A Branch Theory of Temperature Gradient Metamorphism in Snow PDF Download

Author: R. A. Sommerfeld
Publisher:
ISBN:
Category :
Languages : en
Pages : 11

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Author: R. A. Sommerfeld
Publisher:
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Category : Depth hoar
Languages : en
Pages : 6

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Author:
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Category : Forests and forestry
Languages : en
Pages : 304

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Author: H.G. Jones
Publisher: Springer Science & Business Media
ISBN: 9400939477
Category : Science
Languages : en
Pages : 748

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In recent years, much concern has been expressed on the deleterious effects that anthropogenic emissions of acidic pollutants have on ecosystems of both industrialized countries and remote areas of the world. In many of these regions, seasonal snowcover is a major factor in the transfer of atmospheric pollutants, either to terrestrial and aquatic ecosystems or to the more permanent reservoirs of glaciers and ice sheets. The recognition of the role that seasonal snowcovers can thus play in the chemical dynamics of whole ecosystems was recently echoed by the Committee on Glaciology of the National Research Council (National Academy of Sciences, National Academy of Engineering and the Institute of Medicine) which recommended that studies on "Impurities in the snowpack, their discharge into runoff, and management of the problem" be rated at the highest prority level (ref. a). It is in this context that the Advanced Research Institute (ASI) brought together scientists active in the fields of snow physics, snow chemistry and snow hydrology. The programme was structured so as to facilitate the exchange of information and ideas on the theories for the chemical evolution of seasonal snowcovers and snowmelt and on the impact of the chemical composition of the meltwaters on the different components of hydrological systems. As a consequence the ASI also attracted participants from potential users of the information that was disseminated; these were particularly concerned with the effects of snowmelt and snowcover on terrestrial biota and those of lakes and streams.

Author: United States. Rocky Mountain Forest and Range Experiment Stations, Fort Collins, Colo
Publisher:
ISBN:
Category : Forests and forestry
Languages : en
Pages : 360

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Author:
Publisher:
ISBN:
Category : Forests and forestry
Languages : en
Pages : 522

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Author:
Publisher:
ISBN:
Category : Forests and forestry
Languages : en
Pages : 82

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Author: Samuel C. Colbeck
Publisher:
ISBN:
Category : Avalanches
Languages : en
Pages : 24

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Grain growth, bond growth and densification of wet snow are described in terms of the distribution of equilibrium temperature in the snow matrix. At high water saturations the equilibrium temperature increases with grain size; hence, small particles melt away as large particles grow. Melting also occurs at the integrain bonds, causing a low strength and rapid densification. At low saturations the equilibrium temperature is determined by the capillary pressure and the particle sizes have only a second order effect. Therefore, grain growth proceeds slowly and, even at large over-burden pressures, no intergrain melting occurs. At low saturations the water 'tension' acts through a finite area, thus large attractive forces exist between the grains, and the strength of the snow matrix is large. (Author).

Author:
Publisher:
ISBN:
Category : Forests and forestry
Languages : en
Pages : 576

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Author: Patrick Joseph Staron
Publisher:
ISBN:
Category : Avalanches
Languages : en
Pages : 372

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In the presence of a sufficient temperature gradient, snow evolves from an isotropic network of ice crystals to a transversely isotropic system of depth hoar chains. This morphology is often the weak layer responsible for full depth avalanches. Previous research primarily focused on quantifying the conditions necessary to produce depth hoar. Limited work has been performed to determine the underlying reason for the microstructural changes. Using entropy production rates derived from nonequilibrium thermodynamics, this research shows that depth hoar forms as a result of the snow progressing naturally toward thermal equilibrium. Laboratory experiments were undertaken to examine the evolution of snow microstructure at the macro scale under nonequilibrium thermal conditions. Snow samples with similar initial microstructure were subjected to either a fixed temperature gradient or fixed heat input. The metamorphism for both sets of boundary conditions produced similar depth hoar chains with comparable increases in effective thermal conductivity. Examination of the Gibbs free energy and entropy production rates showed that all metamorphic changes were driven by the system evolving to facilitate equilibrium in the snow or the surroundings. This behavior was dictated by the second law of thermodynamics. An existing numerical model was modified to examine depth hoar formation at the grain scale. Entropy production rate relations were developed for an open system of ice and water vapor. This analysis showed that heat conduction in the bonds had the highest specific entropy production rate, indicating they were the most inefficient part of the snow system. As the metamorphism advanced, the increase in bond size enhanced the conduction pathways through the snow, making the system more efficient at transferring heat. This spontaneous microstructural evolution moved the system and the surroundings toward equilibrium by reducing the local temperature gradients over the bonds and increasing the entropy production rate density. The employment of nonequilibrium thermodynamics determined that the need to reach equilibrium was the underlying force that drives the evolution of snow microstructure. This research also expanded the relevance of nonequilibrium thermodynamics by applying it to a complicated, but well bounded, natural problem.