bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model for kinetic grain growth
Authors: Baunach Thorsten , Fierz Charles , Satyawali Pramod K. , Schneebeli Martin 
Published: November 2007

AbstractSnow-cover models are used in many applications in today’s snow and ice research. Descriptions of changes in size and shape are a major problem in modelling the snow cover. Empirical models for kinetic growth under temperature gradients have been developed, as well as more complicated models based upon microstructure. In this work a simple; physically based model is derived which depends on one adjustable geometric factor only Snow texture is described as a body-centred cubic lattice containing source and sink grains. The latter grow as plates due to water-vapour transport in the layer as well as between the layers. The model was implemented in a research version of the one-dimensional snow-cover model SNOWPACK. Model outputs are compared to experiments done in the cold laboratory where sieved snow is subjected to temperature gradients. Disaggregated snow samples are analyzed by digital image processing, by sieving and by visual characterization. In order to determine grain-size as objectively as possible, these various methods are evaluated for compatibility. The new model simulates very well kinetic grain growth for densities of 100–200 kg m−3 and temperature gradients up to –200 Km−1. The model will be incorporated in the operational version of SNOWPACK.
Simulation of surface-hoar layers for snow-cover models
Authors: Föhn Paul M.B. 
Published: November 2007

AbstractDuring two winters, typical meteorological conditions (temperature, humidity, wind, radiation) and snow-surface conditions (snow surface and snow temperatures) were measured to simulate the formation and ablation processes (mainly sublimation) of surface hoar on two level snow plots, situated at 2500 and 1500 m a.s.l. In order to verify the simulated deposition/ablation rates, the surface-hoar mass, thickness and occasionally density were also measured. The evaluation shows that, using the aerodynamic bulk method for the half-hourly simulation periods, >90% of the day/night periods could be rated as either hoar-formation or ablation periods. The simulated sublimation rates (deposition/ablation) deviate in the mean by not more than 10% from the measured amounts! However, some larger deviations are present, mainly during ablation periods with heavy melting. Finally a method is shown for transforming net deposited vapour amounts into surface-hoar layers of a corresponding height in order to produce “layers” which might be integrated into snow-cover simulation models.
Ping-pong ball avalanche experiments
Authors: McElwaine J. , Nishimura K. 
Published: November 2007

AbstractPing-pong ball avalanche experiments have been carried out for the last 3 years at the Miyanomori ski jump in Sapporo, Japan, to study three-dimensional granular flows. Up to 550 000 balls were released near the top of the landing slope. The balls then flowed past video cameras positioned close to the flow, which measured individual ball velocities in three dimensions, and air-pressure tubes at different heights. The flows developed a complicated three-dimensional structure with a distinct head and tail, lobes and “eyes”. “Eyes” have been observed in laboratory granular flow experiments, and the other features are similar not only to snow avalanches” but also to other large-scale geophysical flows. The velocities attained showed a remarkable increase with the number of released balls. A power law for this relation is derived by similarity arguments. The air-pressure data are used to deduce the structure of the airflow around the avalanche and, in conjunction with the kinetic theory of granular matter, to estimate the balance of forces in the avalanche head.
Avalanches: a probabilistic approach to modelling
Authors: Bozhinskiy A. N. , Nazarov A. N. , Chernouss P. A. 
Published: November 2007

AbstractA probabilistic approach to modelling avalanche origin and dynamics is developed. An avalanche process is considered as a single event. As a basis, the physically established deterministic models describing the processes of avalanche origin and motion are used. On the other hand, input data and/or parameters of these models are treated as random variables. The study is restricted only with respect to the dynamic stage of the avalanche process. It is assumed that the initial volume of snow, entrained into the motion, and the coefficients of dry and turbulent friction of the avalanche body are random variables. The other input data are deterministic. Three kinds of distribution laws for random variables are examined: uniform, normal and exponential. Several hundred numerical tests, carried out for the selected avalanche path No. 22 in the Khibiny region, Russia, allowed construction of the distribution functions for the output parameters of the dynamic model. These parameters are the front velocity, the height and the volume of the avalanche body at fixed points of the avalanche path. No very strong dependence of distribution functions on the kind of distribution laws was found. The model and empirical distribution functions are very close to one another for run-out distances and sufficiently close for depths and volumes of snow deposits.
Snow texture: a comparison of empirical versus simulated texture index for Alpine snow
Authors: Plelmeier C. , Schneebeli M. , Stucki T. 
Published: November 2007

AbstractThe texture of snow has a great impact on the mechanical and thermal properties of a snowpack. The texture index (TI) is a new concept to quantify the texture of snow at the micro- and mesoscale, a scale at which the properties of snow layers are responsible for the stability of a snowpack. It is calculated by taking the ratio of mean grain-size (mm) of snow to density (kg m−3) of snow in a given layer. It combines a microstructural with a mesostructural parameter. An empirically derived TI is compared with a simulated TI for laboratory experimental snow and natural snow profiles. TheTI was calculated throughout the development of three temperature-gradient snow experiments from laboratory measurements of grain-size and density. In a one-dimensional finite-element snowpack model (SNOWPACK), the development of the mean grain-size and density of these snow samples was simulated. It can be shown that the measured TI can be predicted by the modelled TI. Furthermore, three natural snow profiles from the Weissfluhjoch (Switzerland) test-field are compared with their simulations in terms of TI. This comparison reveals shortcomings in the measurement of fundamental parameters. It also shows the dependency of a good physical model on quantitative process descriptions at the microscale TheTI can be estimated using the force signal of the SnowMicroPen, a new high-resolution snow micropenetrometer. It is suggested that more accurate classical measurements combined with penetrometer measurements in the immediate vicinity of the snow profile will allow better verification of SNOWPACK simulations.
An accurate shock-capturing finite-difference method to solve the Savage-Hutter equations in avalanche dynamics
Authors: Tai Y. C. , Noelle S. , Gray J. M. N.T. , Hutter K. 
Published: November 2007

AbstractThe Savage-Hutter equations of granular avalanche flows are a hyperbolic system of equations for the distribution of depth and depth-averaged velocity components tangential to the sliding bed. They involve two phenomenological parameters, the internal and the bed friction angles, which together define the earth pressure coefficient which assumes different values depending upon whether the flow is either diverging or contracting. Because of the hyperbolicity of the equations, since velocities may be supercritical, shock waves are often formed in avalanche flows. Numerical schemes solving these free surface flows must cope with smooth as well as non-smooth solutions. In this paper the Savage-Hutter equations in conservative form are solved with a shock-capturing technique, including a front-tracking method. This method can perform for parabolic similarity solutions for which the Lagrangian scheme is excellent, and it is even better in other situations when the latter fails.
Simulating snowmelt processes during rain-on-snow over a semi-arid mountain basin
Authors: Marks Danny , Link Tim , Winstral Adam , Garen David 
Published: November 2007

AbstractIn the Pacific Northwest of North America, significant flooding can occur during mid-winter rain-on-snow events. Warm, wet Pacific storms caused significant floods in the Pacific Northwest in February 1996, January 1997 and January 1998. Rapid melting of the mountain snow cover substantially augmented discharge during these flood events. An energy-balance snowmelt model is used to simulate snowmelt processes during the January 1997 event over a small headwater basin within the Reynolds Creek Experimental Watershed located in the Owyhee Mountains of southwestern Idaho, U.S.A. This sub-basin is 34% forested (12% fir, 22% aspen and 66% mixed sagebrush (primarily mountain big sagebrush)). Data from paired open and forested experimental sites were used to drive the model. Model-forcing data were corrected for topographic and vegetation canopy effects. The event was preceded by cold, stormy conditions that developed a significant snow cover over the sub-basin. The snow cover at sites protected by forest cover was slightly reduced, while at open sites significant snowmelt occurred. The warm, moist, windy conditions during the flooding event produced substantially higher melt rates in exposed areas, where sensible- and latent-heat exchanges contributed 60–90% of the energy for snowmelt. Simulated snow-cover development and ablation during the model run closely matched measured conditions at the two experimental sites. This experiment shows the sensitivity of snowmelt processes to both climate and land cover, and illustrates how the forest canopy is coupled to the hydrologic cycle in mountainous areas.
Aerosol dry deposition measured with eddy-covariance technique at Wasa and Aboa, DronningMaud Land, Antarctica
Authors: Grönlund Anna , Nilsson Douglas , Koponen Ismo K. , Virkkula Aki , Hansson Margareta E. 
Published: November 2007

AbstractInterpretation of ice-core records in terms of changes in atmospheric concentrations requires understanding of the various parameters within air–snow transfer functions. the dry-deposition velocity is one of these parameters, dependent on local meteorological conditions and thereby also affected by climate changes. We have determined aerosol dry-deposition velocities by measurements of aerosol particle-number concentration and the vertical wind component with an eddy-covariance system close to the Swedish and Finnish research stations Wasa and Aboa in Dronning Maud Land, Antarctica. Measurements were performed over a smooth, snow-covered area and over moderately rough, rocky ground during 4 and 19 days, respectively, in January 2000. the median dry-deposition velocity determined 5.25 mabove the surface was 0.33 and 0.80 cm s–1, respectively. the large difference between the two sites was mainly due to the stratification of the surface boundary layer, the surface albedo and the surface roughness height. the dry-deposition number fluxes were dominated by the particle-size modes defined as ultrafine and Aitken, withmean diameters around 14 and 42 nm, respectively. A larger dry-deposition velocity, owing to stronger Brownian diffusion, for the smaller ultrafine mode was verified by the measurements.
Post-depositional movement of methanesulphonic acid at Law Dome, Antarctica, and the influence of accumulation rate
Authors: Curran Mark A.J. , Palmer Anne S. , van Ommen Tas D. , Morgan Vin I. , Phillips Katrina L. , McMorrow Alison J. , Mayewski Paul A. 
Published: November 2007

AbstractA series of ice cores from sites with different snow-accumulation rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. the precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the accumulation rate. At the low-accumulation-rate W20k site (0.17m ice equivalent), MSAwas completely relocated from the summer to winter layer. Moderate movement was observed at the intermediate-accumulation-rate site (0.7m ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-accumulation-rate DE08 site (1.4m ice equivalent). the main DSS record of MSA covered the epoch AD 1727–2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed in the surface layers, outside of the main summer MSA peak,which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770–1800) with high summer nitrate levels. A complex interaction between the gradients in nss-sulphate, nitrate and sea salts (which are influenced by accumulation rate) is believed to control the rate and extent of movement of MSA.
High-resolution fast ion chromatography (FIC) measurements of chloride, nitrate and sulphate along the EPICA Dome C ice core
Authors: Traversi Rita , Becagli Silvia , Castellano Emiliano , Migliori Alessio , Severi Mirko , Udisti Roberto 
Published: November 2007

AbstractFast ion chromatographic (FIC) analysis of the first European Project for Ice Coring in Antarctica (EPICA) Dome C ice core (788m deep) was used to obtain high-resolution profiles for Cl–, NO3– and SO42–, spanning the last 45000 years. About 19 000 determinations for each component, with an average resolution of 4.0 cm, were performed in the field on continuously melted firn- and ice-core sections. the measured core covers the Holocene, the glacial/interglacial transition and about one-third of the last ice age. In the glacial period, mean concentrations of 93.8, 24.4 and 178.4 mg L–1 were calculated for Cl–, NO3– and SO42–, respectively. the mean levels significantly increase in the Last Glacial Maximum (LGM), when these compounds reach values of 149.6, 53.9 and 219.3 mg L–1. During the glacial/interglacial transition, the mean concentrations quickly decrease reaching the typical Holocene values of 19.1, 12.9 and 93.3 mg L–1, for Cl–, NO3– and SO42–, respectively. All species settle on Holocene-like values about 4000 years before the beginning of the warm period (from the isotopic curve) showing a low (chloride) and no (nitrate and sulphate) sensitivity to Antarctic Cold Reversal climatic change. the sulphate decrease is consistent with the dilution factor due to the higher accumulation rate in the interglacial conditions (about 2.5), suggesting no significant change in source intensity or transport efficiency occurred for this component. on the contrary, the Holocene values for chloride and nitrate, being much lower than those measured in the LGM, suggest a source-intensity and transport-efficiency enhancement during the LGM and/or a more effective fixing of HCl and HNO3 in the snow layers through the neutralizing effect of the higher atmospheric dust load.
Dome Concordia ice microstructure: impurities effect on grain growth
Authors: Weiss Jérôme , Vidot Jérôme , Gay Michel , Arnaud Laurent , Duval Paul , Petit Jean Robert 
Published: November 2007

AbstractWe present a detailed analysis of the microstructure in the shallow part (100–580m) of the European Project for Ice Coring in Antarctica (EPICA) ice core at Dome Concordia. In the Holocene ice, the average grain-size increases with depth. This is the normal grain-growth process driven by a reduction of the total grain-boundary energy. Deeper, associated with the Holocene–Last Glacial Maximum (LGM) climatic transition, a sharp decrease of the average grain-size is observed. to explain modifications to the microstructure with climatic change, we discuss the role of soluble and insoluble (microparticles) impurities in the grain-growth process of Antarctic ice, coupled with an analysis of the pinning of grain boundaries by microparticles. Our data indicate that high soluble impurity content does not necessarily imply a slowing-down of grain-growth kinetics, whereas the pinning of grain boundaries by dust particles located along the boundaries does explain modifications to the microstructure (small grain-sizes; change in grain-size distributions, etc.) observed in volcanic ash layers or dusty LGM ice.Moreover, classical mean-field models of grain-boundary pinning are in good quantitative agreement with the evolution of grain-size along the EPICA ice core. This suggests a major role for dust in the modification of shallow polar ice microstructure.
A new method for predicting transport properties of polar firn with respect to gases on the pore-space scale
Authors: Freitag Johannes , Dobrindt Uwe , Kipfstuhl Josef 
Published: November 2007

AbstractIn this study a powerful tool to investigate the permeabilities and effective diffusion coefficients of polar firn is presented using a combination of an experimental method for three-dimensional pore-structure reconstruction and two models to simulate advective and diffusive transports of gases through the pore space. the reconstruction follows a semi-automated digital analysis of serial surface sections. the simulations are based on a three-dimensional lattice Boltzmann formulation. They separately solve the Navier–Stokes equation and the diffusive transport equations. In a first application, effective diffusion coefficients and permeabilities are calculated from firn samples of a core drilled during the North Greenland Traverse 1993–95. the estimated relationships of diffusivity and permeability to the open porosity are expressed by power-law functions with exponents 2.1 and 3.4, respectively.
An investigation of rapid warm transitions during MIS2 and MIS3 using Greenland ice-core data and the CLIMBER-2 model
Authors: Mogensen Irene A. , Johnsen Sigfüs J. , Ganopolski Andrey , Rahmstorf Stefan 
Published: November 2007

AbstractIn the search for abetter understanding of the dominant mechanisms of the Earth’s climate system, we present a study of rapid warm-climate transitions to Dansgaard– Oeschger events as seen in the ice cores from the Greenland ice sheet. We present a continuous δ18O record from the Greenland Icecore Project (GRIP) core with a resolution of 5 years until 50 kyr BP and of 20 years until 100 kyr BP. These data are compared with other high-resolution records, i.e. the Greenland Ice Sheet Project II (GISP2) chemistry record (25 years until 50 kyr BP) and the GRIP Ca2+ record (3 years until 100 kyr BP). All records have been transformed to the GISP2 Meese/Sowers time-scale. the high-resolution records are separated into interstadials and stadials, defined by the GRIP and GISP2 δ18O records. We examine in detail the transitions into the Dansgaard–Oeschger events, and propose a scenario for the changes that occur in the different ice-core records during the approximately 50 years the transition takes. Themain difference from previous studies is the much higher-resolution datasets available until 50 kyr BP; previous high-resolution studies by Taylor and others (1997) have focused on only the Younger Dryas/Preboreal transition. the data are compared to model simulations of the Dansgaard–Oeschger events performed with the CLIMBER-2 model of intermediate complexity (Petoukhov and others, 1998 ; Ganopolski and Rahmstorf, 2001).
A three-dimensional residence-time analysis of potential summertime atmospheric transport to Summit, Greenland
Authors: Miller Jessica E. , Kahl Jonathan D. W. , Heller Fred , Harris Joyce M. 
Published: November 2007

AbstractThe interannual variations in atmospheric transport patterns to Summit, Greenland, are studied using twice-daily, three-dimensional, 10 day backward trajectory data corresponding to the summers (1 June–31 August) of 1989–98. While previous trajectory climatology studies have been prepared for Summit, the present work considers both the horizontal and vertical components of transport. A three-dimensional residence-time methodology is employed to account for both horizontal and vertical components of transport. the vertical transport component is quantified by passing all trajectories through a three-dimensional grid and tracking the time spent (i.e. the residence time) in each gridcell. This method also allows inspection of trajectory altitude distributions corresponding to transport from upwind regions of interest. the three-dimensional residence-time methodology is shown to be a valuable tool for diagnosing the details of long-range atmospheric transport to remote locations. for Summit, we find that the frequent transport from North America tends to occur at low altitudes, whereas transport from Europe is highly variable. Mean summertime flow patterns are described, as are anomalous patterns during 1990,1996 and 1998.
Spatial and temporal variability in isotope composition of recent snow in the vicinity of Vostok station, Antarctica: implications for ice-core record interpretation
Authors: Ekaykin Alexey A. , Lipenkov Vladimir Ya. , Barkov Narcisse I. , Petit Jean Robert , Masson-Delmotte Valerie 
Published: November 2007

AbstractContinuous, detailed isotope (δD and δ18O) profiles were obtained from eight snow pits dug in the vicinity of Vostok station, Antarctica, during the period 1984– 2000. In addition, snow samples taken along the 1km long accumulation-stake profile were measured to determine spatial variability in isotope composition of recent snow. the stacked δD time series spanning the last 55 years shows only weak correlation with the mean annual air temperature recorded at Vostok station. Significant oscillations of both snow accumulation and snow isotope composition with the periods 2.5, 5, 20 and, possibly, ~102 years observed at single points are interpreted in terms of drift of snow-accumulation waves of various scales on the surface of the ice sheet.
Indian monsoon and North Atlantic Oscillation signals reflected by Cl– and Na+ in a shallow ice core from Dasuopu glacier, Xixabangma, Himalaya
Authors: Ninglian Wang , Tandong Yao , Thompson Lonnie G. , Davis Mary E. 
Published: November 2007

AbstractInformation about past atmospheric circulation and climate change can be revealed by the chemical constituents of ice cores. Based on the analytical results of Cl– and Na+ concentrations in an 18.5 m ice core, which contains 14 annual layers, from the Dasuopu glacier, central Himalaya, a significant correlation is found between Cl– and Na+ concentrations. This, along with the average Cl–/Na+ weight ratio of 1.9, indicates that moisture at the drilling site came mostly from oceans. Furthermore, there was a high positive correlation between the Cl–/Na+ ratio in the summer monsoon layers and the monsoon rainfall in northeast India, and there exists a teleconnection between the Cl– and Na+ concentrations in this shallow ice core and the North Atlantic Oscillation.