1,720,973 research outputs found
Equilibrium Tropical Cyclone Size in an Idealized State of Axisymmetric Radiative–Convective Equilibrium
No full textTropical cyclone size remains an unsolved problem in tropical meteorology, yet size plays a significant role in modulating damage. This work employs the Bryan cloud model (CM1) to systematically explore the sensitivity of the structure of an axisymmetric tropical cyclone at statistical equilibrium to the set of relevant model, initial, and environmental external parameters. The analysis is performed in a highly idealized state of radiative–convective equilibrium (RCE) governed by only four thermodynamic parameters, which are shown to modulate the storm structure primarily via modulation of the potential intensity.
Using dimensional analysis, the authors find that the equilibrium radial wind profile is primarily a function of a single nondimensional parameter given by the ratio of the storm radial length scale to the parameterized eddy radial length scale. The former is found to be the ratio of the potential intensity to the Coriolis parameter, matching the prediction for the “natural” storm length scale embedded within prevailing axisymmetric tropical cyclone theory; the Rossby deformation radius is shown not to be fundamental. Beyond this primary scaling, a second nondimensional parameter representing the nondimensional Ekman suction velocity is found to modulate the far outer wind field. Implications of the primary nondimensional parameter are discussed, including the critical role of effective turbulence in modulating inner-core structure and new insight into empirical estimates of the radial mixing length.National Science Foundation (U.S.) (Grant 1032244)United States. Dept. of Energy. Office of Science (Graduate Research Fellowship Program)United States. American Recovery and Reinvestment Act of 2009Oak Ridge Institute for Science and Education (Contract DE-AC05-06OR23100
A QuikSCAT climatology of tropical cyclone size
No full textQuikSCAT data of near-surface wind vectors for the years 1999–2008 are used to create a climatology of tropical cyclone (TC) size, defined as the radius of vanishing winds. The azimuthally-averaged radius of 12 ms−1 [ms superscript -1] wind (r12) [r subscript 12] is calculated for a subset of TCs (N = 2154) whose centers of circulation were clearly identifiable via subjective analysis of the QuikSCAT-analyzed wind field. The outer radius, r0 [r subscript 0], is determined from r12 [r subscript 12] using an outer wind structure model that assumes no deep convection beyond r12 [r subscript 12]. The global median values of r12 [r subscript 12] and r0 {r subscript 0] are 197 km and 423 km, respectively, with statistically significant variation across ocean basins. The global distribution of r12 [r subscript 12] is found to be approximately log-normal, the distribution of r0 [r subscript 0] is quantitatively much closer to log-normal, and the improvement in fit between r12 [r subscript 12] and r0 [r subscript 0] is attributed to the combined effect of the nature of the model employed and the paired distributions of r12 [r subscript 12] and f. Moreover, the normalization employed by Dean et al. (2009) is found to weaken rather than improve the log-normal fit. Finally, within a given storm, both r12 [r subscript 12] and r0 [r subscript 0]tend to expand very slowly with time early in the storm lifecycle and then becomes quasi-constant, though significant variance exists across storms.National Science Foundation (U.S.) (Grant ATM‐ 0850639
On the size distribution of Atlantic tropical cyclones
No full textThe size of a tropical cyclone is known to vary considerably across storms, though little is understood about the environmental and internal factors that modulate it. Making use of newly available extended tropical cyclone records that include information about storm structure, we examine the size distribution of Atlantic tropical cyclones, using as a metric the radius of vanishing storm winds normalized by the theoretical upper bound given by the ratio of the potential intensity to the Coriolis parameter. We find that the distribution of this normalized outer radius is closely log-normal.National Science Foundation (U.S.) (grant ATM-0630690
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
Tropical cyclone cold wake size dataset (AVHRR-only)
No full textMixing of the upper ocean by the wind field associated with tropical cyclones (TCs) creates observable cold wakes in sea surface temperature and may potentially influence ocean heat uptake. The relationship between cold wake size and storm size, however, has yet to be explored. Here we apply two objective methods to observed daily sea surface temperature data to quantify the size of TC-induced cold wakes. The obtained cold wake sizes agree well with the TC sizes estimated from the QuikSCAT-R wind field database with a correlation coefficient of 0.51 and 0.59, respectively. Furthermore, our new estimate of the total cooling that incorporates the variations in the cold wake size provides improved estimates of TC power dissipation and TC-induced ocean heat uptake. This study thus highlights the importance of cold wake size in evaluating the climatological effects of TCs.
The cold wake size (rROI) dataset uploaded here is based on the daily NOAA 1/4° Optimum Interpolation Sea Surface Temperature, AVHRR-only subset (1981–2017). This is corresponding to the AVHRR+AMSR subset (2002-2011) uploaded to doi:10.1594/PANGAEA.907551.
The objective cold wake size metrics (rROI) is derived based on an image processing methods -- the Region of Interest method. More information about the pretreatment and derivation of rROI please refer to Zhang et al. (2019)
Understanding the Post-Landfall Evolution of Tropical Cyclone Wind Field in an Idealized World
No full textLandfalling tropical cyclones bring tremendous coastal and inland hazard, which depends strongly on the evolution of the wind field after the landfall. This work investigates the inland evolution of the tropical cyclone wind field via idealized numerical simulation experiments and existing theories explaining the physics of storms over the ocean. The complicated landfall process is idealized as a transient response of a mature axisymmetric tropical cyclone to instantaneous surface forcings associated with landfall.First, idealized landfall experiments are performed in the f-plane Bryan Cloud Model (CM1), where surface drag coefficient (Cd) and evaporative fraction are individually or simultaneously modified systematically beneath an axisymmetric mature storm. Surface drying stabilizes the eyewall and consequently weakens the overturning circulation, thereby reducing inward angular momentum transport that slowly decays the low-level wind field only within the inner-core. In contrast, surface roughening first weakens the entire low-level wind field rapidly and enhances the overturning circulation dynamically despite the concurrent thermodynamic stabilization of the eyewall; thereafter, the storm gradually decays in a manner similar to drying. As a result, total precipitation temporarily increases with roughening but uniformly decreases with drying. Storm inner size (rmax) and outer size (r34kt) decrease monotonically and rapidly with surface roughening, while the radius of maximum wind can increase with moderate surface drying.Second, the extent to which existing intensity theory formed for tropical cyclones over the ocean can explain the intensity response to idealized landfall is explored in this work. Existing theoretical predictions for the equilibrium response and transient response of storm intensity are compared against the simulated response found in previous idealized simulations. The equilibrium and transient response of storm intensity to combined surface forcings can be reproduced by the product of their individual responses, in line with traditional potential intensity theory. The intensification theory of Emanuel (2012) is generalized for predicting the weakening process and found capable of reproducing the transient intensity decay. Specifically, the rapid initial decay of near-surface wind can be captured by how kinetic energy is instantaneously reduced by surface friction, where the decay is a function of surface roughness.Third, existing structural theory and TC radial length scale formed or identified for storms over the ocean are tested against the idealized landfall experiment where surface is individually dried or roughened. The equilibrium storm radial length scale Vp/ f , defining Vp using the actual maximum wind speed vm, can predict the transient response of storm size r34kt to surface roughening throughout the decay evolution. For surface drying experiments, TC size scales with the intensity after ∼ 12h. The E04 wind field model can generally capture the transient response of TC low-level wind field to individual surface drying and roughening, from rmax to the outer region (r = 600 km). The E04 prediction for these two types of experiments exhibits limited dependence on the subsidence cooling rate wcool applied in the model.Overall, though results are insufficient to explain the complicated wind field evolution of every real-world landfalling storm, it provides a fundamental understanding of how storm low-level wind fields respond to inland surface properties. This work also indicates the potential for existing theory to predict how tropical cyclone intensity evolves after landfall in the real world, which is essential for improving the forecasts on any timescale and the risk assessments
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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