Dragon-kings: mechanisms, statistical methods and empirical evidence

This introductory article presents the special Discussion and Debate volume "From black swans to dragon-kings, is there life beyond power laws?" published in Eur. Phys. J. Special Topics in May 2012. We summarize and put in perspective the contributions into three main themes: (i) mechanisms for dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii) empirical evidence in a large variety of natural and social systems. Overall, we are pleased to witness significant advances both in the introduction and clarification of underlying mechanisms and in the development of novel efficient tests that demonstrate clear evidence for the presence of dragon-kings in many systems. However, this positive view should be balanced by the fact that this remains a very delicate and difficult field, if only due to the scarcity of data as well as the extraordinary important implications with respect to hazard assessment, risk control and predictability.Comment: 20 page

25 Years of Self-organized Criticality: Concepts and Controversies

Introduced by the late Per Bak and his colleagues, self-organized criticality (SOC) has been one of the most stimulating concepts to come out of statistical mechanics and condensed matter theory in the last few decades, and has played a significant role in the development of complexity science. SOC, and more generally fractals and power laws, have attracted much comment, ranging from the very positive to the polemical. The other papers (Aschwanden et al. in Space Sci. Rev., 2014, this issue; McAteer et al. in Space Sci. Rev., 2015, this issue; Sharma et al. in Space Sci. Rev. 2015, in preparation) in this special issue showcase the considerable body of observations in solar, magnetospheric and fusion plasma inspired by the SOC idea, and expose the fertile role the new paradigm has played in approaches to modeling and understanding multiscale plasma instabilities. This very broad impact, and the necessary process of adapting a scientific hypothesis to the conditions of a given physical system, has meant that SOC as studied in these fields has sometimes differed significantly from the definition originally given by its creators. In Bak’s own field of theoretical physics there are significant observational and theoretical open questions, even 25 years on (Pruessner 2012). One aim of the present review is to address the dichotomy between the great reception SOC has received in some areas, and its shortcomings, as they became manifest in the controversies it triggered. Our article tries to clear up what we think are misunderstandings of SOC in fields more remote from its origins in statistical mechanics, condensed matter and dynamical systems by revisiting Bak, Tang and Wiesenfeld’s original papers

Energetic particle influence on the Earth's atmosphere

This manuscript gives an up-to-date and comprehensive overview of the effects of energetic particle precipitation (EPP) onto the whole atmosphere, from the lower thermosphere/mesosphere through the stratosphere and troposphere, to the surface. The paper summarizes the different sources and energies of particles, principally galactic cosmic rays (GCRs), solar energetic particles (SEPs) and energetic electron precipitation (EEP). All the proposed mechanisms by which EPP can affect the atmosphere are discussed, including chemical changes in the upper atmosphere and lower thermosphere, chemistry-dynamics feedbacks, the global electric circuit and cloud formation. The role of energetic particles in Earth’s atmosphere is a multi-disciplinary problem that requires expertise from a range of scientific backgrounds. To assist with this synergy, summary tables are provided, which are intended to evaluate the level of current knowledge of the effects of energetic particles on processes in the entire atmosphere

Impulsive processes in the magnetotail during substorm expansion

Anisotropy and intensity variations of high-energy particles and magnetic variations detected by IMP-J at 37 Re in the central part of the magnetotail within 2 Re of the neutral sheet were studied during a few consecutive substorms on March 3, 1976, and related to a large body of ground observations. A close correlation is usually found between bursts observed in Pi pulsations on the ground (having a duration of about 1 min and usually being repeated in 1–3 min) and high-energy particle bursts observed in the far tail. The magnetic field response is examined relative to the onsets of high-energy particle bursts. A three-dimensional current system RIPD (Reconnection Induced Propagating Disturbance) is constructed which can, in principle, produce the magnetic field variations observed in the boundary part of the plasma sheet (PS). Previously reported properties of high-energy particle bursts (inverse energy dispersion, preferential acceleration of alpha particles, dawn-dusk asymmetry in the acceleration of electrons and protons and transient PS expansions) are found to be typical of these impulsive processes. Together with earlier results, these observations show that the expansion process (identified here as a transient reconnection or explosive tearing mode) clearly operates in an impulsive fashion. The superposition of impulse-induced propagating disturbances necessarily results in complex, variable patterns of magnetic field and thermal plasma behaviour, such as are frequently found in the PS during substorms.           ARK: https://n2t.net/ark:/88439/y027754 Permalink: https://geophysicsjournal.com/article/222 &nbsp

Magnetosheath and solar wind turbulence processes features identification

A different kind of analysis should be applied to a turbulent process, than that applied to a nondisturbed medium. In this work we present the result of extended self-similarity analysis (ESS) by comparing between different turbulent models: Kolmogorov K41 model, She-Leveque (isotropic log-Poisson model) of order 3; Iroshnikov-Kraichnan model and Politano-Pouquet model of order 4. Two regimes were observed for large and small times ales: the Gaussian distribution was used for small times ales for magnetic field fluctuation probability distribution function (PDF), and the Lèvy distribution was used for large-scale timescale non-Gaussian distributions. The intersection of two asymptotes corresponds to approximately 1 s, which agrees with the ion-cyclotron period

Diffusion processes in the transition layer of the Earth's magnetosphere

Turbulence has a different nature in the interplanetary magnetic field and in the transition region, thus it requires a different type of analysis. The "Cluster 2" satellite mission provides magnetic measurements with a temporal resolution of 22.5 Hz. We analysed the evolution of the probability density function over time, as well as that of the structural function. From the analysis we can conclude that for small time scales, the fluctuation distribution differs significantly from the Gaussian. Furthermore, we see that in the foresho k region, the fluctuation be comes almost Gaussian. Using the extended self-similarity structure function we compare the experimental data with the Kolmogorov K41 model. Calculated diffusion coeficients have a good agreement with the analysis of the probability density function and this can prove the existence of superdiffusion processes in the transition region of the Earth's magnetosphere