Um die anderen Arten von Veröffentlichungen zu diesem Thema anzuzeigen, folgen Sie diesem Link: Snow particles.
Zeitschriftenartikel zum Thema „Snow particles“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-50 Zeitschriftenartikel für die Forschung zum Thema "Snow particles" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Zeitschriftenartikel für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
1
Rastello, Marie, Fabrice Rastello, Hervé Bellot, Frédéric Ousset, François Dufour und Lorenz Meier. „Size of snow particles in a powder-snow avalanche“. Journal of Glaciology 57, Nr. 201 (2011): 151–56. http://dx.doi.org/10.3189/002214311795306637.
Der volle Inhalt der QuelleAnnotation:
AbstractLittle quantitative information is available concerning the size of ice particles in the turbulent clouds of powder-snow avalanches. To quantify particle size distributions, we have developed an experimental device that collects particles in real-scale powder avalanches. The device was placed on the concrete bunker of the Swiss Vallée de la Sionne avalanche dynamics test site. On 31 January 2003, a large powder-snow avalanche struck the bunker and we were able to collect particle samples. The collected particles have been photographed and the pictures digitized. An image analysis tool allows us to determine an equivalent particle radius. The captured particles have a geometric mean of 0.16 mm; the largest particles were 0.8 mm in size and the smallest particles 0.03 mm.
2
Heintzenberg, Jost, und Markku Rummukainen. „Airborne particles in snow“. Journal of Glaciology 39, Nr. 132 (1993): 239–44. http://dx.doi.org/10.1017/s0022143000015896.
Der volle Inhalt der QuelleAnnotation:
Abstract In a pilot experiment, airborne particles were shown to exist in snow. In newly deposited snow they could be traced down to 17 cm below the surface. With our particle sensor, the snow was ventilated on the level of expected natural ventilation velocities. We show with a simple deposition model that air/snow exchange of airborne particles must be considered in the interpretation of impurities in snow and glacier ice. However, the relative magnitude of ventilation velocity compared to dry-deposition velocities at the surface is of crucial importance for determining total deposition. In particular, in ice sheets with high ventilation velocities, seasonal variations in atmospheric concentrations can be dampened and age distributions of deposited particles need to be considered similarly to the occlusion of gases.
3
Heintzenberg, Jost, und Markku Rummukainen. „Airborne particles in snow“. Journal of Glaciology 39, Nr. 132 (1993): 239–44. http://dx.doi.org/10.3189/s0022143000015896.
Der volle Inhalt der QuelleAnnotation:
AbstractIn a pilot experiment, airborne particles were shown to exist in snow. In newly deposited snow they could be traced down to 17 cm below the surface. With our particle sensor, the snow was ventilated on the level of expected natural ventilation velocities. We show with a simple deposition model that air/snow exchange of airborne particles must be considered in the interpretation of impurities in snow and glacier ice. However, the relative magnitude of ventilation velocity compared to dry-deposition velocities at the surface is of crucial importance for determining total deposition. In particular, in ice sheets with high ventilation velocities, seasonal variations in atmospheric concentrations can be dampened and age distributions of deposited particles need to be considered similarly to the occlusion of gases.
4
Huang, N., und Z. Wang. „A 3-D simulation of drifting snow in the turbulent boundary layer“. Cryosphere Discussions 9, Nr. 1 (15.01.2015): 301–31. http://dx.doi.org/10.5194/tcd-9-301-2015.
Der volle Inhalt der QuelleAnnotation:
Abstract. The drifting snow is one of the most important factors that affect the global ice mass balance and hydrological balance. Current models of drifting snow are usually one- or two-dimensional, focusing on the macroscopic quantities of drifting snow under temporal average flow. In this paper, we take the coupling effects between wind and snow particles into account and present a 3-D model of drifting snow with mixed grain size in the turbulent boundary layer. The Large Eddy Simulation (LES) method is used for simulating the turbulent boundary layer of the wind field and the 3-D trajectory of every motion snow particle is calculated through Lagrangian Particle Tracking method. The results indicated that the drifting snow in the turbulent boundary layer has apparent 3-D structure and snow streamers, which lead to an intermittent transport of the snow particles and spatial inhomogeneity, and the motion trajectories of snow particles, especially the small snow particles, are obviously affected by the turbulent fluctuation. The macro statistics of drifting snow indicates that the spanwise velocity of snow particles increases with height and is one order smaller than that of streamwise velocity. Furthermore, the diameter distribution of snow particles in the air along the height shows a stratification structure.
5
Zhang, Jie, und Ning Huang. „Simulation of Snow Drift and the Effects of Snow Particles on Wind“. Modelling and Simulation in Engineering 2008 (2008): 1–6. http://dx.doi.org/10.1155/2008/408075.
Der volle Inhalt der QuelleAnnotation:
Coupled equations between wind and saltating particles are presented for a stable wind blowing over an infinite plane bed and the equations are solved for a simplified particle-bed impact process. The calculated results show that the saltating snow particles strongly affect the velocity distribution of the wind, causing a deviation from a logarithmically distributed wind velocity profile. The average height and length of saltating snow particle trajectories exponentially increase as the friction velocity increases; the ejected snow number flux and the streamwise snow transport rate also increase as the friction velocity increases.
6
Yuter, Sandra E., David E. Kingsmill, Louisa B. Nance und Martin Löffler-Mang. „Observations of Precipitation Size and Fall Speed Characteristics within Coexisting Rain and Wet Snow“. Journal of Applied Meteorology and Climatology 45, Nr. 10 (01.10.2006): 1450–64. http://dx.doi.org/10.1175/jam2406.1.
Der volle Inhalt der QuelleAnnotation:
Abstract Ground-based measurements of particle size and fall speed distributions using a Particle Size and Velocity (PARSIVEL) disdrometer are compared among samples obtained in mixed precipitation (rain and wet snow) and rain in the Oregon Cascade Mountains and in dry snow in the Rocky Mountains of Colorado. Coexisting rain and snow particles are distinguished using a classification method based on their size and fall speed properties. The bimodal distribution of the particles’ joint fall speed–size characteristics at air temperatures from 0.5° to 0°C suggests that wet-snow particles quickly make a transition to rain once melting has progressed sufficiently. As air temperatures increase to 1.5°C, the reduction in the number of very large aggregates with a diameter > 10 mm coincides with the appearance of rain particles larger than 6 mm. In this setting, very large raindrops appear to be the result of aggregrates melting with minimal breakup rather than formation by coalescence. In contrast to dry snow and rain, the fall speed for wet snow has a much weaker correlation between increasing size and increasing fall speed. Wet snow has a larger standard deviation of fall speed (120%–230% relative to dry snow) for a given particle size. The average fall speed for observed wet-snow particles with a diameter ≥ 2.4 mm is 2 m s−1 with a standard deviation of 0.8 m s−1. The large standard deviation is likely related to the coexistence of particles of similar physical size with different percentages of melting. These results suggest that different particle sizes are not required for aggregation since wet-snow particles of the same size can have different fall speeds. Given the large standard deviation of fall speeds in wet snow, the collision efficiency for wet snow is likely larger than that of dry snow. For particle sizes between 1 and 10 mm in diameter within mixed precipitation, rain constituted 1% of the particles by volume within the isothermal layer at 0°C and 4% of the particles by volume for the region just below the isothermal layer where air temperatures rise from 0° to 0.5°C. As air temperatures increased above 0.5°C, the relative proportions of rain versus snow particles shift dramatically and raindrops become dominant. The value of 0.5°C for the sharp transition in volume fraction from snow to rain is slightly lower than the range from 1.1° to 1.7°C often used in hydrological models.
7
Shevchenko, Vladimir P., Sergey N. Vorobyev, Ivan V. Krickov, Andrey G. Boev, Artyom G. Lim, Alexander N. Novigatsky, Dina P. Starodymova und Oleg S. Pokrovsky. „Insoluble Particles in the Snowpack of the Ob River Basin (Western Siberia) a 2800 km Submeridional Profile“. Atmosphere 11, Nr. 11 (02.11.2020): 1184. http://dx.doi.org/10.3390/atmos11111184.
Der volle Inhalt der QuelleAnnotation:
Snowpack exhibits properties that make it a unique natural archive of airborne pollution. The data on insoluble particles in the Ob River catchment (Western Siberia) snowpack are limited. Insoluble particles in the snowpack of Western Siberia were studied at 36 sites on a 2800 km submeridional profile from the city of Barnaul to Salekhard in February 2020. Snow samples were collected over the full depth of the snow core, from the surface of the snow cover to the boundary with soil, except for the lower 1–2 cm. After the filtration of melted snow through a 0.45-µm membrane, the particle composition was studied using a scanning electron microscope with an energy microprobe. In the background areas, the concentration of insoluble particles in the snow was below 2 mg/L. Significantly higher particle concentrations were encountered near cities and hydrocarbon production areas. Particulate matter in snow mainly consists of biogenic and lithogenic particles mixed with anthropogenic particles (ash and black carbon aggregates). The proportion of anthropogenic particles increases near cities and areas of active hydrocarbon production.
8
ITO, YOICHI, FLORENCE NAAIM-BOUVET, KOUICHI NISHIMURA, HERVÉ BELLOT, EMMANUEL THIBERT, XAVIER RAVANAT und FIRMIN FONTAINE. „Measurement of snow particle size and velocity in avalanche powder clouds“. Journal of Glaciology 63, Nr. 238 (23.01.2017): 249–57. http://dx.doi.org/10.1017/jog.2016.130.
Der volle Inhalt der QuelleAnnotation:
ABSTRACTParticle 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.
9
Omiya, Satoshi, Atsushi Sato, Kenji Kosugi und Shigeto Mochizuki. „Estimation of the electrostatic charge of individual blowing-snow particles by wind tunnel experiment“. Annals of Glaciology 52, Nr. 58 (2011): 148–52. http://dx.doi.org/10.3189/172756411797252167.
Der volle Inhalt der QuelleAnnotation:
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.
10
SAITOH, K., K. SERA und K. HIRANO. „CHARACTERIZATION OF TOTAL SUSPENDED PARTICULATE (TSP) IN A MOUNTAINOUS REGION IN NORTHERN JAPAN“. International Journal of PIXE 11, Nr. 01n02 (Januar 2001): 11–19. http://dx.doi.org/10.1142/s0129083501000037.
Der volle Inhalt der QuelleAnnotation:
Total suspended particulate (TSP) samples were collected at the west-facing slope (altitude 700 m) of Mt. Moriyoshi in northern Japan, from 24 – 27 June (non-snow-clad period) and 11 – 14 December (snow-clad period) in 1996, with a one-hour sampling interval. The elemental composition and particle shape of TSP samples were determined and/or observed by Particle Induced X-ray Emission (PIXE), a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. In the hourly TSP samples collected during the non-snow-clad period, 27 elements were determined. Na, Mg, Al, Si, S, K, Ca and Fe were found to be the major elemental components. On the other hand, 25 elements, excluding Nd and Mo, were found in the snow-clad period samples, and Cl is a dominant element, i.e., a major element, of the snow-clad period samples, unlike the non-snow-clad period. Comparing the arithmetic means of concentrations of major elements in TSP for non-snow-clad and snow-clad periods, Mg, Al, Si, K, Ca and Fe levels in the snow-clad period are 2 – 4 times as much as those in the non-snow-clad period, and 30 times for Na. S is similar. For temporal variation patterns of element concentrations, the non-snow-clad period is different from the snow-clad period. Al, S, Ca, Ti, Fe, Zn and Pb are similar throughout the non-snow-clad period, and Al, Si, Ca and Fe are similar throughout the snow-clad period. With the aid of SEM and EDX analysis, aggregates of car exhaust particles, soil particles and plant spores were observed in the non-snow-clad period samples. In the snow-clad period samples, small silicon-rich spherical particles, aggregates of car exhaust particles and soil particles were observed.
11
Itagaki, K., und G. E. Lemieux. „Connectivity of snow particles“. Annals of Glaciology 18 (1993): 7–10. http://dx.doi.org/10.1017/s0260305500011174.
Der volle Inhalt der QuelleAnnotation:
An optical system, potentially suitable for quantitative characterization of snow, was conceived and tested. The system uses a laser beam to scan a thick section of snow impregnated with an opaque medium and observes light transmission through the slab.
12
Itagaki, K., und G. E. Lemieux. „Connectivity of snow particles“. Annals of Glaciology 18 (1993): 7–10. http://dx.doi.org/10.3189/s0260305500011174.
Der volle Inhalt der QuelleAnnotation:
An optical system, potentially suitable for quantitative characterization of snow, was conceived and tested. The system uses a laser beam to scan a thick section of snow impregnated with an opaque medium and observes light transmission through the slab.
13
FILHOL, SIMON, und MATTHEW STURM. „The smoothing of landscapes during snowfall with no wind“. Journal of Glaciology 65, Nr. 250 (04.03.2019): 173–87. http://dx.doi.org/10.1017/jog.2018.104.
Der volle Inhalt der QuelleAnnotation:
ABSTRACTEvery winter, snowy landscapes are smoothed by snow deposition in calm conditions (no wind). In this study, we investigated how vertically falling snow attenuates topographic relief at horizontal scales less than or approximately equal to snow depth (e.g., 0.1–10 m). In a set of three experiments under natural snowfall, we observed the particle-scale mechanisms by which smoothing is achieved, and we examined the cumulative effect at the snowpack scale. The experiments consisted of (a) a strobe-light box for tracking the trajectories of snowflakes at deposition, (b) allowing snow to fall through a narrow gap (40 mm) and examining snow accumulation above and below the gap, and (c) allowing snow to accumulate over a set of artificial surfaces. At the particle scale, we observed mechanisms enhancing (bouncing, rolling, ejection, breakage, creep, metamorphism) and retarding (interlocking, cohesion, adhesion, sintering) the rate of smoothing. The cumulative effect of these mechanisms is found to be driven by snowpack surface curvature, introducing a directional bias in the lateral transport of snow particles. Our findings suggest that better quantification of the mechanisms behind smoothing by snow could provide insights into the evolution of snow depth variability, and snow-vegetation interactions.
14
Kuo, Kwo-Sen, William S. Olson, Benjamin T. Johnson, Mircea Grecu, Lin Tian, Thomas L. Clune, Bruce H. van Aartsen, Andrew J. Heymsfield, Liang Liao und Robert Meneghini. „The Microwave Radiative Properties of Falling Snow Derived from Nonspherical Ice Particle Models. Part I: An Extensive Database of Simulated Pristine Crystals and Aggregate Particles, and Their Scattering Properties“. Journal of Applied Meteorology and Climatology 55, Nr. 3 (März 2016): 691–708. http://dx.doi.org/10.1175/jamc-d-15-0130.1.
Der volle Inhalt der QuelleAnnotation:
AbstractA 3D growth model is used to simulate pristine ice crystals, which are aggregated using a collection algorithm to create larger, multicrystal particles. The simulated crystals and aggregates have mass-versus-size and fractal properties that are consistent with field observations. The growth/collection model is used to generate a large database of snow particles, and the single-scattering properties of each particle are computed using the discrete dipole approximation to account for the nonspherical geometries of the particles. At 13.6 and 35.5 GHz, the bulk radar reflectivities of nonspherical snow particle polydispersions differ from those of more approximate spherical, homogeneous, ice–air particle polydispersions that have the same particle size distributions, although the reflectivities of the nonspherical particles are roughly approximated by polydispersions of spheres of 0.1–0.2 g cm−3 density. At higher microwave frequencies, such as 165.5 GHz, the bulk extinction (and scattering) coefficients of the nonspherical snow polydispersions are comparable to those of low-density spheres, but the asymmetry parameters of the nonspherical particles are substantially less than those of spheres for a broad range of assumed spherical particle densities. Because of differences in the asymmetry of scatter, simulated microwave-scattering depressions using nonspherical particles may well exceed those of spheres for snow layers with the same vertical water path. It may be concluded that, in precipitation remote sensing applications that draw upon input from radar and/or radiometer observations spanning a range of microwave frequencies, nonspherical snow particle models should be used to properly interpret the observations.
15
Schnaiter, Martin, Claudia Linke, Inas Ibrahim, Alexei Kiselev, Fritz Waitz, Thomas Leisner, Stefan Norra und Till Rehm. „Specifying the light-absorbing properties of aerosol particles in fresh snow samples, collected at the Environmental Research Station Schneefernerhaus (UFS), Zugspitze“. Atmospheric Chemistry and Physics 19, Nr. 16 (28.08.2019): 10829–44. http://dx.doi.org/10.5194/acp-19-10829-2019.
Der volle Inhalt der QuelleAnnotation:
Abstract. Atmospheric aerosol particles like mineral dust, volcanic ash and combustion particles can reduce Earth's snow and ice albedo considerably even by very small amounts of deposited particle mass. In this study, a new laboratory method is applied to measure the spectral light absorption coefficient of airborne particles that are released from fresh snow samples by an efficient nebulizing system. Three-wavelength photoacoustic absorption spectroscopy is combined with refractory black carbon (BC) mass analysis to determine the snow mass-specific and BC mass-specific absorption cross sections. Fullerene soot in water suspensions are used for the characterization of the method and for the determination of the mass-specific absorption cross section of this BC reference material. The analysis of 31 snow samples collected after fresh snowfall events at a high-altitude Alpine research station reveals a significant discrepancy between the measured snow mass-specific absorption cross section and the cross section that is expected from the BC mass data, indicating that non-BC light-absorbing particles are present in the snow. Mineral dust and brown carbon (BrC) are identified as possible candidates for the non-BC particle mass based on the wavelength dependence of the measured absorption. For one sample this result is confirmed by environmental scanning electron microscopy and by single-particle fluorescence measurements, which both indicate a high fraction of biogenic and organic particle mass in the sample.
16
Bintanja, Richard. „Buoyancy effects induced by drifting snow particles“. Annals of Glaciology 32 (2001): 147–52. http://dx.doi.org/10.3189/172756401781819346.
Der volle Inhalt der QuelleAnnotation:
AbstractSnowdrift is one of the many manifestations of two-phase flows in which the inherently stably stratified drift-density profile acts to destroy turbulence. This can be quantified by using an appropriate “particle” Richardson number, equivalent to thermally stratified flow. This Richardson number is proportional to the mean fall velocity of the particles (averaged over the particle-size spectrum) and the drift density and therefore depends strongly on height above the surface. It exhibits a maximum close to the surface, where drift densities are largest. It then decreases to minimum values at intermediate heights, above which Richardson numbers increase with height. The particle Richardson number and the associated decrease in turbulent exchange coefficient depend strongly on wind speed, particle-eddy exchange coefficient and mean particle radius It is found that particle-buoyancy effects in snowdrift are non-negligible for large wind speeds and large particle-eddy exchange coefficients.
17
Vázquez-Martín, Sandra, Thomas Kuhn und Salomon Eliasson. „Shape dependence of snow crystal fall speed“. Atmospheric Chemistry and Physics 21, Nr. 10 (18.05.2021): 7545–65. http://dx.doi.org/10.5194/acp-21-7545-2021.
Der volle Inhalt der QuelleAnnotation:
Abstract. Improved snowfall predictions require accurate knowledge of the properties of ice crystals and snow particles, such as their size, cross-sectional area, shape, and fall speed. The fall speed of ice particles is a critical parameter for the representation of ice clouds and snow in atmospheric numerical models, as it determines the rate of removal of ice from the modelled clouds. Fall speed is also required for snowfall predictions alongside other properties such as ice particle size, cross-sectional area, and shape. For example, shape is important as it strongly influences the scattering properties of these ice particles and thus their response to remote sensing techniques. This work analyzes fall speed as a function of particle size (maximum dimension), cross-sectional area, and shape using ground-based in situ measurements. The measurements for this study were done in Kiruna, Sweden, during the snowfall seasons of 2014 to 2019, using the ground-based in situ instrument Dual Ice Crystal Imager (D-ICI). The resulting data consist of high-resolution images of falling hydrometeors from two viewing geometries that are used to determine particle size (maximum dimension), cross-sectional area, area ratio, orientation, and the fall speed of individual particles. The selected dataset covers sizes from about 0.06 to 3.2 mm and fall speeds from 0.06 to 1.6 m s−1. Relationships between particle size, cross-sectional area, and fall speed are studied for different shapes. The data show in general low correlations to fitted fall speed relationships due to large spread observed in fall speed. After binning the data according to size or cross-sectional area, correlations improve, and we can report reliable parameterizations of fall speed vs. particle size or cross-sectional area for part of the shapes. For most of these shapes, the fall speed is better correlated with cross-sectional area than with particle size. The effects of orientation and area ratio on the fall speed are also studied, and measurements show that vertically oriented particles fall faster on average. However, most particles for which orientation can be defined fall horizontally.
18
Ida, Shigeru, Tristan Guillot, Ryuki Hyodo, Satoshi Okuzumi und Andrew N. Youdin. „Planetesimal formation around the snow line“. Astronomy & Astrophysics 646 (Februar 2021): A13. http://dx.doi.org/10.1051/0004-6361/202039705.
Der volle Inhalt der QuelleAnnotation:
Context.The formation of rocky planetesimals is a long-standing problem in planet formation theory. One of the possibilities is that it results from gravitational instability as a result of the pile-up of small silicate dust particles released from sublimating icy pebbles that pass the snow line.Aims.We want to understand and quantify the role of the water snow line for the formation of rock-rich and ice-rich planetesimals. In this paper, we focus on the formation of rock-rich planetesimals. A companion paper examines the combined formation of both rock-rich and ice-rich planetesimals.Methods.We developed a new Monte Carlo code to calculate the radial evolution of silicate particles in a turbulent accretion disk, accounting for the back reaction (i.e., inertia) of the particles on their radial drift velocity and diffusion. Results depend in particular on the particle injection width (determined from the radial sublimation width of icy pebbles), the pebble scale height, and the pebble mass flux through the disk. The scale height evolution of the silicate particles, which is the most important factor for the runaway pile-up, is calculated automatically in this Lagrange method.Results.From the numerical results, we derive semi-analytical relations for the scale height of the silicate dust particles and the particle-to-gas density ratio at the midplane, as functions of a pebble-to-gas mass flux ratio and theαparameters for disk gas accretion and vertical/radial diffusion We find that the runaway pile-up of the silicate particles (formation of rocky planetesimals) occurs if the pebble-to-gas mass flux ratio is ≳ [(αDz/αacc)/3 × 10−2]1/2, whereαDzandαaccare theαparameters for vertical turbulent diffusion and disk gas accretion.
19
Pirazzini, R., P. Räisänen, T. Vihma, M. Johansson und E. M. Tastula. „Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet“. Cryosphere 9, Nr. 6 (15.12.2015): 2357–81. http://dx.doi.org/10.5194/tc-9-2357-2015.
Der volle Inhalt der QuelleAnnotation:
Abstract. The albedo of a snowpack depends on the single-scattering properties of individual snow crystals, which have a variety of shapes and sizes, and are often bounded in clusters. From the point of view of optical modelling, it is essential to identify the geometric dimensions of the population of snow particles that synthesize the scattering properties of the snowpack surface. This involves challenges related to the complexity of modelling the radiative transfer in such an irregular medium, and to the difficulty of measuring microphysical snow properties. In this paper, we illustrate a method to measure the size distribution of a snow particle parameter, which roughly corresponds to the smallest snow particle dimension, from two-dimensional macro photos of snow particles taken in Antarctica at the surface layer of a melting ice sheet. We demonstrate that this snow particle metric corresponds well to the optically equivalent effective radius utilized in radiative transfer modelling, in particular when snow particles are modelled with the droxtal shape. The surface albedo modelled on the basis of the measured snow particle metric showed an excellent match with the observed albedo when there was fresh or drifted snow at the surface. In the other cases, a good match was present only for wavelengths longer than 1.4 μm. For shorter wavelengths, our modelled albedo generally overestimated the observations, in particular when surface hoar and faceted polycrystals were present at the surface and surface roughness was increased by millimetre-scale cavities generated during melting. Our results indicate that more than just one particle metric distribution is needed to characterize the snow scattering properties at all optical wavelengths, and suggest an impact of millimetre-scale surface roughness on the shortwave infrared albedo.
20
Pirazzini, R., P. Räisänen, T. Vihma, M. Johansson und E. M. Tastula. „Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet“. Cryosphere Discussions 9, Nr. 3 (30.06.2015): 3405–74. http://dx.doi.org/10.5194/tcd-9-3405-2015.
Der volle Inhalt der QuelleAnnotation:
Abstract. The albedo of a snowpack depends on the single-scattering properties of individual snow crystals, which have a variety of shapes and sizes, and are often bounded in clusters. From the point of view of optical modelling, it is essential to identify the geometric dimensions of the population of snow particles that synthetize the scattering properties of the snowpack surface. This involves challenges related to the complexity of modelling the radiative transfer in such an irregular medium, and to the difficulty of measuring microphysical snow properties. In this paper, we illustrate a method to measure the size distribution of a snow particle parameter, which roughly corresponds to the smallest snow particle dimension, from two-dimensional macro-photos of snow particles taken in Antarctica at the surface layer of a melting ice sheet. We demonstrate that this snow particle metric corresponds well to the optically equivalent effective radius utilized in radiative transfer modelling, in particular when snow particles are modelled with the droxtal shape. The surface albedo modelled on the basis of the measured snow particle metric showed an excellent match with the observed albedo when there was fresh or drifted snow at the surface. In the other cases, a good match was present only for wavelengths longer than 1.4 μm. For shorter wavelengths, our modelled albedo generally overestimated the observations, in particular when surface hoar and faceted polycrystals were present at the surface and surface roughness was increased by millimetre-scale cavities generated during melting. Our results indicate that more than just one particle metric distribution is needed to characterize the snow scattering properties at all optical wavelengths, and suggest an impact of millimetre-scale surface roughness on the shortwave infrared albedo.
21
Issler, Dieter. „Modelling of snow entrainment and deposition in powder-snow avalanches“. Annals of Glaciology 26 (1998): 253–58. http://dx.doi.org/10.3189/1998aog26-1-253-258.
Der volle Inhalt der QuelleAnnotation:
Following Norem’s description of powder-snow avalanche formation and structure, we propose a mathematical model that consists of a suspension layer and a so-called saltation layer. The latter is only a few meters deep and is modelled by depth-averaged mass and momentum balances. In the suspension layer, the mass and momentum balance equations for the mixture are supplemented by the snow mass balance and the transport equations for turbulent kinetic energy and dissipation. Mass and momentum exchange between the two layers is determined by particle settling, turbulent diffusion against the concentration gradient and aerodynamic shear forces. The net erosion or deposition rate is a function of the kinetic energy of the impacting particles. The saltation layer reacts on the suspension layer in that saltating particles extract momentum from the air flow. The preliminary estimates of the model parameters can be refined by means of saltation-trajectory simulations. Three-dimensional simulations with a simplified model have clearly shown the importance of snow erosion and deposition in practical applications. This approach is well suited for coupling to a dense-flow avalanche model.
22
Issler, Dieter. „Modelling of snow entrainment and deposition in powder-snow avalanches“. Annals of Glaciology 26 (1998): 253–58. http://dx.doi.org/10.1017/s0260305500014919.
Der volle Inhalt der QuelleAnnotation:
Following Norem’s description of powder-snow avalanche formation and structure, we propose a mathematical model that consists of a suspension layer and a so-called saltation layer. The latter is only a few meters deep and is modelled by depth-averaged mass and momentum balances. In the suspension layer, the mass and momentum balance equations for the mixture are supplemented by the snow mass balance and the transport equations for turbulent kinetic energy and dissipation. Mass and momentum exchange between the two layers is determined by particle settling, turbulent diffusion against the concentration gradient and aerodynamic shear forces. The net erosion or deposition rate is a function of the kinetic energy of the impacting particles. The saltation layer reacts on the suspension layer in that saltating particles extract momentum from the air flow. The preliminary estimates of the model parameters can be refined by means of saltation-trajectory simulations. Three-dimensional simulations with a simplified model have clearly shown the importance of snow erosion and deposition in practical applications. This approach is well suited for coupling to a dense-flow avalanche model.
23
Sukovich, Ellen M., David E. Kingsmill und Sandra E. Yuter. „Variability of Graupel and Snow Observed in Tropical Oceanic Convection by Aircraft during TRMM KWAJEX“. Journal of Applied Meteorology and Climatology 48, Nr. 2 (01.02.2009): 185–98. http://dx.doi.org/10.1175/2008jamc1940.1.
Der volle Inhalt der QuelleAnnotation:
Abstract Empirical characterization of graupel and snow in precipitating tropical convective clouds is important for refining satellite precipitation retrieval algorithms and cloud-resolving and radiative transfer models. Microphysics data for this analysis were collected by the University of North Dakota (UND) Citation and the National Aeronautics and Space Agency (NASA) DC-8 aircraft during the Tropical Rainfall Measuring Mission (TRMM) Kwajalein Experiment (KWAJEX) in the western tropical Pacific Ocean. An ice particle identification algorithm was applied to two-dimensional optical array probe data for the purpose of identifying ice particle ensembles dominated by graupel or snow particles. These ensembles were accumulated along 1-km flight segments at temperatures below 0°C. A third category, mixed graupel/snow, has characteristics between those of the predominately graupel and snow ensembles and can be used either in combination with the other two categories or separately. Snow particle ensembles compose 80% of UND Citation and 98% of NASA DC-8 ensemble data. For the UND Citation, graupel ensembles compose ∼5% of the total with mixed graupel/snow ensembles composing ∼15%. There were no graupel ensembles in the NASA DC-8 data, which were collected primarily at temperatures <−35°C. Particles too small to classify (<150-μm maximum dimension) compose 56% of UND Citation and 64% of NASA DC-8 particle images. Nearly all these “tiny” particles occur coincident with particles >∼150 μm. Combining data from both aircraft, snow and mixed graupel/snow ensembles were evident over the full range of subfreezing temperatures (from 0° to −65°C) sampled by the aircraft. In contrast, graupel ensembles were present primarily at temperatures >−10°C. Accurate graupel identification was further supported by all graupel ensembles observed either coincident with or within a 10-km horizontal distance of radar-identified convective precipitation structures.
24
Olson, William S., Lin Tian, Mircea Grecu, Kwo-Sen Kuo, Benjamin T. Johnson, Andrew J. Heymsfield, Aaron Bansemer, Gerald M. Heymsfield, James R. Wang und Robert Meneghini. „The Microwave Radiative Properties of Falling Snow Derived from Nonspherical Ice Particle Models. Part II: Initial Testing Using Radar, Radiometer and In Situ Observations“. Journal of Applied Meteorology and Climatology 55, Nr. 3 (März 2016): 709–22. http://dx.doi.org/10.1175/jamc-d-15-0131.1.
Der volle Inhalt der QuelleAnnotation:
AbstractIn this study, two different particle models describing the structure and electromagnetic properties of snow are developed and evaluated for potential use in satellite combined radar–radiometer precipitation estimation algorithms. In the first model, snow particles are assumed to be homogeneous ice–air spheres with single-scattering properties derived from Mie theory. In the second model, snow particles are created by simulating the self-collection of pristine ice crystals into aggregate particles of different sizes, using different numbers and habits of the collected component crystals. Single-scattering properties of the resulting nonspherical snow particles are determined using the discrete dipole approximation. The size-distribution-integrated scattering properties of the spherical and nonspherical snow particles are incorporated into a dual-wavelength radar profiling algorithm that is applied to 14- and 34-GHz observations of stratiform precipitation from the ER-2 aircraftborne High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP) radar. The retrieved ice precipitation profiles are then input to a forward radiative transfer calculation in an attempt to simulate coincident radiance observations from the Conical Scanning Millimeter-Wave Imaging Radiometer (CoSMIR). Much greater consistency between the simulated and observed CoSMIR radiances is obtained using estimated profiles that are based upon the nonspherical crystal/aggregate snow particle model. Despite this greater consistency, there remain some discrepancies between the higher moments of the HIWRAP-retrieved precipitation size distributions and in situ distributions derived from microphysics probe observations obtained from Citation aircraft underflights of the ER-2. These discrepancies can only be eliminated if a subset of lower-density crystal/aggregate snow particles is assumed in the radar algorithm and in the interpretation of the in situ data.
25
Uematsu, Takahiko. „Numerical study on snow transport and drift formation“. Annals of Glaciology 18 (1993): 135–41. http://dx.doi.org/10.1017/s0260305500011393.
Der volle Inhalt der QuelleAnnotation:
A three-dimensional, numerical simulation model for snow transport and drift formation is proposed in which saltation as well as suspension are considered as dynamic behavioral factors of moving snow particles. The procedure for simulation is as follows: (1) Air flow field is simulated solving the Reynolds equations and the continuity equation. (2) Using the result of the air field flow simulation, the blown-snow density field is simulated using the diffusion equations in which the fall velocity of blown snow particles is considered. In the boundary conditions, the particle movement of saltation is taken into consideration. (3) Finally, the snowdrift rate is computed based on the amount of snow particles not transported by saltation. This model was quantitatively tested for the phenomenon of snowdrift development. The computed results showed good agreement with observations.
26
Uematsu, Takahiko. „Numerical study on snow transport and drift formation“. Annals of Glaciology 18 (1993): 135–41. http://dx.doi.org/10.3189/s0260305500011393.
Der volle Inhalt der QuelleAnnotation:
A three-dimensional, numerical simulation model for snow transport and drift formation is proposed in which saltation as well as suspension are considered as dynamic behavioral factors of moving snow particles. The procedure for simulation is as follows: (1) Air flow field is simulated solving the Reynolds equations and the continuity equation. (2) Using the result of the air field flow simulation, the blown-snow density field is simulated using the diffusion equations in which the fall velocity of blown snow particles is considered. In the boundary conditions, the particle movement of saltation is taken into consideration. (3) Finally, the snowdrift rate is computed based on the amount of snow particles not transported by saltation. This model was quantitatively tested for the phenomenon of snowdrift development. The computed results showed good agreement with observations.
27
Hagenmuller, Pascal, Frederic Flin, Marie Dumont, François Tuzet, Isabel Peinke, Philippe Lapalus, Anne Dufour et al. „Motion of dust particles in dry snow under temperature gradient metamorphism“. Cryosphere 13, Nr. 9 (06.09.2019): 2345–59. http://dx.doi.org/10.5194/tc-13-2345-2019.
Der volle Inhalt der QuelleAnnotation:
Abstract. The deposition of light-absorbing particles (LAPs) such as mineral dust and black carbon on snow is responsible for a highly effective climate forcing, through darkening of the snow surface and associated feedbacks. The interplay between post-depositional snow transformation (metamorphism) and the dynamics of LAPs in snow remains largely unknown. We obtained time series of X-ray tomography images of dust-contaminated samples undergoing dry snow metamorphism at around −2 ∘C. They provide the first observational evidence that temperature gradient metamorphism induces dust particle motion in snow, while no movement is observed under isothermal conditions. Under temperature gradient metamorphism, dust particles can enter the ice matrix due to sublimation–condensation processes and spread down mainly by falling into the pore space. Overall, such motions might reduce the radiative impact of dust in snow, in particular in arctic regions where temperature gradient metamorphism prevails.
28
KOBAYASHI, Shun'ichi. „Movement and Deposition of Snow Particles in Snow Storm.“ Journal of Geography (Chigaku Zasshi) 100, Nr. 2 (1991): 240–49. http://dx.doi.org/10.5026/jgeography.100.2_240.
Der volle Inhalt der Quelle
29
Schmidt, D. S., J. D. Dent und R. A. Schmidt. „Charge-to-mass ratio of individual blowing-snow particles“. Annals of Glaciology 26 (1998): 207–11. http://dx.doi.org/10.1017/s0260305500014828.
Der volle Inhalt der QuelleAnnotation:
Determining the electrostatic force acting on saltating snow particles requires knowledge of the electric field in the saltation region and the charge on the particle. To date, measurements of average charge-to-mass ratios for blowing-snow samples have been made but Schmidt and Schmidt (1993) have indicated these may underestimate charge-to-mass ratios for individual particles due to a mixture of positive and negative charge in the samples. This paper reports on measurements of charge-to-mass ratio for individual blowing-snow particles during a moderate blowing-snow storm in southwestern Wyoming. We measured charge-to-mass ratios as large as -208μC,kg-1, significantly higher than the -10μC kg-1measured by Latham and Montagne (1970) and -50μCkg-1measured by Wishart (1970). This large charge-to-mass ratio was accompanied by a distribution of positive and negative charge on the particles, supporting the conclusions of Schmidt and Schmidt (1993).
30
KIMURA, Tadashi. „Measurements of Drifting Snow Particles.“ Journal of Geography (Chigaku Zasshi) 100, Nr. 2 (1991): 250–63. http://dx.doi.org/10.5026/jgeography.100.2_250.
Der volle Inhalt der Quelle
31
Takahashi, Sbuhei. „Characteristics of Drifting Snow at Mizuho Station, Antarctica“. Annals of Glaciology 6 (1985): 71–75. http://dx.doi.org/10.3189/1985aog6-1-71-75.
Der volle Inhalt der QuelleAnnotation:
Observations of drifting snow were carried out at Mizuho Station (70°42'S, 44°20'E, 2230 m above sea level), East Antarctica, in 1982. Drift flux was proportional to about the 8th power of wind velocity above 1 m and about the 4th power below 0.1 m, while snow drift transport rate was proportional to about the 5th power. For drift flux at 1 m height, the power had a temperature dependence, decreasing above -20 °C. Visibility was proportional to about the -8th power of wind velocity; this is explained by the power relation between drift flux and wind velocity. The repose angle of drifting snow particles was observed by the inclination of a cone-shaped deposit on a disk; it was more than 80° when snow was falling and less than 80° without precipitation. The fall velocity of drifting snow particles, obtained by time-marked trajectories of particles, was between 0.3 and 0.9 m/s, and depended on wind velocity and snow particle shape.
32
Takahashi, Sbuhei. „Characteristics of Drifting Snow at Mizuho Station, Antarctica“. Annals of Glaciology 6 (1985): 71–75. http://dx.doi.org/10.1017/s0260305500010028.
Der volle Inhalt der QuelleAnnotation:
Observations of drifting snow were carried out at Mizuho Station (70°42'S, 44°20'E, 2230 m above sea level), East Antarctica, in 1982. Drift flux was proportional to about the 8th power of wind velocity above 1mand about the 4th power below 0.1 m, while snow drift transport rate was proportional to about the 5th power. For drift flux at 1 m height, the power had a temperature dependence, decreasing above -20 °C. Visibility was proportional to about the -8th power of wind velocity; this is explained by the power relation between drift flux and wind velocity. The repose angle of drifting snow particles was observed by the inclination of a cone-shaped deposit on a disk; it was more than 80° when snow was falling and less than 80° without precipitation. The fall velocity of drifting snow particles, obtained by time-marked trajectories of particles, was between 0.3 and 0.9 m/s, and depended on wind velocity and snow particle shape.
33
Wang, Jiabin, Guangjun Gao, Yan Zhang, Kan He und Jie Zhang. „Anti-snow performance of snow shields designed for brake calipers of a high-speed train“. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit 233, Nr. 2 (27.06.2018): 121–40. http://dx.doi.org/10.1177/0954409718783327.
Der volle Inhalt der QuelleAnnotation:
When high-speed trains run on a snowy railway line in cold weather, a large amount of snow and ice will accumulate on the brake calipers, which can lead to huge safety problems. In this paper, to solve this issue, a numerical method based on the detached eddy simulation was used to explore the flow features of a high-speed train running in cold weather. The accuracy of mesh resolution and methodology of Computational Fluid Dynamics (CFD) was validated against the wind tunnel tests. A discrete phase model was used to investigate the process of snow accumulation on the brake calipers by analysing the movement characteristics of snow particles. Based on this analysis, three kinds of anti-snow packing shields for the brake calipers were designed, and the shielding effects were compared via numerical simulations. The results show that a large amount of snow particles below the bogie directly impact the brake calipers causing massive snow packing on the bottom surfaces; some snow particles reflected from the rear equipment cabin cover return to the bogie region and accumulates on the upper surfaces. With the application of anti-snow packing shields with trapezoidal-, triangular- and cambered-shaped openings, the rates of snow accumulation on the brake calipers were reduced by 18.53, 26.68 and 38.81%, respectively. The cambered type provides the best anti-snow packing performance for the brake calipers.
34
SHEN, YI-JUN, und MUH-RONG WANG. „MECHANISM AND PERFORMANCE OF CO2 SNOW JET IN CO-AXIAL TYPE INJECTION SYSTEMS“. International Journal of Modern Physics: Conference Series 19 (Januar 2012): 250–56. http://dx.doi.org/10.1142/s2010194512008823.
Der volle Inhalt der QuelleAnnotation:
This paper describes the characteristics of CO 2 snow formation with co-axial type injection systems. The injection of CO 2 snow flow is controlled by a co-axial type nitrogen auxiliary nozzle. Five cases of co-axial nitrogen nozzle with different diameters and injection types of auxiliary nitrogen are presented. Flow field visualization and spray characteristics are performed by the particle image velocimetry (PIV). Result shows that the CO 2 snow particles would collide with each other and generate lager particles in the recirculation zone of the formation chamber. Results also show that the particle size distribution is influenced by the geometry of the injection device. The length of the formation chamber influence the region and strength of recirculation flow. In the region after reattach zone of recirculation flow, the fine particles deposit on the chamber wall and form a deposition layer. The particles in the main stream further impinge onto the deposition layer and result in the snowballs. It turns out that the mean particle size becomes larger as the length of chamber is increased. Results also show that CO 2 snow jet has higher velocity and the flow-focusing takes place with nitrogen auxiliary gas. Furthermore, the mist layer of the jet flow caused by lower temperature of CO 2 snow is eliminated when co-axial nitrogen flow is injected. The velocity of CO 2 snow jet is increased under higher injection pressure of co-axial nitrogen flow. Furthermore, smaller diameter of nitrogen auxiliary nozzle results in higher injection velocity of CO 2 snow jet. Hence the injection power of the CO 2 snow jet can be controlled by the design of the nitrogen auxiliary nozzle. It will be useful in the medical applications of cryotherapy treatment and the dry cleaning of the semiconductor and solar cell manufacturing processes.
35
Schmidt, D. S., J. D. Dent und R. A. Schmidt. „Charge-to-mass ratio of individual blowing-snow particles“. Annals of Glaciology 26 (1998): 207–11. http://dx.doi.org/10.3189/1998aog26-1-207-211.
Der volle Inhalt der QuelleAnnotation:
Determining the electrostatic force acting on saltating snow particles requires knowledge of the electric field in the saltation region and the charge on the particle. To date, measurements of average charge-to-mass ratios for blowing-snow samples have been made but Schmidt and Schmidt (1993) have indicated these may underestimate charge-to-mass ratios for individual particles due to a mixture of positive and negative charge in the samples. This paper reports on measurements of charge-to-mass ratio for individual blowing-snow particles during a moderate blowing-snow storm in southwestern Wyoming. We measured charge-to-mass ratios as large as -208 μC, kg-1, significantly higher than the -10μC kg -1 measured by Latham and Montagne (1970) and -50 μC kg-1 measured by Wishart (1970). This large charge-to-mass ratio was accompanied by a distribution of positive and negative charge on the particles, supporting the conclusions of Schmidt and Schmidt (1993).
36
SAITOH, KATSUMI, YOSHIHIRO IWATA, KOICHIRO SERA und KOICHIRO HIRANO. „CHARACTERIZATION OF ATMOSPHERIC TOTAL SUSPENDED PARTICULATE (TSP) IN A MIDSIZE CITY IN NORTHERN JAPAN: NON-SNOW-CLAD PERIOD TO SNOW-CLAD PERIOD COMPARISON“. International Journal of PIXE 13, Nr. 01n02 (Januar 2003): 51–64. http://dx.doi.org/10.1142/s0129083503000105.
Der volle Inhalt der QuelleAnnotation:
Total suspended particulate (TSP) samples were collected from three areas (commercial, residential and agricultural) in and near Akita City in northern Japan, from May – June 1996 (non-snow-clad period) and January – February 1997 (snow-clad period), over three days with a one-hour sampling interval for each area. The elemental composition and particle shape of TSP samples were determined and/or observed by Particle Induced X-ray Emission (PIXE) and a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. In the hourly TSP samples collected during the non-snow-clad period, 23 elements were determined for each area, and Na , Mg , Al , Si , S , Cl , K , Ca and Fe were the major components. On the other hand, 25 elements, excluding As and Rb , were found in the snow-clad period samples, and P , Ga , Nb and Mo were only found in the snow-clad-period samples. Dominant elements, i.e., major components, of the snow-clad period were the same as the non-snow-clad period. Comparing the arithmetic means of elemental concentrations in TSP for the non-snow-clad and snow-clad periods, in the commercial area the elemental concentrations in the snow-clad period were the same or lower than those in the non-snow-clad period, with the concentrations of Na , Mg , Al , Si , S , K , Ca , Ti and Fe in particular being markedly lower. In the residential area the concentrations of Na , Mg and Cl were markedly higher in the snow-clad period than in the non-snow-clad period, while the concentrations of the other elements were the same or only slightly lower. In the agricultural area, the concentrations of Na and Cl were markedly higher in the snow-clad period relative to the non-snow-clad period, and the concentrations of the other elements, except for P , were low. The concentrations of the major elements and Pb were particularly low. Thus, in the residential and agricultural areas the effect of northwesterly winter wind on TSP can be observed by Cl , and it is conjectured that soil particles rising up into the air is inhibited by snow accumulation. Soil particles rising up into the air seems to be inhibited by snow accumulation in the commercial area as well. With the aid of SEM and EDX analysis, aggregates of diesel exhaust particles (DEP), soil particles and small silicon-rich spherical particles were observed in the non-snow-clad and snow-clad period samples for each area. In addition, small aluminum-rich and iron-rich spheres were observed during the non-snow-clad period in the commercial area. Zinc-rich fiber was observed during the non-snow-clad period in the residential area.
37
Clément-Rastello, Marie. „A study on the size of snow particles in powder-snow avalanches“. Annals of Glaciology 32 (2001): 259–62. http://dx.doi.org/10.3189/172756401781819283.
Der volle Inhalt der QuelleAnnotation:
AbstractIn this work, we study the size of the particles involved in a powder-snow avalanche. To determine this value, we study all the phenomena encountered by the particles before they arrive in the “body” of the avalanche. We study the boundary layer which is at the bottom of the avalanche. We determine, with the help of experimental data, the range of sizes of particles that can be entrained by the avalanche. We then examine the possibility of these particles reaching the top of the boundary layer and thus taking part in the avalanche. Our final result is that the typical size of particles suspended in a powder-snow avalanche is < 200 μm.
38
Hashimoto, S., S. Zhou, M. Nakawo, M. Shimizu und N. Ishikawa. „Temporal isotope changes in wet snow layers in association with mass exchange between snow particles and liquid water in between the particles“. Annals of Glaciology 40 (2005): 128–32. http://dx.doi.org/10.3189/172756405781813492.
Der volle Inhalt der QuelleAnnotation:
AbstractWe carried out snow-pit observations at Nagaoka, Niigata prefecture, Japan, where the snow layers were at the melting point. It was observed that the water content in the snowpack was nearly constant at approximately 10%, and the coarsening rate of snow particles was about 0.4×10–3mm3 h–1, which was in the range between the rate for dry snow and that for snow soaked in water. The isotope change of snow particles by melting and freezing in a closed system under isothermal conditions at 0˚C was modeled. The temporal change in isotope concentration was calculated for wet snow layers, based on the fractionation between snow particles and liquid water in between the particles, in association with the coarsening of snow particles. The results compared well with field observations. These results suggest that the isotope concentration of the pore water that flows downward from the surface contributed significantly to the isotope change of snow particles.
39
SAITOH, K., Y. IWATA und K. HIRANO. „CHARACTERIZATION OF INSOLUBLE COMPONENTS IN FRESH SURFACE SNOW ON MOUNTAINS IN JAPAN“. International Journal of PIXE 08, Nr. 02n03 (Januar 1998): 147–53. http://dx.doi.org/10.1142/s0129083598000182.
Der volle Inhalt der QuelleAnnotation:
Fresh surface snow samples were collected at the summit or near the summit (700 - 1500 m altitude) of five mountains in Akita Pref., Japan. The elemental composition and particle shape of insoluble material in these snow samples was determined and/or observed by Particle Induced X-ray Emission (PIXE), a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-ray (EDX) analysis. 21 kinds of elements for each mountain snow sample were determined by PIXE. Na , Mg , Al , Si , P , S , Cl , K , Ca , Ti and Fe were the major components in each of the mountain snow samples, and those in relative abundance were almost the same in each case. With the aid of SEM and EDX analysis, silicon-rich small sphere (spherule) particles and aggregates of car exhaust particles were observed in every mountain snow sample. These results are represented as insoluble components of clouds and provide important knowledge for the source and mechanism of snowfall and rainfall at the ground level.
40
Korolev, Alexei, und George A. Isaac. „Shattering during Sampling by OAPs and HVPS. Part I: Snow Particles“. Journal of Atmospheric and Oceanic Technology 22, Nr. 5 (01.05.2005): 528–42. http://dx.doi.org/10.1175/jtech1720.1.
Der volle Inhalt der QuelleAnnotation:
Abstract The data on cloud particle sizes and concentrations collected with the help of aircraft imaging probes [optical array probes OAP-2DC, OAP-2DP, and the High Volume Precipitation Spectrometer (HVPS)] are widely used for cloud parameterization and validation of remote sensing. The goal of the present work is to study the effect of shattering of ice particles during sampling. The shattering of ice particles may occur due to 1) mechanical impact with the probe arms prior to their entering the sample volume, and 2) fragmentation due to interaction with turbulence and wind shear generated by the probe housing. The effect of shattering is characterized by the shattering efficiency that is equal to the ratio of counts of disintegrated particles, to all counts. The shattering efficiency depends on the habit, size, and density of ice particles, probe inlet design, and airspeed. For the case of aggregates, the shattering efficiency may reach 10% or even more. The shattering of ice particles results in an overcounting of small particles and an undercounting of large ones. The number of fragments in the images of shattered particles may reach several hundreds. It was found that particles as small as 600 μm may shatter after impact with the probe arms. The effect of particle shattering should be taken into account during data analysis and carefully considered in future designs of airborne cloud particle size spectrometers.
41
Biegalski, S. R., L. A. Currie, R. A. Fletcher, G. A. Klouda und Rolland Weissenbök. „AMS and Microprobe Analysis of Combusted Particles in Ice and Snow“. Radiocarbon 40, Nr. 1 (1997): 3–10. http://dx.doi.org/10.1017/s0033822200017811.
Der volle Inhalt der QuelleAnnotation:
Ice cores and snow pits of the cryosphere contain particles that detail the history of past atmospheric air compositions. Some of these particles result from combustion processes and have undergone long-range transport to arrive in the Arctic. Recent research has focused on the separation of particulate matter from ice and snow, as well as the subsequent analysis of the separated particles for 14C with accelerator mass spectrometry (AMS) and for individual particle compositions with laser microprobe mass analysis (LAMMA). The very low particulate concentrations in Arctic samples make these measurements a challenge. The first task is to separate the particles from the ice core. Two major options exist to accomplish this separation. One option is to melt the ice and then filter the meltwater. A second option is to sublimate the ice core directly, depositing the particles onto a surface. This work demonstrates that greater control is obtained through sublimation. A suite of analytical methods has been used for the measurement of the carbon in snow and ice. Total carbon was analyzed with a carbon/nitrogen/hydrogen (CHN) analyzer. AMS was used for the determination of carbon isotopes. Since source identification of the carbonaceous particles is of primary importance here, the use of LAMMA was incorporated to link individual particle molecular-structural patterns to the same group of particles that were measured by the other techniques. Prior to this study, neither AMS nor LAMMA had been applied to particles contained in snow. This paper discusses the development and limitations of the methodology required to make these measurements.
42
Yang, Xin, Markus M. Frey, Rachael H. Rhodes, Sarah J. Norris, Ian M. Brooks, Philip S. Anderson, Kouichi Nishimura, Anna E. Jones und Eric W. Wolff. „Sea salt aerosol production via sublimating wind-blown saline snow particles over sea ice: parameterizations and relevant microphysical mechanisms“. Atmospheric Chemistry and Physics 19, Nr. 13 (02.07.2019): 8407–24. http://dx.doi.org/10.5194/acp-19-8407-2019.
Der volle Inhalt der QuelleAnnotation:
Abstract. Blowing snow over sea ice has been proposed as a significant source of sea salt aerosol (SSA) (Yang et al., 2008). In this study, using snow salinity data and blowing snow and aerosol particle measurements collected in the Weddell Sea sea ice zone (SIZ) during a winter cruise, we perform a comprehensive model–data comparison with the aim of validating proposed parameterizations. Additionally, we investigate possible physical mechanisms involved in SSA production from blowing snow. A global chemical transport model, p-TOMCAT, is used to examine the model sensitivity to key parameters involved, namely blowing-snow size distribution, snow salinity, sublimation function, surface wind speed, relative humidity, air temperature and ratio of SSA formed per snow particle. As proposed in the parameterizations of Yang et al. (2008), the SSA mass flux is proportional to the bulk sublimation flux of blowing snow and snow salinity. To convert the bulk sublimation flux to SSA size distribution requires (1) sublimation function for snow particles, (2) blowing-snow size distribution, (3) snow salinity and (4) ratio of SSA formed per snow particle. The optimum model–cruise aerosol data agreement (in diameter range of 0.4–12 µm) indicates two possible microphysical processes that could be associated with SSA production from blowing snow. The first one assumes that one SSA is formed per snow particle after sublimation, and snow particle sublimation is controlled by the curvature effect or the so-called “air ventilation” effect. The second mechanism allows multiple SSAs to form per snow particle and assumes snow particle sublimation is controlled by the moisture gradient between the surface of the particle and the ambient air (moisture diffusion effect). With this latter mechanism the model reproduces the observations assuming that one snow particle produces ∼10 SSA during the sublimation process. Although both mechanisms generate very consistent results with respect to observed aerosol number densities, they correspond to completely different microphysical processes and show quite different SSA size spectra, mainly in ultra-fine and coarse size modes. However, due to the lack of relevant data, we could not, so far, conclude confidently which one is more realistic, highlighting the necessity of further investigation.
43
Pettersen, Claire, Mark S. Kulie, Larry F. Bliven, Aronne J. Merrelli, Walter A. Petersen, Timothy J. Wagner, David B. Wolff und Norman B. Wood. „A Composite Analysis of Snowfall Modes from Four Winter Seasons in Marquette, Michigan“. Journal of Applied Meteorology and Climatology 59, Nr. 1 (Januar 2020): 103–24. http://dx.doi.org/10.1175/jamc-d-19-0099.1.
Der volle Inhalt der QuelleAnnotation:
AbstractPresented are four winter seasons of data from an enhanced precipitation instrument suite based at the National Weather Service (NWS) Office in Marquette (MQT), Michigan (250–500 cm of annual snow accumulation). In 2014 the site was augmented with a Micro Rain Radar (MRR) and a Precipitation Imaging Package (PIP). MRR observations are utilized to partition large-scale synoptically driven (deep) and surface-forced (shallow) snow events. Coincident PIP and NWS MQT meteorological surface observations illustrate different characteristics with respect to snow event category. Shallow snow events are often extremely shallow, with MRR-indicated precipitation heights of less than 1500 m above ground level. Large vertical reflectivity gradients indicate efficient particle growth, and increased boundary layer turbulence inferred from observations of spectral width implies increased aggregation in shallow snow events. Shallow snow events occur 2 times as often as deep events; however, both categories contribute approximately equally to estimated annual accumulation. PIP measurements reveal distinct regime-dependent snow microphysical differences, with shallow snow events having broader particle size distributions and comparatively fewer small particles and deep snow events having narrower particle size distributions and comparatively more small particles. In addition, coincident surface meteorological measurements indicate that most shallow snow events are associated with surface winds originating from the northwest (over Lake Superior), cold temperatures, and relatively high surface pressures, which are characteristics that are consistent with cold-air outbreaks. Deep snow events have meteorologically distinct conditions that are accordant with midlatitude cyclones and frontal structures, with mostly southwest surface winds, warmer temperatures approaching freezing, and lower surface pressures.
44
Maeno, N., R. Naruse, K. Nishimura, I. Takei, T. Ebinuma, S. Kobayabhi, H. Nlshlmura, Y. Kaneda und T. Ishida. „Wind-Tunnel Experiments on Blowing Snow“. Annals of Glaciology 6 (1985): 63–67. http://dx.doi.org/10.3189/1985aog6-1-63-67.
Der volle Inhalt der QuelleAnnotation:
Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm increasing with wind velocity.When wind blew without snow drifting, the static air pressure on the snow surface was smaller at higher levels, the vertical pressure gradient being negative. The pressure gradient became positive when blowing snow was initiated eg +9.6 Pa/m at 11.2 m/s and -8.3 °C. The magnitude of à downward force acting on a saltating snow partice caused by the pressure gradient was not large enough to explain the downward acceleration found from photographic analyses of particle trajectories.Blowing snow particles were charged negatively the magnitude of charge increased with lowering temperature. Increase in vertical heat transfer was found in blowing snow by measuring the temperature of the air at various levels; the increase is reflected on that in the apparent turbulent diffusion coefficient.
45
Maeno, N., R. Naruse, K. Nishimura, I. Takei, T. Ebinuma, S. Kobayabhi, H. Nlshlmura, Y. Kaneda und T. Ishida. „Wind-Tunnel Experiments on Blowing Snow“. Annals of Glaciology 6 (1985): 63–67. http://dx.doi.org/10.1017/s0260305500010004.
Der volle Inhalt der QuelleAnnotation:
Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm increasing with wind velocity.When wind blew without snow drifting, the static air pressure on the snow surface was smaller at higher levels, the vertical pressure gradient being negative. The pressure gradient became positive when blowing snow was initiated eg +9.6 Pa/m at 11.2 m/s and -8.3 °C. The magnitude of à downward force acting on a saltating snow partice caused by the pressure gradient was not large enough to explain the downward acceleration found from photographic analyses of particle trajectories.Blowing snow particles were charged negatively the magnitude of charge increased with lowering temperature. Increase in vertical heat transfer was found in blowing snow by measuring the temperature of the air at various levels; the increase is reflected on that in the apparent turbulent diffusion coefficient.
46
Yamaguchi, Satoru, Atsushi Sato und Michael Lehning. „Application of the numerical snowpack model (SNOWPACK) to the wet-snow region in Japan“. Annals of Glaciology 38 (2004): 266–72. http://dx.doi.org/10.3189/172756404781815239.
Der volle Inhalt der QuelleAnnotation:
AbstractThe snow-cover model SNOWPACK was applied to the wet-snow areas of Japan. Simulated variations of snow type, snow depth and weight, profiles of snow density, temperature and liquid-water content were compared with snow-pit measurements. The snow-depth simulation during early winter agreed with the measurements, but the differences between the simulation and the measurements increased during the course of the melt season. These differences were caused by underestimation of the energy balance at the snow surface, mainly that regarding sensible-heat flux during the melt season. The underestimation was caused by the implicit numerical treatment of the heat-transport equation. Consistent with the underestimation of snowmelt, simulated metamorphosis of compacted particles into melt forms was slower than the change shown by the measurements, and faceted snow particles, which constitute a snow type not actually found in the study area, sometimes appeared in the model. The inaccurate melt treatment also influenced simulated densities, which were larger than the measurements at small densities, while they were smaller than the measurements at large densities. Greater accuracy was achieved when an empirical compressive viscosity formulation for wet snows in Japan was introduced. A new version of SNOWPACK, with an accurate treatment of melt processes, is available.
47
Takeuchi, Masao, und Yoshifumi Fukuzawa. „Light Attentuation and Visibility in Blowing Snow“. Annals of Glaciology 6 (1985): 311–13. http://dx.doi.org/10.1017/s0260305500010752.
Der volle Inhalt der QuelleAnnotation:
Visibility in blowing snow was investigated by measurements of visibility using optical targets, light attenuation of parallel beam and snow concentration and mass flux of airborne snow particles. Visibility is thought to be inversely proportional to extinction coefficient of light according to Koschmeider’s equation of visibility. However, visually observed values are not in accordance with those calculated from extinction coefficient of light when visibility is at a very low range. The extinction coefficient of light is proportional to the total cross section of airborne snow particles in a light path. The total cross section is also in proportion to concentration of airborne snow particles. There are many reported investigations of relation between visibility and snow concentration with widely differing results. The extinction coefficient of light varies with the shape and size of the particles, but cannot totally account for observed differences. Transforming the snow concentration into mass flux of snow particles, a better relation between visibility and mass flux was found. These facts are explained in terms of the size of snow particles which are large enough to be seen. Visibility through visible particles is determined not only by the homogeneous attenuation of light discovered by Koschmeider, but also by the influence of visible particles themselves and their afterimage.
48
Johnson, Jerome B. „A preliminary numerical investigation of the micromechanics of snow compaction“. Annals of Glaciology 26 (1998): 51–54. http://dx.doi.org/10.3189/1998aog26-1-51-54.
Der volle Inhalt der QuelleAnnotation:
A dynamic finite-element computer program was used to examine the evolution of microstructure and its effect on continuum-scale deformation for the constant-speed uniaxial-strain compaction of an aggregate of roughly spherical elastic-plastic particles. Simulation results are used to explain some micromechanical aspects of snow compaction. Different compaction rates were used to examine the limits of quasi-static response and the effects of inertial stresses. Four stages of microstructurally controlled compaction were observed for quasi-static loading: particle re-arrangement, elastic deformation and two stages of plastic deformation. Elastic deformation follows the first critical density caused by the stable random loose-particle packing of rough spheres. Stage III compaction occurs by plastic deformation once stresses acting on particles exceed yield. Stage IV compaction follows a second critical density caused by the stable packing of deformed particles and is also through plastic deformation of particles. During high-speed compaction, inertial stresses propagate particle deformation from the loading platen into the aggregate. As a consequence, particle re-arrangement is limited so that the pressure-density ratio is larger for high-speed compaction than for quasi-static compaction at the same density. Hence, critical densities and the compaction-rate dependence of the pressure-density ratio during compaction of an aggregate of particles composed of rate-independent material are determined by the evolution of microstructure at different compaction rates. Observed pressure-density profiles for polar snow exhibit the same features of critical density and changes in the pressure-density ratio as found in the simulation and consist of four compaction stages: particle re-arrangement and three stages of creep particle deformation each following a critical density. Shear stresses appear to enhance the compaction during the stage III creep deformation of snow.
49
Johnson, Jerome B. „A preliminary numerical investigation of the micromechanics of snow compaction“. Annals of Glaciology 26 (1998): 51–54. http://dx.doi.org/10.1017/s0260305500014543.
Der volle Inhalt der QuelleAnnotation:
A dynamic finite-element computer program was used to examine the evolution of microstructure and its effect on continuum-scale deformation for the constant-speed uniaxial-strain compaction of an aggregate of roughly spherical elastic-plastic particles. Simulation results are used to explain some micromechanical aspects of snow compaction. Different compaction rates were used to examine the limits of quasi-static response and the effects of inertial stresses. Four stages of microstructurally controlled compaction were observed for quasi-static loading: particle re-arrangement, elastic deformation and two stages of plastic deformation. Elastic deformation follows the first critical density caused by the stable random loose-particle packing of rough spheres. Stage III compaction occurs by plastic deformation once stresses acting on particles exceed yield. Stage IV compaction follows a second critical density caused by the stable packing of deformed particles and is also through plastic deformation of particles. During high-speed compaction, inertial stresses propagate particle deformation from the loading platen into the aggregate. As a consequence, particle re-arrangement is limited so that the pressure-density ratio is larger for high-speed compaction than for quasi-static compaction at the same density. Hence, critical densities and the compaction-rate dependence of the pressure-density ratio during compaction of an aggregate of particles composed of rate-independent material are determined by the evolution of microstructure at different compaction rates. Observed pressure-density profiles for polar snow exhibit the same features of critical density and changes in the pressure-density ratio as found in the simulation and consist of four compaction stages: particle re-arrangement and three stages of creep particle deformation each following a critical density. Shear stresses appear to enhance the compaction during the stage III creep deformation of snow.
50
Schneider, Adam, Mark Flanner, Roger De Roo und Alden Adolph. „Monitoring of snow surface near-infrared bidirectional reflectance factors with added light-absorbing particles“. Cryosphere 13, Nr. 6 (01.07.2019): 1753–66. http://dx.doi.org/10.5194/tc-13-1753-2019.
Der volle Inhalt der QuelleAnnotation:
Abstract. Broadband snow albedo can range from 0.3 to 0.9 depending on microphysical properties and light-absorbing particle (LAP) concentrations. Beyond the widely observed direct and visibly apparent effect of darkening snow, it is still unclear how LAPs influence snow albedo feedbacks. To investigate LAPs' indirect effect on snow albedo feedbacks, we developed and calibrated the Near-Infrared Emitting and Reflectance-Monitoring Dome (NERD) and monitored bidirectional reflectance factors (BRFs) hourly after depositing dust and black carbon (BC) particles onto experimental snow surfaces. After comparing snow infrared BRFs to snow specific surface areas (SSAs), we found that both measured and modeled snow infrared BRFs are correlated with snow SSA. These results, however, demonstrate a considerable uncertainty of ±10 m2 kg−1 in the determination of snow SSA from our BRF measurements. The nondestructive technique for snow SSA retrieval that we present here can be further developed for science applications that require rapid in situ snow SSA measurements. After adding large amounts of dust and BC to snow, we found more rapid decreasing of snow BRFs and SSAs in snow with added LAPs compared to natural (clean) snow but only during clear-sky conditions. These results suggest that deposition of LAPs onto snow can accelerate snow metamorphism via a net positive snow grain-size feedback.