bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical avalanche-runout estimation for short slopes in Canada
Authors: Jones Alan S.T. , Jamieson Bruce 
Published: November 2007

AbstractTo develop avalanche runout models for short slopes, field measurements were made at 48 short-slope avalanche paths located in the Coast, Columbia and Rocky Mountains of western Canada, and at several paths in eastern Canada. Field studies included detailed topographic surveys and estimation of the extreme runout position in each path. A statistical runout model was developed using the runout ratio method, for which runout ratios from the four mountain ranges are well fit by an extreme-value type I (Gumbel) distribution when the β point is defined at the uppermost point where the slope is 24°. A second model was developed by regressing the α angle for the extreme runout position on numerous terrain variables. This regression model uses three predictor variables that can be easily measured in the field or on topographic maps. Length-scale effects were noted in both models, but are more pronounced in the runout ratio model. A comparison of models developed using the two methods shows that the runout ratio model estimates more conservative (longer) runout distances than the regression model for most threshold probabilities. Data from 13 additional paths from Switzerland and Québec, Canada, are used to test the models.
Large-scale snow instability patterns in western Canada: first analysis of the CAA–InfoEx database 1991–2002
Authors: Gruber Urs , Hägeli Pascal , McClung David M. , Manners Evan 
Published: November 2007

AbstractDaily weather measurements, snow stability assessments and recorded weak layers of 23 stations covering an observation area of approximately 40 000 km2 in western Canada were analyzed. The study area includes three major mountain ranges with different snow climates. All stations included assess the stability of the snow cover. However, the focus of the avalanche safety program of the different types of operation (heli-ski operation, ski resorts and parks) varies significantly. The three stations in the Coast Mountains show the highest snow stability, followed by the South Columbia Mountains and then the North Columbia and Rocky Mountains. The weather data were analyzed to try to explain some of these differences. Intensive snowfall at relatively high temperatures proved to be important for the higher snow stability over the season in the Coast Mountains. Theweak-layer data were used to complement the snow stability assessments. Most persistent weak layers were reported in the Columbia Mountains, followed by the three stations in the Coast Mountains and trailed by the Rocky Mountains. Although some weather observations indicate climatic reasons for the smaller number of weak layers in the Rocky Mountains, it cannot be excluded that these differences are also related to the different type of operations.
Calculation of two-dimensional avalanche velocities from optoelectronic sensors
Authors: McElwaine Jim N. 
Published: November 2007

AbstractOptoelectronic sensors using infrared light-emitting diodes and photo-transistors have been used for measuring velocities in snow avalanches for more than 10 years in America, Europe and Japan. Though they have been extensively used, how they should be designed and how the data should be processed has received little discussion. This paper discusses how these sensors can be applied to measure two-dimensional velocities. The effects of acceleration and structure in the underlying field of reflectance are carefully accounted for. An algorithm is proposed for calculating the continuous velocity vector of an avalanche, and a sketch of the mathematical analysis given. The paper concludes by suggesting design criteria for such sensors.
Effect of summer snowfall on glacier mass balance
Authors: Oerlemans Johannes , Klok E. J. (Lisette) 
Published: November 2007

AbstractIt has been postulated that heavy summer snowfalls have a large impact on the mass balance of mid-latitude glaciers, because they simultaneously add mass to the glacier and reduce the amount of absorbed solar radiation. An automatic weather station (AWS) on the snout of Morteratschgletscher, Switzerland, registered a large summer snowfall event on 10–11 July 2000. Sonic rangers recorded about 20 cm of new snow on the snout and about 50 cm near the equilibrium line. We have used data from the AWS to study the impact on the melt process. The data show that in the ablation zone of the glacier the snow has melted and the effect on the albedo has disappeared after about 5 days. The suppression of the melt by the high albedo of the fresh snow is an important effect. For the ablation zone we find a feedback factor of about four, that is, the total effect of the snowfall event on the annual specific balance is about four times the amount of mass added during the event. We have also used a mass-balance model with 25 m spatial resolution to assess the impact of the snowfall on the net balance of the entire glacier. We find the strongest effects just below the equilibrium line. Averaged over the glacier, the amount of snow deposited was 224 mm w.e. The calculated effect on the total mass balance of the glacier is 354 mm w.e.
Changes in the shear strength and micro-penetration hardness of a buried surface-hoar layer
Authors: Birkeland Karl W. , Kronholm Kalle , Schneebeli Martin , Pielmeier Christine 
Published: November 2007

AbstractWe investigated a buried surface-hoar layer using the SnowMicroPen (SMP), an instrument designed to measure detailed snowpack profiles.We collected data from two adjacent parts of a slope 6 days apart. In addition, one manual snowpack profile was sampled each day, as well as 50 quantified loaded column tests (QLCTs) which provided an index of shear strength. For the SMP data, a 900 m2 area was sampled on both days in a grid with points 3 mapart, with some sub-areas of more closely spaced measurements. We collected 86 SMP profiles on the first day and 129 on the second day. Our analyses involved manually locating layer boundaries and calculating statistics for the force signal through the surface-hoar layer. The shear strength index increased by 40% between the two sampling days, but the SMP data show no statistical difference in layer thickness, and the mean, minimum, median, and a variety of percentile measures of the SMP force signal through the layer also do not change. Interestingly, the maximum hardness, and the variance and coefficient of variation of the SMP signal, increased. Since the small SMP tip might only break one or a couple of bonds as it passes through the weak layer, we interpret these changes as being indicative of increasing bond strength. Though we cannot specifically tie the increasing maximum hardness of the SMP signal to our QLCT results, our work suggests that the maximum SMP signal within buried surface-hoar layers may be useful for tracking increases in the shear strength of those layers.
Numerical study of the time development of drifting snow and its relation to the spatial development
Authors: Nemoto Masaki , Nishimura Kouichi , Kobayashi Syunichi , Izumi Kaoru 
Published: November 2007

AbstractThe time evolution of drifting snow under a steady wind is estimated using a new numerical model of drifting snow. In the model, Lagrangian stochastic theory is used to incorporate the effect of turbulence on the motion of drifting-snow particles. This method enables us to discuss both the saltation and the suspension process. Aerodynamic entrainment, grain/bed collision (splash process), wind modification and particle size distribution are also taken into account. The calculations show that the time needed by the total mass flux to reach a steady state appears to be 3–5 s. Vertical profiles of horizontal mass flux near the surface show a similar tendency. In contrast, it takes >50 s for the wind speed and the whole mass-flux profile to reach a steady state. This longer time depends on the time-scale of the turbulent diffusion, which is responsible for the mass flux extending to an order of a few meters in height. Applying Taylor’s hypothesis, the estimated length scale at which drifting snow reaches equilibrium is around 400 m. This result is comparable with previously reported field observations.
Hierarchy theory as a conceptual framework for scale issues in avalanche forecast modeling
Authors: Hägeli Pascal , McClung David M. 
Published: November 2007

AbstractAlthough scale issues have been defined to be one of the most crucial topics in geosciences, they have received only limited attention in avalanche research. A thorough understanding of these issues in avalanche forecasting, however, is fundamental for the development of useful prediction models. After the definition of relevant terms, the different aspects of scale issues are introduced in detail. We present hierarchy theory (Ahl and Allen, 1996) as a potential framework for the multi-scale characteristics of the avalanche phenomenon. We suggest a temporal hierarchy, where the main contributing factors are ordered into seven levels according to their temporal-scale characteristics with respect to avalanche forecasting. Within each level there are individual spatial hierarchies, which result in a two-dimensional structure. This process-oriented framework is compared to the data classification scheme of La Chapelle (1980), which is based on informational entropy. Scale issues in prediction modeling and the consequences of the new framework for modeling efforts are discussed in detail.
Implications of spatial distributions of snow mass and melt rate for snow-cover depletion: theoretical considerations
Authors: Essery Richard , Pomeroy John 
Published: November 2007

AbstractSnow becomes patchy while melting, giving a heterogeneous surface with large contrasts in characteristics such as albedo. It is therefore necessary for surface schemes used in atmospheric and hydrological models to represent the influence of heterogeneities in snow cover on scales smaller than the model grid; this is typically done by introducing a snow-cover depletion (SCD) curve relating fractional snow cover to average depth. Here, ad hoc functional forms which have been used for this relationship are first compared with forms obtained for an assumed initial snow distribution undergoing homogeneous melt. The energy available for melt may be heterogeneous, however, and can be influenced by factors that also influence snow distribution, such as slope, aspect and vegetation cover. The modification of SCD curves by spatial variations in melt energy is investigated, and resulting curves are found to be similar to those which would be given by homogeneous melting of a snow cover with greater initial variance. This influence is increased by any negative correlation between snow depth and melt rate.
Glacier winds on Vatnajökull ice cap, Iceland, and their relation to temperatures of its lowland environs
Authors: Björnsson Helgi , Gudmundsson Sverrir , Pálsson Finnur 
Published: November 2007

AbstractDuring the ablation season, the ice cap Vatnajökull (8100 km2) develops its own microclimate that we describe by meteorological data collected during the summers of 1994-2003. Persistent glacier winds are generated down the melting ice cap, whose variations in speed can be related empirically to the temperature fluctuations of the lowland environs of the ice cap. This suggests that climate warming would be accompanied by stronger glacier winds down the outlets of Vatnajökull, producing stronger turbulent fluxes that might amplify the melting rates in the lower ablation areas.
Multi-decadal record of ice dynamics on Daugaard Jensen Gletscher, East Greenland, from satellite imagery and terrestrial measurements
Authors: Stearns Leigh A. , Hamilton Gordon S. , Reeh Niels 
Published: November 2007

AbstractThe history of ice velocity and calving front position of Daugaard Jensen Gletscher, a large outlet glacier in East Greenland, is reconstructed from field measurements, aerial photography and satellite imagery for the period 1950-2001. The calving terminus of the glacier has remained in approximately the same position over the past ∼50 years. There is no evidence of a change in ice motion between 1968 and 2001, based on a comparison of velocities derived from terrestrial surveying and feature tracking using sequential satellite images. Estimates of flux near the entrance to the fjord vs snow accumulation in the interior catchment show that Daugaard Jensen Gletscher has a small negative mass balance. This result is consistent with other mass-balance estimates for the inland region of the glacier.
Estimating the mass balance of Vatnajökull, Iceland, from NOAA AVHRR imagery
Authors: Calluy G.H.K. , Björnsson H. , Greuell J.W. , Oerlemans J. 
Published: November 2007

AbstractWe investigate the possibility of obtaining the mass balance of Vatnajökull, Iceland, from US National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) albedo images for the years 1991-2002. De Ruyter de Wildt and others (2002) demonstrated that the mean potential absorbed radiation (〈Qpot,net〉) averaged over the melting season correlates well with the mean specific mass balance and that 〈Qpot,net〉 can be estimated from the evolution of the surface albedo. Here, we improve the retrieval method of de Ruyter de Wildt and others (2002) by introducing the more realistic 6S atmospheric transfer model and by adding the latest narrow-to-broadband (NTB) albedo conversion equations. Bidirectional reflectance distribution functions for both ice and snow are used where appropriate. We show that the choice of the NTB conversion equations greatly influences the calculated 〈Qpot,net〉. Measured mass balance correlates well with 〈Qpot,net〉 if enough cloud-free images can be found through the year and if the spatial variation in measured mass balances is high enough. The correlation coefficient for all drainage basins combined is 0.92, with a residual standard deviation of 0.18 m w.e. We present an estimated mass-balance series for the whole of Vatnajökull based on our findings. Switching between different AVHRR instruments over time may cause serious errors in the calculated mass balance.
Analysis of the first jökulhlaup at Blåmannsisen, northern Norway, and implications for future events
Authors: Engeset Rune Verpe , Schuler Thomas Vikhamar , Jackson Miriam 
Published: November 2007

AbstractThe first known jökulhlaup from the Blåmannsisen ice cap in northern Norway began on 6 September 2001. It lasted 35 hours and emptied the lake Øvre Messingmalmvatn (∼4.0 × 107m3). Before the event, the lake drained steadily via a rock spillway into Sweden. The water from the jökulhlaup drained into the hydropower reservoir Sisovatn, and so was financially beneficial to Norway. Glaciological data show evidence of glacier retreat and thinning during the last four decades. Glacier thickness decreased in the ablation zone, reducing ice-barrier stability. The lake drained at a water level 40 m below that required to equalize the ice overburden pressure. Measurements show an ice-barrier thinning of 3.5 m since the jökulhlaup occurred. Climate scenarios indicate future negative mass balance and further thinning. The lake volume was 82% full 2.5 years after the event, suggesting a probable repeat interval of 3 years. Future jökulhlaups may be triggered at lower water levels and produce lower discharges.
Ice-volume changes (1936–1990) and structure of Aldegondabreen, Spitsbergen
Authors: Navarro F.J. , Glazovsky A.F. , Macheret Yu.Ya. , Vasilenko E.V. , Corcuera M.I. , Cuadrado M.L. 
Published: November 2007

AbstractAldegondabreen is a small valley glacier, ending on land, located in the Grønfjorden area of Spitsbergen, Svalbard. Airborne radio-echo sounding in 1974/75, using a 440 MHz radar, revealed a polythermal two-layered structure, which has been confirmed by detailed ground-based radio-echo sounding done in 1999 using a 15 MHz monopulse radar. The 1999 radar data reveal an upper cold layer extending down to 90m depth in the southern part of the glacier, where the thickest ice (216 m) was also found. A repeated pattern of diffractions from the southern part of the glacier, at depths of 50–80 m and dipping down-glacier, has been interpreted as an englacial channel which originates in the temperate ice. From joint analysis of the 1936 topographic map, a digital elevation model constructed from 1990 aerial photographs and the subglacial topography determined from radar data, a severe loss of mass during the period 1936–90 has been estimated: a glacier tongue retreat of 930 m, a decrease in area from 8.9 to 7.6 km2, in average ice thickness from 101 to 73 m and in ice volume from 0.950 to 0.558 km3, which are equivalent to an average annual balance of –0.7 mw.e. This is comparable with the only available data of net mass balance for Aldegondabreen (–1.1 and –1.35m w.e. for the balance years 1976/77 and 2002/03) and consistent with the 0.27˚C increase in mean summer air temperature in this zone during 1936–90, as well as the warming in Spitsbergen following the end of the Little Ice Age (LIA), and the general glacier recession trend observed in this region.
Influence of upper-air conditions on glaciers in Scandinavia
Authors: Rasmussen L.A. , Conway H. 
Published: November 2007

AbstractA simple model using once-daily US National Centers for Environmental Prediction/US National Center for Atmospheric Research (NCEP/NCAR) re-analysis upper-air values estimates winter balance, summer balance and net balance at ten glaciers in Norway and two in Sweden with 0.37 ≤ r2 ≤ 0.90. The October-May Arctic Oscillation (AO), an index of sea-level pressure (SLP) in the Northern Hemisphere, correlates with winter balance and net balance with 0.09 ≤ r2 ≤ 0.82, lower than the model in all but 3 of the 24 cases. The October-May North Atlantic Oscillation (NAO), an SLP gradient in the North Atlantic, has lower correlations than the AO for all but 5 of the 24 cases. At all ten glaciers with records beginning before 1987, net balance became more positive after 1988, owing mainly to increased winter balance, with summer balance changing little. Although winter temperatures increased, they were still well below freezing, so the rain-snow division of the precipitation was only slightly affected. Increase in winter balance was due to increased precipitation caused by a change in atmospheric circulation, resulting in more frequent westerly flow concurrent with the warming. At 850 hPa, westerly flow is ≈2.5˚C warmer than easterly flow; westerly flow warmed by ≈ 0.3 °C, easterly by ≈ 0.7 °C. Both the AO and NAO, with which winter balance is positively correlated at all 12 glaciers, were more positive after 1988.
Seasonal patterns of velocity and strain across the tongue of the polythermal glacier midre Lovénbreen, Svalbard
Authors: Rippin David , Willis Ian , Arnold Neil 
Published: November 2007

AbstractTerrestrial surveys to 17 markers distributed across the tongue of the polythermal glacier midre Lovénbreen, Svalbard, are used to calculate annual and seasonal (summer 1998, autumn/winter/ spring 1998/99, summer 1999) patterns of surface velocity and strain. The annual period and the three seasonal periods have similar velocity azimuths and patterns, with fastest velocities along the centre line and in the upper tongue. Velocities in both summers are of similar magnitude, and greater than those in the autumn/winter/spring period. In all periods, longitudinal compression (increasing towards the snout) and transverse and vertical extension dominate the surface strain field. However, an area of longitudinal extension develops in the middle tongue during the 1998 summer. Surface strain patterns are used to estimate the components of the force balance. Basal drag is the dominant force resisting flow, but patterns are rather different between the three seasons. In summer 1998, a slippery spot in the upper-middle tongue is confined to the central part of the glacier. In autumn/winter/spring, this slippery spot has expanded towards the western glacier margin. In summer 1999, it has disappeared, and a slight sticky spot now covers virtually the entire upper and middle tongue. The location and extent of the slippery spot are explained in terms of the distribution of warm and cold ice, and the location and morphology of the subglacial drainage system, which control the patterns of water pressure beneath the glacier tongue.
An estimation of snow accumulation on Svalbard glaciers on the basis of standard weather-station observations
Authors: Grabiec Mariusz 
Published: November 2007

AbstractWinter precipitation in the form of snow is the major factor determining accumulation on Arctic glaciers. In this paper, I present a simple method to assess snow accumulation on the glaciers of Svalbard. I deduce snow accumulation from the sum of winter precipitation and the fraction of precipitation of different types at a reference weather station. The accumulation is then converted to a relevant point on the glacier, using an accumulation gradient and a location coefficient. I apply this algorithm of accumulation assessment to eight glaciers of southern and central Spitsbergen using data from 23 seasons. On the basis of measured accumulation data, the mean error of the calculated accumulation, with no distinction of precipitation types, amounted to 23%. When the distinction between precipitation types is used for glaciers of southern Spitsbergen, the average error of estimation was 19%. Errors result from factors influencing accumulation distribution over the glacier elevation profile (e.g. glacier topography, orography of its surroundings, precipitation inversion). Application of this accumulation algorithm may provide a crucial method of estimating mass balance for glaciers not included in permanent monitoring.
Glacier mass-balance and length variation in Norway
Authors: Andreassen Liss M. , Elvehøy Hallgeir , Kjøllmoen Bjarne , Engeset Rune V. , Haakensen Nils 
Published: November 2007

AbstractThe importance of glaciers in mainland Norway for runoff is reflected in the extensive glacier measurement record. Mass balance has been measured for 42 glaciers. Length (or front-position) records exist for about 60 glaciers, and nearly half of these are presently measured. The mass-balance and front-position data have been analyzed with respect to spatial and temporal variations. The maritime glaciers with a large annual mass turnover have had a mass surplus between 1962 and 2000. In contrast, the continental glaciers with smaller summer and winter balances had a mass deficit over the same period. Since 2001 all monitored glaciers have had a marked mass deficit. The Norwegian glaciers have all retreated during the 20th century. However, both local and regional variations have been observed. Advances were recorded around 1910, around 1930, in the second half of the 1970s and around 1990. This last advance stopped in most glaciers at the turn of the century.