bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrimination of a wet snow cover using passive microwave satellite data
Authors: Walker A.E. , Goodison B.E.
Published: September 2017

Snow-cover monitoring using passive microwave remote sensing methods has been shown to be seriously limited under melt conditions when the snowpack becomes wet. A wet snow indicator has been developed using DMSP SSM/I 37 GHz dual-polarization data for the open prairie region of western Canada. The indicator is used to identify areas of wet snow and discriminate them from areas of snow-free land. Validation and testing efforts have illustrated that the addition of the indicator to the current SSM/I snow water equivalent algorithm provides a more accurate representation of spatial snow coverage throughout the winter season for the open prairie region. The improved spatial and temporal information resulting from the use of the indicator enhances both climatological and hydrological analyses of snow-cover conditions using passive microwave data. Although the wet snow indicator has only been validated for the open prairie region of western Canada, it may also be applicable to other regions of similar terrain and vegetative characteristics. However, in areas of dense vegetation, such as the boreal forest, the performance of the indicator is poor due to the generally low 37 GHz polarization differences of the vegetation cover.
Description of a program for SAR investigation of the Greenland ice sheet and an example of margin change detection using SAR
Authors: Fahnestock Mark A. , Bindschadler Robert A.
Published: September 2017

In order to interpret changes in the Greenland ice sheet as indications of climatic variation, it is necessary to place observations of local changes in a regional context. This requires a comprehensive monitoring effort which addresses both the inland ice and changes in the ice margin. This paper describes the design of a program for regional investigation of the Greenland ice sheet using synthetic aperture radar (SAR), and discusses the utility of SAR data for detection of change in the ice sheet margin.

Comprehensive coverage of the Greenland ice sheet by ERS-1 SAR will allow us to map the boundaries of snow facies on the ice sheet and investigate recent changes in the ice margin. We will use geo-referenced images to map the current boundaries of snow facies, providing a baseline which can be used to detect future change.

We demonstrate the utility of SAR for detecting recent changes in the ice margin. SAR images clearly show the ice edge, moraines, and ice marginal lakes. These features can be compared with published maps and earlier images in order to document changes in the margin of the ice sheet. We show evidence for recession of a section of the western margin of the ice sheet. The recession, which occurred between 1938 and 1978, ranges from a few hundred meters at high elevations to several kilometers at calving faces in both ice marginal lakes and fjords.

ERS-1 SAR will provide the first opportunity to pursue a comprehensive investigation of the state of the Greenland ice sheet. The ability to address conditions on the ice and to look at margin changes in a systematic way will allow us to develop a stronger framework for interpreting changes in the ice sheet in terms of climatic variation.
Hemispheric snow cover from satellites
Authors: Robinson David A.
Published: September 2017

Full hemispheric monitoring of snow cover has been possible since the advent of meteorological satellites in the 1960s. Since that time visible satellite imagery has been used to chart the extent of northern hemisphere snow on a weekly basis. An analysis of monthly snow areas from a consistent U.S. National Oceanic and Atmospheric Administration (NOAA) set, dating back to 1972, finds that hemispheric snow cover has been well below means for the 1972–91 interval since the middle of 1987. Since the late 1970s multichannel data from satellite-borne passive microwave sensors have been used to estimate hemispheric snowpack extent and depth or water equivalent. Microwave extents generally run considerably lower than NOAA visible values due to microwave difficulties in detecting patchy or wet snow, snow lying on unfrozen ground, and snow in forested regions. The relative simplicity of observing hemispheric snow cover from satellites, the potential of integrating these and other sources of data using geographical information system techniques, the critical role that snow cover has in the global heat budget, and the expected role of snow feedbacks in anthropogenic climate change support the continued diligent monitoring of snow cover.
The calculation of surface temperature and albedo of Arctic sea ice from AVHRR
Authors: Lindsay R. , Rothrock D.
Published: September 2017

The temperature and albedo distributions of Arctic sea ice are calculated from images obtained from the AVHRR satellite sensor. The temperature estimate uses a split window correction incorporating regression coefficients appropriate for the arctic atmosphere. The albedo estimate is found assuming a clear and dry atmosphere. Both estimates are made with published correction techniques. Inherent errors due to the uncertainty of the atmospheric interference produced by humidity, aerosols, and diamond dust are judged to be 2–5°C in surface temperature and 0.10–0.20 in surface albedo. Cloudy regions are masked out manually using data from all five channels. The relationship between temperature and albedo is shown for a sample scene. A simple model of a surface composed of only cold, bright ice and warm, dark water is inadequate. Model calculations based on the surface energy balance allow us to relate albedo and temperature to ice thickness and snow-cover thickness and to further assess the accuracy of the surface estimates.
A systematized approach to AVHRR image navigation
Authors: Baldwin D.G. , Emery W.J.
Published: September 2017

Accurate co-location and geo-registration of AVHRR (Advanced Very High Resolution Radiometer) is necessary for most applications involving these data. To obtain the necessary accuracy, most of the current systems available for AVHRR image rectification require corrections to errors arising from several different sources. This paper presents a software package which is able to correct registration errors from all sources using effective roll, pitch, and yaw values determined from ground control point offsets. These effective values are used to establish a baseline registration against which other models are compared. Spacecraft and sampling geometry are revisited in order to systemize and better define the procedure of AVHRR geo-registration. This systematic approach has resulted in a modular software package which has a registration accuracy of 1 satellite pixel, and is easily modified and improved.
The EISMINT benchmarks for testing ice-sheet models
Authors: Huybrechts Philippe , Payne Tony ,   The EISMINT Intercomparison Group
Published: September 2017

We present a series of benchmark experiments designed for testing and comparing numerical ice-sheet models. Following the outcome of two EISMINT workshops organized to intercompare large-scale ice-sheet models currently in operation, model benchmark experiments ate described for ice sheets under fixed and moving margin conditions. These address both steady-state and time-dependent behaviour under schematic boundary conditions and with prescribed physics. A comparison was made of each model’s prediction of basic geophysical variables such as ice thickness, velocity and temperature. Consensus achieved in the model inter-comparison provides reference solutions against which the accuracy and consistency of ice-sheet modelling codes can be assessed.
An ice-shelf model test based on the Ross Ice Shelf, Antarctica
Authors: MacAyeal D. R. , Rommelaere V. , Huybrechts P. , Hulbe C. L. , Determann J. , Ritz C.
Published: September 2017

A standard numerical experiment featuring the Ross Ice Shelf, Antarctica, is presented as a test package for the development and intercomparison of ice-shelf models. The emphasis of this package is solution of stress-equilibrium equations for an ice-shelf velocity consistent with present observations. As a demonstration, we compare five independently developed ice-shelf models based on finite-difference and finite-element methods. Our results suggest that there is little difference between finite-element and finite-difference methods in capturing the basic, large-scale flow features of the ice shelf. We additionally show that the fit between model and observed velocity depends strongly on the ice-shelf temperature field, for which there is presently little observational control. The main differences between model results are due to the equations being solved, the boundary conditions at the ice from and the discretization method (finite element vs finite difference).
Modelling of a marine glacier and ice-sheet-ice-shelf transition zone based on asymptotic analysis
Authors: Chugunov Vladimir A. , Wilchinsky Alexander V.
Published: September 2017

All parts of a two-dimensional, isothermal, stationary marine glacier (grounded ice sheet, ice shelf and transition zone) with constant viscosity are analysed by perturbation methods. In so doing, all zones of different flow patterns can be considered separately. Correlations between spatial scales for all parts can be expressed in terms of the typical ice-surface slope distant from the ocean, which reflects exterior conditions of the glacier’s existence. In considering the ice-sheet–ice-shelf transition zone, a small parameter characterizing the difference between ice and water densities is used. Such an analysis allows us to find boundary conditions at the grounding line for the grounded ice mass. Glacier-surface profiles are determined by numerical methods. The grounding-line position found by using the boundary conditions derived in this paper differs from that obtained by using Thomas and Bentley’s (1978) boundary conditions by about 10% of the grounded ice-stream length.
Ice-sheet surging and ice-stream formation
Authors: Fowler A. C. , Johnson C.
Published: September 2017

A simplified model of ice-sheet behaviour is described. It combines the assumptions of rapid ice flow, high viscous activation energy and realistic sediment-based sliding dynamics to form a non-linear diffusion-type equation which can display relaxation oscillations analogous to those of surging glaciers, and which may be relevant to large-scale surges of the Hudson Strait and Cabot Strait ice streams of the Laurentide ice sheet.

When the physics of this model is applied to a laterally extensive unidirectional ice flow, such as that in the Siple Coast of Antarctica, an appropriate mechanism may exist for the spontaneous generation of ice streams.
Stability of ice rises and uncoupled marine ice sheets
Authors: Hindmarsh R. C. A.
Published: September 2017

An analysis of the linear stability of marine ice sheets uncoupled from associated ice shelves is presented. The principal feature is a zero eigenvalue associated with infinitesimal shifts along the line of neutral equilibrium in phase space, termed the “equilibrium manifold”. A finite-difference scheme is constructed which respects this stability properly.

The zero eigenvalue appears to allow modelling errors to accumulate rather than dissipate as occurs in land-based ice sheets. The practical significance of this is that even rather fine spatial grids may allow substantial numerical error to accumulate.
Model experiments on the evolution and stability of ice streams
Authors: van der Veen C. J. , Whillans I. M.
Published: September 2017

A simple model is developed based on the notion that on active ice streams the resistance to flow is partitioned between basal drag and lateral drag. The relative roles of these sources of resistance is determined by a friction parameter that effectively describes the strength of the bed under the ice stream. Reduction in the basal strength is caused by meltwater production, taken proportional to the product of basal drag and ice speed. The width of the ice stream is governed by the balance between entrainment or erosion of ice from the slow-moving inter-stream ridges and advection from the ridges into the ice stream. Entrainment of ridge ice is parameterized as a function of the shear stress at the lateral margins, in one case proportional to the lateral shear stress and in the second case scaled to ice-stream width. In the first formulation, the model rapidly becomes unstable but, using the second formulation, a steady state is reached with lateral drag providing all or most of the resistance to flow. The results point to the great importance of achieving an understanding of entrainment. With the second model and a wide range of parameter values, there is no cyclic behavior, with rapid flow being followed by a quiescent phase.
Ice-sheets’ surface mass-balance evaluation in the UGAMP GCM: the climate of Antarctica
Authors: Marsiat I.
Published: September 2017

General Circulation Models (GCMs) will be more and more used for coupled climatic simulations involving ice sheets. It is therefore of prime importance to evaluate the performance of these models in simulating the mass balance and climate over ice sheets. The Antarctic climate simulated with the U.K. Universities Global Atmospheric Modelling Programme General Circulation Model (UGAMP GCM, hereafter referred to as the UGCM) is in good agreement with the available observations. In particular, the accumulation pattern appears fairly reasonable. Some imperfections are related to the surface temperature and energy budget but without severe consequences for the atmosphere behaviour. Refining the snow-related parameterizations could improve the results of the model in high latitudes.
Ocean tides under the Filchner-Ronne Ice Shelf, Antarctica
Authors: Smithson M. J. , Robinson A. V. , Flather R. A.
Published: September 2017

A depth-averaged finite-difference numerical model has been used to make a preliminary study of the tides under the Filchner–Ronne Ice Shelf. Open boundary conditions were specified using the global ocean model of Schwiderski. Tidal constituents for the two principal semi-diurnal constituents M2 and S2, and the two principal diurnal constituents Ο1 and K1 were extracted from computed sea-surface elevations by harmonic analysis. Measured values near to the grounding line could only be reproduced satisfactorily by increasing the bottom friction coefficient under the ice to 50 times the open-ocean value. This destroys any agreement near the ice front or at pelagic sites. It is thought that a friction coefficient which varies with distance under the ice would be able to reproduce better all the available measurements. More tidal measurements are required to validate any model of the region with model experiments being used to help pinpoint possible sites for instrument deployment.
Ice-sheet flow features and rheological parameters derived from precise altimetric topography
Authors: Rémy F. , Ritz C. , Brisset L.
Published: September 2017

For the first time high-quality coverage of the ERS-1 radar altimeter provides a very accurate surface topographic map covering 80% of the Antarctic ice sheet that can contribute significantly to glaciological studies such as ice-sheet flow modelling. The topography allows estimation of the ice-flow direction, the balance velocity and the basal shear stress. A relationship between shear stress, basal temperature and a parameter related to strain rate helps in mapping the behaviour anomalies of these parameters. Longitudinal stress, sliding, bedrock topography and variation in the pre-exponential factor of the flow law are found to play a major role in the ice-flow pattern. This relation can also be used to estimate rheological parameters: the Glen exponent n is found to be 1 for T < −10°C and 3–4 for higher temperatures, where Q is found to be 70 kJ mol−1.
Isostatic uplift in the late Weichselian Barents Sea: implications for ice-sheet growth
Authors: Siegert M. J. , Fjeldskaar W.
Published: September 2017

Results from a recent time-dependent ice-sheet modelling study of the late Weichselian Svalbard—Barents Sea ice sheet suggest that, under environmental conditions representative of those during the late Weichselian, ice derived solely from Svalbard may have occupied only the relatively shallow (<300 m water depth) northwestern Barents Sea, with other deeper regions remaining free of grounded ice (Siegert and Dowdeswell, 1995a). However, late Weichselian geological information from the 400 m deep Bjørnøyrenna (southern Barents Sea) indicates that grounded ice was present in an area modelled by Siegert and Dowdeswell (1995a) as free of ice (e.g. Laberg and Vorren, in press a). Isostatic uplift of the central Barents Sea may have reduced the relative sea level and hence provided a mechanism by which grounded ice could have migrated from relatively shallow regions of the Barents Sea into, previous to uplift, deeper water. We have used an isostatic Earth model to determine the geometry of an isostatic forebulge within the late Weichselian Barents Sea, caused by ice loads over Svalbard, Franz Josef Land, Novaya Zemlya and Fennoscandia. These data were then used as input to a time-dependent glaciological model, in order to predict further information about the magnitude of bedrock uplift required to allow grounded ice to flow from Svalbard into the central and southern Barents Sea. Our experiments suggest that grounded ice, originating from Svalbard, is able to form over Sentralbanken, providing that at least 60 m of uplift is achieved in the central Barents Sea. Grounded ice within Bjørnøyrenna was only predicted when the amplitude of the local forebulge exceeded 250 m.
250 000 years in the history of Greenland’s ice sheet
Authors: Weis Magnus , Hutter K. , Calov Reinhard
Published: September 2017

Calculations have been conducted for the geometric evolution of the Greenland ice sheet through the last 250 000 years of its climate history. An extended version of Calov’s three-dimensional ice-sheet model is used, i.e. ice is modelled as a viscous thermomechanically coupled fluid with power-law rheology underlain by a heat-conducting lithosphere susceptible to bedrock sinking. The shallow-ice approximation is imposed and the simplified equations are numerically integrated by finite-difference approximation using a centred staggered Arakawa grid. This system is driven by data obtained from the European Greenland Ice Core Project (GRIP). The parameterization of the atmospheric temperature is based on data from Ohmura, precipitation data are taken from Ohmura and Reeh and implemented as shown by Calov. Topographic data for the present observed conditions are those of Letréguilly. The resultant 250 kyear model integrated topography is quite close to that obtained from a steady-state calculation under present conditions. For the calculations presented, Greenland’s north dome seems to be more sensitive to changes in precipitation than its south dome. While the height of the north dome is directly related to the atmospheric temperature, the height of the south dome is inversely related to this variable. In the south, changes in ice dynamics due to a change in ice temperature oppose changes in precipitation. The calculations are visualized in a short video clip that is kept on file with the authors.
Models for strain localization in Law Dome, Antarctica
Authors: Rowden-Rich R. J. M. , Wilson C. J. L.
Published: September 2017

A finite-element model was implemented that relates the computed flow to some field and fabric observations recorded on the Law Dome ice cap, East Antarctica. The results of the model suggest that the general ice flow is markedly affected by the bedrock topography. The zones of measured anomalous flow correlate with significant changes in the modelled stress within the ice mass. Stress increases of up to 50% above the reduced model shear stress were obtained in the models where the ice moved over a bedrock rise. Stress relaxation also occurs in the ice mass as the ice moves downward to a lee depression. There is a marked oscillation in the direction of principal stress and this is responsible for the progressive development of a set of high stress zones that are superimposed on the down-slope ice movement.
Greenland under changing climates: sensitivity experiments with a new three-dimensional ice-sheet model
Authors: Fabre Adeline , Letréguilly Anne , Ritz Catherine , Mangeney Anne
Published: September 2017

A new three-dimensional, time-dependent ice-sheet model, including the calculation of the coupled temperature and velocity fields, isostatic adjustment of the bedrock and a mass-balance parameterization, was used to reconstruct the evolution of the Greenland ice sheet in response to a climate history derived from the oxygen-18 measured in the GRIP ice core. Steady-state experiments were done to test the sensitivity of the model, first to variations of poorly known parameters, secondly to different climates. These experiments show that the modelled ice sheet is not very sensitive to variations in the geothermal heat flux, but very sensitive to changes in the accumulation.
Indications of melt in near-surface ice-core stratigraphy: comparisons with passive-microwave melt signals over the Greenland ice sheet
Authors: Rowe Clinton M. , Anderson Mark R. , Mote Thomas L. , Kuivinen Karl C.
Published: September 2017

During the summer of 1993, a field program was conducted to collect several shallow firn cores from two locations in the southern region of the Greenland ice sheet. Stratigraphic evidence of melt from these cores was used for comparison with satellite-derived indications of melt.

The shallow firn cores were examined for stratigraphic evidence of past melt events and were sampled for oxygen-isotope analysis to delineate the annual accumulation layers in the snowpack. The relative intensity of each year’s summer melt episode was compared to the corresponding melt frequency derived from microwave emissions. This comparison demonstrates that a linkage between the stratigraphic record and microwave data can be established. Both data sets indicate that there was less melt during the late 1970s and early 1980s than during the late 1980s, in general agreement with climate observations.
Recent variations and regional relationships in Northern Hemisphere snow cover
Authors: Robinson David A. , Frei Allan , Serreze Mark C.
Published: September 2017

An analysis of snow-cover variability over Northern Hemisphere land masses reveals a continuation of the subnormal coverage that began in the late 1980s (relative to the 1972–present interval). While the 1994 snow year (September 1993–August 1994) exhibited a return to near-normal hemispheric extent, only three months during this period had above-normal coverage. Only 11 of the past 88 months (through October 1994) have been above the norm. Deficits have been most common in spring, over both the Eurasian and North American continents. This is a hemisphere-wide situation; positive correlations are identified between hemispheric and regional snow extents in spring, as well as in fall and winter. A number of significant associations are also recognized between regions during these three seasons; however, it is uncommon to see more than 50% of the variance in one region explained by another. These correlations are most common between adjacent regions, but some are found between regions on different continents. Only in spring are significant positive relationships between non-adjacent regions on the same continent observed.
Accumulation in Antarctica and Greenland derived from passive-microwave data: a comparison with contoured compilations
Authors: Zwally H. Jay , Giovinetto MARIO B.
Published: September 2017

The annual rate of net mass accumulation at the surface in the Antarctic and Greenland ice sheets is determined from firn emissivity based on Nimbus-5 ESMR and Nimbus-7 THIR data. In this study the determinations are limited to the areas of dry-snow facies and are based on a hyperbolic function of emissivity. Two coefficients of the function are selected for particular regions of each ice sheet after a comparison with field data selected for their reliability (82 stations in East Antarctica, 69 stations in West Antarctica and 89 stations in Greenland). Derived accumulation values are produced for grid-point locations 100 km apart which cover 56–94% of the dry-snow areas and 32–58% of the accumulation areas of each ice sheet. These values are compared with interpolated values obtained from the latest contoured compilations of field data. The means of derived values for East and West Antarctica are 12% and 39% larger, respectively, than the mean obtained from interpolated values, suggesting that the isopleth patterns as drawn in the compilation of field data lead to underestimates. The mean of derived values for Greenland is 5% smaller than the mean obtained from interpolated values, suggesting that the compilation of field data may lead to small overestimates that are within the error of determination and the variability of accumulation. Improving facies zonation and the determination of coefficients for the areas of upper percolation facies should improve these preliminary assessments.
A 1000 year climate ice-core record from the Guliya ice cap, China: its relationship to global climate variability
Authors: Thompson L. G. , Mosley-Thompson E. , Davis M.E. , Lin P.N. , Dai J. , Bolzan J.F. , Yao T.
Published: September 2017

In 1992, an American-Chinese expedition successfully recovered three ice cores (308.6, 93.2 and 34.5m) from the Guliya ice cap (summit 6710 m a.s.l) in the far western Kunlun on the Qinghai–Tibetan Plateau, China. Guliya resembles a “polar” icecap with 10 m, 200 m and basal temperatures of –15.6°, –5.9° and –2.1°C, respectively. The 308.6 m core to bedrock is the longest ice core retrieved from an elevation greater than 4000 m a.s.l. and provides the first ice-core history from the western side of the Qinghai Plateau. The Plateau experiences a pronounced annual precipitation cycle during which 70–80% of annual total precipitation falls in the summer monsoon season. This leads to a marked visible stratigraphy in the glaciers which allows accurate dating of the ice cores and reconstruction of the net mass accumulation.

This paper presents (1) the results of the geophysical program to determine ice thickness, ice flow and surface topography, (2) an assessment of net accumulation from stake measurements, snow pits and shallow core samples, and (3) the analyses of the upper 100 m of the 308.6 m core which provide a 1000 year history, including the ‘“Little Ice Age”, which is compared with Chinese historical records. Extended periods of positive accumulation on Guliya are closely contemporaneous with dry periods in eastern China. A trans-Pacific teleconnection is suggested by the strong temporal coherence between extended wet and dry phases on Guliya and on the Quelccaya ice cap, Peru.
Thickening of Jakobshavns Isbræ, West Greenland, measured by airborne laser altimetry
Authors: Thomas R. , Rkabill W. , Frederick E. , Jezek K.
Published: September 2017

NASA flights over southern Greenland in 1991, 1992 and 1993, using a scanning laser altimeter with Global Positioning System (GPS) navigation, have demonstrated a capability to measure ice-surface elevations to an accuracy of 10-15 cm. Flights over Jakobshavns Isbræ revealed winter thickening by several meters between September 1991 and April 1992. By July 1993, surface elevations showed a small additional increase, possibly associated with the cold 1992 summer. Data collected over the ice sheet east of Jakobshavns Isbræ show negligible change over the same period; but further south, at latitude 65 N, the western part of the ice sheet appears to have thickened by up to 2 m between 1980 and 1993. It is clear that such measurements must be continued over many years, both to quantify the effects of inter-annual variability and to measure long-term trends. To this end, we plan to complete a first survey of all major drainage basins on the ice sheet in May-June 1994, and then to resurvey all flight lines at 5a intervals, with more frequent flights over selected routes.
Coastal-change and glaciological maps of Antarctica
Authors: Williams Richard S. , Ferrigno Jane G. , Swithinbank Charles , Lucchitta Baerbel K. , Seekins Barbara A.
Published: September 2017

In spite of their importance to global climate and sea level, the mass balance of the Antarctic ice sheet and the dynamics of the coast of Antarctica are largely unknown. In 1990, the U.S. Geological Survey, in cooperation with the Scott Polar Research Institute. U.K., began a long-term coastal mapping project in Antarctica that is based on analysis of Landsat images and ancillary sources. The project has live objectives: (1) to determine coastline changes that have occurred between the mid-1970s and the late 1980s/early 1990s; (2) to establish an accurate base-line series of 24 1: 1 000 000 scale maps that define the glaciological characteristics of the coastline: (3) to determine velocities of outlet glaciers, ice streams and ice shelves: (4) to compile a comprehensive inventory of outlet glaciers and ice streams: and (5) to compile a 1: 5 000 000 scale map of Antarctica derived from the 24 maps. Analysis of images used in producing the first five of the 24 maps has shown that ice fronts, iceberg tongues and glacier tongues are the most dynamic and changeable features in the coastal regions of Antarctica. Seaward of the grounding line of outlet glaciers, ice streams and ice shelves, the floating margin is subject to frequent, large calving events and rapid flow. Although calving does occur along ice walls, the magnitude of their change on an annual to decadal basis is generally not discernible on Landsat images; therefore, ice walls can be used as relatively stable reference features for measuring other changes along the coast. Velocities of outlet glaciers, ice streams and ice shelves range from 0.1 to several kilometers per year.
Sensitivity experiments to sea surface temperatures, sea-ice extent and ice-sheet reconstruction, for the Last Glacial Maximum
Authors: Ramstein G. , Joussaume S.
Published: September 2017

For the Last Glacial Maximum, (LGM; 21 000 BP), simulations using atmospheric general-circulation models (AGCMs) are very sensitive to the prescribed boundary conditions. Most of the recent numerical experiments have used the CLIMAP (1981) data set for ice-sheet topography, sea-ice extent and sea surface temperatures (SSTs). To demonstrate the impact of ice-sheet reconstruction on the LGM climate, we performed two simulations: one using CLIMAP (1981) ice-sheet topography, the other using the new reconstruction provided by Peltier. We show that, although the geographical structure of the annually averaged temperature is not modified, there are important seasonal and regional impacts on the temperature distribution. In a second step, to analyze the effects of cooler SSTs and sea-ice extent, we performed a simulation using CLIMAP (1981) for the ice-sheet topography, but with present SSTs. We find that the cooling due to ice sheets for the LGM climate is one-third of the global annually averaged cooling, and dial the southward shift of the North Atlantic low in winter is not due to sea-ice extent, but is an orographic effect due to the Laurenride ice sheet. This set of sensitivity experiments allows us also to discriminate between thermal and orographic forcings and to show the impact of the ice-sheet topography and cooler SSTs on the pattern of planetary waves during the LGM climate.
The influence of the albedo-temperature feed-back on climate sensitivity
Authors: Bintanja Richard , Oerlemans Johannes
Published: September 2017

A vertically integrated, zonally averaged energy-balance climate model coupled to a two-dimensional ocean model with prescribed overturning pattern is employed to assess the seasonally and latitudinally varying response of the climate system to changes in radiative forcing. Since the sensitivity of the climate system depends on its actual state, considerable attention is given to the correct simulation of the important features of the present-day climate (such as surface air temperature, sea-ice and snow amount and meridional energy transport). The climate variability induced by the various elements of the albedo-temperature (e.g. sea-ice and snow) feed-back is quantified. It appears that the variability caused by sea-ice variations is approximately twice as large as for snow variations.
Simulating the effects of mean annual air-temperature changes on permafrost distribution and glacier size: an example from the Upper Engadin, Swiss Alps
Authors: Hoelzle Martin , Haeberli Wilfried
Published: September 2017

Models are developed to simulate changes in permafrost distribution and glacier size in mountain areas. The models exclusively consider equilibrium conditions. As a first application, the simplified assumption is used that one single parameter (mean annual air temperature) is changing.

Permafrost distribution patterns are estimated for a test area (Corvatsch-Furtschellas) and for the whole Upper Engadin region (eastern Swiss Alps) using a relation between permafrost occurrence as indicated by BTS (bottom temperature of the winter snow cover) measurements, potential direct solar radiation and mean annual air temperature. Glacier sizes were assessed in the same region with data from the World Glacier Inventory database. The simulations for the glaciers are based on the assumption that an increase or decrease in equilibrium-line altitude (ELA) would lead to a mass-balance change. Model calculations for potential future changes in ELA and mass balance include estimated developments of area, length and volume. Mass changes were also calculated for the time period 1850–1973 on the basis of measured cumulative length change, glacier length and estimated ablation at the glacier terminus.

For the time period since 1850, permafrost became inactive or disappeared in about 15% of the area originally underlain by permafrost in the whole Upper Engadin region, and mean annual glacier mass balance was calculated as −0.26 to −0.46 m w.e.a−1 for the larger glaciers in the same area. The estimated loss in glacier volume since 1850 lies between 55% and 66% of the original value. With an assumed increase in mean annual air temperature of +3°C, the area of supposed permafrost occurrence would possibly be reduced by about 65% with respect to present-day conditions and only three glaciers would continue to partially exist.
Studies of Icebergs, Ice Fronts and Ice Walls using Side-Scanning Sonar
Authors: Klepsvik John O. , Fossum Bjørn A.
Published: September 2017

During the Norwegian Antarctic Research Expedition of 1978–79, a number of experiments were carried out using side-scanning solar techniques for under-water mapping of icebergs, ice fronts, and ice walls, and for studies of active ploughing areas off ice fronts. This paper presents the techniques and some results, together with views on operational and environmental aspects of using side-scanning sonar in the Antarctic. From the sonographs it is possible to measure depths of icebergs and ice fronts, and to estimate the magnitudes of shape anomalies. Vertical profiles of ice fronts show great variations depending on whether they are grounded or floating. Also, the acoustic signatures vary according to the elapsed time since calving.
Viscoelastic analysis of Calving Glaciers
Authors: Reddy D. V. , Bobby W. , Arockiasamy M. , Dempster R. T.
Published: September 2017

Calving of floating ice shelves is studied by a viscoelastic finite-element analysis. The fan-shaped breaking-up of glaciers due to forces that cause bending on creeping ice is assumed to be axisymmetric. Bending may be due to geometry of the bcdrock, action of tides and waves, and imbalance (at the ice front) between the stress in the ice and the sea-water pressure.

The bulk and shear moduli of the ice are represented by relaxation functions of the Prony series, which is a discrete relaxation spectrum composed of a constant and a summation of exponential terms. These properties are also functions of temperature, that varies over the thickness of the ice shelf. The temperature distribution across the thickness of the ice is obtained from calculations based on a linear dependence of thermal conductivity on the temperature. Numerical results are presented for various calving mechanisms. A computer code, VISIC1, is developed by modifying a finite-element viscoelastic code, VISICE, for floating ice islands. The buoyancy of the water is taken into account by a Winkler spring model, with the spring force determined from displaced volume. Locations of crack initiation obtained from the analysis are used to predict the iceberg size immediately after calving.
Tabular Icebergs: Implication from Geophysical Studies of Ice Shelves
Authors: Shabtaie Sion , Bentley Charles R.
Published: September 2017

Recent geophysical and glaciological investigations of the Ross Ice Shelf have revealed many complexities in the ice shelf that can be important factors in iceberg structure. The presence of rift zones, surface and bottom crevasses, corrugations, ridges and troughs, and other features could substantially modify the hydraulics of iceberg towing and lead to disintegration of the berg in the course of transport.

The relationships between the elevation above sea-level and total ice thickness for three ice shelves (Ross, Brunt, and McMurdo) are given; from them, expressions for the thickness/freeboard ratios of tabular icebergs calved from these ice shelves are obtained. The relationships obtained from the measured values of surface elevation and ice thickness are in agreement with models derived assuming hydrostatic equilibrium.

Areas of brine infiltration into the Ross Ice Shelf have been mapped. Examples of radar profiles in these zones are shown. Absorption from the brine layers results in a poor or absent bottom echo. It is probable that little saline ice exists at the bottom of the Ross Ice Shelf front due to a rapid bottom melting near the ice front, and that the thickness of the saline ice at the bottom of icebergs calving from the Ross Ice Shelf is no more than a few meters, if there is any at all.

We have observed many rift zones on the ice shelf by airborne radar techniques, and at one site the bottom and surface topographies of (buried) rift zones have been delineated. These rift zones play an obvious role in iceberg formation and may also affect the dynamics of iceberg transport. Bottom crevasses with different shapes, sizes, and spacings are abundant in ice shelves; probably some are filled with saline ice and others with unfrozen sea-water. Existence of these bottom crevasses could lead to a rapid disintegration of icebergs in the course of transport, as well as increasing the frictional drag at the ice-water boundary.

Radar profiles of the ice-shelf barrier at four sites in flow bands of very different characteristics are shown. In some places rifting upstream from the barrier shows regular spacings, suggesting a periodic calving. Differential bottom melting near the barrier causes the icebergs to have an uneven surface and bottom (i.e. dome-shaped).

Electrical resistivity soundings on the ice shelf can be applied to estimate the temperature-depth function, and from that the basal mass-balance rate. With some modifications, the technique may also be applied to estimating the basal mass-balance rates of tabular icebergs.
Iceberg-Seabed Interaction (Northern Labrador Sea)
Authors: Barrie J. V.
Published: September 2017

Large-scale furrows occurring in unconsolidated Quaternary sediments on the Labrador Shelf are considered to be gouge marks of bottom-dragging icebergs. Side-scan sonograph mosaics from the northern Labrador Shelf were constructed for two bathymetric interbank areas. They reveal that both relict ice bottom gouging and modern iceberg scouring have taken place at water depths greater than 180 m. The recent scours are linear to curvilinear to crater-like in form, with average widths of 30 m at a mean scour depth of 5 m and lengths in excess of 3 km. The dominant scour trend is north-south, reflecting the Labrador Current.

Impedance of icebergs by bottom interaction is primarily a function of the gross iceberg size and shape, sediment encountered by the keel, and prevailing current. For modern scouring, frequencies of detectable impact decrease exponentially with increasing scour depth, and scour depth is inversely proportional to the sediment shear and compressive strengths.
The Physical Processes involved in the Melting of Icebergs (Invited paper)
Authors: Huppert Herbert E.
Published: September 2017

The causes of iceberg deterioration can be discussed under three broad headings: wave-induced melting at the water line; breaking; and melting at the top, bottom, and sides. A short summary of current understanding under the first two headings is presented. It is then argued, under the third heading, that the melt rate at the sides of a tabular Antarctic iceberg is likely to exceed that at the top and bottom. The behaviour of the entraining plume which forms at the side of an iceberg when it melts in water of uniform salinity is outlined. Another form of convection, occurring when the ambient water is stratified, is then described; in this case the melt water spreads out in a series of almost horizontal layers. Finally, field observations on iceberg melting are discussed.
Iceberg Dynamical Modelling
Authors: Mauviel F.
Published: September 2017

Experimental tests were carried out on model icebergs. Natural drift tests with a 1:100 scale model on Brienzer See, Switzerland, show the effects of various environmental conditions. Froude similitude formed the basis for these tests. Other experiments, carried out with a 1:60 model in St. Malo harbour, France, show the need for information obtained at this scale, and include assessments of the drag coefficients for various model shapes with or without insulation skirts on the model, the effects of added mass and rotation of the model, and steering possibilities.
The Location of Impurities in Antarctic Ice
Authors: Wolff E.W. , Mulvaney R. , Oates K.
Published: September 2017

Analysis of an ice sample with an estimated age of 125 years, from the Antarctic Peninsula, using a scanning electron microscope with a cold stage and an X-ray micro-analysis facility, shows that H2SO4 occurs mainly at triple junctions. Sea salts show no such localization. The different behaviour may be due to the freezing-point behaviour of each chemical substance, and to the effect this has both in the atmosphere and during recrystallization in the ice sheet. If this finding applies generally to other parts of the Antarctic ice sheet, it has major implications for many of the physical properties of Antarctic ice. In particular, it leads to a better understanding of the d.c. electrical conductivity of such ice.
Texture of Polar Firn for Remote Sensing
Authors: Alley R.B.
Published: September 2017

Knowledge of the texture of polar firn is necessary for interpretation of remotely sensed data. We find that dry polar firn is an irregularly stratified, anisotropic medium. Grains in firn may be approximated as prolate spheroids with average axial ratios as high as 1.2 or greater and with a preferred orientation of long axes clustered around the vertical. Such elongate grains are preferentially bonded near their ends into vertical columns, so that grain bonds show a preferred horizontal orientation. The grain-size distribution is similar in most firn and the normalized distribution is stationary in time, but the distribution is somewhat different in depth hoar. Fluctuations of firn properties are large near any depth, but decrease with increasing depth. With increasing depth, anisotropy of surfaces decreases, bond size relative to grain size decreases slightly, and number of bonds per grain and fraction of total grain surface in bonds increase. Grain size increases linearly with age below 2 to 5 m, but increases more rapidly in shallower firn.
Internal Reflecting Horizons in Spitsbergen Glaciers
Authors: Bamber J. L.
Published: September 2017

A single pronounced internal reflecting horizon has been observed on radio echo-sounding from over 30 glaciers in Spitsbergen. They are often present along the entire length of the glacier, remaining at a fairly constant depth (100–200 m) below the ice surface. Echo-strength data from radio echo-sounding have been used to obtain reflection coefficients, for these horizons, of between -15 and -25 dB. Combined with results of ice-core studies, the possible causes of this internal layer are investigated. The presence of water is found to be the most likely explanation, indicating the existence, at depth, of a layer of temperate ice.
MACRO AND MICROSCOPIC MORPHOLOGY OF LYSSA BODY IN DOG
Authors: Sultana N. , Afrin M. , Amin T. , Afrose M.
Published: September 2017

With the aim to study the gross and histomorphology of the lyssa body of dog, seven heads were collected from the healthy adult dogs used for dissection purpose in the laboratory of the Department of Anatomy and Histologyat Bangladesh Agricultural University, Mymensingh. The gross parameters such as weight, length and width were recorded for respective specimens.The present study revealed that the dog lyssa was pinkish white coloured and situated along the median plane on the ventral surface of the free portion of the tongue. The lyssa had more or less rod shaped. The weight, length and width of the lyssa were measured as 0.11 ± 0.01gm, 3.96 ± 0.4cm and 0.28 ± 0.03cm, respectively.Then the specimens were processed for histomorphology and stained with Hematoxylin and Eosin. The present study noticed that the entire body of the lyssa was formed from adipose tissue and striated muscle bundles, encircled by a thick connective tissue capsule of mainly collagen fibers.These results will be helpful to study the further functional importance of the lyssa body in dog.