1,720,970 research outputs found
Jan Mayen glacier changes between 2000-2020 in historic, climatic, oceanic, and geographic context
Get PDFJan Mayen is a small, remote, glacierized volcanic island in the North Atlantic between Greenland, Svalbard, Iceland, and Scandinavia. Its most recent glacier map (RGI) is based on airphotos from 1949-1975, and only the glacier Sørbreen has previously been studied in detail. This thesis presents the first study of glacier fluctuations for the entire island, including the retreat of marine-terminating glaciers from historic maps since 1861 and the annual to decadal frontal variations of 16 of the island’s 20 glaciers from satellite imagery. Between 2000 and 2020, Jan Mayen lost 2.2 km2 or 2% of its ice area and had a frontal ablation of 0.20 km3. Glaciers retreated 20-460 m with an average annual retreat rate (-9±7 m/yr) slower than in the surrounding regions, while Jan Mayen’s temperature increased more. Correlation analysis with 18 climatic and oceanic parameters suggests that the main driver of Jan Mayen’s glacier fluctuations is PDD.NSER
Thermokarst distribution and susceptibility in Yukon: lakes, landslides and pingos
No full textThe most tangible consequence of permafrost thaw is thermokarst, which is landscape destabilization resulting from ground ice melt. The main objective of this thesis was to model and map thermokarst susceptibility across Yukon, Canada. An inventory of 3376 historically mapped thermokarst landform point locations was extracted from the Yukon Geological Survey’s Digital Surficial Geology dataset. Of these, 25 lakes, 27 landslides and 93 pingos in the Dawson City study area were manually delineated on the World Imagery baselayer in order to assess their morphology and distribution relative to similar landforms in other regions. Subsequently, generalized linear models of thermokarst susceptibility in Yukon were constructed using a range of topographic, geologic, environmental and climatic predictor variables from existing regional or global datasets. A novel potential surface radiation adjustment was developed to correct for seasonal snow cover. Using the mapped thermokarst landforms in the Dawson City study area as a training dataset set, the resulting optimal lake and landslide susceptibility models use slope as the sole predictor variable, while the pingo susceptibility model uses profile curvature. Overall, 3, 34 and 0.1 % of Yukon is modelled as being highly susceptible to thermokarst lake, landslide and pingo development, respectively. The models were evaluated using the Yukon thermokarst point location dataset, randomly distributed points, and select multivariate logistic models. The thermokarst lake susceptibility model performed best overall. This study shows that relatively simple modelling techniques can be effective in mapping thermokarst susceptibility, and highlights the importance of rigorous, up-to-date thermokarst landform inventories to aid in future modelling efforts
Flow obstructions in valley glaciers
Get PDFix, 149 leaves : ill. ; 29 cm.Valley glaciers often occur within complex dendritic systems where tributary glaciers
contribute ice mass and blocking potential to the trunk glacier. Analysis of glacier
inventories and maps in the regions of Svalbard, East Greenland, Yukon Territory and the
Thompson Glacier system indicates that trunk - tributary intersections commonly occur at
angles between 45° and 90°. An analogue material with flow properties similar to creep
in pure ice has been used to simulate flow in a model valley glacier. The model and a
series of blockages were constructed based on dimensions derived from the inventory and
map analysis. The angled blockage indicates lower overall velocity rates and appears to
have a funnelling rather than blocking affect on the analogue material. The perpendicular
obstruction that blocked half the width of the model valley caused a piling up of analogue
material prior to a release into the unobstructed side of the valley
Macrophysical properties and a climatology of Arctic coastal fog in East Greenland
Get PDFArctic summer fog is a major transportation hazard and has implications for the cryospheric energy balance. In this thesis, the climatology and macrophysical properties of fog along the coast of East Greenland are explored, and local to mesoscale environmental conditions studied to explain regional differences. Using a combination of long-term synoptic weather observations and Integrated Global Radiosonde Archive data, novel automated methods were developed to classify liquid fog thermodynamic structure and calculate fog top elevation. Six fog types were identified; several of which could be associated with advection fog formation and dissipation processes. Temperature inversions during fog were deeper and stronger compared to non-fog conditions. At Low-Arctic locations fog was geometrically thin and occurred below the temperature inversion. Fog was thicker in the High-Arctic, often penetrating the inversion layer. The radiosonde data analysis and automated methods presented are applicable to any synoptic Arctic weather station with present weather codes.Natural Sciences and Engineering Research Council of Canada; Alberta Innovates Technology Futures
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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