bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of saltation layer of drifting snow
Authors: Sato Takeshi , Kosugi Kenji , Sato Atsushi 
Published: November 2007

AbstractThe saltation length of aeolian snow particles and a new parameter, the ejection factor, which expresses the degree of erosion due to drifting snow, were obtained as functions of friction velocity by means of wind-tunnel experiments for semi-hard snow cover. The saturated-snowdrift transport rate was also obtained experimentally as a function of friction velocity. Based on these characteristics and the parameter, the development of the saltation layer of drifting snow along the fetch was simulated under various conditions such as snow hardness, wind speed and snowfall intensity. The main results are as follows. The developing distance denoting the distance required for the saltation layer to attain saturation, X sat, is determined by saltation length, ejection factor and saturated-snowdrift transport rate, all of which depend on wind speed. It is also affected by the magnitude of snowdrift transport rate at the starting point and by the intensity of snowfall if it exists. The dependence of Xsat on wind speed is not simple in the case of semi-hard snow cover: Xsat increases with wind speed under weak to moderate wind conditions and then decreases under moderate to strong wind conditions. It is sensitive to snow hardness: it is about one order longer on hard snow cover than on semi-hard snow cover. Snowfall reduces not only the value of Xsat but also its dependence on snow hardness.
Spatial variability of micropenetration resistance in snow layers on a small slope
Authors: Kronholm Kalle , Schneebeli Martin , Schweizer Jürg 
Published: November 2007

AbstractThe mechanisms leading to dry-snow slab release are influenced by the three-dimensional variability of the snow cover. We measured 113 profiles of penetration resistance with a snow micropenetrometer on an alpine snow slope. Seven distinct layers were visually identified in all snow micropenetrometer profiles. The penetration resistance of adjacent layers did not change abruptly, but gradually across layer boundaries that were typically 2 mm thick. In two layers, penetration resistance varied around 200% over the grid, possibly due to wind effects during or after layer deposition. Penetration resistance varied around 25%in five layers. Statistically significant slope-scale linear trends were found for all layers. The semivariogram was used to describe the spatial variation. Penetration resistance was autocorrelated, but the scale of variation was layer-specific. A buried layer of surface hoar was the most critical weak layer. It had little spatial variation. The layers in the slab above had higher spatial variation. The penetration resistance of each snow layer had distinct geostatistical properties, caused by the depositional processes.
Impact of artificial snow and ski-slope grooming on snowpack properties and soil thermal regime in a sub-alpine ski area
Authors: Keller Thomas , Pielmeier Christine , Rixen Christian , Gadient Florian , Gustafsson David , Stähli Manfred 
Published: November 2007

AbstractEarlier studies have indicated that the soil on groomed ski slopes may be subjected to more pronounced cooling than the soil below a natural snowpack. We analyzed the thermal impacts of ski-slope preparation in a sub-alpine ski resort in central Switzerland (1100ma.s.l.) where artificial snow was produced. Physical snow properties and soil temperature measurements were carried out on the ski slope and off-piste during winter 1999/2000. The numerical soil–vegetation–atmosphere transfer model COUP was run for both locations, with a new option to simulate the snowpack development on a groomed ski slope. Snow density, snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did not affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The newly implemented option proved to be a useful strategy for simulating the snowpack of a ski slope. However, snow density was underestimated by the model as it could not account adequately for compaction due to grooming traffic. Our study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil.
Ice fabric evolution process understood from anisotropic distribution of a-axis orientation on the GRIP (Greenland) ice core
Authors: Miyamoto Atsushi , Shoji Hitoshi , Hori Akira , Hondoh Takeo , Clausen Henrik B. , Watanabe Okitsugu 
Published: November 2007

AbstractTo better understand how ice fabric evolves in polar ice sheets, we use X-ray diffraction to measure ice crystal orientations. X-ray measurement equipment which can measure the orientation of the c axis and a axis of each crystal in a thin section with high measurement accuracy was developed. In this study, we present a-axes orientation distribution of the deep part of the GRIP (Greenland summit) ice core. At some depths, we find an anisotropic distribution of a-axes orientation. Long-term uniaxial compression tests are also carried out on the GRIP ice core to investigate the ice fabric evolution process. The c-axis orientation distribution develops into a stronger single maximum as the strain increases up to about 20% strain. We find that the a axes of each grain also tend to cluster close to nearly a mutual direction. We discuss the development process of ice fabrics, taking into consideration the distribution of the a-axis orientations. It is suggested that these fabrics may be attributed to a local simple shear deformation in the deep part of an ice sheet.
Relation of measured basal temperatures and the spatial distribution of the geothermal heat flux for the Greenland ice sheet
Authors: Greve Ralf 
Published: November 2007

AbstractThe thermomechanical, three-dimensional ice-sheet model SICOPOLIS is applied to the Greenland ice sheet. Simulations over two glacial–interglacial cycles are carried out, driven by a climatic forcing interpolated between present conditions and Last Glacial Maximum anomalies. Based on the global heat-flow representation by Pollack and others (1993), we attempt to constrain the spatial pattern of the geothermal heat flux by comparing simulation results to direct measurements of basal temperatures at the GRIP, NorthGRIP, Camp Century and Dye 3 ice-core locations. The obtained heat-flux map shows an increasing trend from west to east, a high-heat-flux anomaly around NorthGRIP with values up to 135 mWm–2 and a low-heat-flux anomaly around Dye 3 with values down to 20 mW m–2. Validation is provided by the generally good fit between observed and measured ice thicknesses. Residual discrepancies are most likely due to deficiencies of the input precipitation rate and further variability of the geothermal heat flux not captured here.
Seismic emissions from a surging glacier: Bakaninbreen, Svalbard
Authors: Stuart Graham , Murray Tavi , Brisbourne Alex , Styles Peter , Toon Sam 
Published: November 2007

AbstractBakaninbreen is a polythermal glacier in southern Spitsbergen, Svalbard, which surged between 1985 and 1995. For 9 days in spring 1987, when the surge front was travelling at ∼2.5-3.0 m d–1, three single-component geophones and two accelerometers were deployed in a T-shaped array immediately downstream of the surge front to record seismic emissions. The events were characterized by their waveforms and spectral content. At least three different categories have been identified: impulsive P- and S-waveforms, surface P- and S-wave trains, and harmonic (75-130 Hz) events. We interpret the impulsive events to originate at the base of the glacier, at or downstream of the surge front; the surface P- and S-wave trains from near-surface brittle fracture associated with the surface expression of the surge front itself; and the harmonic events from deep sources that involve resonance in a water-filled fracture, associated with the base of the surge front. We believe the basal events are related to the activation of stagnant ice downstream of the surge front, which allows water to access the bed and provides the mechanism for its propagation.
Regional and temporal variation of accumulation around NorthGRIP derived from ground-penetrating radar
Authors: Steinhage Daniel , Eisen Olaf , Clausen Henrik Brink 
Published: November 2007

AbstractDuring the summer of 2003, a ground-penetrating radar survey around the North Greenland Icecore Project (NorthGRIP) deep ice-core drilling site (75˚06’N, 42˚20’W; 2957ma.s.l.) was carried out using a shielded 250 MHz radar system. The drill site is located on an ice divide, roughly 300 km north-northwest of the summit of the Greenland ice sheet. More than 430 km of profiles were measured, covering a 10 km by 10 km area, with a grid centered on the drilling location, and eight profiles extending beyond this grid. Seven internal horizons within the upper 120 m of the ice sheet were continuously tracked, containing the last 400 years of accumulation history. Based on the age-depth and density-depth distribution of the deep core, the internal layers have been dated and the regional and temporal distribution of accumulation rate in the vicinity of NorthGRIP has been derived. The distribution of accumulation shows a relatively smoothly increasing trend from east to west from 145 kgm–2a–1 to 200 kg m–2 a -1 over a distance of 50 km across the ice divide. The general trend is overlain by small-scale variations on the order of 2.5 kgm–2a-1 km- 1 , i.e. around 1.5% of the accumulation mean. The temporal variations of the seven periods defined by the seven tracked isochrones are on the order of ± 4% of the mean of the last 400 years, i.e. at NorthGRIP ± 7 kg m–2 a-1. If the regional accumulation pattern has been stable for the last several thousand years during the Holocene, and ice flow has been comparable to today, advective effects along the particle trajectory upstream of NorthGRIP do not have a significant effect on the interpretation of climatically induced changes in accumulation rates derived from the deep ice core over the last 10 kyr.
On the growth of ice cover in the Sea of Okhotsk with special reference to its negative correlation with that in the Bering Sea
Authors: Rikiishi Kunio , Takatsuji Shinya 
Published: November 2007

AbstractCharacteristic features of the growth of sea-ice extent in the Sea of Okhotsk are discussed statistically in relation to the surface wind and air temperature over the Okhotsk basin. It is shown that cold-air advection from the continent is not the only factor for the growth of ice extent: air-mass transformation with fetch (downwind distance from the coast) is another important factor. Using weekly growth rates of ice extent and objectively analyzed meteorological data, it is shown that the ice cover extends when cold northerly/northwesterly winds blow, whereas the ice cover retreats when warm northeasterly/easterly winds blow. It is concluded that the advance/retreat of the Sea of Okhotsk ice cover is largely determined by the atmospheric circulation, which is in turn controlled by the position and intensity of the Aleutian low. Occasional out-of-phase fluctuations between the Sea of Okhotsk and Bering Sea ice covers are found to occur when an intensified Aleutian low is located in the mid-western part of the Bering Sea and induces cold northwesterly winds to the Okhotsk basin and warm southeasterly winds to the Bering Sea, or when a weakened Aleutian low is displaced eastward and induces cold northeasterly winds to the Bering Sea and warm northeasterly winds to the Okhotsk basin.
The influence of drifting snow on the location of glaciers on western Spitsbergen, Svalbard
Authors: Jaedicke Christian , Gauer Peter 
Published: November 2007

AbstractOn western Spitsbergen, Svalbard, the amount of winter precipitation is insufficient to maintain the present-day mass balance of the local glaciers. Additional snow mass must be added to the precipitation to reach the observed accumulation rates of the glaciers. It was assumed in previous work that this additional mass is transported onto the glaciers by drifting snow and snow avalanches. This study is a first attempt to quantify the amount of snow mass added to the glacier mass balance by wind-transported snow. The wind field over an area of 60 × 50 km2 on western Spitsbergen was simulated for 24 idealized weather types by a mesoscale meteorological model on a 750 m grid. The resulting wind velocities and directions were coupled to a two-level snowdrift model. The model output clearly shows erosion and accumulation areas in the terrain. Comparison with the present glacier locations suggests that the glacier accumulation areas coincide with low wind speeds. Moreover, exposed areas with high wind speeds are mostly glacier-free in reality. Thus, the wind field and corresponding snowdrift gives an indication of the location of the present glaciers on western Spitsbergen.
ICESat measurement of Greenland ice sheet surface slope and roughness
Authors: Yi Donghui , Jay Zwally H. , Sun Xiaoli 
Published: November 2007

AbstractThe Ice, Cloud and land Elevation Satellite (ICESat) in its 8 day repeat orbit mode provided data not only on the along-track surface slope, but also on the cross-track surface slope from adjacent repeat ground tracks. During the first 36 days of operation, four to five such repeat orbits occurred within 1 km in the cross-track direction. This provided an opportunity to use ICESat data to measure surface slope in the cross-track direction at 1 km scale. An algorithm was developed to calculate the cross-track surface slope. Combining the slopes in the cross-track and along-track directions gives a three-dimensional surface slope at 1 km scale. The along-track surface slope and surface roughness at 10km scale are also calculated. A comparison between ICESat surface elevation and a European Remote-sensing Satellite (ERS-1) 5 km digital elevation model shows a difference of 1–2 m in central Greenland where the surface slope is small, and >20m at the edge of Greenland where the surface slope is large. The large elevation difference at the edge is most likely due to the slope-induced error in radar altimeter measurement. Accurate surface slope data from ICESat will help to correct the slope-induced error of radar altimeter missions such as Geosat, ERS-1 and ERS-2.
High-resolution reconstruction of Polar Ural glacier mass balance for the last millennium
Authors: Kononov Yuriy M. , Ananicheva Maria D. , Willis Ian C. 
Published: November 2007

AbstractOur ultimate objective is to study the mass-balance variations of Polar Ural glaciers during the last millennium. We use mass-balance data for two glaciers between 1957 and 1981, climate data obtained by instrumental observations during the 20th century, and tree-ring data compiled for the last 1000 years. Because there is a high correlation between measured glacier mass-balance and climate variables, we reconstruct glacier mass balance for the 20th century using regression equations. Similarly, we use regression equations relating measured climatic variables to tree-ring widths to reconstruct glacier mass balance for the last millennium. According to our reconstructions, the most extensive period of negative mass balance occurred in the late 10th/early 11th century AD, which corresponds to the Medieval Warm Period. A prolonged period of positive glacier mass balance began after the mid-11th century, a time commonly accepted as the onset of the Little Ice Age. This cooling period has three maxima, the last from the early 17th to mid-19th century. Until the beginning of the 20th century, cumulative mass balance over the last millennium varied between ±8mw.e. However, glacier mass balance in the second half of the 20th century is lower than it has been for the past millennium, and cumulative mass balance is now -10mw.e. Polar Ural glaciers are important indicators of regional climate change and should be incorporated into a worldwide glacier-monitoring programme.
Interannual variability in the spatial distribution of winter accumulation at a high-Arctic glacier (Finsterwalderbreen, Svalbard), and its relationship with topography
Authors: Hodgkins Richard , Cooper Richard , Wadham Jemma , Tranter Martyn 
Published: November 2007

AbstractGlacier mass balance and hydrology are strongly influenced by the distribution of snow accumulation at the start of the melt season. Two successive end-of-winter snow-cover surveys at Finsterwalderbreen, Svalbard, are here used to investigate the interannual variability in the spatial distribution of accumulation, and its relationship with topography. 40–62% of the variance in snow depth was not determined by elevation (assessed by linear regression of snow depth on surface elevation), which could not therefore necessarily be used as a sole predictor of the spatial distribution of accumulation here. Principal components (PC) analysis of the topographic variables elevation, slope, north–south and east–west aspects shows that only two of six PCs, determined for 2years’ sampling locations, had maximum loadings on altitude; aspect was more important, with maximum loadings on four PCs. Hierarchical cluster analysis was then applied to these PCs: significant correlations with accumulation in each of two terrain clusters were given by (1) elevation and slope, (2) east–west aspect only (1999); (1) elevation only, (2) no significant correlations (2000). There is strong interannual variability not only in the magnitude of winter accumulation (0.41 mw.e. in 1999, 0.58 mw.e. in 2000), but also in its spatial distribution, and its relationship with topography.
Geometry changes on Svalbard glaciers: mass-balance or dynamic response?
Authors: Hagen Jon Ove , Eiken Trond , Kohler Jack , Melvold Kjetil 
Published: November 2007

AbstractThe geometry of glaciers is affected by both the mass balance and the dynamics. We present repeated GPS measurements of longitudinal altitude profiles on three glaciers in Svalbard and show that surface altitude changes alone cannot be used to assess the mass balance. The three measured glaciers are in different dynamic modes, and the observed changes in geometry are strongly affected by the dynamics. Nordenskiöldbreen shows no significant change in the geometry, indicating that the mass balance is in steady state with the dynamics. On Amundsenisen the surface has lowered by 1.5–2.0 ma–1 in the lower part of the accumulation area at 520–550m a.s.l., indicating that the ice flux is higher than the mass-balance input, probably due to a surge advance of the glacier further downstream affecting the higher part of the drainage area. On Kongsvegen the opposite situation was found. Here the geometry of the profile showed a clear build-up of 0.5 ma–1 in the accumulation area and a lowering of 1 ma–1 in the lower part of the ablation area. The ice velocity is very low, giving a negligible vertical velocity component and an ice flux that is far smaller than the mass-balance flux, indicating that the glacier is building up towards a surge advance. Our results show that if mapping of height changes is to be used to monitor the response of the glaciers to climate change, both surface net mass-balance data and dynamic data are needed.
Interpretation of the anomalous growth of Austfonna, Svalbard, a large Arctic ice cap
Authors: Raper Vivienne , Bamber Jonathan , Krabill William 
Published: November 2007

AbstractAs previously reported, repeat-pass airborne laser altimetry measurements made in May 1996 and May 2002 show a large positive ice-surface elevation change rate over parts of the accumulation area of Austfonna, eastern Svalbard. The maximum growth rate is estimated to be equivalent to a 35–40% increase in snowfall over the area of thickening. Thinning is observed at lower elevations. Here we discuss in detail the possible causes of these elevation changes, including ice-cap dynamics and/or firn density changes, and conclude that sea-ice loss producing a localized increase in precipitation over Austfonna remains the most convincing explanation. This study highlights the problems of interpreting relatively short-term altimetry measurements where auxiliary data are limited in both spatial and temporal extent.
Assessment of combined glacier and tree-ring studies to constrain latitudinal climate forcing of Scandinavian glacier mass balances
Authors: Jansson Peter , Linderholm Hans W. 
Published: November 2007

AbstractAssessing climate change and its effects on the cryosphere is important, and individual proxies are commonly used for such assessments. We have investigated the possibility of combining glacier mass balance and tree-ring data to better understand regional climate variability in Scandinavia. There are substantial differences between climate information in mass-balance and tree-ring data. Summer balance (bS) is strongly related to summer temperature, while winter balance (bW) is less readily interpreted in terms of a climate signal. Tree rings are good summer temperature proxies, but due to the complexity of tree growth factors (e.g. the effect of the previous winter’s climate) tree-ring records do not exclusively represent summer temperatures. Combining bS and tree-ring records will not likely yield additional summer climate information. The relationship of mass balance with the Arctic Oscillation is stronger than with the North Atlantic Oscillation, especially for northernmost Sweden, whereas no such correlations were found for tree-ring data. The agreement between bN records from both maritime south-central Norway and continental northernmost Sweden and tree-ring data from Jämtland, in a maritime/continental climate transition zone, suggests possibilities to combine mass-balance and tree-ring data to provide information about climate over the entire year on interannual timescales.
Fresh-water discharge from Greenland using regional climate simulations
Authors: Sood Abha 
Published: November 2007

AbstractThe annual mass budget of the Greenland ice sheet (1992) and the fresh-water flux from Greenland including the coasts is determined using high-resolution regional climate model (REMO) simulations. The climate model is modified to include processes such as lateral flow over Greenland using a newly developed routing scheme, the effect of sub-grid-scale surface heterogeneity (orography) on surface temperature and runoff and an improved snow and ice model for the Greenland ice sheet for surface processes on the ice sheet. The high-resolution (0.125˚ grid size) simulations of accumulation and runoff fields are also assessed compared to the lower-resolution (0.5˚ grid size) simulations.