mulvaney and others, 1988; Wolff and others, 1988) that some of the impurities in ice are localised. For samples from Dolleman Island in the Antarctic Peninsula, sulphuric acid was found at very high concentrations at the triple junctions (where three grains meet). No such localisation was found for sea salt elements, which are the other major soluble impurity. We believe that the acid is sufficiently concentrated at ice-sheet temperatures to remain liquid, forming a network of sub-micron veins through the ice.

We used a scanning electron microscope (SEM) fitted with an X-ray microanalysis system and a cold stage that holds samples below −160°C. Located at the University of Lancaster, the instrument allows frozen samples to be investigated with elemental analysis carried out at a resolution of the order of 1 micron.

Further experiments have yielded similar results for other samples from the same ice core. However, we have not yet found a method of cutting and cooling the samples that gives quantitatively reproducible data, so that it is too early to say what proportion of the acid in the sample is at the triple junctions.

Nonetheless, we have now also seen S at several triple junctions in ice from Site G in central Greenland. The sample includes part of the material from the 1783 Laki volcanic eruption. We have still to look at samples from other sites, but are reassured that the positive result is not confined to one ice core.

This work, still at a formative stage, has posed some important questions:

(1) For us there is the technical question of how we obtain reproducible quantitative results.

(2) How widespread is the phenomenon, and how much of the acid is at triple junctions? This is the next phase of studies at Lancaster, and is likely to include a study of older ice, and of temperate ice.

(3) Why is the acid at triple junctions, and why is sea salt not found there? This must be due to processes in the atmosphere or snowpack, and is likely to be related to the eutectic temperatures of impurity/water mixtures. Thus the distribution may influenced by changes in climate or chemistry. For instance, Wisconsin-age ice in Greenland is neutral, any acid having reacted with alkali dusts. How did this affect the impurity distribution?

(4) If the distribution does change as a result of a changed environment, does this affect the physical properties of the ice itself? In particular, is the presence or absence of liquid at the junctions a contributory factor to the changes in rheology between Wisconsin and Holocene ice? We are far into the realms of speculation here, but this does have the potential to be an interesting long-timescale feedback to climatic and environmental changes.
An automatic system for controlling snow on roofs
Authors: Tamura Moriaki
Published: September 2017

In Honshu Island, Japan, tremendous amounts of snow falls over a vast area facing the Sea of Japan. The depth of deposited snow sometimes exceeds 2 m, even in urban areas. The weight of snow on roofs can damage conventional wooden houses. It is of great importance, therefore, to monitor and control roof snow loads.

A model system has been developed for controlling snow on roofs. A precipitation detector capable of differentiating between solid and liquid precipitation and a water gauge for detecting the meltwater from a roof are combined to estimate the roof snow load. When the calculated load exceeds a critical value, an electric heater on the roof is energized to melt a portion of the snow. The whole system is controlled by a personal computer. The system was tested for about a month in 1990 with satisfactory results.
The dynamic friction characteristics of a rapidly sheared granular material applied to the motion of snow avalanches
Authors: Dent J.D.
Published: September 2017

A numerical simulation of simple two-dimensional shear of round uniform grains is used to investigate the dynamic friction characteristics of the layer of snow at the base of an avalanche. For steady, uniform flow on a uniform flat surface, the dynamic friction coefficient transmitted through the shear array is found as it varies with the shear speed and normal force applied to the top of the shear layer, and the properties of the particles in the shear layer.

For this simple model, the flow in the shear layer is found to be independent of the total number of layers in the shear flow. A slip plane is formed along which most of the shearing motion takes places, so that the shear is confined to just two layers of particles which slide over one another. In the absence of gravity this slip plane jumps up and down randomly within the shear layer, which is otherwise composed of agitated semi-dispersed particles.
Estimating snow avalanche runout distances from topographic data
Authors: Fujisawa K. , Tsunaki R. , Kamiishi I.
Published: September 2017

To protect rural areas and roads from disasters caused by snow avalanches, avalanche hazard maps are being developed. In Japan, when determining snow avalanche runout distances, empirical values are normally used. These assume that the line-of-sight angle at the starting point of an avalanche, viewed from its runout point, is less than 18° for surface-layer avalanches and less than 24° for full-depth layer avalanches. This rule of thumb ignores topographic features of the slope carrying the large mass of snow. We have made analyses to find a method that can obtain the avalanche runout distance, taking into consideration the longitudinal profiles of the sites, using regression analyses on data from 66 avalanches. The line-of-sight angle can be expressed sufficiently by functions, such as line-of-sight angle between the starting point of an avalanche and a point on its course of flow 10° in gradient, an angle at the starting point of an avalanche, and the curvature of an approximate quadratic curve of topography. Based on statistics for the above relationship, we have established four different ranking categories to classify the degree of hazard. If the starting points of avalanches are known, hazardous areas can automatically be ranked on a basis of topographic data.
A two-dimensional computational model of turbulent atmospheric surface flows with drifting snow
Authors: Liston G.E. , Brown R.L. , Dent J.D.
Published: September 2017

A physically based computational model of drifting snow in two-dimensional terrain is developed. The model considers the case where wind speeds are low enough to neglect the transport of particles from the saltation layer into the turbulent flow field. The model has two distinct parts, one describing the turbulent airflow, and a second describing the mass-transport process and resulting snow-accumulation patterns produced by saltation transport. The turbulent-flow model consists of a general solution of the time-averaged, two-dimensional Navier-Stokes equations, where the k-∊ turbulence model is used to close the system of equations. The turbulent-flow model is coupled to a saltation model to compute the time evolution of the surface wind fields and snowdrift formation in the vicinity of a solid fence. Modeled wind fields and snow-accumulation profiles are similar to published field and experimental data.
Changes in areal extent, elevation and volume of Athabasca Glacier, Alberta, Canada, as estimated from a series of maps produced between 1919 and 1979
Authors: Reynolds J. R. , Young G. J.
Published: September 2017

Changes in planimetric area, elevation and volume were calculated for Athabasca Glacier, Alberta, Canada, below 2400 m elevation for the period 1919–79 from maps produced using aerial or terrestrial photogrammetry. Map contours were digitized and converted into raster digital elevation models (DEMs). Comparison of the models allowed changes in volume and elevation to be estimated. In the time of record, the glacier lost 2.344 × 108 m3 of volume and downwasted significantly.

There are several sources of error associated with DEM generation and construction: source maps have spatially variable uncertainty in vertical estimation, associated with the photogrammetric process used; small errors are introduced in the creation of raster DEMs as a result of fitting surfaces to digitized contours; errors of registration, leading to errors in estimation of vertical change over time, can be of significance, especially when comparing maps produced by different photogrammetric techniques.

These errors are quantified and displayed in transect and map form. Especially with maps only 2 years apart in time, errors are often greater than actual changes in surface elevation. The magnitude of the errors involved in the comparison of maps made with a 2 year interval would suggest that 5 or 10 years between successive mappings might have been more scientifically justifiable and more cost effective.
Numerical simulation of fluctuations of Hintereisferner, Ötztal Alps, since AD 1850
Authors: Schlosser Elisabeth
Published: September 2017

A one-dimensional ice flow model was adapted to reconstruct fluctuations of Hintereisferner, Ötztal Alps, since the last postglacial maximum in the mid-19th century. Both front positions and longitudinal ice thickness profiles were considered.

As forcing function the specific mass balance was used. The model was calibrated with the period 1953–91, because since 1953 the mass balance has been determined directly. For the period before 1953, as a first step so-called dendro-mass balances (derived from tree rings) were used. Then the mass balance was also parameterized as a function of temperature and precipitation from adjacent climate stations. With both forcings Hintereisferner could be reconstructed back to about 1850 with an accuracy that lies within the accuracy of the model (200 m grid-point distance).
Modelling of Last Glacial Maximum ice sheets using different accumulation parameterizations
Authors: Fabre Adeline , Ritz Catherine , Ramstein Gilles
Published: September 2017

We use a three-dimensional thermomechanical ice-sheet model, previously tested on the Greenland ice sheet, to reconstruct Last Glacial Maximum (LGM) ice sheets. We compare the effects on the results of the ice-sheet model of three different accumulation parameterization schemes. In the first and second schemes, LGM precipitation is computed from the present precipitation, taking and not taking into account moisture transport. In the third scheme, LGM precipitation and surface temperatures are computed using outputs of an atmospheric global circulation model (AGCM), treated in anomaly mode.

Results are compared to the last reconstruction of the Northern Hemisphere ice sheets (Peltier, 1994), computed using global rebound rates in a visco-elastic model of the Earth’s crust. The first two accumulation parameterizations do not give satisfactory reconstructions of the LGM ice sheets, since they are unable to compute realistic LGM climatic conditions. The third method gives very satisfactory results, which leads us to conclude that the best way to obtain realistic LGM climatic conditions is to use AGCM outputs.
Volumetric variations of Glacier de Sarennes, French Alps, during the last two centuries
Authors: Valla François , Piedallu Christian
Published: September 2017

Glacier de Sarennes, located in the heart of the French Alps, has been observed closely since 1906 and regularly measured (snow accumulation, ablation and mass balance) since 1948. Several publications have stemmed from this research, such as the 1906 and 1958 glaciological maps and the 1981 and 1991 photogrammetric analyses. In 1992, a field radar campaign determined the ice thickness and allowed the drawing of the bedrock map with reasonable accuracy. The Little Ice Age stage was reconstructed with the bedrock tracks, in 1995.

The above-mentioned documents were digitized, and the computer program Arc-Info permitted the calculation of the successive volume stages occupied by the glacier from 1850 to 1991. Cross-sections and slope profiles illustrate the evolution of the thickness of Glacier de Sarennes during the last 150 years. All of these results, consistent with the variation of the mass balance observed or estimated, show the main conclusion: compared with today, the glacier was about four times more voluminous 90 years ago (i.e. it has lost three-quarters of its ice volume) and five times bigger one and a half centuries ago.
The reaction of mountain glaciers to climatic change under continental conditions
Authors: Kunakhovitch M. G. , Sokalskaya A. M.
Published: September 2017

Data on the distribution of accumulation with elevation were used to calculate ablation, internal accumulation, annual mass balance and glacier runoff for the Tien Shan glaciers with a total area of about 15 500 km2. The altitudinal profile of normalized ablation is approximated by an exponential curve. Mass-balance components and glacier runoff are calculated for the whole possible range of glacier equilibrium-line positions in the major river and lake basins of the Tien Shan.

For steady state it was found that the equilibrium line rises from 3600 m in western areas to 4400 m in the east, whilst the accumulation area ratio and glacier runoff increase eastward from 63% to 71%, and from 600 to 1200 mm, respectively. Losses of meltwater runoff for internal accumulation average 7% (5–11%).

In abnormally warm years, mass balance may reach –2300 mm w. e. in the west and –855 mm in the east and in the internal Tien Shan (Khan Tengry massif). Glacier runoff volume in those years has been estimated at 40 km3 year–1, which is 2.5 times as large as for the steady state.
Surface reflectance of Hintereisferner, Austria, from Landsat 5 TM imagery
Authors: Koelemeijer Robert , Oerlemans Johannes , Tjemkes Stephen
Published: September 2017

Landsat 5 Thematic Mapper observations are used to derive the horizontal distribution of reflectance over Hintereisferner in Austria. To analyze temporal evolution of surface reflectance, three different dates are considered. The retrieval method adopts the linear relation between the planetary and surface reflectance, which follows directly from the principles of invariance. Constants in this linear relation are determined using a simple two-stream radiation model for each of the three days under consideration. From a comparison with observations the retrieved albedo is shown to compare favorably with ground observations.
Airborne bidirectional radiances of snow-covered surfaces in Montana, U.S.A.
Authors: Hall D.K. , Foster J.L. , Irons J.R. , Dabney P.W.
Published: September 2017

Bidirectional radiance measurements of various snow-covered surfaces have been acquired using the Advanced Solid-State Array Spectro-radiometer (ASAS) which was flown on the NASA C-130 aricraft over Glacier National Park, Montana on 14 March 1991. A frozen lake, a snow-covered meadow, a mixed coniferous/deciduous forest and a dense coniferous forest were studied. Knowledge of the bidirectional reflectance characteristics of various snow-covered surfaces is key to calculation of albedo from satellite sensors in the future. While the reflectance characteristics of pure snow targets have been measured from the ground, aircraft and satellites, very few bidirectional reflectance data exist for surface covers of mixed snow and vegetation. Analysis of the 14 March 1991 ASAS data show that the anisotropic reflectance of snow was strong over the snow-covered frozen lake but slightly dampened over the meadow because of the presence of low vegetation. Over the dense coniferous forest, strong backscatter was observed while higher radiances in both the forward and aftward sensor view zenith directions was measured over the mixed forest. Snow that was known to be beneath the coniferous forest canopy was not detected in our data.
Passive microwave measurements of tundra and taiga snow covers in Alaska, U.S.A.
Authors: Sturm Matthew , Grenfell Thomas C. , Perovich Donald K.
Published: September 2017

The microwave emissivity of two snow covers was measured in Alaska in March, 1990. Observations were made on taiga snow near Fairbanks that was 0.83 m thick with a 0.55 m thick basal layer of depth hoar. Other measurements were made on the tundra snow cover at Imnaviat Creek north of the Brooks Range which was 0.27 to 0.64 m thick and consisted of two or more wind slabs overlying a depth hoar layer 0.14 to 0.26 m thick. Density, crystal structure, and grain size were similar in tundra and taiga depth hoar layers.

Emissivity was measured at 18.7 and 37 GHz using radiometers mounted on a 1.5 m tall bipod. Measurements were made on undisturbed snow, and then several snow layers were removed and additional measurements were made. This sequence was repeated until all snow had been removed. Effective emissivity values for the full snow depth ranged from 0.6 (37 GHz, H-pol) to 0.95 (18.7 GHz, V-pol) and were similar for both taiga and tundra snow covers. For both snow covers, there was a marked reduction in the effective emissivity (eeff) from that of the underlying ground with a maximum reduction of about 30%. All of the reduction was found to occur within the depth hoar layer. Maximum reduction in eeff could be caused by a depth hoar layer 0.3 m thick. Overlying wind slab or new snow were nearly “invisible”, increasing the effective emissivity only by a small amount due to self-emittance. Thus, it was difficult to distinguish the two different snow covers on the basis of their emissivity, since both contained 0.3 m of depth hoar or more.
Passive microwave-derived spatial and temporal variations of summer melt on the Greenland ice sheet
Authors: Mote Thomas L. , Anderson Mark R. , Kuivinen Karl C. , Rowe Clinton M.
Published: September 2017

Passive microwave-brightness temperatures over the Greenland ice sheet are examined during the melt season in order to develop a technique for determining surface-melt occurrences. Time series of Special Sensor Microwave/ Imager (SSM/I) data are examined for three locations on the ice sheet, two of which are known to experience melt. These two sites demonstrate a rapid increase in brightness temperatures in late spring to early summer, a prolonged period of elevated brightness temperatures during the summer, and a rapid decrease in brightness temperatures during late summer. This increase in brightness temperatures is associated with surface snow melting. An objective technique is developed to extract melt occurrences from the brightness-temperature time series. Of the two sites with summer melt, the site at the lower elevation had a longer period between the initial and final melt days and had more total days classified as melt during 1988 and 1989. The technique is then applied to the entire Greenland ice sheet for the first major surface-melt event of 1989. The melt-zone signal is mapped from late May to early June to demonstrate the advance and subsequent retreat of one “melt wave”. The use of such a technique to determine melt duration and extent for multiple years may provide an indication of climate change.
Data set of Arctic AVHRR imagery for the study of leads
Authors: Fetterer Florence , Hawkins Jeffrey
Published: September 2017

Under the Office of Naval Research-sponsored Arctic Leads Accelerated Research Initiative (ARI), a data set of Advanced Very High Resolution Radiometer (AVHRR) imagery covering the years 1988 through 1992 is being constructed. Relatively cloud-free imagery is selected from image hardcopies. Each image examined is subjectively ranked on the percentage of each sea or seas it covers, and the cloudiness of the image within each sea. The images are then logged in a spreadsheet. From the spreadsheet, about 20 images per month (for the year 1989) are ordered from the National Oceanic and Atmospheric Administration for processing. The image data are calibrated and mapped to one of two grids, which together cover most of the Arctic at 1 km per pixel. Care has been taken to match the grid and the projection to that of Special Sensor Microwave Imager (SSM/I) data distributed by the National Snow and Ice Data Center (NSIDC). The 1989 data set is complete at this time. Presently, data are distributed to the Remote Sensing Working Group of the ARI. NSIDC will distribute the data set to a wider audience at a later date.
Mapping of glacial motion and surface topography of Hielo Patagónico Norte, Chile, using satellite SAR L-band interferometry data
Authors: Rignot Eric , Forster Rick , Isacks Bryan
Published: September 2017

The first topographic and ice-motion maps of the northwestern flank of Hielo Patagónico Norte (HPN, northern Patagonia Icefield), in Chile, were produced using satellite synthetic-aperture interferometric radar data acquired by NASA’s Spaceborne Imaging Radar C instrument in October 1994. The topographic map has a 10 m vertical precision with a 30 m horizontal spacing, which should be sufficient to serve as a reference for monitoring future mass changes of the icefield. The ice-motion map is accurate to within 4 mm d−1 (or 1 m a−1). The radar-derived surface topography and ice velocity are used to estimate the ice discharge from the accumulation area of four outlet glaciers, and the calving flux and mass balance of Glaciar San Rafael. The results demonstrate the use of SAR interferometry for monitoring glaciological parameters on a spatial and temporal scale unattainable by any other means.
Experimental fracture and mechanical properties of Antarctic ice: preliminary results
Authors: Rist M. A. , Sammonds P. R. , Murrell S. A. F. , Meredith P. G. , Oerter H. , Doake C. S. M.
Published: September 2017

An experimental study of the fracture mechanics and rheology of ice from the Ronne Ice Shelf, Antarctica, is currently being undertaken. The apparent critical stress-intensity factor (or apparent fracture toughness, KQ) for crack propagation has been measured using a three-point bend method for inducing crack growth perpendicular to the axis of cylindrical ice-core specimens. Tensile crack nucleation under applied uniaxial compressive stress has also been evaluated. Both methods have allowed a profile of ice elastic and fracture properties with depth through the ice shelf to be constructed. Preliminary results indicate that the measured elastic modulus increases with depth through the firn and upper meteoric ice before reaching a constant value in the deeper, dense meteoric and basal marine ice. The resistance to fracture, as measured by changes in apparent fracture toughness and crack-nucleation stress, increases with depth right through the firn and meteoric ice layers. A simple fracture mechanics model applied to the Ronne Ice Shelf indicates that crevasses form from small surface cracks, less than 40 cm deep, which quickly grow to depths of 40–60m and then remain stable.
Polythermal modelling of steady states of the Antarctic ice sheet in comparison with the real world
Authors: Hansen I. , Greve R.
Published: September 2017

An approach to simulate the present Antarctic ice sheet with reaped to its thermomechanical behaviour and the resulting features is made with the three-dimensional polythermal ice-sheet model designed by Greve and Hutter. It treats zones of cold and temperate ice as different materials with their own properties and dynamics. This is important because an underlying layer of temperate ice can influence the ice sheet as a whole, e.g. the cold ice may slide upon the less viscous binary ice water mixture.

Measurements indicate that the geothermal heat flux below the Antarctic ice sheet appears to be remarkably higher than the standard value of 42 m W m−2 that is usually applied for Precambrian shields in ice-sheet modelling. Since the extent of temperate ice at the base is highly dependent on this heat input from the lithosphere, an adequate choice is crucial for realistic simulations. We shall present a series of steady-state results with varied geothermal heat flux and demonstrate that the real ice-sheet topography can be reproduced fairly well with a value in the range 50–60 m W m−2. Thus, the physical parameters of ice (especially the enhancement factor in Glen’s flow law) as used by Greve (1995) for polythermal Greenland ice-sheet simulations can be adopted without any change. The remaining disagreements may he explained by the neglected influence of the ice shelves, the rather coarse horizontal resolution (100 km), the steady-state assumption and possible shortcomings in the parameterization of the surface mass balance.
A 1200 year record of accumulation from northern Greenland
Authors: Friedmann Arne , Moore John C. , Thorsteinsson Thorsteinn , Kipfstuhl Josef , Fischer Hubertus
Published: September 2017

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

Relatively large variations in accumulation rate over time are seen in all the cores. We have compared the resulting accumulation-rate record, which should be related to changes in local air temperature over northern Greenland, with Scandinavian tree-ring records and have interpreted the data as showing an early Medieval Warm Epoch, but no pronounced “Little Ice Age” and no unequivocal greenhouse warming effect as yet in northern Greenland.
Arctic and Antarctic precipitation simulations produced by the NCAR community climate models
Authors: Bromwich David H. , Chen Biao , Tzeng Ren-Yow
Published: September 2017

Precipitation predictions from globai-climate models (GCMs) for the ice-covered Arctic Ocean and the ice sheets of Antarctica are among the most important aspects of the inferred response of the polar areas to climate change. It is generally recognized that the atmospheric hydrologic cycle, which includes precipitation as a key part, is one of the components of the climate system that GCMs do not handle particularly well.

The present-day atmospheric-moisture budget poleward of 70° latitude in both hemispheres, as represented by two versions of the NCAR (U.S. National Center for Atmospheric Research) community climate model (CCM1 and CCM2), is compared with observational analyses. The quantities examined on the seasonal and annual timescales are precipitation, evaporation/sublimation and atmospheric poleward moisture transport. The results are discussed in terms of the physiographic and climatic characteristics of both polar regions and how the particular models handle moisture transport: CCM1 uses the positive-moisture fixer and CCM2 the semi- Lagrangian transport. A particularly important test both for models and for observations is the degree to which the independently determined moisture-budget quantities actually balance. Deficiencies of both observations and models are discussed.
Climate, the Antarctic ice sheet and ground heat flux
Authors: Paltridge Garth W. , Zweck Christopher M.
Published: September 2017

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state height h and potential basal temperature Tb. Tb determines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values of h and Tb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.
Antarctic moisture flux and net accumulation from global atmospheric analyses
Authors: Budd W.F. , Reid P. A. , Minty L.J.
Published: September 2017

Previous attempts to derive the Antarctic surface net accumulation distribution from atmospheric-moisture fluxes, in reasonable agreement with the observed distribution, have encountered many difficulties. The present analysis uses the Australian Bureau of Meteorology Global Atmospheric Assimilation and Prediction Scheme (GASP), which has been operational since 1989, to derive the net air-mass and moisture fluxes over the Antarctic. It is shown that the annual mean net surface accumulation closely resembles the glaciologically observed distribution and provides a physical basis for the observed pattern, through the moisture transports. The variations with latitude and elevation and through the annual cycle are also well reproduced. Although some mass-closure errors still exist, they are expected to become insignificant with the new generation of improved analysis schemes. Consequently the atmospheric analyses can provide a sound basis for both assessing the performance of global climate models in simulating Antarctic accumulation rates and monitoring long-term changes which may occur with global warming.
Simulation of past variability in seasonal snow in the Southern Alps, New Zealand
Authors: Fitzharris B.B. , Garr C.E.
Published: September 2017

There are no systematic measurements of seasonal snow in the Southern Alps, New Zealand, so little information is available as to its past variability. To rectify this, a conceptual model is developed that calculates seasonal snow deposition, ablation and accumulation. The model is based on daily temperature and precipitation data from long-established climate stations about the Southern Alps. Output is given as daily specific net balance of snow at five elevation bands from 1000 to 2200 m and as total water stored as seasonal snow over several major river catchments. Model output is in general agreement when tested against the few historical observations of snow and is tuned to the long-term water balance. A chronology of seasonal snow is reconstructed from 1931 to 1993. Area-averaged annual maxima average 366 mm. They show no trend, but large inter-annual variability from less than 200 to over 650 mm w.e. Seasonal snow can peak at any time between September and January.
Measurements of the Radiation Temperature of Antarctic Icebergs and the Surrounding Surface Water
Authors: Foldvik A. , Gammelsrød T. , Gjessing Y.
Published: September 2017

During the Norwegian Antarctic Research Expedition 1978–79, temperature measurements of a number of icebergs and the surrounding surface water were made, using an airborne precision radiation thermometer. All icebergs were embedded in cold water-masses with temperatures generally below 0°C and thus the observed temperature anomalies were relatively small, ΔT ≈ 1 deg. Examples of the influence of icebergs on the sea surface temperature including a possible example of upwelling will be shown. The temperature of the snow-covered iceberg surface was almost constant with individual variations ΔT ≈ 0.2 deg. Local minima indicative of snow-covered crevasses were observed.
The Flexural Response of a Tabular Ice Island to Ocean Swell
Authors: Goodman D. J. , Wadhams P. , Squire V. A.
Published: September 2017

Measurements of surface strain and vertical heave responses to swell were made on a tabular ice island in Kong Oscars Fjord, east Greenland, in September 1978. At two sites surface strain was measured with a wire strainmeter of 2 m gauge length, and heave was measured with a vertical accelerometer. While the first site was occupied a simultaneous measurement of ambient wave energy was made with a wave buoy. The results show that the ice island flexes and heaves in response to the longest component only of the forcing wave field, at periods above 16 s, and with a mean strain amplitude of the order of 5 × 10−7. The results are compared with theoretical calculations of the response of a thick floating beam. In the light of the theory, the flexural behaviour of tabular icebergs and sea-ice floes is considered and their critical size ranges in relation to sea state are estimated.
Numerical Models for the Prediction of Iceberg Drift
Authors: Napoleoni J. G.
Published: September 2017

In order to avoid the risk of icebergs colliding with drilling vessels and installations in the Labrador Sea, it would be useful to predict iceberg drift. Relevant information on fluid dynamics is summarized, followed by a discussion of various drift models. After commenting on the numerical results obtained with these models, a method is proposed for analysing past trajectories of an iceberg in order to determine coefficients necessary for predicting its drift. The theoretical results are then compared with drift and sea-current and wind data obtained in the Labrador Sea. If accurate prediction of iceberg drift is to be achieved, reliable prediction of oceanic factors is just as important as a knowledge of iceberg characteristics. The techniques developed and tested in the Labrador Sea are helpful whether icebergs are considered as a problem or as a desirable resource.