1,721,149 research outputs found
Limits to predictability of the asymptotic state of the Atlantic Meridional Overturning Circulation in a conceptual climate model
Full text linkAnticipating critical transitions in the Earth system is of great societal
relevance, yet there may be intrinsic limitations to their predictability. For
instance, from the theory of dynamical systems possessing multiple chaotic
attractors, it is known that the asymptotic state depends sensitively on the
initial condition in the proximity of a fractal basin boundary. Here, we
approach the problem of final-state sensitivity of the Atlantic Meridional
Overturning Circulation (AMOC) using a conceptual climate model, composed of a
slow bistable ocean coupled to a fast chaotic atmosphere. First, we explore the
occurrence of long chaotic transients in the monostable regime, which can mask
a loss of stability near bifurcations. In the bistable regime, we explicitly
construct the chaotic saddle using the edge tracking technique. Quantifying the
final-state sensitivity through the maximum Lyapunov exponent and the lifetime
of the saddle, we find that the system exhibits a fractal basin boundary with
almost full phase space dimension, implying vanishing predictability of the
second kind near the basin boundary. Our results demonstrate the usefulness of
studying non-attracting chaotic sets in the context of predicting climatic
tipping points, and provide guidance for the interpretation of
higher-dimensional models such as general circulation models
AMS Mathematical Review of the journal paper: From Symmetry Breaking to Poisson Point Process in 2D Voronoi Tessellations: the Generic Nature of Hexagons
No full textThis is an American Mathematical Society (AMS) MathSciNet Review of the paper by Lucarini, Valerio (I-BOLO-P
Thermodynamic Insights into Transitions Between Climate States Under Changes in Solar and Greenhouse Forcing
No full textA detailed thermodynamic, sensitivity analysis of the steady state climate system is performed with respect to the solar constant S* and the carbon dioxide concentration of the atmosphere, [CO2]. Using PlaSim, an Earth-like general circulation model of intermediate complexity, S* is modulated between 1,160 and 1,510 Wm-2 for values of [CO2] ranging from 90 to 2,880 ppm. It is observed that in a wide parameter range, which includes the present climate conditions, the climate is multistable, i.e. there are two coexisting attractors, one characterised by warm, moist climates (W) and the other by a completely frozen sea surface (Snowball Earth, SB). For both sets of states, empirical relationships for surface temperature, material entropy production, meridional energy transport, Carnot efficiency and dissipation of kinetic energy are constructed in the para- metric plane ([CO2], S*). Linear relationships are found for the two transition lines (W ? SB and SB ? W) in ([CO2], S*) between S* and the logarithm of [CO2]. The dynamical and thermodynamical properties of W and SB are completely different. W states are dominated by the hydrological cycle and latent heat is prominent in the material entropy production. The SB states are mainly dry cli- mates where heat transport is realized through sensible heat fluxes and entropy mostly generated by dissipation of kinetic energy. It is also shown that the Carnot- like efficiency regularly increases towards each transition between W and SB and that each transition is associated with a large decrease of the Carnot efficiency indicating a restabilisation of the system. Furthermore, it has been found that in SB states, changes in the vertical temperature structure are responsible for the observed changes in the meridional transport
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
Extreme Events: From Statistics to Dynamics
No full text<p>Seminar given at Uni. Reading, June 7th 2018</p>
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