As an inhomogeneous mixture of pure ice, brine, air and solid salts the physical properties of sea ice depend on its highly temperature-dependent microstructure. Understanding the microstructure and the way it responds to variations in temperature and salinity is crucial in developing an improved understanding of the interaction between sea ice and the environment. However, measurements monitoring the internal structure of sea ice are difficult to obtain without disturbing its natural state. We have recently developed an application of cross-borehole d.c. resistivity tomography to make in situ measurements that resolve the anisotropic resistivity structure of first-year sea ice. We present results from measurements made in 2008 off Barrow, Alaska, and in 2009 off Ross Island, Antarctica. the sea ice in these two regions forms in different environments: at Barrow, relatively quiescent conditions typically lead to a predominance of columnar ice, while more turbulent conditions and underwater ice formation in McMurdo Sound tend to produce a larger component of frazil or platelet ice. Interpretation of the resistivity measurements carried out in association with temperature and salinity data collected simultaneously allows both observation of the temporal evolution of the ice structure and, in the case of the Antarctic measurements, the identification of different ice types.

Ice-penetrating radar sounding is a powerful geophysical tool for studying terrestrial and planetary ice with a rich glaciological heritage reaching back over half a century. Recent years have also seen rapid growth in both the radioglaciological community itself and in the scope and sophistication of its analysis of ice-penetrating radar data. This has been spurred by a combination of growing datasets and improvements in computational resources as well as advances in radar sounding instrumentation and platforms. Together, these developments are transforming the field and highlight exciting paths forward for future innovation and investigation.

Observations were made on thermal modification due to cooling when air flows from a grass-covered area onto a melting snow surface. To clarify the relation between such modification of air and snowmelt, the downwind variation of temperature, humidity and wind speed, together with net radiation and spatial variation of snowmelt were observed at a small snow patch measuring 70 m long and 30 m wide. When air temperature was between 10 and 20°C, with nearly neutral stratification over the upwind grass-covered area, air temperature at 0.1 m level decreased by 4 to 9°C over the downwind distance of 48 m above the snow patch, and so the sensible heat flux decreased in the downwind direction. As a result of such cooling, snowmelt in the central part of the snow patch was found to be about 25% smaller than near its edge. This value can be explained by the decrease of the total heat flux toward the snow surface due to the air modification.

The precision of radar altimetry above an ice sheet can improve glaciological studies such as mass balance surveys or ice-sheet flow models, the first by comparing altimetric data at different times (see this issue), the second by testing or constraining models with data. This paper is a first step towards the latter. From a precise topography deduced by inversion of altimetric data (Remy and others, 1989), we calculate ice-flow direction, balance velocity and basal shear stress. The rheological parameters involved in the relation linking velocity, stress and temperature are then derived by least-squares regression. Ice flow is well represented by setting the Glen parameter, n to 1 ± 0.25 and the activation energy as 70 ± 10 kJ mol−1.

Snow stratigraphy was obtained in the laboratory and field, using a FM-CW radar system having microwave frequencies ranging from 2-8 GHz and from 6-12 GHz. A multi-layered model consisting of artificial snow such as glass beads or polystyrene plastics was used in the laboratory. In the field, the thickness of an individual layer within a snowpack was determined by analyzing the profile of responses from interfaces within the snowpacks. Large anomalies of the responses which produce misleading results, were found to have been caused mainly by multi-reflection between stratified layers as well as residual mismatch reflection in the system’s components.

The physical properties of a snowpack were measured by digging a snow pit. The comparison of the microwave responses in the profile with the visual stratigraphic layering of snow was made by inserting a reflection plate between individual layers within the snowpack,

The snow compression test is a snow stability test where an isolated column of snow is progressively loaded by tapping on it to induce failure in a possible weak layer. The test result provides valuable information about the propensity of failure initiation within the snowpack. However, different persons might tap with different force and thus reduce the reproducibility of the test results. The aim of this work was to quantify the influence of different test persons and different snowpacks on snow compression test results. We therefore let 62 persons tap on a stress measurement plate during a workshop of the European Avalanche Warning Services. Moreover, in the field, we performed stress measurements during 116 snow compression tests with 13 persons at eight different locations in the Alps. Data on persons’ body features and snow properties were also collected. Our results show that the stresses that reach a weak snow layer due to tapping are influenced by both the snowpack as well as different persons. Still, the data's scattering is surprisingly small for lower loading steps and decreases with depth. Therefore, we can deduce that, especially when avalanche conditions are particularly dangerous, snow compression test results are quite reproducible.

The Mars polar caps are highly interesting features of Mars and have received much recent attention, with new and exciting data on morphology, basal units and layered outcroppings. We have examined the climatological, glaciological and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a fine-scale optical examination of ice in a borehole, to study the stratigraphy, geochemistry and geochronology of the ice, is feasible. This information will enable reconstruction of the development of the cap as well as understanding the properties of its ice. We present visible imagery taken of dust inclusions in archived Greenland ice cores as well as in situ images of accreted lithologic inclusions in West Antarctica, and we argue for use of this kind of data for Mars climate reconstruction as has been successful with Greenland and Antarctic ice-core analysis.

To investigate short-term flow-pattern variations of a temperate glacier, longitudinal surface strain was measured with a wire strainmeter in the ablation area of Koryto glacier, Kamchatka, Russia. Strain-rate anomalies were observed in late summer 2000 that were triggered by a water overflow from a moulin near the measurement site followed by the drainage of accumulated water. The strain event started with (compressive) strain rates of >–10–3 d–1 lasting for 6 hours, which then became tensile. Similar strain-rate variations were observed again on the next day. During the event, basal sliding speed measured at the margin in the lower reach of the glacier fluctuated by about ±50% of the daily mean. Smaller and larger sliding speeds corresponded to the compressive and tensile surface strains, respectively. These measurements suggest that the storage and sudden drainage of water caused spatially non-uniform water-pressure fluctuations along the glacier, changing the sliding regime over short time periods.

Even though the danger-level verification indicated in a bulletin should be a priority aim of avalanche-forecast services, there are no easily applicable verification methods available today. The main difficulty lies in the fact that avalanche observation is no longer sufficient. Therefore, it is necessary to verify the actual condition of the snow-pack stability, particularly concerning low danger levels. This work introduces a procedure for “a posteriori” field verification of danger level, both in space and time (24–72 hours). The method is based on the following elements: avalanche-activity survey, observation of cross-country skiers’ activity, snow profiles and “Rutschblock” tests. These elements, relating both to time and the examination zone, are combined to provide an objective danger degree according to the European avalanche-danger scale. The method was used experimentally in the winter of 1993–94 in the Dolomites and subsequently, in the winter of 1995–96 in the Catalan Pyrenees. As far as 24 hour forecasts are concerned, the method has shown a forecast reliability of 93% in the Dolomites and 76% in the Catalan Pyrenees, while 48 hour forecasts have given values of 89% and 64%, respectively. The lower degree of forecast reliability in the Catalan Pyrenees is accounted for by the unusual weather conditions of winter 1995–96, which was very snowy and characterized by few foreseeable avalanche conditions. The practical application of the proposed verification method has given encouraging results, thus allowing experts to find the main errors in order to improve future forecasts. However, simpler survey procedures are necessary in order to operate on a regional scale. The method is suitable for further development relating to verification of both degree of danger and danger localization.

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.

Lützowholmbukta, East Antarctica, is covered by fast ice except during a short period in April and May, but occasionally the ice cover breaks up and floats out of the bay.

The fast ice was observed every day using NOAA-7, 8 infra-red imagery. The satellite signal was received at Syowa Station, located on Ongul Island. In addition, aerial photographs and video pictures were taken using aircraft every fortnight.

In 1983, before the break-up of the fast ice in April, a distinctive increase of the infra-red radiance (NOAA AVHRR) was observed, even though the aerial observation showed no change. The increase of the radiance was estimated to be 5°C. It was in this area, where the higher infra-red signal was observed, where the fast ice broke up. In December, in the central part of the northern area of the fast ice, the hummock-ice zone formed in a triangular shape. Before the hummock-ice zone floated out, observation of the infra-red radiance showed that the temperature of the ice had decreased by 3°C.

Antarctic ice-elevation maps are presented, based on 4 000 measurement points, analysed from traverses made by constant-density balloons. These balloons were launched during the Tropical Wind, Energy Conversion and Reference Level Experiment (TWERLE). The TWERLE data yielded daily maps of the elevation of the 150 mbar pressure surface in the southern hemisphere. These maps serve as a reference level from which the altimeter readings are subtracted to yield the ice elevation.

The accuracy of the ice-elevation data is estimated at better than 60 m. The accuracy of the contouring depends on the density of measurements in the particular area. Two contouring techniques were used. One is based on generating elevation data at fixed grid-points from arbitrarily distributed measurements, using Cressman's method. The second is a surface spline interpolation technique by Duchon.

The elevation data are of special value on the inland plateau areas. There, the typical distance between balloon measurements is sufficiently small, relative to the typical distance between contour lines at 100 m intervals. Furthermore, the inland areas are the least accessible to other mapping techniques.

A cloud screening method initially generated to mask cloud contaminated pixels over the ocean in visible/infrared imagery, has been revised and adapted to detect clouds over Arctic regions with encouraging results. Although the method is quite successful in eliminating very cold clouds, it underestimates low level clouds. However, this does not appear to interfere with monitoring of ice related features such as leads or the ice edge in Advanced Very High Resolution Radiometer (AVHRR) scenes. The method uses: a multiple-band approach to produce signatures not readily available in single channel data, an edge detection/dilation technique to locate features in the clouds and to join isolated edges, and a polygon identification technique to remove noise in the form of isolated pixels and separate clear regions from cloud contaminated areas. The method has been tested over a limited set of data with consistent results. Initial evaluation of the usefulness of this cloud-detection algorithm in data-fusion experiments indicate a potential in locating areas in AVHRR data which are cloud contaminated and which could yield a far superior representation of the ice features if replaced with data from a different sensor such as the Special Sensor Microwave/lmager (SSM/I).

Traditional models of Glaciol isostasy, derived predominantly for studying the response of the earth to the retreat of Northern Hemisphere ice sheets since the last ICC age, use earth models which assume constant lithospheric thickness. For Antarctica, where the continent below the ice sheet is two separate land masses differing in geological form, the assumption thai a uniform lithosphere can explain isostatic bchavioitr is questionable. Here, a method to calculate the glacio-isostatic adjustment of the continent with a laterally varying lithospheric thickness IS presented. The method is then used in a time-dependent ice-sheet model to model the isostatic response of the continent when the ice sheet passes through a Glaciol/interglacial transition. Various relations bet ween the “crustal thickness” beneath Antarctica, derived from seismic data, and the “lithospheric thickness” estimate used in glacio-isostatic calculations are assumed in a sensitivity study. Using the simplest relationships between crustal and lithospheric thickness, the greatest sensitivity of the ice sheet to the crustal structure of Antarctica is not in the interior but at coastal locations, particularly near the major ice shelves. During periods of ice-sheet advance the grounding-line migration of the shelves varies according to the depression of the earth peripheral to the ice sheet. The peripheral depression depends on the regional elasticity of the lithosphere which is controlled by the lithospheric thickness. Therefore the capacity for the ice sheet to advance varies with the regional thickness of the crust.

Phases of seismic P-wave reflections from the bed of Ice Stream B ata site on its ice plain have been examined. The survey comprised a 36 km line at ashallow angle (18°) to ice movement and four 3.6 km cross lines. Reversed-phase and unreversed-phase reflections each characterize about half the bed. The corresponding zones can be correlated in stripes quasi-parallel to ice movement. We take this as support for a model previously developed that relates the zones to different types of subglacial sediment dragged along by the ice. There is also evidence for patches of pooled water.

The morphology of snow crystals growing at a low temperature has been experimentally studied. The habit and the morphological instability of the crystals vary remarkably with air pressure. In addition, the morphological instability of the crystals depends not only on air pressure but also on supersaturation, crystal size, the ratio of growth rates and the ratio of axial lengths. It is supposed from the experimental results that long prisms with small skeletal structures forming at low supersaturation are precipitating in polar regions.

Large scale melting phenomena like meltwater drainage channels and meltwater accumulation basins or frozen “lakes” have been surveyed on the land ice mass in Dronning Maud Land, Antarctica. These melting features were also detected in a Landsat Thematic Mapper (TM) image recorded on 12 February 1990. Image processing techniques such as principal component (PC) analysis, band ratioing and histogram-equalizing are carried out to emphasize the melting phenomena. Interestingly, a histogram-equalized single TM Band 5 image appears to be a good discriminator, leaving the melting phenomena as bright areas in the TM scene. The largest frozen “lake” is close to 1km wide while some of the drainage channels stretch more than 5 km. There is also a comparison of satellite-derived and in situ reflectance and temperature. The atmospheric corrected satellite data underestimate surface snow albedo by about 16% while TM measurements of surface temperature are 2° to 6°C lower than that measured on the ground.

Antarctic sea ice plays a key role in the present climate system, providing a regulating balance between the atmosphere and ocean heat fluxes, as well as influencing the salt fluxes and deep water formation over the continental shelves. The severe winter environmental conditions of the Antarctic sea-ice zone make it difficult to observe many of the physical characteristics in a comprehensive way. The inter-relations between the variables mean that much can be learnt from the observations of some features along with detailed numerical modelling of the whole system and the interactions between the variables. This study therefore aims to use numerical modelling of the atmosphere, sea ice and surface mixed-layer ocean in the sea-ice zone, together with observations to simulate a comprehensive range of parameters and their variability through the annual cycle to provide a basis for further observations and model validation for the present climate.

The model includes a coupled atmospheric general circulation model with an interactive dynamic and thermodynamic sea-ice model and surface mixed-layer ocean. The deep ocean and ocean surface conditions outside the sea-ice zone are constrained to the present mean climate conditions to ensure no climatic drift. The sca-ice model is similar to previous published versions, bill has refined schemes for partitioning of the freezing of frazil ice within the leads and under the ice floes, and for rafting. These perform well in both polar regions with the same physics. The model simulates the annual cycle of atmospheric and sea-ice features well in comparison with data from the global atmospheric analyses, the satellite sensing of sea ice, and the limited in situ surface observations.

The output from the model also includes: all components of the heart fluxes, atmospheric profiles and surface temperatures for air, ice and ice-ocean mixtures, open-water fractions, surface snow and snow-ice depths, and the sea-ice convergence-divergence and drift. The comparison of these features with additional observations provides a means for further validating the model and representing the present climate more closely.

The amount of snow cover in the Lake Biwa catchment area has changed significantly from 1.9 × 1012kg in 1974 to 0.3 × 1012kg in 1979. The amount of snow cover was less in the warmer winter and when the amount of snow cover was less than 1012 kg, the average amount of snow cover in recent years, the lowest dissolved-oxygen concentration in the deep layer rapidly decreases. Climatic warming will significantly decrease the amount of snow cover in Lake Biwa catchment area and the dissolved-oxygen concentration in the deep layer of the lake, which may further enhance eutrophication of the lake.