146,906 research outputs found
Mariner\u27s Compass quilt by Blenda B. Ralphs Snow
No full textImage of Mariner\u27s Compass quilt created in1944 by Blenda B. Ralphs Snow. Also includes questionnaires describing the quilt completed by Ann Marshall as part of the Utah Quilt Guild\u27s documentation days held from 1988-1994. The quilt was made by Blenda B. Ralphs Snow in 1944, Ferron, Utah; estimated date of fabric in quilt 1950; owned by Anne Marshal
Carolina Lily quilt, made by Blenda B. Ralphs Snow
No full textImage of Carolina Lily quilt created in 1945 by Blenda B. Ralphs Snow. Also includes questionnaires describing the quilt completed by Ann Marshall as part of the Utah Quilt Guild\u27s documentation days held from 1988-1994. This quilt was made by Blenda B. Ralphs Snow in 1945, Ferron, Utah; owned by Ann Marshal
SNOWMIP2: An evaluation of forest snow process simulation
No full textThe Northern Hemisphere has large areas that are forested and seasonally snow covered. Compared with open areas, forest canopies strongly influence interactions between the atmosphere and snow on the ground by sheltering the snow from wind and solar radiation and by intercepting falling snow, and these influences have important consequences for the meteorology, hydrology and ecology of forests. Many of the land surface models used in meteorological and hydrological forecasting now include representations of canopy snow processes, but these have not been widely tested in comparison with observations. Phase 2 of the Snow Model Intercomparison Project (SnowMIP2) was therefore designed as an intercomparison of surface mass and energy balance simulations for snow in forested areas. Model forcing and calibration data for sites with paired forested and open plots were supplied to modelling groups. Participants in 11 countries contributed outputs from 33 models, and results are published here for sites in Canada, the USA and Switzerland. On average, the models perform fairly well in simulating snow accumulation and ablation, although there is a wide inter-model spread and a tendency to underestimate differences in snow mass between open and forested areas. Most models capture the large differences in surface albedos and temperatures between forest canopies and open snow well. There is, however, a strong tendency for models to underestimate soil temperatures under snow, particularly for forest sites, and this would have large consequences for simulations of runoff and biological processes in the soil
Implications of spatial distributions of snow mass and melt rate for snow-cover depletion: observations in a subarctic mountain catchment
No full textSpatial statistics of snow water equivalent (SWE) and melt rate were measured using spatially distributed, sequential ground surveys of depth and density in forested, shrub and alpine tundra environments over several seasons within a 185 km(2) mountain catchment in Yukon Territory, Canada. When stratified by slope/aspect sub-units within landscape classes, SWE frequency distributions matched the log-normal, but multiclass surveys showed a more bimodal distribution. Within-class variability of winter SWE could be grouped into (i) windswept tundra and (ii) sheltered tundra/forest regimes. During melt, there was little association between the standard deviation and mean of SWE. At small scales, a negative correlation developed between spatial distributions of pre-melt SWE and melt rate where shrubs were exposed above the snow. This was not evident in dense-forest, alpine-tundra or deep-snowdrift landscape classes. At medium scales, adja-negative SWE and melt-rate correlations were also found between mean values from adjacent slope sub-units of the tundra landscape class. The medium-scale correlation was likely due to slope effects on insolation and blowing-snow redistribution. At the catchment scale, the correlation between mean SWE and melt rate from various landscape classes reversed to a positive one, likely influenced by intercepted and blowing regimes, shrub exposure during melt and adiabatic cooling with elevation rise. Covariance at the catchment scale resulted in a 40% acceleration of snow depletion. These results suggest that the spatial variability and covariability of both SWE and melt rate are scale- and landscape-class-specific and need to be considered in a landscape-stratified manner at the appropriate scale when snow depletion is described and the snowmelt duration predicted.</p
Modeling Wet-Snow Shedding from Current-Carrying Conductors
No full textThe initiation of wet-snow shedding from currentcarrying conductors was studied experimentally and theoretically. A suspended cable with cylindrical snow accretion was considered, and some of the snow properties at the end of sleeve were measured and calculated until snow shedding. The current in the cable appears to be a heat source which accelerates snow melting, similarly to air temperatures above freezing, wind and heat radiation. All of these effects were taken into account to study how they contribute to the snow-shedding process. The properties observed were the liquid water content, density, and profile of snow at the end of a snow sleeve. As the snow warms, if the liquid water content and density increase to high enough levels, adhesion to the cable is weakened so that the end of the snow sleeve turns downward and then falls off. The experimental procedure involved forming a wet-snow sleeve on a suspended cable with negligible sag, frequently measuring snow properties of interest under controlled ambient conditions, and observing the deformation of the snow-sleeve until shedding occurred. The theoretical model applies the heat balance of the snow sleeve to calculate the effects of the heat sources mentioned, and simulates water percolation in the cross-section at the end of the snow sleeve from the top half downward. The model provides the rate of increase of liquid water content and density of snow in the end section, and predicts the deflection of the same section together with the time when this section is detached from the cable and snow sheds. The theoretical results were compared to the experimental observations, and satisfactory coincidence was observed in most of the cases examined
Living Snow Fences; TR-460, 2006
No full textBlowing snow can cause significant problems for mobility and safety during winter weather in three distinct ways. It may drift onto the road, thus requiring almost continuous plowing while the wind is blowing (which may occur when a given winter storm is over). Snow may drift onto wet pavement (perhaps caused by ice control chemicals) and dilute out the chemicals on the road, creating ice on the road. And sufficient blowing snow can cause a major deterioration in visibility on the road, a factor which has been shown to be significant in winter crashes.
The problem of blowing snow can be very effectively addressed by creating a snow storage device upwind of the road that requires protection from snow drifting. Typically, these storage devices are fences. Extensive design guidance exists for the required height and placement of such fences for a given annual snowfall and given local topography. However, the design information on the placement of living snow fences is less complete. The purpose of this report is to present the results of three seasons of study on using standing corn as snow fences. In addition, the experience of using switch grass as a snow storage medium is also presented. On the basis of these experimental data, a design guide has been developed that makes use of the somewhat unique snow storage characteristics of standing corn snow fences.
The results of the field tests on using standing corn showed that multiple rows of standing corn store snow rather differently than a traditional wooden snow fence. Specifically, while a traditional fence stores most of the snow downwind from the fence (and thus must be placed a significant distance upwind of the road to be protected, specifically at least 35 times the snow fence height) rows of standing corn store the majority of the snow within the rows. Results from the three winters of testing show that the standing corn snow fences can store as much snow within the rows of standing corn as a traditional fence of typical height for operation in Iowa (4 to 6 feet) can store. This finding is significant because it means that the snow fences can be placed at the edge of the farmer’s field closest to the road, and still be effective. This is typically much more convenient for the farmer and thus may mean that more farmers would be willing to participate in a program that uses standing corn than in traditional programs.
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On the basis of the experimental data, design guidance for the use of standing corn as a snow storage device in Iowa is given in the report. Specifically, it is recommended that if the fetch in a location to be protected is less than 5,000 feet, then 16 rows of standing corn should be used, at the edge of the field adjacent to the right of way. If the fetch is greater than 5,000 feet, then 24 rows of standing corn should be used. This is based on a row spacing of 22 inches. Further, it should be noted that these design recommendations are ONLY for the State of Iowa. Other states of course have different winter weather and without extensive further study, it cannot be said that these guidelines would be effective in other locations with other winter conditions
Intercomparison of snow density measurements: bias, precision, and vertical resolution
No full textDensity is a fundamental property of porous media such as snow. A wide range of snow properties and physical processes are linked to density, but few studies have addressed the uncertainty in snow density measurements. No study has yet quantitatively considered the recent advances in snow measurement methods such as micro-computed tomography (uCT) in alpine snow. During the MicroSnow Davos 2014 workshop, different approaches to measure snow density were applied in a controlled laboratory environment and in the field. Overall, the agreement between uCT and gravimetric methods (density cutters) was 5 to 9 %, with a bias o
Micrometeorological processes driving snow ablation in an Alpine catchment
No full textMountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micrometeorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological model (ARPS) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modelled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances except for very strong wind conditions. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is below a critical value. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover. Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.<br/
Summer snow extent heralding of the winter North Atlantic Oscillation
No full text[1] Winter climate over the North Atlantic and European sector is modulated by the North Atlantic Oscillation (NAO). We find that the summer extent of snow cover over northern North America and northern Eurasia is linked significantly (p < 0.01) to the upcoming winter NAO state. Summers with high/low snow extent precede winters of low/high NAO index phase. We suggest the linkage arises from the summer snow-associated formation of anomalous longitudinal differences in surface air temperature with the subpolar North Atlantic. Our findings indicate the seasonal predictability of North Atlantic winter climate may be higher and extend to longer leads than thought previously
Adhesion of Wet Snow to Different Cable Surfaces
No full textCohesion of snow and its adhesion to cable surfaces are the decisive factors for wet-snow shedding from power-line cables. Knowing the adhesive strength of snow is essential to predict when snow will shed and what consequences it will have on the elements of the transmission line. It also appears to be a basic input for simulating wet-snow shedding. Snow adhesion depends on several parameters, among which snow liquid water content and density, and cable surface geometry were examined experimentally. In particular, the adhesion of wet-snow samples to flat surfaces of different roughness, and to stranded cable surfaces was examined in this study. Two series of experiments were conducted to measure shear adhesive strength as well as tensile adhesive strength of snow. Shear adhesive strength was measured with a centrifuge adhesion test device where a snow sample was placed on a beam, which was then rotated with increasing angular frequency until detachment, the angular frequency at detachment being proportional with shear adhesive force and strength. The tensile adhesive tests were carried out with a material test machine on a semi-spherical snow sample. The sample was compressed slowly at a constant speed until it reached a predefined compressive force limit, and then a tensile load was applied until the detachment of snow. The main observations showed that adhesion was strongest for a critical value of liquid water content, that shear adhesive strength was greatest on stranded cable surfaces, and that tensile adhesive strength was weaker on stranded than on flat cable surfaces
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