Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 87-95). Also available on the World Wide Web.

Memoire (M.A.)-- Universite du Quebec a Chicoutimi, 1993. / Ce travail de recherche a été réalisé à l'UQAC dans le cadre du programme de maîtrise en arts plastiques extensionné de l'UQAM à l'UQAC. CaQCU Document électronique également accessible en format PDF. CaQCU

Thesis (M.SC.) - Carleton University, 2007. / Includes bibliographical references (p. 154-161). Also available in electronic format on the Internet.

Thesis (doctoral)--Uppsala University, 1995. / Includes bibliographical references (p. 238-249) and index.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 208-213.

No description available.

abstract: Many previous investigators highlight the importance of snowfall to the water supply of the western United States (US). Consequently, the variability of snowpack, snowmelt, and snowfall has been studied extensively. Snow level (the elevation that rainfall transitions to snowfall) directly influences the spatial extent of snowfall and has received little attention in the climate literature. In this study, the relationships between snow level and El Niño-Southern Oscillation (ENSO) as well as Pacific Decadal Oscillation (PDO) are established. The contributions of ENSO/PDO to observed multi-decadal trends are analyzed for the last ~80 years. Snowfall elevations are quantified using three methods: (1) empirically, based on precipitation type from weather stations at a range of elevations; (2) theoretically, from wet-bulb zero heights; (3) theoretically, from measures of thickness and temperature. Statistically significant (p < 0.05) results consistent between the three datasets suggest snow levels are highest during El Niño events. This signal is particularly apparent over the coastal regions and the increased snow levels may be a result of frequent maritime flow into the western US during El Niño events. The El Niño signal weakens with distance from the Pacific Ocean and the Southern Rockies display decreased snow level elevations, likely due to maritime air masses within the mid-latitude cyclones following enhanced meridional flow transitioning to continental air masses. The modulation of these results by PDO suggest that this El Niño signal is amplified (dampened) during the cold (warm) phase of the PDO particularly over Southern California. Additionally, over the coastal states, the La Niña signal during the cold PDO is similar to the general El Niño signal. This PDO signal is likely due to more zonal (meridional) flow throughout winter during the cold (warm) PDO from the weakening (strengthening) of the Aleutian low in the North Pacific. Significant trend results indicate widespread increases in snow level across the western US. These trends span changes in PDO phase and trends with ENSO/PDO variability removed are significantly positive. These results suggest that the wide spread increases in snow level are not well explained by these sea surface temperature oscillations. / Dissertation/Thesis / Ph.D. Geography 2011

Vegetation cover of 24 ski slopes both with artificial and natural snow was studied; on each slope 5 phytocenological relevés measuring 4 x 4 metres were taken. A method of direct gradient analysis (RDA) was used to detect differences in composition of phytocenological reléves on the ski slopes with natural or artificial snow. However, no impact of use of artificial snow on vegetation was identified. During the winter season of 2009 and of 2010 samples of artificial and natural snow were taken for chemical analyses. The chemical composition differed significantly; artificial snow contained more NO3-, SO42- and Ca2+ ions and its pH was more alkaline in comparison with natural snow.

Le pergélisol est une composante majeure du système climatique terrestre. Avec le réchauffement du climat, la dégel du pergélisol profite à l'activité biochimique qui décompose davantage de matière organique dans les sols arctiques et la rejette dans l'atmosphère sous forme de gaz à effet de serre (CO2, CH4). Ce phénomène pourrait constituer une rétroaction climatique positive majeure. Prédire ces effets nécessite d'étudier l'évolution du régime thermique du pergélisol ainsi que des facteurs qui l'influencent. Le manteau neigeux, de par son pouvoir isolant, contrôle les échanges de chaleur entre le sol et l'atmosphère une grande partie de l'année. Le flux de chaleur à travers la neige dépend de la hauteur du manteau neigeux et de la conductivité thermique des couches de neige qui le constituent. Ces deux variables sont elles-même très dépendantes des conditions climatiques et de la présence de végétation. Nous réalisons ici le suivi des propriétés de la neige et du sol d'un site haut arctique de toundra herbacée (Île Bylot, 73N), et d'un site bas arctique à la frontière de la toundra arbustive et forestière (Umiujaq, 56N). Nous utilisons les données issues de stations de mesure automatiques complétées par des mesures manuelles. Une attention particulière est portée sur la conductivité thermique de la neige, car peu de données sont disponibles pour les régions arctiques. Le modèle numérique couplé ISBA-Crocus est ensuite utilisé pour simuler les propriétés de la neige et du sol des deux sites étudiés. Les résultats sont comparés aux mesures de terrain afin d'évaluer la capacité du modèle à simuler le régime thermique des sols arctiques.Nous avons pu caractériser les interactions atmosphère-neige-végétation qui façonnent la structure des manteaux neigeux arctiques. Le vent et la redistribution de neige qu'il induit sont des paramètres fondamentaux qui déterminent la hauteur et la conductivité thermique de la neige. Un couvert végétal haut et dense (arbustes, arbres) piège la neige soufflée et l'abrite du tassement éolien. De plus, la structure ligneuse des massifs arbustifs soutient la masse de neige et empêche son tassement. Cet abri procure à la neige une capacité d'isolation élevée qui retarde le gel du sol dès les premières accumulations. Le refroidissement atmosphérique se poursuivant, le manteau neigeux peu épais est soumis à un gradient thermique élevé qui provoque d'importants transferts de vapeur d'eau depuis le sol et les couches de neige basales, vers les couches supérieures et l'atmosphère. La croissance de givre de profondeur qui s'opère, favorisée à la fois par le gradient thermique élevé et la faible densité de la neige, aboutit à la formation de couches très isolantes en contact avec la surface du sol. Tant que le sol demeure relativement chaud, la croissance de givre de profondeur perdure. Finalement, des épisodes de fonte peuvent avoir lieu en automne durant la mise en place du manteau neigeux dans les régions arctiques. Le regel de la neige peut rapidement annuler ou même temporairement inverser l'effet isolant des interactions neige-végétation. Une surface de neige gelée ne subit pas l'effet du vent et empêche sa redistribution. La formation de croûtes de regel à forte conductivité thermique accélère le refroidissement du sol. Le manteau neigeux affecté par la fonte au début de l'hiver a donc une capacité d'isolation diminuée qui pourrait entraver le réchauffement des sols arctiques. Nos résultats de simulation montrent que ces différents effets ne sont pas correctement représentés dans les modèles de neige. Les erreurs dans les conductivités thermiques de la neige simulées sont particulièrement problématiques puisqu'elles interviennent lors de la période de gel du sol. Étant donné l'étendue des régions affectées par le pergélisol, ces erreurs sur la modélisation de la neige arctique pourraient significativement affecter les simulations climatiques et les projections de la hausse des températures globales. / Permafrost is a major component of the Earth climatic system. Global warming provokes the degradation of permafrost which favors biogeochemical activity in Arctic soils. The decomposition of organic matter increases and results in the release of high amounts of greenhouse gases (CO2 and CH4) to the atmosphere. By amplifying the greenhouse effect induced by human activities, this phenomenon may constitute one of the strongest positive feedbacks on global warming. Predicting these effects requires to study the evolution of the permafrost thermal regime and the factors governing it. The snowpack, because of its insulating effect, modulates the heat fluxes between permafrost and atmosphere most of the year. The snow insulating capacity depends on snow height and thermal conductivity. These two variables are highly dependent on climatic conditions and on the presence of vegetation. Here we monitor the snow and soil physical properties at a high Arctic site typical of herbaceous tundra (Bylot Island, 73°N), and at a low Arctic site situated at the limit between shrub and forest tundra (Umiujaq, 56°N). We use data from automatic measurement stations and manual measurements. A special attention is given to the snow thermal conductivity because very few data are available for Arctic regions. Results are interpreted in relation to vegetation type and atmospheric conditions. The numerical coupled model ISBA-Crocus is then used to simulate snow and soil properties at our sites. Results are compared to field data in order to evaluate the model capacity to accurately simulate the permafrost thermal regime.We managed to describe atmosphere-snow-vegetation interactions that shape the structure of Arctic snowpacks. Wind and the snow redistribution it induces are fundamental parameters governing snow height and thermal conductivity. A high vegetation cover (i.e. shrubs and forest) traps blowing snow and shields it from wind compaction. Vegetation growth thus favors the formation of an insulating snowpack which slows down or even prevents soil freezing. Furthermore, the shrubs woody structure supports the snow mass and prevents the resulting compaction of bottom snow layers. Thus sheltered, snow in shrubs develops a high insulating capacity which delays soil freezing. Continued atmospheric cooling increases the thermal gradient in the snow, maintaining large water vapor transfers from the soil and the snow basal layers to upper layers and atmosphere. The growth of depth hoar, enhanced by the large thermal gradient and the low snow density, results in the formation of highly insulating snow layers thus constituting a positive feedback loop between soil temperature and snow insulation. As long as the soil stays relatively warm, depth hoar growth persists. Finally, if warm spells occur in autumn, they can trigger the partial melting of the early snowpack which can cancel or temporarily reverse the insulating effect of snow-vegetation interactions. A frozen snow surface prevents snow drifting and its redistribution. The presence of highly conductive refrozen layers facilitates soil cooling and reduces the thermal gradient. An early snowpack affected by melting is thus less insulative which could hamper Arctic soil warming. Simulation results show that these different effects are not correctly represented in snow models. Errors in the estimated snow thermal conductivities are particularly problematic as they highly affect the simulation of soil freezing. Given the area of permafrost-affected regions, these errors on Arctic snow modelling could significantly impact climate simulations and the global warming projections.

Nesse estudo foram mapeadas e mensuradas as variações de área, elevação mínima e orientação das geleiras da Colômbia e da Venezuela (trópicos internos), entre os anos 1985-2015. Para o mapeamento das áreas das geleiras foram utilizadas como base imagens Landsat, sensores TM, ETM+ e OLI. Às imagens selecionadas foi aplicado o Normalized Difference Snow Index (NDSI), no qual são utilizadas duas bandas em que o alvo apresenta comportamento espectral oposto ou com características bem distintas: bandas 2 e 5 dos sensores TM e ETM+ e bandas 3 e 6 do sensor OLI. Os dados de elevação e orientação das massas de gelo foram obtidos a partir do Modelo Digital de Elevação SRTM (Shuttle Radar Topography Mission – v03). Em 1985, a soma das áreas das sete geleiras estudadas correspondia a 92,84 km², enquanto no último ano estudado (2015/2016) esse valor passou para 36,97 km². A redução de área ocorreu em todas as geleiras analisadas, com taxas de retração anual variando entre 2,49% a.a. e 8,46% a.a. Houve retração das áreas de gelo localizadas em todos os pontos cardeais considerados, bem como, elevação da altitude nas frentes de geleiras. Além da perda de área ocorrida nas menores altitudes, onde a taxa de ablação é mais elevada, também se observou retração em alguns topos, evidenciado pela ocorrência de altitudes menores nos anos finais do estudo, em comparação com os anos iniciais. Como parte das geleiras colombianas está localizada sobre vulcões ativos, essas áreas sofrem influência tanto de fatores externos, quanto de fatores internos, podendo ocorrer perdas de massa acentuadas causadas por erupção e/ou terremoto. / In this study, glaciers located in Colombia and Venezuela (inner tropics) were mapped between 1985-2015. The area of these glaciers was measured and the variations that occurred in each glacier were compared to identify whether the glacier was growing or shrinking. The minimum elevation of the glaciers fronts and the aspect of the glaciers were analyzed. The glaciers areas ware obtained by the use of Landsat images, TM, ETM+ and OLI sensors. The Normalized Difference Snow Index (NDSI) was applied to the selected images, in which two bands were used, where the ice mass has opposite (or very different) spectral behavior: bands 2 and 5 from sensors TM and ETM+, and bands 3 and 6 from sensors OLI. The elevation and the aspect data of the glaciers were obtained from SRTM (Shuttle Radar Topography Mission – v03) Digital Elevation Model. In 1985/1986, the sum of the areas of the seven studied glaciers corresponded to 92.84 km², while in the last year analyzed (2015/2016), this value shrank to 36.97 km². The area shrinkage occurred in all the glaciers that were mapped, with annual decline rates ranging from 2.49%/year to 8.46%/year. It is also possible to observe a decrease of the ice covered in all aspects considered, as well as an elevation in all glaciers fronts. In addition to the area loss occurred at lower altitudes, where the ablation rate is higher than in higher altitudes, shrinkage in some mountain tops was also present, which is evidenced by the occurrence of lower maximum elevations in the final years of the study, when compared with the initial years. Considering that part of the Colombian’s glaciers are located on active volcanoes, these areas are influenced by external and internal factors, and the occurrence of volcanic eruption and/or earthquake can cause sharp mass losses.