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

Ice thickness measurements have been carried out at the mouths of ice streams D and E, West Antarctica using a surface-based impulse radar. These studies have been undertaken as a part of the continuing effort to understand the state of the West Antarctica ice sheet and its response to climate change. Thickness measurements will be used in the mass balance calculation currently in progress and to better understand features in the surface topography seen at low angle sun illumination in the satellite imagery. Results show that the discharge areas of ice streams D and E are thickening by approximately 1 m per year, and thus that these ice streams are probably loosing mass. Aperiodic wavelike features in the surface topography are described which pose interesting questions about migration of the grounding line and ice-stream dynamics.

A new theory, in which friction is interpreted as the energy flux required to form surface at contact asperities, is applied to sliding on ice and snow. The results of this theoretical investigation show that in dry friction the relevant contact areas are of almost molecular scale. The properties of the interface layer in ice and snow friction arc poorly known, so that the implications of this new theory are somewhat speculative. However, qualitative agreement with experimental data is good, and the theory provides explanations to the success of some empirically developed methods of improving the frictional properties of skis and sledges.

A dynamic finite-element computer program was used to examine the evolution of microstructure and its effect on continuum-scale deformation for the constant-speed uniaxial-strain compaction of an aggregate of roughly spherical elastic-plastic particles. Simulation results are used to explain some micromechanical aspects of snow compaction. Different compaction rates were used to examine the limits of quasi-static response and the effects of inertial stresses. Four stages of microstructurally controlled compaction were observed for quasi-static loading: particle re-arrangement, elastic deformation and two stages of plastic deformation. Elastic deformation follows the first critical density caused by the stable random loose-particle packing of rough spheres. Stage III compaction occurs by plastic deformation once stresses acting on particles exceed yield. Stage IV compaction follows a second critical density caused by the stable packing of deformed particles and is also through plastic deformation of particles. During high-speed compaction, inertial stresses propagate particle deformation from the loading platen into the aggregate. As a consequence, particle re-arrangement is limited so that the pressure-density ratio is larger for high-speed compaction than for quasi-static compaction at the same density. Hence, critical densities and the compaction-rate dependence of the pressure-density ratio during compaction of an aggregate of particles composed of rate-independent material are determined by the evolution of microstructure at different compaction rates. Observed pressure-density profiles for polar snow exhibit the same features of critical density and changes in the pressure-density ratio as found in the simulation and consist of four compaction stages: particle re-arrangement and three stages of creep particle deformation each following a critical density. Shear stresses appear to enhance the compaction during the stage III creep deformation of snow.

This paper presents a partial analysis of data from an extensive series of laboratory indentation tests. The tests were conducted using flat indentors pushing against sheets of fresh-water ice of thickness 65 to 115 mm. The aspect ratio ranged from 0.9 to 2.6 with indentor velocities of 10 to 80 mm s−1. Details of an ice failure mode known as “crushing with flaking” are studied by making use of measured force-displacement signals and high-speed photography. With these test conditions, ice failure is associated with a production of symmetrical flakes which emanate simultaneously up and down. The failure begins in the middle level of the ice sheet as a rapid expansion of the ice. The post-peak phase of the ice failure involves loss ol the ice material over the whole contact area. The amount of ice that is extruded after the occurrence of the peak force is characterized by a finite failure depth parameter. According to present data, this failure depth is around 70% of the total depth of crushing and flaking that occur during a cycle of loading and unloading.

In the southwestern part of the Sea of Okhotsk off Hokkaido, sea-ice drift characteristics are investigated using the ice and water velocities obtained from a moored upward-looking acoustic Doppler current profiler (ADCP) during the winters of 1999–2001. Using hourly-mean values of these data along with the wind data measured at a nearby coastal station, the wind factor and turning angle of the relative velocity between the ice and water velocities with respect to the wind are calculated assuming free drift under various conditions. Since the simultaneous sea-ice draft data are also available from a moored ice-profiling sonar (IPS), we examine the dependence of drift characteristics on ice thickness for the first time. As ice thickness increases and wind decreases, the wind factor decreases and the turning angle increases, as predicted by the theory of free drift. This study clearly shows the utility of the moored ADCP measurement for studying sea-ice drift, especially with the simultaneous IPS measurement for ice thickness, which cannot be obtained by other methods.

Avalanches are a widespread hazard that cause serious damage in the southeastern Tibetan Plateau. Abundant solid precipitation and high relief are favourable for avalanche occurrence. The monsoon climate brings a lot of precipitation which, however, is not well distributed. Avalanches are most common around the margins of the plateau. Wet snow avalanches occur most frequently. Based on data on precipitation and topographical relief, a map is drawn showing the areal distribution of avalanche hazards.

Snow cover in the intermittent snow zone of the Sierra Nevada can occupy more than 10 000 km2 of the mountain range, but it has received relatively little attention in river forecasting. Snow is deposited at lower elevations only during the cold storms of winter, and remains there only for a few days or weeks. When cold storms have created a thin snow cover at low elevations, a subsequent warm storm can melt this snow in just a few hours and increase the runoff response dramatically. Operational hydrological models and river-forecasting procedures have tended to overlook contributions from the intermittent-snow zone, focusing instead on rainfall-runoff or melt from the snowpack zone at higher elevations. Data-collection efforts are minimal in this zone, too. Ideally, spatially distributed models of snowmelt and runoff generation are needed to account for the typically large differences in snow cover on different aspects in the intermittent snow zone. Although aircraft and satellite imagery would be most desirable to monitor the distribution of snow cover in the intermittent-snow zone, even a few climate stations that report precipitation type and snow presence would be a major improvement over the present situation in the Sierra Nevada.

During the ablation season, the ice cap Vatnajökull (8100 km2) develops its own microclimate that we describe by meteorological data collected during the summers of 1994-2003. Persistent glacier winds are generated down the melting ice cap, whose variations in speed can be related empirically to the temperature fluctuations of the lowland environs of the ice cap. This suggests that climate warming would be accompanied by stronger glacier winds down the outlets of Vatnajökull, producing stronger turbulent fluxes that might amplify the melting rates in the lower ablation areas.

Water vapor in snow is responsible for two main processes connected to almost all studies where snow cover is involved: the snow-density change with time and snow recrystallization. Both processes are the result of a balance between evaporation and condensation on individual snow-crystal surfaces. However, such micro-scale mass balance has rarely been considered as a component of “macro-” heat and mass transfer in snow cover. The present work is an attempt to find a way of combining these two mass-exchange processes, as occurs in Nature. Density change and snow recrystallization rates are analyzed based on recently published temperature field observations around individual snow crystals, combined with experimental data on temperature distributions and recrystallization rates in snow under applied temperature gradients.

Occurrences of tephra layers in four ice cores from Antarctica are reviewed. A new tephra, informally named the Vostok tephra, is described from a depth of 100.85 m in an ice core from Vostok station. Ice associated with four tephra layers at depths between 1390 and 1450 m in the Byrd station ice core shows increased levels of sulfate and nitrate which correlate well with peaks in particle concentrations. High levels of sulfate and nitrate are also associated with the Vostok tephra.

Tephra offer great potential as stratigraphic markers and should be useful in providing time planes as well as assisting in correlation between widely spaced ice cores.

We examine the melting of sea ice versus freshwater ice in laboratory experiments and with one-dimensional model simulations. Our primary aim is to investigate the vertical partitioning of heat between thinning and internal phase changes. In agreement with our general understanding of the two ice types, we find that freshwater ice quickly starts thinning and then keeps a constant melt rate for constant external heat input. In contrast, sea ice starts thinning later but then thins faster than freshwater ice. This temporal evolution is caused by the substantial amount of heat that is used for internal phase changes in sea ice. Those internal phase changes give rise to a nonlinear temperature profile in the sea ice during the entire melting period, whereas freshwater ice quickly reaches its melting temperature throughout its entire thickness. Infrared imagery provides additional insights into the surface temperature of both ice types during melting. We find that, during melting, sea ice can have a mean surface temperature several tenths of a degree above 0°C because of meltwater-filled millimetre-scale dimples at the ice surface.

The dimensionless form of the field equations and boundary conditions governing plane flow of a grounded cold ice sheet emerge from balance statements of mass, momentum, and energy. They constitute an amended version of a reduced model of ice-sheet flow, due to Morland (1984) and Hutter (1983), and circumvent the restrictions imposed by the reduced model, namely the neglect of the longitudinal stretching effects. The amended version permits satisfaction of mass balance at the ice divide for arbitrary basal sliding conditions and gives a better reproduction of the local flow features.

Under very mild simplifying assumptions, namely that horizontal thermal conduction can be ignored close to the divide, we present a numerical analysis of the ice divide which has second-order accuracy. This analysis permits determination of the temperature profile, velocity, and stress distributions in a symmetric ice divide, provided that the ice-divide height, the local behavior of the accumulation and surface-temperature functions, and the geothermal heat flow are prescribed.

A distributed snowmelt prediction model was developed for a mountain area. Topography of the study area was represented by a digital map. Cells On the map were divided into three surface-cover types; deciduous forest, evergreen forest and deforested area. Snowmelt rates for each cell were calculated by an energy balance method. Meteorological elements were estimated separately in each cell according to topographical characteristics and surface-cover type. Distributions of water equivalent of snow cover were estimated by the model. Snowmelt runoff in the watershed was also simulated by snowmelt rates calculated by the model. The model showed thai the snowmelt period and snowmelt runoff after timber harvests would be about two weeks earlier than under the forest-covered condition.

A three-dimensional (3-D), high-resolution, non-linearly viscous, non-isothermal ice-sheet model is employed to calculate the “present-day” equilibrium regime of the Antarctic ice sheet and its evolution during the last glacial cycle. The model is augmented by an approximate formula for ice-sheet basal temperature, based on a scaling of the thermodynamic equation for the ice flow. Steady-state solutions for both the shape and extent of the areas of basal melting (or freezing) are shown to be in good agreement with those obtained from the solution of the full 3-D thermodynamic equation. The solution for the basal temperature field of the West Antarctic Siple Coast produces areas at the pressure-melting point separated by strips of frozen-to-bed ice, the structure of which is reminiscent of Ice Streams A–E. This configuration appears to be robust, preserving its features in spite of climatic changes during the last glacial cycle. Ice Stream C seems to be more vulnerable to stagnation, switching to a passive mode at least once during the penultimate interglacial. We conjecture that the peculiarities of local topography determine the unique behavior of Ice Stream C: reduced basal stress and, consequently, relatively weak warming due to internal friction and basal sliding is not able to counteract the advective cooling during the periods of increased snowfall rate.

A series of new synthetic armored cables were developed and tested to ensure that they were suitable for use with the RECoverable Autonomous Sonde (RECAS), which is a newly designed freezing-in thermal ice probe. The final version of the cable consists of two concentric conductors that can be used as the power and signal lines. Two polyfluoroalkoxy jackets are used for electrical insulation (one for insulation between conductors, and the other for insulation of the outer conductor). The outer insulation layer is coated by polyurethane jacket to seal the connections between the cable and electrical units. The 0.65 mm thick strength member is made from aramid fibers woven together. To hold these aramid fibers in place, a sheathing layer was produced from a polyamide fabric cover net. The outer diameter of the final version of the cable is ~6.1 mm. The permissible bending radius is as low as 17–20 mm. The maximal breaking force under straight tension is ~12.2 kN. The cable weight is only ~0.061 kg m−1. The mechanical and electrical properties and environmental suitability of the cable were determined through laboratory testing and joint testing with the probe.

With decreases in Arctic sea-ice extent in recent years, the Northern Sea Route (NSR) and Northwest Passage (NWP), which we collectively term the Arctic Sea Route (ASR), have become open for navigation more frequently. The ASR connects the Pacific and Atlantic Oceans, with the NSR following the Siberian coast, and the NWP following the north coast of North America. This study evaluated long-term ice concentrations along both routes using microwave data from the SMMR and SSM/I sensors, and analyzed details using data from the AMSR-E passive microwave sensor. The data were used to determine the number of navigable days according to various sea-ice concentrations. Analysis of SMMR and SSM/I data showed a remarkably large number of navigable days on the NSR since 1995. For the NWP, the low resolution of the SMMR and SSM/I data for the Canadian Arctic Archipelago made analysis difficult, but long-term change in the sea-ice distribution on the ASR was indicated. Analysis of the AMSR-E microwave sensor data revealed navigable days along the NSR in 2002 and from 2005 to 2009 (except 2007). For navigation purposes, the sea-ice decrease in specific regions is important, as well as the decrease across the Arctic Ocean as a whole. For the NWP, numerous navigable days were identified in the period 2006–08.

The major factor shaping the coast of the micro-tidal Baltic Sea is wave activity, the impact of which is limited by the presence or absence of sea ice. Existing studies have revealed almost no correlation between the annual mean wave height and the duration of the ice season. We attempt to evaluate the correlation between ice season duration and bulk wave energy flux (wave power), mean energy and average wave height over the ice-free season for three segments of the Estonian coast (Vilsandi, Pakri and Narva-Joesuu). Statistically significant correlation at the 95% confidence level exists between the duration of the ice season at Vilsandi (a site fully open to the predominant winds) and bulk wave energy flux derived from both observed and modelled wave properties. Similarly strong correlation exists between the mean wave energy and the duration of the ice season at the largely sheltered Narva-Joesuu site.

The “stop-and-go” kinematic Global Positioning System (GPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality receivers operated as reference pivots, while two similar receivers traveled to grid stations. Each station was occupied for 25s. The method is rapid and reliable. Each survey was completed within 2 weeks. Calculated horizontal strain rates are accurate to 1%. Relative vertical velocities are accurate to 20 mm km1 a-1. Maps of the four horizontal velocity gradients, relative vertical velocity and surface elevation are presented. The vertical velocity pattern is used to identify the part of the topography that forms stationary waves and that which is migrating. No strong quantitative link is found between the pattern in horizontal strain rate and surface topography. In particular, there is no evidence that the topography is relaxing toward isostasy. None of the “weir-type” sticky spots, which are commonly observed with other glaciers, is found but there could be two of the “submerged-boulder type”, which cause lateral flow diversion. Evidence for “hot stripes” and zones of preferred crystal orientation is not found.

A plane, gravity-driven, steady flow of a polar ice sheet over a horizontal bedrock, with no-slip basal conditions, is considered. The ice is modelled as a linearly viscous, incompressible and anisotropic fluid, with evolving orthotropic fabric depending on local strain rates and deformations. For prescribed free-surface elevation and non-uniform temperature field, the ice velocities required to maintain the assumed geometry are calculated by using the finite-element method. The focus is on the mechanism of dynamic (migration) recrystallization occurring near the base ofan ice sheet and leading to significant weakening, and ultimately to the complete loss, of the anisotropic fabric developed in the upper part of the ice cap. The weakening of the fabric with increasing strain rate and temperature is modelled by means of a scaling function depending continuously on a single effective strain-rate invariant. The results of numerical calculations demonstrate the effect of the recrystallization process on the overall flow rate of the ice sheet, and normalized velocity and strain-rate depth profiles are compared for flows with and without recrystallization involved to illustrate the effect of this mechanism on the large-scale behaviour of polar ice sheets.