bluuebunny/crossref_metadata_2025_split huggingface dataset:
Albedo Of Snow, Ice Sheets and Snow-Covered Sea Ice In General Circulation Models
Authors: Marshall Susan E. , Warren Stephen G. 
Published: September 2017

We have developed a physically-based parameterization for snow albedo, for the visible and near-infrared spectral regions used in general circulation models (GCMs). Snow albedo depends primarily on snow grain size, and also on solar zenith angle, snow thickness, impurity content, and atmospheric transmittance. This parameterization is now available as a Fortran subroutine. Simpler, but less accurate, parameterizations have also been developed which depend only on grain size or thickness. Since GCMs do not compute snow grain size, we also developed a method to estimate grain size based on the air temperature and the snow age.Our parameterization for snow albedo is being incorporated in the NCAR Community Climate Model (CCM) in place of the existing empirical parameterization for snow albedo, to determine the effect of this improvement on the model's performance, and the results will be discussed. However, additional aspects of the treatment of the radiative properties of snow and ice were also capable of improvement and are being changed in the CCM. In particular, it is important to recognize that sea ice is often snow-covered and in that case has an albedo as high as that of snow, and that southern hemisphere sea ice is nearly always snow-covered, even through the melting season. The surface albedo for the Antarctic ice sheet should be about 0.83, but it had been set to 0.71 in the CCM, The CCM has been calculating temperatures too warm over Antarctica, and this low albedo contributed to that error.
Extracting Climatic Information From Observations Of Icebergs In The Southern Ocean
Authors: Orheim Olav 
Published: September 2017

Antarctic iceberg observations provide two types of climatic information: (1) the rate of iceberg calving gives the main negative term in the mass balance of Antarctica; (2) the distribution of icebergs in the Southern Ocean is related to various factors including sea-ice extent and ocean conditions. This paper discusses climatic information obtained both from modern iceberg observations, and from historical data.The main modern data source is the international iceberg observation programme, initiated in 1981. This has generated a database which now contains observations of size and position of 150 000 icebergs in the Southern Ocean. Other recent data sources include observations from 1974 of icebergs of over 22 km length by the Navy/NOAA Joint Ice Center (which now total nearly 100 bergs). Historical sources include both scientific and commercial (whaling) expeditions.Three conclusions can be drawn from the recent iceberg data.
(1)For the past seven years annual calving rates of icebergs less than 22 km in length have been approximately constant both in numbers and total mass, and have exceeded the annual mean mass of bergs over 22 km calved during the same period.(2)The annually-calved mass of gigantic icebergs of length over 22 km, has varied more than two orders of magnitude during the past two decades. The mass of calved gigantic icebergs alone exceeded continental snow accumulation in 1967, 1986 and 1987.(3)Mean iceberg calving rate exceeds continental snow accumulation rate.These results are discussed in relation to Antarctic mass balance and sea level.Historical observations of iceberg distributions in the Southern Ocean differ from recent observations by showing: (i) higher frequencies of bergs at lower latitudes, (ii) a larger proportion of large bergs, and (iii) a more uniform iceberg distribution throughout the region. Comparisons between past and present distribution patterns indicate that there must be errors, including exaggerations and selective reporting, in the historical data. Such observations should therefore not be used uncritically to make climatic conclusions.Bearing in mind the potential flaws in historical data there still appears to be real variations with time in iceberg distribution. These include higher frequencies of bergs at lower latitudes during the past century and the first decades of this century, than at present. Expanded northern range of the bergs would occur if one or more of the following conditions then applied: (1) calved icebergs were larger; (2) sea ice was more extensive in time and space; (3) ocean temperatures were lower; (4) ocean (wind) conditions were such that northward advection rates were higher. The importance of each of these conditions is discussed.
A one-dimensional model of the evolution of snow-cover characteristics
Authors: Yamazaki Takeshi , Kondo Junsei , Sakuraoka Takashi , Nakamura Toru 
Published: September 2017

A one-dimensional model has been developed to simulate the evolution of snow-cover characteristics using meteorological data. This model takes into account the heat balance at the snow surface and heat conduction in the snow cover as well as liquid water flow and densification. The basic variables of the model are snow temperature, liquid water content, snow density and the solid impurities density. With these four variables, the model can calculate albedo, thermal conductivity, liquid water flux, snow depth, water equivalent and the amount of runoff.Diurnal variation of profiles of snow temperature, water content and snow density, and meteorological elements were observed at Mount Zao Bodaira, Yamagata Prefecture, Japan. Simulated diurnal variation patterns of each component by the model were in good agreement with the observations. Moreover, the snow-cover characteristics were simulated for three 90-day periods with meteorological data and snow pit observations at Sapporo. It was found that the model was able to simulate long-period variations of albedo, snow depth, snow water equivalent and the snow density profile.
Avalanche modelling and integration of expert knowledge in the ELSA system
Authors: Buisson Laurent , Charlier Claude 
Published: September 2017

The choice of the best protection system against avalanches on a particular path requires an accurate description, or image, of these avalanches. In order to get this image, avalanche consultants can use several numerical models which are often difficult to handle. Moreover, these models deal only with a part of the phenomena involved in avalanches and ignore the others. As a result, the consultants must use their experience and knowledge to imagine the avalanches on any particular path.This paper presents ELSA (Etude et Limites de Sites Avalancheux), a computer system dedicated to the modelling of the knowledge of avalanche experts and to the integration of the new symbolic computer models with the classical numerical models. The basic aim of integration is to build a unique computer system incorporating all these models.After a description of the terrain representation, we present the different scenarios that ELSA takes into account. Then, the methods which deal with some phenomena occurring in avalanches are described. The problems involved in the integration of these methods close this paper.
Field test of a new snow-particle counter (SPC) system
Authors: Sato Takeshi , Kimura Tadashi , Ishimaru Taminoe , Maruyama Toshisuke 
Published: September 2017

The optical system of the snow-particle counter (SPC), which was developed by Schmidt in 1977, has been improved. A laser diode is used as a light source, achieving uniform sensitivity to a blowing snow particle regardless of the location of particle trajectory within a sampling volume. The light entering a slit, which may be affected by a blowing snow particle, is perfectly detected by use of a piano-cylindrical lens and a dual-type photodiode. A signal processor has been developed to get output voltage proportional to the mass flux of blowing snow.From the estimates based on blowing snow characteristics and wind speed profile, the new SPC system can accurately detect all the particles of effective sizes at least at a height above 0.1 m when the wind speed at a height of 1 m is less than 15 m s−1.Considering the Fraunhofer diffraction by both the wire and the particle, the relation between a particle diameter and sensor output of the new SPC system is derived from the calibration with spinning wires.Mass flux obtained with the new SPC system was found to be close to that with a snow trap. The system was operated continuously for at least nine days using two 35 A h lead batteries.
Numerical modelling of the historic front variation and the future behaviour of the Pasterze glacier, Austria
Authors: Zuo Z. , Oerlemans J. 
Published: September 2017

An ice-flow model is used to simulate the front variations of the Pasterze glacier, Austria. The model deals explicitly with the ice flux from sub-streams and tributaries to the main ice stream. The dynamic calibration method adopted successfully calibrates the ice-flow model under a non-steady-state condition. Despite the complexity of the glacier geometry, the ice dynamics of the Pasterze are adequately simulated.Results of the sensitivity experiments suggest that the Pasterze glacier has been in a non-steady state most of the time and has a response time of 34–50 years.Projections of the behaviour of the Pasterze in the next 100 years are made under various climate scenarios. Results suggest that the Pasterze will undergo a substantial retreat if there is future warming. The glacier is likely to retreat 2–5 km by the year 2100. The ice volume could be reduced by 24–63% by the end of the 21st century.
Dynamic behavior of Glaciar Perito Moreno, southern Patagonia
Authors: Skvarca Pedro , Naruse Renji 
Published: September 2017

Frontal oscillations since the beginning of the 20th century are known at Glaciar Perito Moreno, an eastward outlet glacier of Hielo Patagónico Sur (southern Patagonia ice field). In 1900, the calving front was located about 1 km from the opposite bank. From 1935 to 1988, ruptures of ice-dams occurred at intervals of 1–5 years. Although this glacier has thus oscillated, it can be regarded as having been in a rather stable condition during the last half-century. Ice thickness in the ablation area has also remained unchanged from 1990 to 1996. The near-steady behavior of Glaciar Perito Moreno may be attributed to a regulating effect of the calving rate, namely, a decrease in the ablation amount due to calving with a retreat of the glacier.Using 12 m long ablation poles, ice-flow velocities at the ablation area were measured several times in 1993 and 1994. The velocity in the early summer (November) was found to be slightly larger than the annual mean. It is concluded that basal sliding is significant throughout the year at this temperate glacier, with large fluctuations within a short period.
100 years of ice dynamics of Hintereisferner, Central Alps, Austria, 1894–1994
Authors: Span N. , Kuhn M. H. , Schneider H. 
Published: September 2017

Velocity measurements carried out on Hintereisferner, Central Alps, Austria, provide the unique opportunity to study 100 years of ice dynamics of this glacier. During this time, three periods of accelerated flow occurred, around 1920, in 1940 and in the 1970s; but only around 1920 did the acceleration actually lead to an advance of about 60 m. The velocity increased from 30 m year−1 in 1914 to more than 120 m year−1 in 1919, and doubled during the accelerations of 1940 and 1980. In the course of the third event, the velocity increase spread over a period of more than a decade (1965–79) with a comparatively low maximum. These velocity changes cannot be explained by increased deformation velocity due to increased ice thickness alone.Time series of the velocities at various locations along the glacier are given for the entire period, and an attempt was made to construct a time series of the velocity at a point 2 km from the strongly retreating front. The flow divergence was about 0.1 per year in the lowest 2 km, and emergence velocities reached 5 myear−1.
Complex ice stream flow revealed by sequential satellite imagery
Authors: Scambos Ted A. , Bindschadler Robert 
Published: September 2017

The velocity field of the confluence area of two large ice stream tributaries forming Ice Stream D in West Antarctica is studied using sequential Landsat images. Sequential satellite image analysis allows for a very high density of velocity measurements, based on computer-measured displacements of features such as crevasses, crevasse scars, and ice mounds recognizable in both images. Automated displacement measurement of these features results in a detailed map of surface velocities from which surface-horizontal strain-rate fields can be calculated. Correlations between the surface morphology, the velocity field, and the strain-rate field of Ice Stream D reveal a number of important characteristics of ice stream flow:• the characteristic flowband appearance of streaming ice is present at velocities from below 100 m a−1 to above 350 m a−1;• in the upstream areas, there appears to be no sharp transition between “sheet” flow, typical of the surrounding ice sheet, and “streaming” flow;• the fastest moving portions of the ice stream are nearly devoid of surface topography undulations;• the confluence area is characterized by acceleration of the ice in the slower tributary as it impinges on faster-moving ice, and by highly convergent flow. Velocity in the faster-moving tributary changes little, and there is no persistent evidence of the shear margins of the joined tributaries downstream of the confluence.This study demonstrates that sequential satellite image analysis, coupled with computer-determined displacement measurements, can provide accurate velocity and strain-rate information on a regional scale rapidly and cost-effectively. Such data sets are required for modelling ice sheet evolution, and for monitoring any changes in ice flow within the ice streams.
Velocity measurements and changes in position of Thwaites Glacier/iceberg tongue from aerial photography, Landsat images and NOAA AVHRR data
Authors: Ferrigno J.G. , Lucchitta B.K. , Mullins K.F. , Allison A.L. , Allen R.J. , Gould W.G. 
Published: September 2017

The Thwaites Glacier/iceberg tongue complex has been a significant feature of the Antarctic coastline for at least 50 years. In 1986, major changes began to occur in this area. Fast ice melted and several icebergs calved from the base of the iceberg tongue and the terminus of Thwaites Glacier. The iceberg tongue rotated to an east-west orientation and drifted westward. Between 1986 and 1992, a total of 140 km of drift has occurred.Remote digital velocity measurements were made on Thwaites Glacier using sequential Landsat images to try to determine if changes in velocity had occurred in conjunction with the changes in ice position. Measurements on Landsat images from 1972 and 1984 revealed an average annual velocity of 2.62 km a−1 during that time period, and measurements on images from 1984 and 1990 an average annual velocity of 2.84kma−1, an increase of more than 8%. Estimates made on Thwaites Glacier by others using earlier data contained enough uncertainty that it was impossible to determine a velocity profile over a longer period of time. Examination of the morphology of the glacier/iceberg tongue showed no evidence of surge activity.
Texture-based classification of cloud and ice-cap surface features
Authors: Rees W.G. , Lin I-I 
Published: September 2017

It is well known that the interpretation of high resolution (<100 m) visible and near infrared (e.g. Landsat) imagery of large ice masses is hindered by the uniform reflectivity of snow, ice and cloud surfaces. Such interpretation is at present largely performed manually, but there is a good prospect that it could be automated by the incorporation of image texture. This paper describes preliminary work towards the identification of the most appropriate texture technique, or combination of techniques, and assesses the likely performance of such methods.Different textures are identified with different types of surface cover, and the use of these differences to classify images is investigated. Specifically, we compare a traditional texture measure, the Grey Level Co-occurrence Matrix (GLCM), with a modification of a relatively new technique, fractional Brownian motion (FBM). These two methods are applied to three Landsat MSS images of the Nordaustlandet ice cap, Svalbard. The classification accuracy, computation time and memory required, advantages and limitations of the two methods are compared. The GLCM technique appears to be able to distinguish three groups of image classes, namely dry snow, wet snow, and melt features, ablation areas or cloud cover. The FBM technique is computationally more efficient, and though it performs in general less well than the GLCM technique it gives better discrimination of cloud cover.
Stochastic perturbation of divide position
Authors: Hindmarsh R. G. A. 
Published: September 2017

Perturbation of divide position is considered by a linearization about the Vialov–Nye solution and also about related solutions with O(1) relief. Relaxation times of one-sixteenth the fundamental thickness/accumulation-rate time-scale are found for the Vialov–Nye configuration, while substantial basal topography can halve the rate of relaxation. Steady divide position is most sensitive to anti-symmetric accumulation-rate distributions near the divide, but transient divide motion is most strongly excited by anti-symmetric accumulation rate variations halfway between the margin and the divide. Relaxation times for the Antarctic Peninsula divide position are estimated to be around 200 years, while the larger Greenland ice sheet has a divide-position relaxation time of around 600 years.Modelling accumulation rate as a white-noise process permits analysis of divide perturbation as a (stochastic) Ornstein–Uhlenbeck process, where the standard deviation of the response is proportional to the standard deviation of the forcing. If observed accumulation-rate variability in the Antarctic Peninsula were anti-symmetric about the divide, it would be sufficient to force the divide position to fluctuate with standard deviation 10–20 times the depth of the ice sheet. There appears to be sufficient noise to cause Raymond bumps to be spread significantly. More data on the statistical variation of accumulation with position are needed. Random forcing will increase the complexity of any fold structures created in the divide region and in particular the number of such structures intersecting any borehole.
Numerical modelling of a fast-flowing outlet glacier: experiments with different basal conditions
Authors: Pattyn Frank 
Published: September 2017

Recent observations in Shirase Drainage Basin. Enderby Land, Antarctica, show that the ice sheet is thinning at the considerable rate of 0.5–1.0 m a −1. Surface velocities in the stream area reach more than 2000 ma−1, making Shirase Glacier one of the fastest-flowing glaciers in East Antarctica. A numerical investigation of the present stress field in Shirase Glacier shows the existence of a large transition zone 200 km in length where both shearing and stretching are of equal importance, followed by a stream zone of approximately 50 km, where stretching is the major deformation process.In order to improve insight into the present transient behaviour of the ice-sheet system, a two-dimensional time-dependent flowline model has been developed, taking into account the ice-stream mechanics. Both bedrock adjustment and ice temperature are taken into account and the temperature field is fully coupled to the ice-sheet velocity field.Experiments were carried out with different basal motion conditions in order to understand their influence on the dynamic behaviour of the ice sheet and the stream area in particular. Results revealed that when basal motion becomes the dominant deformation process, (partial) disintegration of the ice sheet is counteracted by colder basal-ice temperatures due to higher advection rates. This gives rise to a cyclic behaviour in ice-sheets response and large changes in local imbalance values.
On the effect of sea-ice dynamics on oceanic thermohaline circulation
Authors: Hibler W. D. , Zhang Jinlun 
Published: September 2017

An idealized planetary flat-bottom geostrophic ice–ocean model is constructed with boundaries at latitudes 5° and 65° N and longitudes 50° W and 10° E in order to approximate the North Atlantic. The model is driven by fixed zonally averaged wind, surface air temperatures and surface ocean salinity. A dynamic thermodynamic sea-ice model is coupled to the ocean model. Only the thermodynamic insulating effects of the sea ice are considered, and no salt fluxes due to melting and freezing are included. Four equilibrium simulations of about 5000 years each are performed: two with interactive sea ice with and without ice dynamics, and two control simulations with either a fixed or no ice cover.In the two simulations including interactive sea ice, characteristic oscillations in the ice thickness and ocean temperature are found to occur. The oscillations are smaller when sea-ice dynamics are included. The dominant oscillation occurs at about a 5 year period, with the key feature being that the presence of sea ice tends to insulate the ocean and hence allows an oceanic warming. This warming in turn eventually causes a melt-back of the ice and a subsequent cool-down of the ocean. Oscillations at longer periods of about 20 years in the thermohaline circulation are also observed. These longer-period oscillations are particularly pronounced in the northward surface water transport.
Physical Characteristics and Life Expectancy of Tabular Antarctic Icebergs
Authors: Orheim Olav 
Published: September 2017

The Norwegian Antarctic Research Expedition 1978-79 landed on 24 tabular icebergs and flew over many others in the South Atlantic and the Weddell Sea between latitudes 54 and 76°S. Data were obtained on surface mass balance, stratigraphy, density, 10 m temperatures, crevassing, distribution, and age. Ice thicknesses were measured by airborne radio echo-sounding.All icebergs had experienced surface melting. However, on icebergs south of 66°S., the annual surface melting was only a few centimetres of water equivalent. The average surface mass balance was near zero. Typically the 10 m temperature had increased from about -20° C at the time of calving to -10° C. Only icebergs that had moved northwards from the continent into the west wind drift had snow temperatures close to 0° C. Internal temperatures are increased mainly by the refreezing of percolating melt and rain water. This increased the densities of the upper layers by 100 to 150 kg m-3 above those of nearby ice shelves.All icebergs measured by radio echo-sounding showed variations in thickness of about 20% of the mean thickness. Nearly all had a convex profile across the short axis and were tilted. An average thickness/freeboard curve indicates that icebergs less than 225 m thick will have permeable layers below sea-level. The ratio of freeboard to thickness varied from 0.21 for a 100 m thick berg to 0.14 for a 350 m thick iceberg.All icebergs showed systematic surface crevassing parallel with their sides, the crevasse intensity decreasing with distance from the edge. Icebergs with their smallest dimension greater than 400 m usually had a central zone with little crevassing. Grounded icebergs showed severe crevassing, and could not thereafter survive long periods in open water. Bottom crevasses were not detected.