The amount of acidity in precipitation has been measured in heavy-snowfall regions facing the Sea of Japan. The average pH value of precipitation measured throughout the year at Nagaoka was 4.80 during 4.5 years, 1987–92. During winter the pH value is lower and electric conductivity higher. The spatial distribution of chemical components in new-fallen snow was studied along a 55 km-long sampling route. Results from four surveys showed that acidic snows have average pH values of 4.63–4.90. From the distribution of anion and cation concentration in new-fallen snow, it is concluded that strong northwest monsoons during winter bring an abundance of snow with salt components and many non-salt components from the Sea of Japan and also, possibly, from the Asian continent.

Electrification of snow particles during blizzards creates forces that may strongly effect their trajectories in saltation along a charged surface. This paper shows the results of adding such forces to the equations of motion for saltation. Evaluating these equations requires knowledge of the electric-field strength very near the surface, and a review shows that such measurements are lacking. However, extrapolation of reported measurements from greater heights agrees with the electric field computed for a bed of spherical particles. In this hypothetical field, the equations of motion predict large changes in saltation length that might occur as particles pass over surfaces with positive and negative sign. Such changes apparently coincide with surface erosion and deposition.

To protect rural areas and roads from disasters caused by snow avalanches, avalanche hazard maps are being developed. In Japan, when determining snow avalanche runout distances, empirical values are normally used. These assume that the line-of-sight angle at the starting point of an avalanche, viewed from its runout point, is less than 18° for surface-layer avalanches and less than 24° for full-depth layer avalanches. This rule of thumb ignores topographic features of the slope carrying the large mass of snow. We have made analyses to find a method that can obtain the avalanche runout distance, taking into consideration the longitudinal profiles of the sites, using regression analyses on data from 66 avalanches. The line-of-sight angle can be expressed sufficiently by functions, such as line-of-sight angle between the starting point of an avalanche and a point on its course of flow 10° in gradient, an angle at the starting point of an avalanche, and the curvature of an approximate quadratic curve of topography. Based on statistics for the above relationship, we have established four different ranking categories to classify the degree of hazard. If the starting points of avalanches are known, hazardous areas can automatically be ranked on a basis of topographic data.

A project was started in 1990 to rationalize the avalanche warning and evacuation system. The major items in the model project were: (1) zoning methods for dangerous areas; (2) establishment of a surveillance system; and (3) methods of determining a warning and evacuation standard. Since the scale of a snow avalanche cannot be predicted, areas with more than 30 KN m2 of impact are identified. Equipment for conducting automatic surveillance and data processing was developed to telemeter snow and weather data. Issuing warning or evacuation advice is the focus of the discussion. Judgment is based on information on current conditions obtained from a telemeter and from residents, and on information provided by forecasts of snowfall and temperatures until the following morning. Two methods of judgment are under consideration: one is to set out a standard value based on meteorological data obtained by observation, the other is based on a discriminant of danger level.

This paper describes theoretically the formation of air gaps at the lower boundary of a snow cover during basal melting. In general, initiation of the formation of air gaps is dependent on both the horizontal heterogeneity of the snowmelt rate and viscous deformation. From this point of view, we propose a dimensionless parameter ξ (bridge-effect ratio) which is a function of the amplitude and wavelength of the heterogeneity of the snowmelt rate at the base, and the density, thickness and viscosity of the snow. This parameter expresses the heterogeneity of the normal stress at the base. We derive a necessary condition for air-gap formation in terms of the bridge-effect ratio, and show that a large amplitude, a small wavelength, a high density, a thin layer and/or high viscosities are favorable for air-gap formation.

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.

The winter snow on the Arctic slope of Alaska lasts for nine months each year, yet little is known about it from a scientific point of view. Its quantity has been seriously underestimated (by a factor of three) in the weather service records, and the directions and magnitudes of wind-transported snow were unknown before the studies reported here. Our measurements of snow on the tundra indicate two major types which differ in depth, density, overall structure, and thermal characteristics: the veneer facies, lying on and interacting with the tundra, and the drift facies which forms in certain topographic settings. The flux of windblown snow has been determined by repeated measurements on three carefully selected “drift traps”, such as river banks, which are large enough so they do not fill during the winter. The measurements span 30 years to show year-to-year variability. The largest transport of snow is from the prevailing easterly winds; about half as much is transported by storm winds from the west. The lowest amount is transported by katabatic drainage winds which flow from the south out of the Brooks Range; they extend a variable, and largely unknown, distance northward onto the Arctic slope before they yield to the stronger easterly and westerly winds.

During the winters of 1990, 1991 and 1992, a field study of stability parameters for forecasting slab avalanches was conducted in the Cariboo and Monashee mountains of western Canada. In a level study plot at 1900 m and on nearby slopes, the shear strength of the weak snowpack layer judged most likely to cause slab avalanches was measured with a 0.025 m2 shear frame and a force gauge. Based on the ratio of shear strength to stress due to the snow load overlying the weak layer, a simple stability parameter and a more theoretically based stability index which corrects the strength for normal load were calculated. These stability parameters are compared with avalanche activity reported for the same day within approximately 30 km of the study plot. Each stability parameter is assessed on the basis of the number of days that it successfully predicted one or more potentially harmful avalanches and the number of days that it successfully predicted no potentially harmful avalanches. Both parameters predicted correctly on at least 75% of the 70 days they were evaluated. The simpler empirical stability parameter worked as well as the one that corrects strength for normal load. For large-scale forecasting of dry-snow slab avalanches, shear frame stability parameters appear to be a useful addition to meteorological data, snowpack observations and slope tests.

A continuum theory of mixtures is applied to model snow as a mixture of an elastic solid and an elastic fluid. Three wave types, two dilational and one rotational, are shown to exist. Numerical evaluation shows velocity and attenuation increasing with frequency for all three waves. Wave velocity increases with increasing density while attenuation decreases with increasing density for all three waves. The first dilational wave is associated with the pore fluid, has a slow wave speed and is highly attenuated. This wave exhibits diffusive behavior at low frequencies and nondispersive behavior at high frequencies. The second dilation wave is associated with the solid ice material. It is the fastest of the three wave types and does not appreciably attenuate. Nondispersive wave behavior characterizes this wave at low and high frequencies. The rotational wave occurs only in the solid, is the least attenuated of all three waves, and propagates at velocities greater than that of the first, but less than that of the second, dilational wave. The rotational wave exhibits nondispersive behavior at low and high frequencies. Wave velocities and attenuation show behavior that is in agreement with existing experimental data.

A physically based computational model of drifting snow in two-dimensional terrain is developed. The model considers the case where wind speeds are low enough to neglect the transport of particles from the saltation layer into the turbulent flow field. The model has two distinct parts, one describing the turbulent airflow, and a second describing the mass-transport process and resulting snow-accumulation patterns produced by saltation transport. The turbulent-flow model consists of a general solution of the time-averaged, two-dimensional Navier-Stokes equations, where the k-∊ turbulence model is used to close the system of equations. The turbulent-flow model is coupled to a saltation model to compute the time evolution of the surface wind fields and snowdrift formation in the vicinity of a solid fence. Modeled wind fields and snow-accumulation profiles are similar to published field and experimental data.

A constitutive theory of snow is developed to describe the mechanical properties of snow in terms of the properties of the ice grains and the necks that interconnect them. The principle of virtual work is used to calculate the stresses in the particles and necks. A number of different deformation mechanisms are investigated and, depending upon the deformation mechanism which is dominant for given load conditions, different equations are used to calculate the strains in the grains and necks. These strains around a representative ice grain are then averaged and scaled to obtain the global strains in the snow. The theory is then compared with experimental data to determine if the mechanical properties of snow can be adequately represented. Results show that the constitutive theory does work, but that it is cumbersome to implement, and that for practical use substantial computational capability is needed.

An extreme value (Gumbel) distribution was evaluated as a model of maximum run-out distances of avalanches in southwest Montana defined in terms of dimensionless ratios. The run-out ratios are defined relative to an arbitrarily defined reference point. The development and analysis of the statistical model were based on data taken from surveys of 24 avalanche paths. The technique bears promise as a user-friendly tool; however, due to the small vertical drop of avalanches in southwest Montana, the model appears to be quite sensitive to measurement errors in the field. This sensitivity also seems to depend on the definition of the reference point. Comparison with models developed for other mountain ranges indicates that models developed for one range cannot be used to estimate accurately maximum avalanche run-out distances in other mountain ranges until influencing factors are better understood.

The effective thermal conductivity of a snow cover is estimated assuming an idealized collection of uniformly packed ice spheres. An effective thermal conductivity is calculated based on the thermal resistance due to ice-grain contacts or bonds, the pore space/ice acting in series and the unobstructed pore. It is shown to depend very strongly on the snow density and intergranular bonding and, to some extent, on temperature. Conductivity tends to increase as density and the ratio of the contact radius to ice-sphere radius increase. The ice network is generally determined to be the most influential in determining the effective thermal conductitivity. Calculated results fall within the range of empirically determined values.

The radiative-transfer theory and the Rayleigh scattering model were used to obtain the microwave brightness temperatures from dry snowpacks on the ground, which was modelled by a scattering dielectric layer and an underlying homogeneous half-space. The total radio brightness at the radiometer was the sum of the direct and diffuse radiation field intensities. The result of the model application was in good agreement with the observational data, which were obtained through the airborne experiments for the MOS-1 Verification Program around Asahikawa, Hokkaido, Japan, in February 1988.

The region along the Sea of Japan is unusual in that it has very heavy snow and rather mild winter temperatures. Three major snow-removal technologies currently practised in the region, i.e. use of snow-removal machines, snow-melting pipe system and snow-dumping channel network, are described and their practice, engineering and economical aspects discussed.

During two winters, 1990–92, the dynamic structures of snow avalanches were studied in western Norway. Artificially released wet-snow avalanches ran down the avalanche chute and stopped in front of the retaining dam. Running velocity distributions were obtained not only by video tape recorder, but also by various other recording instruments. Internal velocity was derived for the last avalanche by frequency analysis of impact pressure and optical sensor data. The vertical velocity shear of the avalanche flow has been estimated to be in the range 1–10 s−1.

Methods for monitoring cloud development over the Sea of Japan under the winter monsoon are presented for the purpose of developing a snowfall forecasting system. The three-dimensional shape of aligned cumulus rows has been identified using Landsat TM data. Data on water vapor and cloud liquid-water contents over the Sea of Japan have also been obtained, but for a different case, using two microwave bands of MSR (23.8 GHz and 31.4 GHz) and two thermal infrared bands of VTIR aboard MOS-1. Using these data, characteristics of the streak-like cloud under a winter monsoon airflow are identified.