1,720,958 research outputs found
Combining point correlation maps with self-organizing maps to investigate atmospheric teleconnection patterns in climate model data
Full text linkA new method for identifying teleconnection patterns in gridded climate data is presented. Point correlation maps constructed from NCEP/NCAR reanalysis sea level pressure (SLP) for the period 01.1984-12.2005 are used to train a self-organizing map (SOM), which topologically orders the patterns and provides a measure of frequency of pattern occurrence. Well known patterns can be identified within the SOM, such as the NAO, ENSO and the PNA, however the flexibility of the SOM allows these patterns to be viewed as part of a continuum of patterns, each identifiable as a variation within a defined teleconnection pattern. As the SOM is a non-linear method, asymmetries between patterns generated from opposite centres of action are revealed. Clustering the SOM patterns identifies the regions of the SOM corresponding to different teleconnection types by classifying similar patterns together. This retains the continuum of patterns, but allows generalization and characterization of the teleconnections present in the data. The patterns identified by the SOM can be used to evaluate the teleconnections in climate model SLP data. Point correlation maps are determined for the model data and compared to the SOM. By matching each of the NCEP/NCAR correlation maps and each of the model correlation maps with their most similar pattern on the SOM, discrepancies between the datasets are revealed. Additionally, the base points corresponding to the correlation maps for each teleconnection show the regions important to their existence. Differences in the location of the base points between NCEP/NCAR and the models provide insight into the biases underlying the model deviations from reality. The method can be extended to investigate other variables, for example the SOM can be trained using both SLP and geopotential height to investigate the 3D structure of teleconnections, while the location of the base points of the correlation maps for certain patterns can be used to assess the impact of teleconnections, such as rainfall and temperature patterns. <br/
Identifying Teleconnection Patterns from Point Correlation Maps using Self Organizing Maps
Full text linkTo identify atmospheric teleconnection patterns in 60 years of NCEP temperature, pressure and geopotential height anomalies, point correlation maps are presented to a Self Organizing Map (SOM), which topologically orders the patterns and provides a measure of frequency of pattern occurrence. Well known patterns can be identified within the SOM, such as the NAO, ENSO and the PNA, however the flexibility of the SOM allows these patterns to be viewed as part of a spectrum, or continuum, of patterns, each identifiable as a variation within a defined teleconnection pattern. The SOM patterns are then clustered to reduce the number of patterns and explore the separation of distinct patterns from the spectrum. Idealized periodic patterns of increasing complexity are used to test and explain the method.To assess the robustness of the method a SOM was constructed using point correlation maps for 60 years of NCEP surface temperature anomalies. Point correlation maps for the first and last 30 years are then compared to the SOM patterns constructed from the whole period. The patterns were robust and the pattern frequency data was able to identify the increased frequency of ENSO Modoki in the second half of the data, as observed in other studies, illustrating the method’s capability to detect changes within teleconnection patterns over time.This method can be extended by the use of correlation maps from multiple variables presented simultaneously to the SOM, helping to investigate the relationship between different aspects of the atmosphere. For example, correlation maps for surface temperature, surface pressure and geopotential height can be combined to evaluate the state of the atmosphere associated with specific patterns and how changes in the structure affect the form of the teleconnection patterns. Similar insights can be gained by using time lagged point correlation maps to investigate the predictability of teleconnection patterns
Assessing teleconnections patterns in climate models using a combination of point correlation maps and self-organizing maps
No full textA new method to identify and evaluate teleconnection patterns in gridded climate data is presented. A large set of point correlation maps (one for each grid point) is used to train a self-organizing map (SOM). This combines the teleconnection identification properties of point correlation maps with the ability of SOMs to group similar patterns together on a topological grid and provides a frequency of occurrence for each pattern. Once the SOM is trained it is used as a reference for comparison to other sets of correlation maps. A SOM trained using point correlation maps calculated from NCEP/NCAR sea level pressure reanalysis for the period 01.1948-12.2005 is presented and the patterns found compared to point correlation maps from several climate models. By matching each NCEP/NCAR correlation map and each model correlation map with their most similar pattern on the SOM, discrepancies between the datasets are revealed, such as differences in the frequency of occurrence or shifts in the spatial structure of teleconnections. The base points corresponding to the correlation maps for each teleconnection show the regions important for their existence. Differences in the base point locations between NCEP/NCAR and the models provide insight into the physical biases underlying the model deviations from reality. Prominent patterns are identified by the SOM, such as the NAO, ENSO and the PNA, however the flexibility of the SOM allows these patterns to be viewed as a continuum of patterns, each identifiable as a variation within a defined teleconnection. As the SOM is a non-linear method, asymmetries between patterns generated from opposite centres of action are revealed. Clustering the SOM patterns identifies the regions of the SOM corresponding to each teleconnection type by classifying similar patterns together, which retains the continuum of patterns, but allows general characterization of the teleconnections present in the data
Recommended from our members
The vertical structure of oceanic Rossby waves: a comparison of high-resolution model data to theoretical vertical structures
Full text linkTests of the new Rossby wave theories that have been developed over the past decade to account for discrepancies between theoretical wave speeds and those observed by satellite altimeters have focused primarily on the surface signature of such waves. It appears, however, that the surface signature of the waves acts only as a rather weak constraint, and that information on the vertical structure of the waves is required to better discriminate between competing theories. Due to the lack of 3-D observations, this paper uses high-resolution model data to construct realistic vertical structures of Rossby waves and compares these to structures predicted by theory. The meridional velocity of a section at 24° S in the Atlantic Ocean is pre-processed using the Radon transform to select the dominant westward signal. Normalized profiles are then constructed using three complementary methods based respectively on: (1) averaging vertical profiles of velocity, (2) diagnosing the amplitude of the Radon transform of the westward propagating signal at different depths, and (3) EOF analysis. These profiles are compared to profiles calculated using four different Rossby wave theories: standard linear theory (SLT), SLT plus mean flow, SLT plus topographic effects, and theory including mean flow and topographic effects. Our results support the classical theoretical assumption that westward propagating signals have a well-defined vertical modal structure associated with a phase speed independent of depth, in contrast with the conclusions of a recent study using the same model but for different locations in the North Atlantic. The model structures are in general surface intensified, with a sign reversal at depth in some regions, notably occurring at shallower depths in the East Atlantic. SLT provides a good fit to the model structures in the top 300 m, but grossly overestimates the sign reversal at depth. The addition of mean flow slightly improves the latter issue, but is too surface intensified. SLT plus topography rectifies the overestimation of the sign reversal, but overestimates the amplitude of the structure for much of the layer above the sign reversal. Combining the effects of mean flow and topography provided the best fit for the mean model profiles, although small errors at the surface and mid-depths are carried over from the individual effects of mean flow and topography respectively. Across the section the best fitting theory varies between SLT plus topography and topography with mean flow, with, in general, SLT plus topography performing better in the east where the sign reversal is less pronounced. None of the theories could accurately reproduce the deeper sign reversals in the west. All theories performed badly at the boundaries. The generalization of this method to other latitudes, oceans, models and baroclinic modes would provide greater insight into the variability in the ocean, while better observational data would allow verification of the model findings
OER - the Southampton experience
No full textThe Southampton experience of OER has been successful in repurposing over 50 CAT points of climate change resources. There is evidence of culture change amongst those staff who have contributed resources when clearing third party material, and successful negotiations with publishers have depended upon establishing contacts and networking in order to side-step a standardized web process. The level of resource required to repurpose materials means it is unrealistic to expect a widespread take up in UK educational institutions unless, at a national level, the community can negotiate agreements with the major scientific publishers. The requirement of authors to relinquish their copyright when publishing journals has significantly impeded open access in this project. Local repositories offer a more user friendly interface than JorumOpen
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
- …
