1,720,957 research outputs found
The forcing of mean sea level variability around Europe
No full textMean sea level variability around the European coasts is explored on the basis of regional sea level indices derived through Empirical Orthogonal Function Analysis (EOF) of tidegauge records. The regional indices are cross-correlated amongst themselves and against the major regional and climatic indices. The analysis is done for the whole year as well as seasonally. The effect of coherent atmospheric pressure signals is explored by comparing the results of the analysis before and after the data are corrected for the atmospheric pressure effects. The North Atlantic Oscillation Index (NAO) and the Mediterranean Oscillation Index are the major regional indices which are found to be significantly correlated with sea level variability around Europe. Their correlation is positive for the Northern European coast and negative for the Mediterranean coasts. The NAO influence causes an anti-correlation between northern and southern European sea level. This is stronger in winter and weakens significantly or disappears completely during the summer. When the NAO influence was removed from the regional mean sea level indices the cross correlation between the various regions was reduced. However, residual spatial coherency indicated that probably there are other mechanisms causing spatial coherency. No statistically significant correlation with the Southern Oscillation Index (SOI) was found
A New Statistical Modelling Approach to Ocean Front Detection from SST Satellite Images
Full text linkOcean fronts are narrow zones of intense dynamic activity that play an important role in global ocean-atmosphere interactions. Owing to their highly variable nature, both in space and time, they are notoriously difficult features to adequately sample using traditional in-situ techniques. In this paper we propose a new statistical modelling approach to detecting and monitoring ocean fronts from AVHRR SST satellite images that builds on the 'front following' algorithm of Shaw and Vennell (2000). Weighted local likelihood is used to provide a smooth, non-parametric description of spatial variations in the position, mean temperature, width and temperature change of an individual front within an image. Weightings are provided by a Gaussian kernel function whose width is automatically determined by likelihood cross-validation. The statistical model fitting approach allows estimation of the uncertainty of each parameter to be quantified, a capability not possessed by other techniques. The algorithm is shown to be robust to noise and missing data in an image, problems that hamper many of the existing front detection schemes. The approach is general and could be used with other remotely sensed data sets, model output or data assimilation products
Sea level extremes in Southern Europe
No full textKnowledge of sea level extremes is important for coastal planning purposes. Temporal changes in the extremes may indicate changes in the forcing parameters, most probably the storm surges. Sea level extremes and their spatial and temporal variability in southern Europe are explored on the basis of 73 tide gauge records from 1940. This study uses all data available to infer risks at the coast caused by extreme sea levels. Extreme values of 250 cm are observed at the Atlantic coasts with smaller values in the Mediterranean where, with the exception of the Strait of Gibraltar and the Adriatic Sea, the extreme values are less than 60 cm. At the Adriatic Sea values of up to 200 cm are found. When the tidal contribution is removed the differences between the various areas reduce. The spatial distribution of the extremes of the tidal residuals is well represented by the hindcast of a two-dimensional hydrodynamic model forced by the atmospheric pressure and the wind, although the model underestimates the extremes. Higher return levels (200–300 cm for the 50-year return level) are observed in the Atlantic stations due to the larger tides. In the Mediterranean, higher values are found in the northern Adriatic (between 150 and 200 cm) while in the rest of the domain they vary between 20 and 60 cm. The nonlinear interaction between tides and surges is negligible in the Mediterranean, thus the joint tides-surges distribution can be applied. The interannual and decadal variability in time of extremes is caused by mean sea level changes. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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