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Ito Y.,Nagoya University | Ito Y.,IRSTEA | Ito Y.,Snow and Ice Research Center | Naaim-Bouvet F.,IRSTEA | And 5 more authors.
Journal of Glaciology | Year: 2017

Particle size, particle speed and airflow speed have been measured in the powder snow clouds of avalanches to investigate the suspension and transportation processes of snow particles. The avalanches were artificially triggered at the Lautaret full-scale avalanche test-site (French Alps) where an ultrasonic anemometer and a snow particle counter were setup in an avalanche track for measurements. Relatively large particles were observed during passage of the avalanche head and then the size of the particles slightly decreased as the core of the avalanche passed the measurement station. The particle size distribution was well fitted by a gamma distribution function. A condition for suspension of particles within the cloud based on the ratio of vertical velocity fluctuation to particle settling velocity suggests that the large particles near the avalanche head are not lifted up by turbulent diffusion, but rather ejected by a process involving collisions between the avalanche flow and the rough snow surface. Particle speeds were lower than the airflow speed when large particles were present in the powder cloud. © The Author(s) 2017.

Hiranuma N.,Karlsruhe Institute of Technology | Augustin-Bauditz S.,Leibniz Institute for Tropospheric Research | Bingemer H.,Goethe University Frankfurt | Budke C.,Bielefeld University | And 41 more authors.
Atmospheric Chemistry and Physics | Year: 2015

Immersion freezing is the most relevant heterogeneous ice nucleation mechanism through which ice crystals are formed in mixed-phase clouds. In recent years, an increasing number of laboratory experiments utilizing a variety of instruments have examined immersion freezing activity of atmospherically relevant ice-nucleating particles. However, an intercomparison of these laboratory results is a difficult task because investigators have used different ice nucleation (IN) measurement methods to produce these results. A remaining challenge is to explore the sensitivity and accuracy of these techniques and to understand how the IN results are potentially influenced or biased by experimental parameters associated with these techniques.

Within the framework of INUIT (Ice Nuclei Research Unit), we distributed an illite-rich sample (illite NX) as a representative surrogate for atmospheric mineral dust particles to investigators to perform immersion freezing experiments using different IN measurement methods and to obtain IN data as a function of particle concentration, temperature (T), cooling rate and nucleation time. A total of 17 measurement methods were involved in the data intercomparison. Experiments with seven instruments started with the test sample pre-suspended in water before cooling, while 10 other instruments employed water vapor condensation onto dry-dispersed particles followed by immersion freezing. The resulting comprehensive immersion freezing data set was evaluated using the ice nucleation active surface-site density, ns, to develop a representative ns(T) spectrum that spans a wide temperature range (g'37 °C < T < g'11 °C) and covers 9 orders of magnitude in ns.

In general, the 17 immersion freezing measurement techniques deviate, within a range of about 8 °C in terms of temperature, by 3 orders of magnitude with respect to ns. In addition, we show evidence that the immersion freezing efficiency expressed in ns of illite NX particles is relatively independent of droplet size, particle mass in suspension, particle size and cooling rate during freezing. A strong temperature dependence and weak time and size dependence of the immersion freezing efficiency of illite-rich clay mineral particles enabled the ns parameterization solely as a function of temperature. We also characterized the ns(T) spectra and identified a section with a steep slope between g'20 and g'27 °C, where a large fraction of active sites of our test dust may trigger immersion freezing. This slope was followed by a region with a gentler slope at temperatures below g'27 °C. While the agreement between different instruments was reasonable below ∼ g'27 °C, there seemed to be a different trend in the temperature-dependent ice nucleation activity from the suspension and dry-dispersed particle measurements for this mineral dust, in particular at higher temperatures. For instance, the ice nucleation activity expressed in ns was smaller for the average of the wet suspended samples and higher for the average of the dry-dispersed aerosol samples between about g'27 and g'18 °C. Only instruments making measurements with wet suspended samples were able to measure ice nucleation above g'18°C. A possible explanation for the deviation between g'27 and g'18 °C is discussed. Multiple exponential distribution fits in both linear and log space for both specific surface area-based ns(T) and geometric surface area-based ns(T) are provided. These new fits, constrained by using identical reference samples, will help to compare IN measurement methods that are not included in the present study and IN data from future IN instruments. © 2015 Author(s). CC Attribution 3.0 License.

Tomabechi T.,Hokkaido University of Science | Chiba T.,Hokkaido University of Science | Sato T.,Snow and Ice Research Center | Tsutsumi T.,Japan Building Research Institute | And 2 more authors.
Journal of Structural and Construction Engineering | Year: 2011

Even in the region with less snowfall, snow accretion to exterior wall surface and structural members of high rise building in Tokyo metropolitan region has frequently occurred. Concern about human damage produced by snow blocks falling including snow accretion has been pointed out. Therefore, it is important to build method of countermeasures against snow accretion for buildings. To accumulate technical data for countermeasures against snow accretion, the authors studied basic characteristics of snow accretion on structural members both observationally and experimentally. First, field observation for snow accretion on structural members was performed in Sapporo of Hokkaido. When the snow accretion occurred during the observation, daily mean wind speed was more than 3.0 m/s. The snow accretion occurred around the stagnation of wind, which was formed in the vicinity of structural members. Next, wind tunnel test, for usual shape members such as steel pipes and flat plates, was performed. The snow accretion amount on the steel pipe increased with the diameter and it depended on the surface roughness in case of the steel pipe 216mm in diameter. The snow accretion amount on the steel plates decreased with attack angle. Through the observation and the wind tunnel test on snow accretion characteristics, technical data of countermeasures against snow accretion for buildings was obtained.

Hirashima H.,Snow and Ice Research Center | Yamaguchi S.,Snow and Ice Research Center | Sato A.,Snow and Ice Research Center | Lehning M.,Institute for Snow and Avalanche Research
Cold Regions Science and Technology | Year: 2010

Liquid water movement in snow is an important aspect of wet snow metamorphism and is vital for forecasting wet snow avalanches. However, despite its importance, liquid water movement is over-simplified in the current version of the numerical model SNOWPACK, yielding an inadequate simulation of the water content profile. In general, estimations of liquid water flux in porous materials are based on hydraulic conductivity and suction. This paper presents a water transport model based on the van Genuchten formulation, with parameters obtained from gravity drainage column experiments. Simulations that try to describe the capillary barrier between layers of different grain sizes lead to long computation times because of the small time increments required. In this study, a new algorithm was developed and incorporated in the water transport model in order to simulate the capillary barrier using relatively long time increments (60. s). The model was then used to simulate water movement between snow layers of different grain size. The results confirm that a water-saturated layer forms at the boundary between fine and underlying very coarse snow, which is consistent with observations.The new water transport model was incorporated in SNOWPACK, which then produced an unstable water-saturated layer at the boundary between different grain sizes. Simulation results from the SNOWPACK model were compared with measurements. The main achievement in this study is that the natural capillary barrier was documented and then reproduced using the modified SNOWPACK model. Nevertheless, much work has still to be done to get fully satisfactory results for the reproducibility of grain size and liquid water content. © 2010 Elsevier B.V.

Hirashima H.,Snow and Ice Research Center | Yamaguchi S.,Snow and Ice Research Center | Katsushima T.,National Institute of Technology, Toyama College
Cold Regions Science and Technology | Year: 2014

A multi-dimensional water transport model for a snowpack was developed to reproduce preferential flow. Darcy-Buckingham's law and the van Genuchten model were used to simulate water movement. Parameters for the van Genuchten model were determined as functions of snow density and grain size, based on a previous gravity drainage column experiment. Water entry suction was newly incorporated to simulate liquid water infiltrating dry snow, based on the results of a previous capillary pressure experiment. Heterogeneity of grain size and snow density were also implemented. Heterogeneity alone was not sufficient for the development of preferential flow paths. When both water entry suction and heterogeneity were implemented, the model could simulate the formation of a preferential flow path. Validation of the simulation results by comparison with the results of a previous laboratory experiment showed that the simulated preferential flow path reproduced the experimental result fairly well. The size of the preferential flow path was negatively correlated with grain size and positively correlated with the water supply rate in both the simulation and the experiment. Comparison of the time series of suction between the simulation and the experimental result suggested that some additional measurements need to be obtained experimentally to improve the accuracy of the model. Sensitivity experiments showed that grain size and snow density heterogeneity affected both the size of the preferential flow path and the arrival time of liquid water at the snow base. These results suggest that more measurements of small-scale spatial variability in natural snow are needed to improve the model. © 2014 Elsevier B.V. All rights reserved.

Wever N.,WSL Institute for Snow and Avalanche Research SLF | Fierz C.,WSL Institute for Snow and Avalanche Research SLF | Mitterer C.,WSL Institute for Snow and Avalanche Research SLF | Hirashima H.,Snow and Ice Research Center | And 2 more authors.
Cryosphere | Year: 2014

The runoff from a snow cover during spring snowmelt or rain-on-snow events is an important factor in the hydrological cycle. In this study, three water balance schemes for the 1 dimensional physically-based snowpack model SNOWPACK are compared to lysimeter measurements at two alpine sites with a seasonal snow cover, but with different climatological conditions: Weissfluhjoch (WFJ) and Col de Porte (CDP). The studied period consists of 14 and 17 yr, respectively. The schemes include a simple bucket-type approach, an approximation of Richards Equation (RE), and the full RE. The results show that daily sums of snowpack runoff are strongly related to a positive energy balance of the snow cover and therefore, all water balance schemes show very similar performance in terms of Nash-Sutcliffe efficiency (NSE) coefficients (around 0.63 and 0.72 for WFJ and CDP, respectively) and 2 values (around 0.83 and 0.72 for WFJ and CDP, respectively). An analysis of the runoff dynamics over the season showed that the bucket-type and approximated RE scheme release meltwater slower than in the measurements, whereas RE provides a better agreement. Overall, solving RE for the snow cover yields the best agreement between modelled and measured snowpack runoff, but differences between the schemes are small. On sub-daily time scales, the water balance schemes behave very differently. In that case, solving RE provides the highest agreement between modelled and measured snowpack runoff in terms of NSE coefficient (around 0.48 at both sites). At WFJ, the other water balance schemes loose most predictive power, whereas at CDP, the bucket-type scheme has an NSE coefficient of 0.39. The shallower and less stratified snowpack at CDP likely reduces the differences between the water balance schemes. Accordingly, it can be concluded that solving RE for the snow cover improves several aspects of modelling snow cover runoff, especially for deep, sub-freezing snow covers and in particular on the sub-daily time scales. The additional computational cost was found to be in the order of a factor of 1.5-2.

Sakurai S.,Hokkai Gakuen University | Abe O.,Snow and Ice Research Center | Joh O.,Hokkaido University
Journal of Structural and Construction Engineering | Year: 2012

In estimating the unbalanced snow loads on roofs of buildings in structural design, it is important to consider the influence of wind action on drift of snow accumulation. In our previous papers, based on wind tunnel tests about various shapes of roofs, we have discussed the possibility of estimating snow accumulation patterns by using the characteristics of the gradient of wind pressure distribution from windward to leeward on roof. That is, in the area of negative pressure on roof snow depth distribution tends to increase to leeward when pressure distribution decrease to leeward, and conversely, the former decreases when the latter increases. On the other hand, in the area of positive pressure on roof such relationships are reversed. fri order to predict snow accumulations for arbitrary inclination of span roofs, we propose a new method to estimate the unbalanced snow distribution coefficients by applying the relationships between the wind pressure coefficients and the unbalanced snow distribution coefficients.

Mughal U.N.,Industrial Technology Group | Virk M.S.,Industrial Technology Group | Kosugi K.,Snow and Ice Research Center | Mochizuki S.,Snow and Ice Research Center
Cold Regions Science and Technology | Year: 2016

Icing load and icing rate are necessary feedback variables for an intelligent anti/de-icing system to work effectively in harsh cold environment of high north. These parameters may 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. © 2016 Elsevier B.V.

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