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Wind-tunnel and numerical experiments were performed to investigate the effects of snowfall on the wind profile and the development of drifting snow. Wind profiles and mass-flux profiles of drifting snow were measured with and without artificial snowfall over a snow surface within the tunnel. Wind and shear-stress profiles and the impact speeds of the snowflakes during snowfall were also investigated numerically. During snowfall, snowflakes transfer part of their horizontal momentum to the air, which increases the stress close to the snow surface; however, the resultant modifications of the wind profiles are small. Because snowflakes have large momentum, the decomposed snow crystals that result from their collision with a surface can form a saltation layer, even over a hard snow surface where entrainment of the grains from the surface does not occur. Additionally, during snowfall, the threshold friction velocity can be lower than the impact threshold because snowflake fragmentation facilitates snow drifting. The broken crystals contribute to the increase in the number of drifting snow grains, even below the impact threshold.

Link to publishers version: 10.1016/j.coldregions.2016.03.012 Icing load and icing rate are necessary feedback variables for an intelligent anti/de-icing systemtowork effectively in harsh cold environment of high north. These parametersmay be measured by axial loadings or by rotational loadings, as a function of current demand. However the former may not necessarily be dynamic, whereas the later necessarily be rotational. Sufficiently at a fixed rpm, a mathematical model between additional polar moment of inertia vs electrical demand of the sensor can be established to analytically shape the icing load and icing rate adequately as hypothesized in Cost 727. This paper aims to develop such model and is validated using experimental data from a case study conducted by Atmospheric Icing Research Team of Narvik University College at Cryospheric Environmental Simulator, Snow and Ice Research Center, (NIED) Japan.

AbstarctThere are some reports on the measurement of the charge-to-mass ratio of blowing-snow particles, but there are few studies concerned with individual snow-particle charge. We measured the charge-to-mass ratios using snow particles selected according to size, and discussed individual charges. Experiments were conducted in a cryogenic wind tunnel. Charge-to-mass ratios measured in our experiment were all negative and their absolute values tended to increase with a decrease in particle diameter. Individual snow-particle charges were calculated from the average of particle diameter distributions. The charges were all approximated by the power function of diameter at each temperature. Assuming that the coefficient of these approximations is a function of air temperature, we could easily predict the individual snow-particle charge.

Under strong wind conditions, snowflakes break upon collision with a snow surface, and their fragments are blown away; this leads to the development of drifting snow. If these fragments accumulate, the density of the deposited snow would exceed that of new snow deposited under calm conditions. In this study, experiments on the processes of fracture and accumulation of snowflakes were conducted in a cold wind tunnel and field observations were also carried out. The experimental results obtained by using artificial snowflakes are as follows: snowflakes do not break if U1 The observational results for natural snowflake collisions almost agreed with the experimental results. These findings can be used in a model of drifting snow to explicitly describe the effect of snowfall on drifting snow and they will be useful in understanding the wind speed dependence of the new snow density.

2006年2月10日,秋田県仙北市の乳頭温泉鶴の湯の裏山の3カ所において相次いで発生した乾雪表層雪崩により,1名が死亡,16名がけがをした.雪崩発生の翌日に現地調査を行い,雪崩の状況やデブリの状態などを明らかにした.また,同日に積雪断面観測を行い,発生日未明から積もり始めた新雪層の構造を明らかにするとともに,ハンドテストによって弱層の存在を確認し,その勇断強度を測定した.さらに,1週間後および3月下旬の融雪期にも現地調査を行った.また,積雪変質モデル(SNOWPACK)を用いて積雪構造と積雪安定度のシミュレーションを行った.これらの結果から,この雪崩は,強い降雪が続く中で新雪層の積雪安定度が低下し,その内部に何らかの原因で生じた弱層をすべり面として発生したと考えられる.

This paper describes the indoor snowfall simulation chamber and its application for evaluating visibility performance of vision-based sensors affected by environmental conditions. First, vision-based safety sensors are introduced and outdoor environmental requirements for these sensors are discussed. And also, the relationship between the visibility and the performance of vision based sensors is discussed and the current problems for evaluating visibility performance are described. Next, the indoor snowfall simulation method using expanded polystyrene beads (EPB) is explained and the spectral transmission measurement equipment for evaluating the visibility reduction is presented. Finally, the visibility reduction caused by simulated and artificial snowfall are measured for verifying the proposed indoor snowfall simulation chamber. Preliminary experiments are also carried out in both snowfall systems in order to evaluate various kinds of vision-based safety sensors for personal care robots.

We observed broadband snow albedos in the visible and the near infrared spectral regions with snow pit works of several-day intervals, during the winters of 2001/2002 and 2002/2003 at Shinjo, Japan. We examined the dependence of albedos on snow grain size and on concentration of snow impurities, comparing observations and theoretical calculations using a radiative transfer model for atmosphere-snow system. The comparisons revealed that the snow was contaminated by strong absorptive impurities such as soot additional to moderate absorptive impurities such as mineral dust. Snow albedo reduction after snowfalls (snow aging effect on albedo) observed in both spectral regions corresponded to the growth tendency of snow grains and the increasing concentration of snow impurities with elapsed time after snowfalls. Measurement of the atmospheric aerosols above the snow surface using a laser optical particle counter suggested that wet deposition of atmospheric aerosols caused snow impurities of more than 1 ppmw in mass concentration.

To observe aeolian dust in high mountainous areas, two sets of automatic weather station including visibility meters have been installed on the slopes of the Tianshan Mountains and the Kunlun Mountains. The two observation sites are at a height of about 2500 m above sea level, and those slopes face to the Taklimakan Desert. The aeolian dust climbs the slopes with anabatic wind in daytime. Horizontal mass transportation of dust over the slopes on a fine day was estimated using the data set of visibility and wind speed, and its daily and seasonal variations were analyzed. Before this analysis, visibility was converted to dust concentration via a relationship determined by visibility meter and an optical panicle counter in a laboratory. It has been recognized that the mass transportation over the slopes reflects activity of the dust outbreak at the foot areas.

回転楕円体および角柱でモデル化した飛雪粒子がランダムに方位していると仮定して,スノー・パーティクル・カウンター(SPC)で測定される飛雪流量と真の飛雪流量の比を理論的に求めた.また,粒子形状の異なる雪を使用してSPCとネット式吹雪計による飛雪流量の比較実験を行った.理論的検討より,粒子形状が回転楕円体の場合は非球形度が増すほど,角柱の場合は薄く板状に近づくほど,あるいは細長くなるほど,SPCで測定される飛雪流量はより過大に評価されることが明らかになった.比較実験の結果は理論的検討の結果と整合するものであった.すなわち,飛雪粒子が樹枝状結晶(人工雪)の破壊されたものからなる時は,SPCによる飛雪流量はネット式吹雪計によるものよりかなり大きくなるが,飛雪粒子が粒状の時は両者はほぼ一致する.Sato et al.(1993)による野外におけるSPCとネット式吹雪計の比較観測の結果について,本研究の結果に基づき再検討し,雪面が硬く削剥が生じないような特殊な場合を除けばSPCによる飛雪流量の測定が概ね正確であることを示した.