1,721,011 research outputs found
Recent trends in the atmospheric circulation
Get PDFTo build confidence in projections of future change, models should be able to reproduce observed trends in the current climate. However, despite successes in modelling some aspects of climate change associated with the rise in global temperature, models struggle to capture trends in various regional and circulation-driven features. The broad aim of this thesis is to develop new tools to study recent large-scale trends in the climate system, with a particular focus on the contribution of the atmospheric circulation.
The main approach is to explore the range of trends in the initialised hindcasts of a near-term prediction model, DePreSys3, and use these to provide context for observed trends. In the tropics, upper-level temperature trends in the hindcasts are cooler than in the equivalent free-running model, bringing them into agreement with reanalyses, and the improvement is explained through linear surface temperature scaling theory. Much of the improvement is shown to occur through capturing the magnitude of SST warming in the tropical Pacific. The hindcasts also support a robust weakening of the NH Hadley Cell, in line with pressure observations.
A key conclusion is that the hindcasts are consistent with a remarkably wide range of trends over much of the climate system, most notably in the Arctic. Sea ice trends are constrained by the initialisation and explain very little of this spread; instead, the spread in hindcast Arctic warming, as well as in Eurasian cooling and even global surface temperature trends, is mainly a function of trends in annular mode-like structures. While not always a dominant contributor to the observed trend, this highlights the role that seasonal variability, likely atmospheric in origin, can play in modulating multidecadal trends.
Despite considerable ensemble spread, the hindcasts also support the emergence of poleward jet shifts on the global scale. The effect of the tropical Pacific on the jets is more subtle than on tropical temperature trends, but it does appear to contribute to the improvement in the hindcast wind trends, as well as regional temperature and circulation trends.
Finally, a novel budget-based method is developed to quantify the dynamical contribution to atmospheric temperature trends. The dynamical and diabatic contributions largely balance each other, and trends are identified in the mean and eddy circulations. Trends in the ERA5 budget terms largely lack significance after accounting for temporal autocorrelation, suggesting that a longer observational record may be necessary to achieve robust trends
Compound Precipitation and Wind Extremes over Europe and their relationship to Extratropical Cyclones
No full textExtratropical cyclones and their associated extreme precipitation and wind cause large
damage and loss of life over Europe. When such extremes occur at the same time and same
place they can cause even greater risks. Knowing more about the frequency and spatial
pattern of these extremes over Europe and their relationship to cyclones is important for
forecasting, the (re)insurance industry and emergency planners. This thesis takes both an
Eulerian and a Lagrangian perspective to investigate compound precipitation and wind
extremes over Europe and within cyclones. Observational data including ERA5 as well as
a high resolution climate model, GloSea5, is used to do this.
Over Europe high co-occurrence is found over western coasts and low co-occurrence is
found over eastern coasts. These results are found to be robust over different timescales and
datasets. Cyclones are found to be strongly associated with compound extremes, given an
extreme co-occurring event the chance of a cyclone being nearby is more than 70% for much
of Europe. Using an objective feature tracking method, insight into the frequency, spatial
pattern and footprint size of extremes within cyclones from a Lagrangian perspective is
given. Wind extreme footprints have almost double the area of precipitation and are 5
times larger than compound. The spatial pattern of extremes does not vary much during
a cyclones lifecycle, however, the frequency does. The frequency of extreme wind peaks at
maximum intensity, within the cold conveyor belt to behind the cold front. The frequency
of precipitation and compound extremes peak 6 hours before maximum intensity, ahead
of the cyclone centre, in the warm conveyor belt and warm front. The spatial structure
of extremes within cyclones are very consistent and vary little with seasonality, intensity
and speed. The frequency of extremes and footprint size however varies largely.
GloSea5 is evaluated against ERA5, to find out how well it can represent extremes from
both an Eulerian and Lagrangian perspective and to be used to investigate unprecedented
extremes using the UNSEEN method. Substantial differences in magnitude are found between precipitation and wind extremes between the datasets, however, compound extremes
compare well spatially over Europe. GloSea5 represents the general structure of extremes
within cyclones well. However, extremes at the cyclone centre tend to be overestimated and
regions with the largest frequencies of extremes are underestimated, particularly within
cyclones at maximum intensity. Despite biases in GloSea5 it is shown to have a reasonable
representation of the storm tracks over Europe and the North Atlantic and can simulate
the variability in cyclone frequency well. Although GloSea5 underestimates the number
of storms over Europe there are still winters in GloSea5 with unprecedented number of
storms for some locations. Extreme storm seasons over Europe and over particular locations arise from a variety of winter mean circulation types. GloSea5 has shown that it can replicate circulation patterns that appear feasible in and similar to the real world.
Stormy seasons in GloSea5 are found that produce circulation patterns that are unrealised
in the observational record. These large scale dynamics drive large numbers of storms over
Central and Southern Europe. GloSea5 represents the size of extreme wind, precipitation
and compound footprints very well. It is possible in the current climate to get storms with
footprints of extremes almost double the size of that seen historically
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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