Soft Snow Research Articles

Comparative analysis of FEM tire-soft snow interaction and theoretical model based on Bekker’s coefficients

Tire-deformable terrain interaction is a complex phenomenon that has proven difficult to characterize accurately and comprehensively using numerical models. While researchers have attempted to develop various numerical models to estimate tire behavior on deformable terrain, the most accurate models to date rely on empirical data and are only applicable to specific rolling conditions. In this research paper, a comparison between theoretical mechanics and a finite element method (FEM) model of a rigid tire rolling on a layer of soft snow is presented. The goal is to compare the data obtained from the FEM tire-soft snow interaction analysis with the data generated by a theoretical numerical model. The FEM snow model is developed using the Drucker-Prager cap material model while the tire is assumed rigid. The assumption of the rigid tire can provide reasonably accurate results in the case of the soft snow interaction model. The theoretical pressure-sinkage coefficients of the Bekker equation (kc, kϕ and n) for soft snow are calculated by simulating vertical penetration tests in the FEM snow model. The results of the pressure distribution and rolling resistance due to compaction obtained by the FEM and the theoretical model results are then compared.

Perlite Has Similar Diffusion Properties for Oxygen and Carbon Dioxide to Snow: Implications for Avalanche Safety Equipment Testing and Breathing Studies

On average, one hundred people die each year under avalanche snow. Despite extensive global research on gas exchange in buried avalanche victims, it remains unclear how the diffusion of respiratory gases affects survival under avalanche snow. This study aims to determine how oxygen and carbon dioxide diffuse through snow, as well as through wet and dry perlite, which may serve as a surrogate for avalanche snow. A custom-made apparatus to study the diffusion of respiratory gases consisted of a plastic cylinder (1200 mm long, ID 300 mm) with 13 gas sampling needles evenly spaced along the axis of the cylinder filled with the tested material. Following 60 min of free diffusion, gas samples were analyzed using a vital signs monitor with a module for respiratory gas analysis (E-CAiOVX, Datex-Ohmeda, GE Healthcare, Chicago, IL, USA). A combination of 16% oxygen, 5% carbon dioxide, and 79% nitrogen was used. The rates of diffusion for both respiratory gases were comparable in snow and both forms of perlite. Oxygen propagated faster than carbon dioxide. Due to similar diffusion characteristics to snow, perlite possesses the potential to stand in as an effective substitute for soft snow for the study of respiratory dynamics, for conducting breathing experiments, and for testing avalanche safety equipment.

Lemming winter habitat: the quest for warm and soft snow.

During the cold arctic winter, small mammals like lemmings seek refuge inside the snowpack to keep warm and they dig tunnels in the basal snow layer, usually formed of a soft depth hoar, to find vegetation on which they feed. The snowpack, however, is a heterogenous medium and lemmings should use habitats where snow properties favor their survival and winter reproduction. We determined the impact of snow physical properties on lemming habitat use and reproduction in winter by sampling their winter nests for 13years and snow properties for 6years across 4 different habitats (mesic, riparian, shrubland, and wetland) on Bylot Island in the Canadian High Arctic. We found that lemmings use riparian habitat most intensively because snow accumulates more rapidly, the snowpack is the deepest and temperature of the basal snow layer is the highest in this habitat. However, in the deepest snowpacks, the basal depth hoar layer was denser and less developed than in habitats with shallower snowpacks, and those conditions were negatively related to lemming reproduction in winter. Shrubland appeared a habitat of moderate quality for lemmings as it favored a soft basal snow layer and a deep snowpack compared with mesic and wetland, but snow conditions in this habitat critically depend on weather conditions at the beginning of the winter. With climate change, a hardening of the basal layer of the snowpack and a delay in snow accumulation are expected, which could negatively affect the winter habitat of lemmings and be detrimental to their populations.

Drone-Borne Ground-Penetrating Radar for Snow Cover Mapping

Ground-penetrating radar (GPR) is one of the most commonly used instruments to map the Snow Water Equivalent (SWE) in mountainous regions. However, some areas may be difficult or dangerous to access; besides, some surveys can be quite time-consuming. We test a new system to fulfill the need to speed up the acquisition process for the analysis of the SWE and to access remote or dangerous areas. A GPR antenna (900 MHz) is mounted on a drone prototype designed to carry heavy instruments, fly safely at high altitudes, and avoid interference of the GPR signal. A survey of two test sites of the Alpine region during winter 2020–2021 is presented, to check the prototype performance for mapping the snow thickness at the catchment scale. We process the data according to a standard flow-chart of radar processing and we pick both the travel times of the air–snow interface and the snow–ground interface to compute the travel time difference and to estimate the snow depth. The calibration of the radar snow depth is performed by comparing the radar travel times with snow depth measurements at preselected stations. The main results show fairly good reliability and performance in terms of data quality, accuracy, and spatial resolution in snow depth monitoring. We tested the device in the condition of low snow density (<200 kg/m3) and this limits the detectability of the air–snow interface. This is mainly caused by low values of the electrical permittivity of the dry soft snow, providing a weak reflectivity of the snow surface. To overcome this critical aspect, we use the data of the rangefinder to properly detect the travel time of the snow–air interface. This sensor is already installed in our prototype and in most commercial drones for flight purposes. Based on our experience with the prototype, various improvement strategies and limitations of drone-borne GPR acquisition are discussed. In conclusion, the drone technology is found to be ready to support GPR-based snow depth mapping applications at high altitudes, provided that the operators acquire adequate knowledge of the devices, in order to effectively build, tune, use and maintain a reliable acquisition system.

Sexual Dimorphism and Adaptations in the Forelimb of the Snow Leopard ( Panthera uncia )

Snow leopards (Panthera uncia) are notoriously difficult to research and classified as vulnerable by the IUCN. There are only 5,000 mature individuals left inhabiting the rugged terrains of Afghanistan, China, Mongolia, and Uzbekistan. P. uncia is unique compared to other felids because it lives in harsh winter climates, attacks by pouncing from above, and scales great steep slopes in the snow instead of hunting in packs or across long distances. In this study, two specimens of P. uncia (1M/1F) were dissected, and their forelimb myology thoroughly documented. Findings revealed notable, sexually dimorphic and functional differences in the forelimb of P. uncia compared to other pantherine felids. Male snow leopards generally exhibit greater bone mass and more extensive muscle attachments, useful for male-male competition and other situations of increased aggression. Despite the larger body mass of our P. uncia male specimen (39 kg vs. 36 kg), most of the forelimb muscle masses of the male were comparable to the female, indicating that his forelimb muscles were relatively smaller for his body size. In the male, m. rhomboideus pars cervicalis was stouter and more robust than m. rhomboideus pars thoracis, and had an expanded origin compared to the female. This difference could allow for more powerful scapular retraction during grappling with prey or an adversary. M. triceps brachii caput longum and laterale was longer in the male, resulting in a stronger lever for extension of the elbow. The seven subdivisions of mm. pectorales in the male were organized from superficial to deep, versus eight subdivisions arranged from cranial to caudal in the female. The mm. pectorales of the male did not insert onto the lesser tubercle of the humerus, and the muscles bellies exhibited less fusion. The pectoral and scapular musculature of P. uncia are enlarged compared to other pantherines. This morphology likely provides extra forelimb power and stability for climbing steep terrains. Muscle pectoralis profundus of P. uncia is substantially larger than in other felids with five bellies, and only one belly was observed for m. pectoralis superficialis. This configuration may be helpful for climbing and pouncing. P. uncia was found to possess a diminutive bony clavicle, which may provide stability to the forelimb. M. brachialis had three bellies and fused with m. cleidobrachialis, and the m. biceps brachii tendon of insertion bifurcated to attach on both the ulna and radial tuberosity. All bellies of mm. brachialis, pectoralis superficialis, and cleidobrachialis attached to the lateral bifurcation of the m. biceps brachii tendon. Additional muscular heads and insertions around the elbow provide stability and leverage to the joint. This morphology suggests a greater need for power and stability in the forelimbs of P. uncia and may help with scaling through rugged terrain and manipulation of prey. Intrinsic manus muscles are enlarged, forming a widened surface area to distribute body weight while walking on soft snow.

Functional Adaptations in the Forelimb of the Snow Leopard (Panthera uncia).

The snow leopard (Panthera uncia) is anatomically and physiologically adapted for life in the rocky terrain of alpine zones in Central and South Asia. Panthera uncia is scansorial, and typically hunts solitarily by using overhead ambush of prey, rather than the typical stalking pattern of other large pantherines. In this study, we conducted dissections, detailed documentation, and illustrated the forelimb anatomy of two adult P. uncia specimens (1M/1F). Qualitative and quantitative data revealed an intriguing combination of functional adaptations illustrating a balance between the diverse demands of head-first descent, pouncing, climbing across rocky terrain, restraint of large prey, rapid pursuit, and navigating deep snow. In many forelimb proportions, P. uncia is intermediate between the cursorial Acinonyx jubatus (cheetah) and the scansorial forest dwelling Panthera onca (jaguar). Enlarged scapular and pectoral musculature provide stability to the shoulder girdle during grappling with large prey, as well as support during jumping and climbing. A small, unarticulated bony clavicle may provide greater stability to the forelimb, while still allowing flexibility. In the brachium and antebrachium of P. uncia, there is a functional compromise between the powerful grip needed for grasping large prey and the stability necessary for rapid pursuit of prey over uneven, rocky terrain. A unique bifurcation in the tendon of m. biceps brachii may provide additional functional stability at the radiohumeral joint. Intrinsic muscles of the palmar manus are broad and fleshy, acting as an enlarged surface area to evenly distribute body weight while walking on soft snow. However, muscles that act to provide fine manual manipulation are reduced, as in other large prey specialists. Overall, P. uncia displays morphological adaptive parallels with scansorial, large prey specializing pantherines, such as P. onca, while also showing adaptations for running.

Effect of flexural stiffness distribution of a ski on the ski–snow contact pressure in a carved turn

The design of the flexural stiffness distribution of a ski is one of the important factors in its development. On the other hand, the ski–snow contact pressure during a turn is thought to be an important factor in a skier’s feeling. However, the relationship between the flexural stiffness distribution and ski–snow contact pressure has not been made clear. The purpose of this study was to understand how flexural stiffness distribution affects the contacting pressure, applying load, and ski–snow contacting condition through measurement on these items. The measurement system consisted of a ski deflection sensor beam with bending sensors, pressure sensors installed near the ski edge, and four points of load cells connected between the binding plate and the ski. Measurements were performed on the different flexural stiffness distributions of Skis A and B on hard snow and soft snow surfaces. The peak of the flexural stiffness of Ski A was on the boot center, and Ski B was stiffer with a peak under the heel of the boot. An increase in the flexural stiffness under the heel of the boot for Ski B caused less deflection in the rear part of the ski, and the applied force from the binding plate shifted forward. By fitting the ski deflection on the snow groove, so the rear section of the ski after the pressure peak fitted on the sliding surface of the snow groove, the compression zone increased and the sliding zone was reduced in Ski B. The pressure peak in Ski A was under the boot center, whereas, for Ski B it was behind the boot center. These results show that changes in flexural stiffness distribution alter ski deflection and ski–snow contact pressure.

Portable bevameter for measuring snow properties in field

Mechanical properties of snow related to snowmobiles or similar lightweight tracked vehicles aren't widely researched today and it is difficult to find data. One challenge is that snow properties constantly are changing due to aging, climate conditions and location. Also the measuring procedure is difficult since aged snow often contains layers with various densities and hardness. Soil is to some extent similar to snow, in the context that both are granular materials. The bevameter is a popular device for measuring soil properties, however this device needs to be scaled in order to meet criteria of target for research, i.e. in this case snowmobiles. In this paper a new type of portable bevameter is presented, which is designed and built for measuring snow properties in the field. Results from initial tests are also presented. The aim with the bevameter is to measure snow properties which can be used to simulate the interaction between a snowmobile and soft snow. The designed bevameter can be towed with one snowmobile to the field to execute measurements. One full set of test results is introduced and parameters for simulations are extracted from the result data. The parameters from the data were usable but the quality of the measurements can be improved. One problem with the data collected was noise, which was caused by the interaction between the mechanical parts and the low mass of the bevameter. Furthermore, the usability can be improved by reducing cables which can be hard and fragile during cold weather and by replacing the laser distance-sensor with a string wire potentiometer which isn't sensitive to snow dropping in the measurement area. With some improvements the constructed bevameter is a very useful tool which can be used for field measurements to determine snow properties for snowmobile-size vehicle simulations.

Two Poems

On My Way to Cantonese Class I pass under century-old banyans on Nathan Road, their scaly bark studded with ferns, trunks leaning against iron frames. I weave among shoppers ducking air-conditioner rain. M’ ho yi si – Excuse me I mutter as an old lady, with grey bun, elbows past. I am on my way to Cantonese class. After twenty years in Hong Kong Garbage has become laap sap for me. The fermenting fusion of durian, chow fan, and chicken wings smells the same in any language. Yet I long to uncover more layers of Hong Kong’s midden heap. In Cantonese class I ask too many questions. The teacher is kind, but I stall the lesson. The blond Brit next to me taps his foot in irritation. M’ ho lam gam doh – Don’t think too much the teacher writes on the whiteboard in both languages, stares directly at me. Memorize the measure words with each noun. Test next week! Sweat beads on my upper lip. Will I pass? I often get them wrong. Such hard work as my memory gapes like a sinkhole in an old district, exposing tree roots, shards of blue and white porcelain. What a time to learn that Cantonese is not a romance language. After class, I wait at the red light. A gangly young girl in a pink tutu, pink tights, matching trainers on wheels, flashing hazard lights on her heels, pushes past me to cross. M’ ho yi si – Excuse me she says. So polite! Siu sum, I call – Be careful! She pauses at the traffic island, takes my advice without glancing at my face to see who warns her. COVER FEATURE HONG KONG Two Poems by Kate Rogers Lamma Island Tofu-fa On the broken trail to Mot tat a field of white ginger lilies flags us down. We shrug off our packs. Huddled among ruins to our left, a stone house red clay roof sloping, doorway gaping like an old man sleeping. A wriggly-tin shed shades wooden tubs of tofu. We sit at a plank table. A tiny woman with a toothless smile, trembling, blue-veined hands, carries a tray. Tofu-fa is heaped like soft snow in turquoise plastic bowls. I love the tofu’s smooth surface but crave the sight of golden sugar pocking its face, tofu puddled in ginger syrup – its sharp scent, clearing my nostrils with the first spoonful. Dusk creeps under our table grey as the old woman’s dog. The old woman dozes on her low stool beside the shed, bathed in the milk of the moon. NATHAN ROAD PHOTO: SIRIWAN LEOWRATSAMEE/UNSPLASH Kate Rogers’s poem “Baba Yaga’s Child” won second place in the 2018 Big Pond Rumors Contest (Canada). Her work was shortlisted for the 2017 Montreal International Poetry Prize and is forthcoming in Algebra of Owls (UK). Her poems have appeared in the Guardian. 62 WLT SPRING 2019 ...

Numerical Reconstruction of Traumatic Brain Injury in Skiing and Snowboarding.

Proper evaluation of ski helmet designs and safety standards should rely on head impact conditions involved in skiing and snowboarding head injuries. To study these impacts, main crash scenarios involving head injuries are numerically replicated. Multibody models of skiers and snowboarders were developed to investigate five common crash scenarios involved in traumatic brain injury: forward and sideways skiing falls, snowboarding backward falls, collisions between users and collisions with obstacles. For each scenario, the influence of crash conditions on head impact (location, speed, linear and rotational accelerations) and risk of injury are evaluated. Crash conditions were initial velocity, user height, position and approach angle, slope steepness, obstacles, and snow stiffness. One thousand one hundred forty-nine crashes were simulated and three significant levels of impact conditions were discriminated over the investigated crash scenarios: 1) the smallest normal-to-slope impact velocities (6 km·h; 22 km·h) and peak linear accelerations (42g; 75g) were obtained during forward and sideways skiing falls; 2) snowboarding backward falls and collisions between users were associated with high normal-to-surface impact velocities (26 km·h; 32 km·h) and head accelerations (80g; 149g) above one published threshold for mild traumatic brain injury but below the pass/fail criteria of helmet standard tests; 3) collisions with obstacles were associated with high normal-to-surface impact velocities (19 km·h; 35 km·h) and the highest head accelerations (626g; 1885g). Current impact conditions of helmet standard evaluations consistently replicate collisions with obstacles, but need to be revised to better reflect other significant crash scenarios leading to traumatic brain injury.

Ice Contact-Bonding in Air and in the Presence of an Aqueous Sodium Chloride Solution

AbstractSnow compacting on roads may become hazardous for traffic. Chemicals such as sodium chloride are therefore often used to prevent crust formation. Melting has been believed to be the mechanism through which a chemical does this. A recent study, however, indicates that reduced contact-bonding between ice crystals may be important. This hypothesis was tested by designing an experimental set-up capable of measuring the contact-bond strength between ice and a substrate. In this paper, ice–ice contact bonding was measured in air and in a sodium chloride solution. The study showed a statistically significant decrease in the median bonding force, from 0.57 N in air to 0.33 N in solution. The weakened contact-bonding in presence of a solution might explain the soft and noncompacting snow often seen on roads, an insight which might allow a more-efficient use of chemicals during snowfall.

Slip resistance of winter footwear on snow and ice measured using maximum achievable incline

Protective footwear is necessary for preventing injurious slips and falls in winter conditions. Valid methods for assessing footwear slip resistance on winter surfaces are needed in order to evaluate footwear and outsole designs. The purpose of this study was to utilise a method of testing winter footwear that was ecologically valid in terms of involving actual human testers walking on realistic winter surfaces to produce objective measures of slip resistance. During the experiment, eight participants tested six styles of footwear on wet ice, on dry ice, and on dry ice after walking over soft snow. Slip resistance was measured by determining the maximum incline angles participants were able to walk up and down in each footwear–surface combination. The results indicated that testing on a variety of surfaces is necessary for establishing winter footwear performance and that standard mechanical bench tests for footwear slip resistance do not adequately reflect actual performance.Practitioner Summary: Existing standardised methods for measuring footwear slip resistance lack validation on winter surfaces. By determining the maximum inclines participants could walk up and down slopes of wet ice, dry ice, and ice with snow, in a range of footwear, an ecologically valid test for measuring winter footwear performance was established.

Soft and Hard Slab Snow Dynamic Response to Explosives Used in Avalanche Hazard Mitigation

AbstractAvalanche mitigation routinely uses explosives to both initiate avalanches and test slope stability. This project aimed to verify past findings and further develop an understanding of explosive shockwave interactions with hard and soft slab conditions within 2–5 m of the detonation. Pentolite cast boosters (0.9 and 0.45 kg) were detonated at 0.0, 0.5, 1.0, 1.5, and 2.0 m above the snow. Six orthogonally paired accelerometers inserted into the snowpack recorded snow accelerations. High-pressure sensors located at and above the snow surface measured air overpressures. Distances were scaled to trinitrotoluene (TNT) equivalents to aid in explosive placement comparisons. A substantial advantage was recorded in snow accelerations attributable to elevating explosives above the snow surface. Elevating charges not only increased overall response, but also increased the effective range and depth with no penalty in shock attenuation rates. Using attenuation relationships, a method for predicting the maximum ...

On-ice vibroseis and snowstreamer systems for geoscientific research

We present implementations of vibroseis system configurations with a snowstreamer for over-ice long-distance seismic traverses (>100 km). The configurations have been evaluated in Antarctica on ice sheet and ice shelf areas in the period 2010–2014. We discuss results of two different vibroseis sources: Failing Y-1100 on skis with a peak force of 120 kN in the frequency range 10–110 Hz; IVI EnviroVibe with a nominal peak force of 66 kN in the nominal frequency range 10–300 Hz. All measurements used a well-established 60 channel 1.5 km snowstreamer for the recording. Employed forces during sweeps were limited to less than 80% of the peak force. Maximum sweep frequencies, with a typical duration of 10 s, were 100 and 250 Hz for the Failing and EnviroVibe, respectively. Three different concepts for source movement were employed: the Failing vibrator was mounted with wheels on skis and pulled by a Pistenbully snow tractor. The EnviroVibe was operated self-propelled on Mattracks on the Antarctic plateau. This lead to difficulties in soft snow. For later implementations the EnviroVibe with tracks was put on a polyethylene (PE) sled. The sled had a hole in the center to lower the vibrator baseplate directly onto the snow surface. With the latter setup, data production varied between 20 km/day for 6-fold and 40 km/day for single fold for 9 h/day of measurements. The combination of tracks with the PE-sled was especially advantageous on hard and rough surfaces because of the flexibility of each component and the relatively lose mounting. The systems presented here are suitable to obtain data of subglacial and sub-seabed sediment layers and englacial layering in comparable quality as obtained from marine geophysics and land-based explosive surveys. The large offset aperture of the streamer overcomes limitations of radar systems for imaging of steep along-track subglacial topography. With joint international scientific and logistic efforts, large-scale mapping of Antarctica's and Greenland's subglacial geology, ice-shelf cavity geometries and sea-bed strata, as well as englacial structures can be achieved.

Wie häufig und warum stürzen Skifahrer und Snowboarder?

Injuries in alpine skiing and snowboarding are mainly caused by falls. In 2002, a study was conducted to gain insight into the risk factors for falls when skiing or snowboarding. Since then, the evolution of skiing, snowboarding and safety equipment, as well as slope preparation, may have altered the frequency of falls while skiing or snowboarding. In total, 1436 male and female skiers and snowboarders from all age groups were interviewed from February until April 2012, in 6 Tyrolean ski resorts. The questionnaire was nearly identical to that used in 2002. It contained questions concerning personal characteristics, falls, equipment and risk taking behaviour. The incidence of falls among skiers was 0.076 ± 0.21 per hour and that among snowboarders was 0.429 ± 0.70 per hour. Age (OR: 0.96; CI:0.95 - 0.97), soft snow conditions (OR: 4.1; CI:1.9 - 8.8) and poor skiing skills (beginners and intermediates) (OR: 2.6; CI: 1.2 - 8.1) were predictive for falls during skiing. Poor snowboarding skills (beginners and intermediates) (OR: 8.3; CI:3.1 - 27.4), wearing a helmet (OR: 2.3; CI: 1.2 - 4.6) and alcohol consumption (OR: 2.1; CI: 1.2 - 3.9) were predictive for falls during snowboarding. The incidence of falls among skiers and snowboarders was substantially lower when compared to that in 2002. Improvements in skiing and snowboarding equipment as well as slope preparation may have contributed to this favourable development. We strongly assume that the lowering in fall incidence may positively affect the injury incidence.

Stress measurements in the snow cover below localized dynamic loads

In the majority of fatal snow avalanches, skiers and snowmobilers trigger the initial failure in a weak layer by applying load to the snow cover. Understanding how stresses from dynamic surface loads transmit through the snow cover can help people avoid situations where they can trigger avalanches. We build on previous studies that provided more qualitative statements to a quantitative analysis about how the snow cover affects stress transmission. We quantified the upper snow cover for the experiments according to a bridging index which is the uniform hand hardness index of a particular layer in the snow cover multiplied by the thickness of that layer. Capacitive sensors were used to measure peak stress below dynamic surface loads within the mountain snow cover. The sensors were used on 33 separate field days to collect over 1420 measurements of loading by skiers and snowmobiles. In order to visualize this measured stress, static stress calculations for an elastic homogeneous 2D snow cover were calibrated to show measured stress values of loading caused by the passage of a snowmobile. The change in 2D shape and magnitude of the induced stress was plotted for three “typical” snow cover structures. Relatively soft snow allowed the specific levels of dynamic stress to penetrate deeper into the snow cover, thus increasing the probability of initiating a failure in a weak layer. Whereas, supportive snow limited the depth that the dynamic stress penetrated by spreading it out laterally. The added stress was then related to localized slope stability using stability indices. Bridging index thresholds of 130 to 190 for skiers and 160 to 260 for snowmobiles yielded stability index values greater than 1.5. Due to the high variability in the stress measurements, bridging index values for 77 skier-triggered avalanche slopes were computed and compared to the values found from the stability index analysis.

Resonance Strategies of Sámi Reindeer Herders in Northernmost Finland during Climatically Extreme Years

This study focuses on the resonance strategies of Sámi reindeer herders in four reindeer-herding cooperatives in northernmost Finland in climatically extreme years, specifically those occurring during the period 1970–2007. “Resonance” is an instinctive and indwelling reaction of a herder to a specific change (in contrast to coping, which is a more general response). The study is based on interviews with herders, field experiences, reindeer population statistics, and weather data. Before the 1960s, herders were able to deal with changing weather conditions by using intensive herding techniques and semi-tame reindeer. After the 1960s, reindeer became wilder because of the use of snowmobiles and more extensive herding techniques. The herders of the fell and forest cooperatives did not have sufficient means to prevent the serious reindeer losses in 1972–74, which resulted from two years of hard snow and ice cover, hot summers, and the free ranging of loose herds. In each of the four cooperatives studied, most of the old siida herds were combined, and one solution to handling large, loose herds was to build fences between cooperatives. Since the 1990s, all four cooperatives have used diverse herding and pasture rotation strategies to cope with the critical winter months. The herding techniques and the human-reindeer relationship in the fell cooperatives have differed from those in the forest cooperatives mainly because of differences in pasture types, topography, and microclimate. The contrast can be seen particularly in snow and ice conditions, as open fell regions have a thin and compact snow cover, whereas forest regions typically have deep, soft snow. This research shows that the resonance strategies of Sámi reindeer herders are both heterogeneous and dynamic: herders change them constantly, drawing on both old and new techniques to deal with the variable weather.

Parameter study using a finite element simulation of a carving Alpine ski to investigate the turn radius and its dependence on edging angle, load, and snow properties

For ski manufacturers, it is important to know how a given ski-binding system performs under different loading conditions. Important performance parameters are the ski deformation and the resulting turn radius. This study focuses on carving turns. The aims of this study were: (1) to investigate the dependence of the turn radius on edging angle, load on the binding, and snow hardness using a finite element (FE) simulation, and (2) to compare the results with predictions of a frequently used model introduced by Howe. The FE simulation used a quasi-static approach (similar to Howe’s model), but the ski–snow interaction model incorporated the groove that forms in the snow during a carved turn. Up to edging angles of 40°, the results of the FE simulation agreed well with Howe’s model. However, for large edging angles (>50°) the calculated turn radius leveled out, whereas Howe’s model tends to zero. This effect was more pronounced for soft snow than for hard snow conditions. Increasing forces on the binding caused a decrease in the calculated turn radii. In summary, the FE simulation showed that particularly at large edging angles the groove in the snow needs to be considered in models of the ski–snow interaction or in computations of the turn radius.

The spatial structure of habitat selection: A caribou's-eye-view

Greater understanding of habitat selection requires investigation at the scales at which organisms perceive and respond to their environment. Such knowledge could reveal the relative importance of factors limiting populations and the extent of response to habitat changes, and so guide conservation initiatives. We conducted a novel, spatially explicit analysis of winter habitat selection by caribou ( Rangifer tarandus) in Newfoundland, Canada, to elucidate the spatial scales of habitat selection. We combined conventional hierarchical habitat analysis with a newly developed geospatial approach that quantifies selection across scales as the difference in variance between available and used sites. We used both ordination and univariate analyses of lichen and plant cover, snow hardness and depth. This represents the first use of ordination with geostatistics for the assessment of habitat selection. Caribou habitat selection was driven by shallow, soft snow and high cover of Cladina lichens and was strongest at feeding microsites (craters) and broader feeding areas. Habitat selection was most evident at distance lags of up to 15 km, perhaps an indication of the perceptual abilities of caribou.

New Insight To Old Hypotheses: Ruffed Grouse Population Cycles

We examined factors hypothesized to influence Ruffed Grouse (Bonasa umbellus) population cycles by evaluating 13 a priori models that represented correlations between spring counts of male Ruffed Grouse drumming displays and these factors. We used AICc to rank the relative ability of these models to fit the data and used variance components analysis to assess the amount of temporal process variation in Ruffed Grouse spring counts explained by the best model. A hypothesis representing an interaction between winter precipitation and winter temperature was the top-ranked model. This model indicated that increased precipitation during cold winters (soft snow cover for roosting) was correlated with higher grouse population indices, but that increased precipitation during warm winters (snow crust effect) was correlated with lower spring counts. The highest ranked model (AICc weight = 0.45), explained only 17% of the temporal process variation. The number of migrating Northern Goshawks (Accipiter gentilis), which has been correlated with grouse cycles in previous studies, does not adequately explain, by itself, the variation in annual population indices of Ruffed Grouse. Other factors not considered in our analysis, such as endogenous mechanisms, parasites, or interactions among factors may also be important, which suggest that mechanisms mediating the Ruffed Grouse cycle still require investigation.