Thematische Bibliographien / Snow particles

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Auswahl der wissenschaftlichen Literatur zum Thema „Snow particles“

Autor: Grafiati

Veröffentlicht am 29. Juni 2021

Zuletzt aktualisiert am 18. Februar 2022

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Zeitschriftenartikel zum Thema "Snow particles"

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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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Dissertationen zum Thema "Snow particles"

Axebrink, Emma. „Automatic Classification of Snow Particles“. Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-86017.

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The simplest form of a snow particle is a hexagonal prism which can grow into a stellar crystal by growing branches from the six corners of the prism. The snow particle is affected by the temperature and supersaturation in the air, giving its unique form. Manual classification of snow particles based on shape is tedious work. Convolutional Neural Network (CNN) can therefor be of great assistance and are common in automatic image processing. From a data set consisting of 3165 images sorted into 15 shape classes, a sub set of 2193 images and 7 classes was used. The selected classes had the highest number of snow particle images and were used to train, validate and test on. Four data sets were constructed and eight models were used to classify the snow particles into seven classes. To reduce the amount of training data needed pretrained versions of neural networks AlexNet and ResNet50 were used with a technique called transfer learning. The 2193 images make up the first data set, Data set 1. To handle unbalanced classes in the first data set Synthetic Minority Oversampling Technique (SMOTE) was used to increase the number of snow particles in classes with few examples, creating Data set 2. A third data set was constructed to mimic a real world application. The data for training and validation was increased with SMOTE, while the test data only consisted of real snow particles. The performance of both ResNet50 and AlexNet on the data met the requirements for a practical application. However, ResNet50 had a higher overall accuracy, 72%, compared to AlexNet 69% on the evaluated data set. A t-test was conducted with a significance of p < 1·10−8. To enhance the shape of the snow particles a Euclidean Distance Transform (EDT) was used, creating Data set 4. However, this did not increase the accuracy of the trained model. To increase the accuracy of the models more training data of snow particles is needed, especially for classes with few examples. A larger data set would also allow more classes to be included in the classification.

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Dave, Palak P. „A Quantitative Analysis of Shape Characteristics of Marine Snow Particles with Interactive Visualization: Validation of Assumptions in Coagulation Models“. Scholar Commons, 2018. https://scholarcommons.usf.edu/etd/7279.

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The Deepwater Horizon oil spill that started on April 20, 2010, in the Gulf of Mexico was the largest marine oil spill in the history of the petroleum industry. There was an unexpected and prolonged sedimentation event of oil-associated marine snow to the seafloor due to the oil spill. The sedimentation event occurred because of the coagulation process among oil associated marine particles. Marine scientists are developing models for the coagulation process of marine particles and oil, in order to estimate the amount of oil that may reach the seafloor along with marine particles. These models, used certain assumptions regarding the shape and the texture parameters of marine particles. Such assumptions may not be based on accurate information or may vary during and after the oil spill. The work performed here provided a quantitative analysis of the assumptions used in modeling the coagulation process of marine particles. It also investigated the changes in model parameters (shape and texture) during and after the Deepwater Horizon oil spill in different seasons (spring and summer). An Interactive Visualization Application was developed for data exploration and visual analysis of the trends in these parameters. An Interactive Statistical Analysis Application was developed to create a statistical summary of these parameter values.

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Tse, Ka-ki. „Multiple scattering of waves by dense random distributions of particles for applications in light scattering by noble metal nanoparticles and microwave scattering by terrestrial snow /“. access full-text access abstract and table of contents, 2009. http://libweb.cityu.edu.hk/cgi-bin/ezdb/thesis.pl?phd-ee-b23750558f.pdf.

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Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Electronic Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.

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Sobhani, Negin. „Applications, performance analysis, and optimization of weather and air quality models“. Diss., University of Iowa, 2017. https://ir.uiowa.edu/etd/5996.

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Atmospheric particulate matter (PM) is linked to various adverse environmental and health impacts. PM in the atmosphere reduces visibility, alters precipitation patterns by acting as cloud condensation nuclei (CCN), and changes the Earth’s radiative balance by absorbing or scattering solar radiation in the atmosphere. The long-range transport of pollutants leads to increase in PM concentrations even in remote locations such as polar regions and mountain ranges. One significant effect of PM on the earth’s climate occurs while light absorbing PM, such as Black Carbon (BC), deposits over snow. In the Arctic, BC deposition on highly reflective surfaces (e.g. glaciers and sea ices) has very intense effects, causing snow to melt more quickly. Thus, characterizing PM sources, identifying long-range transport pathways, and quantifying the climate impacts of PM are crucial in order to inform emission abatement policies for reducing both health and environmental impacts of PM. Chemical transport models provide mathematical tools for better understanding atmospheric system including chemical and particle transport, pollution diffusion, and deposition. The technological and computational advances in the past decades allow higher resolution air quality and weather forecast simulations with more accurate representations of physical and chemical mechanisms of the atmosphere. Due to the significant role of air pollutants on public health and environment, several countries and cities perform air quality forecasts for warning the population about the future air pollution events and taking local preventive measures such as traffic regulations to minimize the impacts of the forecasted episode. However, the costs associated with the complex air quality forecast models especially for simulations with higher resolution simulations make “forecasting” a challenge. This dissertation also focuses on applications, performance analysis, and optimization of meteorology and air quality modeling forecasting models. This dissertation presents several modeling studies with various scales to better understand transport of aerosols from different geographical sources and economic sectors (i.e. transportation, residential, industry, biomass burning, and power) and quantify their climate impacts. The simulations are evaluated using various observations including ground site measurements, field campaigns, and satellite data. The sector-based modeling studies elucidated the importance of various economical sector and geographical regions on global air quality and the climatic impacts associated with BC. This dissertation provides the policy makers with some implications to inform emission mitigation policies in order to target source sectors and regions with highest impacts. Furthermore, advances were made to better understand the impacts of light absorbing particles on climate and surface albedo. Finally, for improving the modeling speed, the performances of the models are analyzed, and optimizations were proposed for improving the computational efficiencies of the models. Theses optimizations show a significant improvement in the performance of Weather Research and Forecasting (WRF) and WRF-Chem models. The modified codes were validated and incorporated back into the WRF source code to benefit all WRF users. Although weather and air quality models are shown to be an excellent means for forecasting applications both for local and hemispheric scale, further studies are needed to optimize the models and improve the performance of the simulations.

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Yndestad, Leif Kåre Hornnes. „Particle-based Powder-snow Avalanche Simulation Using GPU“. Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for datateknikk og informasjonsvitenskap, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15063.

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The main focus of this thesis was the simulation of a powder-snow avalanche flow. The simulation were implemented using the particle-based simulation solution SPH, from a mathematical model describing powder-snow flow dynamics. The simulation was accelerated by applying the computational power of the GPU, in order to provide a faster simulation time than would have been achieved on the CPU.

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Yam, Emily M. „The Role of Bacteria-Particle Interactions in Marine Snow Dynamics“. W&M ScholarWorks, 2007. http://www.vims.edu/library/Theses/Yam07.pdf.

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Vigano, Alessandro. „Experimental and numerical modeling of wet snow accretion on structures“. Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2012. https://theses.hal.science/docs/00/78/61/89/PDF/A_VIGANO_PhD.pdf.

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Ce travail est consacré à l'étude du givrage atmosphérique des structures par accrétion de neige collante qui peut conduire à des dommages sévères aux structures. Les particules à la base de ce type d'accrétions sont caractérisées par un mélange d'eau et glace quantifié dans cette étude par un paramètre sans dimension : la teneur en eau liquide: TEL définie comme le ratio de la masse liquide sur la masse totale de la particule. La définition de la TEL considérée dans ce travail est différente de celle utilisée en aéronautique. Dans cette étude, la neige collante a été reproduite avec une températures ambiante négative. L'approche expérimentale, mise en oeuvre dans une soufflerie climatique, est consacrée à l'étude de l'effet de la TEL sur l'accrétion de neige sur une structure de test. La TEL est ajustée en modifiant la température ambiante. Les résultats sont synthétisés par le coefficient β défini comme le ratio entre le flux massique de l'accrétion, et le flux massique de neige incidente. Un premier modèle numérique évalue les conditions aux limites pour le modèle d'accrétion : c. à. D. La distribution en taille des particules à l'amont de la structure et la TEL associée. La première partie du modèle numérique d'accrétion concerne l'analyse du comportement des particules à proximité de la structure expérimentale quantifié par le nombre de Stokes. La capacité des particules à impacter la structure est synthétisé par le coefficient de collision n1. L'analyse du coefficient expérimental β, en fonction de n1 est développée. Ceci permet l'étude de la capacité des particules à s'accrocher à la surface en fonction de la TEL. Le résultat est évalué par le coefficient de collage n2. La seconde partie expose une approche pour modéliser la forme d'accrétion, par le coefficient de collage n2, en s'appuyant sur l'angle d'impact entre la particule et la surface. Des perspectives sont proposées
The present work aims at studying the atmospheric phenomenon of wet-snow accretion to structures. This phenomenon may induce severe damages to structures. Freezing particles which generate wet-snow accretions are characterized by a mixed phase ice/water. The particle state in this framework is quantified by a dimensionless parameter: the liquid water content LWC defined as the ratio of the particle liquid mass to the whole particle mass. This LWC definition is different form the aeronautical one. In this work, wet snow is produced with an ambient temperature below 0°C. Both experimental and numerical approaches are undertaken to investigate the subject. The experimental approach, undertaken in a climatic wind tunnel, is based on the LWC effect on the accretions obtained on a test structure. The particle LWC is tuned by adjusting the ambient temperature of the test chamber. The results are synthesized by a coefficient β defined as the ratio of the accretion mass flux to the snow mass flux. A first numerical model assesses the boundary conditions of the accretion model, i. E. The particle size distribution upstream the structure and the associated LWC. The first part of accretion model concerns the study of the particle behavior close to the structure which is quantified with a Stokes number. The efficiency of particles to impact the structure is synthesized by a dimensionless parameter n1. The analysis of the experimental coefficient β according to n1 is developed. This allows to study the efficiency of particles to stick on the structure as a function of the LWC. The result is synthesized by the n2 coefficient. The second part concerns an attempt to model the accretion shape by the sticking efficiency n2 as a function of the particle-surface angle of impact. A series of perspectives are presented

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Sinclair, James R. „Positioning and timing calibration of SNO+“. Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/57182/.

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The Sudbury Neutrino Observatory solved the solar neutrino problem, confirming neutri- nos have non-zero masses. Massive neutrinos raise questions about the nature of neutrinos, implying physics beyond the standard model and potentially a solution to the observed matter-antimatter asymmetry in the universe. The Sudbury Neutrino Observatory is be- ing upgraded, with the goal of probing the nature of neutrino masses. The experiment will also study reactor, geo, supernovae and solar neutrinos. The upgrade is characterised by changing the target mass from heavy water to scintillator. Using scintillator allows for the lowering of the energy threshold, but this increases sensitivity to backgrounds. To meet the requirements of the physics on detector performance, a detailed optical calibration is needed. Due to increased background sensitivity, a new external LED-based calibration system has been developed and the existing laser calibration system has been modified to meet radiopurity requirements. This thesis describes the the development and imple- mentation of both of these calibration systems. With a study of the potential use of the LED system to monitor the detector's structure, enabling a better definition of the fiducial volume by reducing the effects of external backgrounds. An assessment of the impact of these systems on the detector performance will be presented.

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Guidi, Lionel. „Particle flux transformation in the mesopelagic water column: process analysis and global balance“. Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85946.

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Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).

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Tuzet, François. „Dépôt, devenir et impact radiatif des impuretés dans le manteau neigeux : analyse des processus, simulations numériques et implications“. Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30316.

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L'une des propriétés les plus fascinantes de la neige est sa blancheur, capable de transformer complètement un paysage en quelques heures. Cette couleur vient de la capacité unique de la neige à réfléchir le rayonnement solaire dans les longueurs d'onde visibles, c'est-à-dire son fort albédo. Cette particularité de la neige est d'une importance cruciale pour le bilan énergétique de surface et par conséquent pour un large éventail de questions sociales, écologiques et climatiques. La blancheur de la neige peut, cependant, être altérée par la présence d'impuretés absorbantes. Dans les Alpes européennes, deux types d'impuretés absorbantes impactent significativement l'évolution saisonnière du manteau neigeux : le carbone suie et les poussières minérales du Sahara. Cette thèse vise à mieux comprendre et modéliser le dépôt, l'évolution et l'impact de ces impuretés absorbantes sur les manteaux neigeux saisonniers des Alpes françaises. À cette fin, trois problématiques principales sont abordées : * Quels types d'impuretés absorbantes sont présents dans un manteau neigeux saisonnier alpin et en quelle quantité? Avec quelle incertitude peut-on estimer leurs concentrations à partir de mesures? * Quels impacts radiatifs ont les dépôts d'impuretés absorbantes sur l'évolution du manteau neigeux et comment varient t-ils d'une année à l'autre? * Peut-on modéliser cet impact en se servant des modèles de manteau neigeux et des modèles atmosphériques de chimie-aérosols? Tout d'abord, une représentation explicite du dépôt et de l'évolution des impuretés absorbantes a été implémentée dans le modèle détaillé de manteau neigeux SURFEX/ISBA-Crocus. Ces nouveaux développements permettent de modéliser l'assombrissement de la surface de la neige par les impuretés absorbantes (impact direct) ainsi que leurs interactions avec le métamorphisme de la neige (impacts indirects). Les simulations de l'enneigement au Col de Porte, forcées par des flux de dépôt d'impuretés absorbantes provenant du modèle atmosphérique de chimie-aérosols ALADIN-Climate, mettent en évidence un raccourcissement de la saison de neige allant jusqu'à 9 jours en raison du carbone suie et des poussières minérales sahariennes. Ensuite, une campagne de terrain de deux ans a été menée au site d'étude du Col du Lautaret. Pendant deux saisons d'hiver, la concentration en impuretés absorbantes ainsi que les propriétés physiques et optiques du manteau neigeux ont été mesurées chaque semaine. Ce jeu de données unique est d'abord utilisé pour ouvrir la voie à une nouvelle méthode visant à estimer le profil vertical de concentration en impuretés absorbantes dans la neige à partir de mesures de profils d'irradiance spectrale. L'évaluation de cette méthode par rapport aux mesures chimiques met en évidence la difficulté d'établir un lien entre la chimie de la neige et ses propriétés optiques. Une seconde étude compare ensuite les mesures d'albédos spectraux, les mesures chimiques d'impuretés absorbantes et des simulations du manteau neigeux.[...]
One of the most fascinating properties of snow is its whiteness, and its ability to fully transform a landscape in a couple of hours. This color is due to the unique ability of snow to reflect solar radiation in the visible wavelengths, i.e. its high albedo. This particularity of snow is of crucial importance for the surface energy budget and consequently for a wide range of social, ecological and climatic issues. However, the whiteness of the snow cover can be altered by the presence of Light Absorbing Particles (LAPs) on and close below its surface. In the European Alps, two types of LAPs are suspected to have a significant impact on the evolution of seasonal snow: Black Carbon (BC) and Saharan mineral dust. This thesis aims at a better understanding and modelling of the deposition, evolution and impact of LAPs on the seasonal snowpack in the French Alps. To this aim, three main questions are addressed: * What types of LAPs are present in a seasonal alpine snowpack and in what quantity? How well can we estimate their concentration in snow based on measurements? * What is the impact of LAPs on snowpack evolution and how does this impact vary in time? * Are we able to model this impact using state-of-the-art atmospheric chemical transport models and detailed snowpack models? First, an explicit representation of LAPs was implemented in the detailed snowpack model SURFEX/ISBA-Crocus. These new developments enable to account for darkening of the snow surface by LAPs (direct impact) as well as their interactions with snow metamorphism (indirect impacts). Snowpack simulations at Col de Porte (1326 m a.s.l.) using LAP deposition fluxes from an atmospheric model highlight a shortening of the snow season by up to 9 days due to BC and dust. Second, a two-year field campaign was conducted at Col du Lautaret study site (2058 m a.s.l, French Alps). During two winter seasons, concentrations of LAPs as well as physical and optical properties of the snowpack were measured weekly from the onset to the total melt-out of the snowpack. This unique dataset was first used to pave the way for a novel method to estimate vertical profiles of LAP concentration in snow from spectral irradiance profile measurements. This method was evaluated against chemical measurements pointing out difficulties to relate snow chemistry to its radiative properties. A second study was then dedicated to the comparison of spectral albedo measurements, chemical measurements of LAPs near the surface and snowpack simulations. This latter study corroborates the issue previously mentioned and points out a gap in the current understanding of chemical measurements of BC in snow. The impact of LAPs at Col du Lautaret over the two years was evaluated using the ensemble modeling framework of SURFEX/ISBA-Crocus. We estimated that the shortening of the snow season due to LAPs was around 10±5 and 11±1 days for both seasons respectively. The studies of the impact of LAP carried out at a single location during this thesis pave the way for a larger scale study of the impacts of LAP deposition across the Alps over longer periods

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Bücher zum Thema "Snow particles"

Sunagawa, Ichiro. Morphology of Crystals : Part A : Fundamentals Part B : Fine Particles, Minerals and Snow Part C: The Geometry of Crystal Growth by Jaap van Suchtelen. Springer, 2011.

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Sunagawa, Ichiro. Morphology of Crystals: Part A: Fundamentals Part B: Fine Particles, Minerals and Snow Part C: The Geometry of Crystal Growth by Jaap van Suchtelen (Materials Science of Minerals and Rocks). Springer, 2007.

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Buchteile zum Thema "Snow particles"

Alldredge, Alice L. „In Situ Collection and Laboratory Analysis of Marine Snow and Large Fecal Pellets“. In Marine Particles: Analysis and Characterization, 43–46. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm063p0043.

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Davidson, Cliff I., Michael H. Bergin und Hampden D. Kuhns. „The Deposition Of Particles and Gases to Ice Sheets“. In Chemical Exchange Between the Atmosphere and Polar Snow, 275–306. Berlin, Heidelberg: Springer Berlin Heidelberg, 1996. http://dx.doi.org/10.1007/978-3-642-61171-1_12.

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Ilgasheva, Ekaterina O., Ilya V. Yarmoshenko, Georgy P. Malinovskiy und Andrian A. Seleznev. „Anthropogenic Particles in the Snow Cover in the Area of the Ice Race Track“. In Springer Proceedings in Earth and Environmental Sciences, 79–88. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-49468-1_11.

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Huber, Christoph, Heinrich Reister, Thomas Binner und Bernhard Weigand. „A New Process to Evaluate the Risk of an Engine Power Drop Caused by Snow Particles“. In Progress in Vehicle Aerodynamics and Thermal Management, 18–31. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-67822-1_2.

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Budd, W. F. „The Drifting of Nonuniform Snow Particles1“. In Studies in Antarctic Meteorology, 59–70. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/ar009p0059.

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Levy, B., W. Liu und S. Gilbert. „Directed Photocurrents in Nanostructured SnO2/TiO2/Ru(II)L2(CNS)2 Heterojunctions“. In Fine Particles Science and Technology, 343–70. Dordrecht: Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-0259-6_26.

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Hime, A. „Results and Implications of First SNO“. In Dark Matter in Astro- and Particle Physics, 553–63. Berlin, Heidelberg: Springer Berlin Heidelberg, 2002. http://dx.doi.org/10.1007/978-3-642-55739-2_52.

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Li, Zheshen, Qinlin Guo und Preben J. Møller. „Electronic properties of Cu clusters and islands and their reaction with O2 on SnO2(110) surfaces“. In Small Particles and Inorganic Clusters, 550–53. Berlin, Heidelberg: Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-642-60854-4_132.

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Wang, Li, Wen Yue Bi, Xing Dong Zhang, Xin Gang Yu, Hong Quan Bao und Hui Feng Zhao. „AFM Investigation of Nano Particle Incorporated Sb Doped SnO₂ Films“. In Key Engineering Materials, 1799–801. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-410-3.1799.

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Bassey, Enobong E., Krishnamachar Prasad und Philip Sallis. „Surface Structure and Particle Analysis of Combined SnO2 and ZnO Nanoparticles Prepared for Gas Sensing“. In Proceedings of the 8th Pacific Rim International Congress on Advanced Materials and Processing, 2157–62. Cham: Springer International Publishing, 2013. http://dx.doi.org/10.1007/978-3-319-48764-9_268.

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Konferenzberichte zum Thema "Snow particles"

Veselovska, Ganna, und Grigoriy Khlopov. „Backscattering of electromagnetic waves by snow particles“. In 2016 IEEE International Conference on Mathematical Methods in Electromagnetic Theory (MMET). IEEE, 2016. http://dx.doi.org/10.1109/mmet.2016.7544126.

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Romanova, Daria, Sergei Strijhak und Matvey Kraposhin. „Development of snowYadeFoam solver for snow particles simulation“. In 2020 Ivannikov Ispras Open Conference (ISPRAS). IEEE, 2020. http://dx.doi.org/10.1109/ispras51486.2020.00032.

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Song, Yixuan, und Matthew J. Rau. „Characterization of Aggregate Disruption Using Organic Marine Particles and Particle Tracking Measurements in Rotating/Oscillating Aggregation Tanks“. In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5499.

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Abstract The fate of particulate matter in the ocean is determined in large part by its size and settling rate. Disaggregation, caused by turbulence-induced shear, acts to fracture or erode large particles into slower-settling sub-aggregates and primary particles. The strength and breakup response of organic marine aggregates (i.e. marine snow particles consisting of phytoplankton) is poorly understood, limiting our ability to accurately predict marine particle transport effects on the global carbon cycle. A study was conducted to enable the investigation of disaggregation effects on these organic marine particle aggregates. Due to the fragile nature of the Phytoplankton cells and their resulting aggregates, test facilities that do not rely on external sampling or pumps are required. A novel rolling aggregation tank was developed that can both aggregate phytoplankton cells under varying hydrodynamic conditions and then expose them to calibrated shear forces using laminar oscillating flow. The theory behind the operation of this tank is presented along with the necessary operating conditions to create stable regions within the tank where particle settling effects are minimal but shear is still representative of values expected in the open ocean. Phytoplankton was cultured in the laboratory to create simulated marine snow particles in the open ocean for disaggregation experiments. The procedure to calculate and track the shear-history of each aggregate is described and how the data generated from this facility will be used to quantify disaggregation parameters relevant for population balance modeling is discussed.

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Sasaki, Mikio, Takahiro Takeuchi und Hiroshi Takahashi. „Energy Loss in Snow-Water Mixture Flow“. In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45493.

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Energy losses in the solid-water mixture flow where the density of solid is nearly equal to that of fluid were observed in horizontal pipelines. The observation was carried out to investigate the influence that the specific gravity of the solid particles exerted on the energy loss. A relative friction factor based on the friction factor of the pure water flow becomes larger as the solid concentration increases in the mixture flow of solid particles with the specific gravity 0.86 and 1.04. The relative friction factor is given with the Froude number, the solid concentration and the specific gravity of solid.

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Sansalone, John, Donald W. Glenn, III und Kim Howerter. „Heavy Metal Partitioning to Particles in Snow Exposed to Urban Traffic - Distribution across the Particle Gradation“. In Ninth International Conference on Urban Drainage (9ICUD). Reston, VA: American Society of Civil Engineers, 2002. http://dx.doi.org/10.1061/40644(2002)203.

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Rawlins, Katherine. „A Function to Describe Attenuation of Cosmic Ray Air Shower Particles in Snow“. In The 34th International Cosmic Ray Conference. Trieste, Italy: Sissa Medialab, 2016. http://dx.doi.org/10.22323/1.236.0628.

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Kleinkort, Cameron, Gwo-Jong Huang, V. N. Bringi und Branislav M. Notaros. „Polarimetric scattering analysis of snow and ice particles using field measurements by 2D-video disdrometer“. In 2015 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium). IEEE, 2015. http://dx.doi.org/10.1109/usnc-ursi.2015.7303571.

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Yao, Ailing, Shaoyong Yu, Jinpeng Li, Haidong Di und Yubo Wang. „Fiber-Reinforced Asphalt Macadam Sealing with Rubber Particles and Its Ice-Breaking and Snow-Melting Properties“. In 20th COTA International Conference of Transportation Professionals. Reston, VA: American Society of Civil Engineers, 2020. http://dx.doi.org/10.1061/9780784482933.127.

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Talovskaya, Anna V., Egor G. Yazikov, Ekaterina A. Filimonenko, Natalia P. Samokhina, Tatyana S. Shakhova und Irina A. Parygina. „Element composition of solid airborne particles deposited in snow in the vicinity of gas-fired heating plant“. In XXII International Symposium Atmospheric and Ocean Optics. Atmospheric Physics, herausgegeben von Gennadii G. Matvienko und Oleg A. Romanovskii. SPIE, 2016. http://dx.doi.org/10.1117/12.2249309.

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Lee, Jin-Woo, Kuk Jin Jung, Morely Sherman, Hyun Sin Kim und Youn-Jea Kim. „Experimental and Numerical Analysis on the Performance of Spiral Two-Fluid Atomizer Using DPM Method“. In ASME 2020 Fluids Engineering Division Summer Meeting collocated with the ASME 2020 Heat Transfer Summer Conference and the ASME 2020 18th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/fedsm2020-20350.

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Abstract A two-fluid atomizer has been frequently used in a wide range of industries for various purposes such as painting, cleaning particles and snow making. In particular, the manufacturing of advance semiconductors using sensitive devices such as organic light emitting diodes (OLED) and dynamic random access memory (DRAM), require high performance nozzle. The droplets sprayed with a high relative gas velocity are widely used for cleaning particles. In this paper, two-fluid atomizer is numerically studied according to four variables to confirm the effect on the atomizer performance. The numerical results using the discrete phase model (DPM) with several break-up models are compared with the experimental data measured by the phase doppler particle analyzer (PDPA). Design of experiment (DOE) and genetic algorithm (GA) were used to obtain design points, and conduct sensitivity analysis, respectively. The results showed that the WAVE model has a good agreement compared to the other models, and the orifice diameter is a crucial factor for this model to determine the performance of Weber number and pressure.

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Berichte der Organisationen zum Thema "Snow particles"

Thurston, Alison, Zoe Courville, Lauren Farnsworth, Ross Lieblappen, Shelby Rosten, John Fegyveresi, Stacy Doherty, Robert Jones und Robyn Barbato. Microscale dynamics between dust and microorganisms in alpine snowpack. Engineer Research and Development Center (U.S.), März 2021. http://dx.doi.org/10.21079/11681/40079.

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Dust particles carry microbial and chemical signatures from source regions to deposition regions. Dust and its occupying microorganisms are incorporated into, and can alter, snowpack physical properties including snow structure and resultant radiative and mechanical properties that in turn affect larger-scale properties, including surrounding hydrology and maneuverability. Microorganisms attached to deposited dust maintain genetic evidence of source substrates and can be potentially used as bio-sensors. The objective of this study was to investigate the impact of dust-associated microbial deposition on snowpack and microstructure. As part of this effort, we characterized the microbial communities deposited through dust transport, examined dust provenance, and identified the microscale location and fate of dust within a changing snow matrix. We found dust characteristics varied with deposition event and that dust particles were generally embedded in the snow grains, with a small fraction of the dust particles residing on the exterior of the snow matrix. Dust deposition appears to retard expected late season snow grain growth. Both bacteria and fungi were identified in the collected snow samples.

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