Variability of North Atlantic hurricanes: seasonal versus individual-event features

Tropical cyclones are affected by a large number of climatic factors, which translates into complex patterns of occurrence. The variability of annual metrics of tropical-cyclone activity has been intensively studied, in particular since the sudden activation of the N Atl in the mid 1990's. We provide first a swift overview on previous work by diverse authors about these annual metrics for the NAtl basin, where the natural variability of the phenomenon, the existence of trends, the drawbacks of the records, and the influence of global warming have been the subject of interesting debates. Next, we present an alternative approach that does not focus on seasonal features but on the characteristics of single events [Corral et al Nature Phys 6, 693, 2010]. It is argued that the individual-storm power dissipation index (PDI) constitutes a natural way to describe each event, and further, that the PDI statistics yields a robust law for the occurrence of tropical cyclones in terms of a power law. In this context, methods of fitting these distributions are discussed. As an important extension to this work we introduce a distribution function that models the whole range of the PDI density (excluding incompleteness effects at the smallest values), the gamma distribution, consisting in a power-law with an exponential decay at the tail. The characteristic scale of this decay, represented by the cutoff parameter, provides very valuable information on the finiteness size of the basin, via the largest values of the PDIs that the basin can sustain. We use the gamma fit to evaluate the influence of sea surface temperature (SST) on the occurrence of extreme PDI values, for which we find an increase around 50 % in the values of these basin-wide events for a 0.49 degC SST average difference. ...Comment: final version available soon in the 1st author's web, http://www.crm.cat/Researchers/acorral/Pages/PersonalInformation.asp

La fi del nostre sistema econòmic: una perspectiva des de les ciències experimentals

2 pagesAquest no és un article gens habitual per a una revista com Omnis Cellula, ni per la temàtica (la crisi terminal del nostre sistema econòmic i possiblement social) ni per qui l'escriu (un físic teòric reconvertit a oceanògraf físic). Així i tot, seria difícil negar la pertinència de la discussió aquí presentada, vivint com vivim en el nostre dia a dia el col·lapse progressiu del nostre sistema de ciència, fruit de la degradació progressiva del conjunt de l'economia i del sistema social del qual ens havíem dotat i que anomenem estat del benestarPeer Reviewe

Dynamic effect of quasi-geostrophic turbulence on ocean surface as derived from satellite imagery

Martech 2009 Third Marine Technology Workshop, 19-20 november 2009, Vilanova i la Geltrú, Barcelona.-- 1 page, 1 figurePeer reviewe

La Fi del nostre sistema econòmic: una perspectiva des de les ciències experimentals

Aquest no és un article gens habitual per a una revista com Omnis Cellula, ni per la temàtica (la crisi terminal del nostre sistema econòmic i possiblement social) ni per qui l'escriu (un físic teòric reconvertit a oceanògraf físic). Així i tot, seria difícil negar la pertinència de la discussió aquí presentada, vivint com vivim en el nostre dia a dia el col·lapse progressiu del nostre sistema de ciència, fruit de la degradació progressiva del conjunt de l'economia i del sistema social del qual ens havíem dotat i que anomenem estat del benestar

Relevance of multifractal textures in static images

In the latest years, multifractal analysis has been applied to image analysis. The multifractal framework takes advantage of multiscaling properties of images to decompose them as a collection of different fractal components, each one associated to a singularity exponent (an exponent characterizing the way in which that part of the image evolves under changes in scale). One of those components, characterized by the least possible exponent, seems to be the most informative about the whole image. Very recently it has been proposed an algorithm to reconstruct the image from this component, just using physical information conveyed by it. In this paper, we will show that the same algorithm can be used to assess the relevance of the other fractal parts of the image

Description, modeling and forecasting of data with optimal wavelets

Cascade processes have been used to model many different self-similar systems, as they are able to accurately describe most of their global statistical properties. The so-called optimal wavelet basis allows to achieve a geometrical representation of the cascade process-named microcanonical cascade- that describes the behavior of local quantities and thus it helps to reveal the underlying dynamics of the system. In this context, we study the benefits of using the optimal wavelet in contrast to other wavelets when used to define cascade variables, and we provide an optimality degree estimator that is appropriate to determine the closest-to-optimal wavelet in real data. Particularizing the analysis to stock market series, we show that they can be represented by microcanonical cascades in both the logarithm of the price and the volatility. Also, as a promising application in forecasting, we derive the distribution of the value of next point of the series conditioned to the knowledge of past points and the cascade structure, i.e., the stochastic kernel of the cascade process.

Desastres naturals, multifractals i xarxes climàtiques: tres exemples de complexitat a geociència

La Terra, el nostre planeta, és un sistema d'una complexitat enorme. Geo�� sics, geoquímics, geòlegs, oceanògrafs, hidròlegs, meteoròlegs, climatòlegs, ecòlegs, etc., fa molt de temps que lluiten contra aquesta complexitat. En els darrers anys la ciència dels sistemes complexos està oferint noves perspec�� ves per entendre millor el sistema Terra. En aquest ar�� cle considerem tres exemples: la grandària dels desastres naturals, els senyals mul�� fractals i les xarxes climà�� ques