Tag Archives: Adaptation and Self-Organizing Systems

Dynamical complexity in micro-scale disk-wind systems [GA]

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http://arxiv.org/abs/2304.12696


Powerful winds at accretion disk scales have been observed in the past 20 years in many AGN, the so called Ultra-Fast Outflows (UFOs). Outflows are intimately related to mass accretion due to the conservation of angular momentum, and therefore are a key ingredient of most accretion disk models around BHs. At the same time, nuclear winds and outflows can provide the feedback which regulates the joint BH and galaxy growth. We reconsider UFO observations in the framework of the Magneto-Hydrodynamic Disk Wind (MHDW) scenario and study their statistical properties. We derive the typical wind-activity history in our sources by assuming that it can be statistically described by population functions. We study the statistical properties of UFOs from the literature and derive the distribution functions of the ratio $\bar \omega$ between the mass outflow and inflow rates, and the ratio $\lambda_w$ between the mass outflow and the Eddington accretion rates. We study the links between $\bar \omega$ and $\lambda_w$ and the Eddington ratio $\lambda={L_{bol}}/{L_{Edd}}$. We find that the distribution functions of $\bar \omega$ and $\lambda_w$ can be described as power laws above some threshold, suggesting that there may be many wind sub-events for each major wind event in each AGN activity cycle, which is a fractal behaviour in agreement with current MHDW and Chaotic Cold Accretion theories. We then introduce a simple cellular automaton to investigate how the dynamical properties of an idealized disk-wind system changes following the introduction of simple feedback rules. We find that without feedback the system is over-critical. Conversely, if feedback is present, the system can be driven toward self organized criticality. Our results corroborate the hypothesis that AGN feedback is a necessary key ingredient in disk-wind systems, and thus, in shaping the co-evolution of galaxies and supermassive BHs.

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F. Fiore, M. Gaspari, A. Luminari, et. al.
Wed, 26 Apr 23
12/62

Comments: Back to Astronomy & Astrophysics, revised manuscript after referee report

Self-Organization In Stellar Evolution: Size-Complexity Rule [SSA]

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http://arxiv.org/abs/2202.02318


Complexity Theory is highly interdisciplinary, therefore any regularities must hold on all levels of organization, independent on the nature of the system. An open question in science is how complex systems self-organize to produce emergent structures and properties, a branch of non-equilibrium thermodynamics. It has long been known that there is a quantity-quality transition in natural systems. This is to say that the properties of a system depend on its size. More recently, this has been termed the size-complexity rule, which means that to increase their size, systems must increase their complexity, and that to increase their complexity they must grow in size. This rule goes under different names in different disciplines and systems of different nature, such as the area-speciation rule, economies of scale, scaling relations (allometric) in biology and for cities, and many others. We apply the size-complexity rule to stars to compare them with other complex systems in order to find universal patterns of self-organization independent of the substrate. Here, as a measure of complexity of a star, we are using the degree of grouping of nucleons into atoms, which reduces nucleon entropy, increases the variety of elements, and changes the structure of the star. As seen in our previous work, complexity, using action efficiency, is in power law proportionality of all other characteristics of a complex system, including its size. Here we find that, as for the other systems studied, the complexity of stars is in a power law proportionality with their size – the bigger a system is, the higher its level of complexity is – despite differing explosion energies and initial metallicities from simulations and data, which confirms the size-complexity rule and our model.

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T. Butler and G. Georgiev
Mon, 7 Feb 22
25/46

Comments: 20 pages, 3 figures, 11 tables, 9 equations, Conference on Complex Systems CCS2017, Cancun, Mexico, Sattelite meeting “Efficiency in complex systems”

Episodic deluges in simulated hothouse climates [EPA]

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http://arxiv.org/abs/2111.03109


Earth’s distant past and potentially its future include extremely warm “hothouse” climate states, but little is known about how the atmosphere behaves in such states. One distinguishing characteristic of hothouse climates is that they feature lower-tropospheric radiative heating, rather than cooling, due to the closing of the water vapor infrared window regions. Previous work has suggested that this could lead to temperature inversions and significant changes in cloud cover, but no previous modeling of the hothouse regime has resolved convective-scale turbulent air motions and cloud cover directly, thus leaving many questions about hothouse radiative heating unanswered. Here, we conduct simulations that explicitly resolve convection and find that lower-tropospheric radiative heating in hothouse climates causes the hydrologic cycle to shift from a quasi-steady regime to a “relaxation oscillator” regime, in which precipitation occurs in short and intense outbursts separated by multi-day dry spells. The transition to the oscillatory regime is accompanied by strongly enhanced local precipitation fluxes, a significant increase in cloud cover, and a transiently positive (unstable) climate feedback parameter. Our results indicate that hothouse climates may feature a novel form of “temporal” convective self-organization, with implications for both cloud coverage and erosion processes.

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J. Seeley and R. Wordsworth
Mon, 8 Nov 21
16/69

Comments: N/A

Testing Self-Organized Criticality Across the Main Sequence using Stellar Flares from TESS [SSA]

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http://arxiv.org/abs/2109.07011


Stars produce explosive flares, which are believed to be powered by the release of energy stored in coronal magnetic field configurations. It has been shown that solar flares exhibit energy distributions typical of self-organized critical systems. This study applies a novel flare detection technique to data obtained by NASA’s TESS mission and identifies $\sim10^6$ flaring events on $\sim10^5$ stars across spectral types. Our results suggest that magnetic reconnection events that maintain the topology of the magnetic field in a self-organized critical state are ubiquitous among stellar coronae.

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A. Feinstein, D. Seligman, M. Günther, et. al.
Thu, 16 Sep 21
53/54

Comments: 6 pages, 3 figures, Submitted to journal

Dynamo and the Adiabatic Invariant [EPA]

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http://arxiv.org/abs/2108.11548


The paper considers dynamo generated by a shallow fluid layer in a celestial body (planet or star). This dynamo is based on the extra invariant for interacting magnetic Rossby waves. The magnetohydrodynamics (MHD) is linearized on the background of strong toroidal magnetic field. The extra invariant is used to show that the background field is maintained.

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A. Balk
Fri, 27 Aug 21
28/67

Comments: 12 pages, 2 figures

Unveiling the singular dynamics in the cosmic large-scale structure [CEA]

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http://arxiv.org/abs/1912.00868


Gravitational collapse of cold dark matter leads to infinite-density caustics that seed the primordial dark-matter halos in the large-scale structure. The development of these caustics begins, generically, as an almost one-dimensional phenomenon with the formation of pancakes. Focusing on the one-dimensional case, we identify a landscape of so far unknown singularities in the particle acceleration that emerge after the first crossing of particle trajectories. We complement our fully analytical studies by high-resolution N-body simulations and find outstanding agreement, particularly shortly after the first crossing. We develop the methods in 1D but outline briefly the necessary steps for the 3D case.

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C. Rampf, U. Frisch and O. Hahn
Tue, 3 Dec 19
35/90

Comments: 5 pages + references, 2 figures, to be submitted to PRL (the accompanied numerical code can be downloaded from this https URL)

How complex is the cosmic web? [CEA]

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http://arxiv.org/abs/1911.11029


The growth of large-scale cosmic structure is a beautiful exemplification of how complexity can emerge in our Universe, starting from simple initial conditions and simple physical laws. Using {\enzo} cosmological numerical simulations, I applied tools from Information Theory (namely, “statistical complexity”) to quantify the amount of complexity in the simulated cosmic volume, as a function of cosmic epoch and environment. This analysis can quantify how much difficult to predict, at least in a statistical sense, is the evolution of the thermal, kinetic and magnetic energy of the dominant component of ordinary matter in the Universe (the intragalactic medium plasma). The most complex environment in the simulated cosmic web is generally found to be the periphery of large-scale structures (e.g. galaxy clusters and filaments), where the complexity is on average $\sim 10-10^2$ times larger than in more rarefied regions, even if the latter dominate the volume-integrated complexity of the simulated Universe. If the energy evolution of gas in the cosmic web is measured on a $\approx 100 $ $\rm kpc/h$ resolution and over a $\approx 200$ $\rm Myr$ timescale, its total complexity is the range of $\sim 10^{16}-10^{17} \rm ~bits$, with little dependence on the assumed gas physics, cosmology or cosmic variance.

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F. F.Vazza
Tue, 26 Nov 19
29/66

Comments: 18 pages, 20 figures. MNRAS accepted, in press

Observations of Turbulent Magnetic Reconnection Within a Solar Current Sheet [SSA]

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http://arxiv.org/abs/1808.06071


Magnetic reconnection is a fundamental physical process in various astrophysical, space, and laboratory environments. Many pieces of evidence for magnetic reconnection have been uncovered. However, its specific processes that could be fragmented and turbulent have been short of direct observational evidence. Here, we present observations of a super-hot current sheet during SOL2017-09-10T X8.2-class solar flare that display the fragmented and turbulent nature of magnetic reconnection. As bilateral plasmas converge toward the current sheet, significant plasma heating and non-thermal motions are detected therein. Two oppositely directed outflow jets are intermittently expelled out of the fragmenting current sheet, whose intensity shows a power-law distribution in spatial frequency domain. The intensity and velocity of the sunward outflow jets also display a power-law distribution in temporal frequency domain. The length-to-width ratio of the current sheet is estimated to be larger than theoretical threshold of and thus ensures occurrence of tearing mode instability. The observations therefore suggest fragmented and turbulent magnetic reconnection occurring in the long stretching current sheet.

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X. Cheng, Y. Li, L. Wan, et. al.
Tue, 21 Aug 18
46/71

Comments: 15 pages, accepted for publication in ApJ, any comments are welcome!

Dynamical generalizations of the Drake equation: the linear and non-linear theories [IMA]

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http://arxiv.org/abs/1805.09058


The Drake equation pertains to the essentially equilibrium situation in a population of communicative civilizations (CCs) of the Galaxy, but it does not describe dynamical processes which can occur in it. Both linear and non-linear dynamical population analysis is build out and discussed instead of the Drake equation.

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A. Panov
Thu, 24 May 18
14/58

Comments: 10 pages, 5 figures

Energy Transfer and Spectra in Simulations of Two-dimensional Compressible Turbulence [GA]

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http://arxiv.org/abs/1802.08228


We present results of high-resolution numerical simulations of compressible 2D turbulence forced at intermediate spatial scales with a solenoidal white-in-time external acceleration. A case with an isothermal equation of state, low energy injection rate, and turbulent Mach number $M\approx0.34$ without energy condensate is studied in detail. Analysis of energy spectra and fluxes shows that the classical dual-cascade picture familiar from the incompressible case is substantially modified by compressibility effects. While the small-scale direct enstrophy cascade remains largely intact, a large-scale energy flux loop forms with the direct acoustic energy cascade compensating for the inverse transfer of solenoidal kinetic energy. At small scales, the direct enstrophy and acoustic energy cascades are fully decoupled at small Mach numbers and hence the corresponding spectral energy slopes comply with theoretical predictions, as expected. At large scales, dispersion of acoustic waves on vortices softens the dilatational velocity spectrum, while the pseudo-sound component of the potential energy associated with coherent vortices steepens the potential energy spectrum.

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A. Kritsuk
Fri, 23 Feb 18
20/64

Comments: 10 pages, 6 figures. To appear in: Turbulence in Complex Conditions, Proc. Euromech/Ercoftac Colloquium 589, ed. M. Gorokhovski, Springer, 2018

Dynamics of homogeneous shear turbulence: A key role of the nonlinear transverse cascade in the bypass concept [CL]

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http://arxiv.org/abs/1705.02842


To understand the self-sustenance of subcritical turbulence in spectrally stable shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain and analyzed the dynamical processes in Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of perturbation harmonics due to the shear flow non-normality. This non-normality-induced, or nonmodal growth is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space appears to be the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade that exemplifies a well-known bypass scenario of subcritical turbulence. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process varies, but always remains quite large. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.

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G. Mamatsashvili, G. Khujadze, G. Chagelishvili, et. al.
Tue, 9 May 17
27/82

Comments: 22 pages, 24 figures

Reversing the irreversible: from limit cycles to emergent time symmetry [CL]

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http://arxiv.org/abs/1703.09696


In 1979 Penrose hypothesized that the arrows of time are explained by the hypothesis that the fundamental laws are time irreversible. That is, our reversible laws, such as the standard model and general relativity are effective, and emerge from an underlying fundamental theory which is time irreversible. In Cort\^{e}s and Smolin (2014a, 2014b, 2016) we put forward a research program aiming at realizing just this. The aim is to find a fundamental description of physics above the planck scale, based on irreversible laws, from which will emerge the apparently reversible dynamics we observe on intermediate scales. Here we continue that program and note that a class of discrete dynamical systems are known to exhibit this very property: they have an underlying discrete irreversible evolution, but in the long term exhibit the properties of a time reversible system, in the form of limit cycles. We connect this to our original model proposal in Cort\^{e}s and Smolin (2014a), and show that the behaviours obtained there can be explained in terms of the same phenomenon: the attraction of the system to a basin of limit cycles, where the dynamics appears to be time reversible. Further than that, we show that our original models exhibit the very same feature: the emergence of quasi-particle excitations obtained in the earlier work in the space-time description is an expression of the system’s convergence to limit cycles when seen in the causal set description.

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M. Cortes and L. Smolin
Thu, 30 Mar 17
67/69

Comments: 22 pages, 8 figures

On the complexity and the information content of cosmic structures [CEA]

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http://arxiv.org/abs/1611.09348


The emergence of cosmic structure is commonly considered one of the most complex phenomena in Nature. However, this complexity has never been defined nor measured in a quantitative and objective way. In this work we propose a method to measure the information content of cosmic structure and to quantify the complexity that emerges from it, based on Information Theory. The emergence of complex evolutionary patterns is studied with a statistical symbolic analysis of the datastream produced by state-of-the-art cosmological simulations of forming galaxy clusters. This powerful approach allows us to measure how many bits of information are necessary to predict the evolution of energy fields in a statistical way, and it offers a simple way to quantify when, where and how the cosmic gas behaves in complex ways. The most complex behaviors are found in the peripheral regions of galaxy clusters, where supersonic flows drive shocks and large energy fluctuations over a few tens of million years. Describing the evolution of magnetic energy requires at least a twice as large amount of bits than for the other energy fields. When radiative cooling and feedback from galaxy formation are considered, the cosmic gas is overall found to double its degree of complexity. In the future, Cosmic Information Theory can significantly increase our understanding of the emergence of cosmic structure as it represents an innovative framework to design and analyze complex simulations of the Universe in a simple, yet powerful way.

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F. Vazza
Tue, 29 Nov 16
21/77

Comments: 15 pages, 14 figures. MNRAS accepted, in press

Near-exponential surface densities as hydrostatic, nonequilibrium profiles in galaxy discs [GA]

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http://arxiv.org/abs/1609.08957


Apparent exponential surface density profiles are nearly universal in galaxy discs across Hubble types, over a wide mass range, and a diversity of gravitational potential forms. Several processes have been found to produce exponential profiles, including the actions of bars and spirals, and clump scattering, with star scattering a common theme in these. Based on reasonable physical constraints, such as minimal entropy gradients, we propose steady state distribution functions for disc stars, applicable over a range of gravitational potentials. The resulting surface density profiles are generally a power-law term times a Sersic-type exponential. Over a modest range of Sersic index values, these profiles are often indistinguishable from Type I exponentials, except at the innermost radii. However, in certain parameter ranges these steady states can appear as broken, Type II or III profiles. The corresponding velocity dispersion profiles are low order power-laws. A chemical potential associated with scattering can help understand the effects of long range scattering. The steady profiles are found to persist through constant velocity expansions or contractions in evolving discs. The proposed distributions and profiles are simple and solve the stellar hydrodynamic equations. They may be especially relevant to thick discs, which have settled to a steady form via scattering.

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C. Struck and B. Elmegreen
Thu, 29 Sep 16
58/76

Comments: 12 pages, 4 figures, no tables, accepted for the MNRAS

Universal Behavior of X-ray Flares from Black Hole Systems [HEAP]

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http://arxiv.org/abs/1411.4209


X-ray flares have been discovered in black hole systems, such as gamma-ray bursts, the tidal disruption event Swift J1644+57, the supermassive black hole Sagittarius A$^*$ at the center of our Galaxy, and some active galactic nuclei. Their occurrences are always companied by relativistic jets. However, it is still unknown whether there is a physical analogy among such X-ray flares produced in black hole systems spanning nine orders of magnitude in mass. Here we report the observed data of X-ray flares, and show that they have three statistical properties similar to solar flares, including power-law distributions of energies, durations, and waiting times, which both can be explained by a fractal-diffusive self-organized criticality model. These statistical similarities, together with the fact that solar flares are triggered by a magnetic reconnection process, suggest that all of the X-ray flares are consistent with magnetic reconnection events, implying that their concomitant relativistic jets may be magnetically dominated.

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F. Wang, Z. Dai, S. Yi, et. al.
Tue, 18 Nov 14
18/79

Comments: 23 pages, 4 tables, 6 figures. Accepted for publication by ApJS

Self-organized criticality in a spherically closed cellular automaton: Modeling soft gamma repeater bursts driven by magnetic reconnection [HEAP]

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http://arxiv.org/abs/1408.1206


A new cellular automaton (CA) model is presented for the self-organized criticality (SOC) in recurrent bursts of soft gamma repeaters (SGRs), which are interpreted as avalanches of reconnection in the magnetosphere of neutron stars. The nodes of a regular dodecahedron and a truncated icosahedron are adopted as spherically closed grids enclosing a neutron star. It is found that the system enters the SOC state if there are sites where the expectation value of the added perturbation is nonzero. The energy distributions of SOC avalanches in CA simulations are described by a power law with a cutoff, which is consistent with the observations of SGR 1806-20 and SGR 1900+14. The power-law index is not universal and depends on the amplitude of the perturbation. This result shows that the SOC of SGRs can be illustrated not only by the crust quake model but also by the magnetic reconnection model.

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K. Nakazato
Thu, 7 Aug 14
18/46

Comments: 6 pages, 5 figures, accepted for publication in PRD

Self-organisation and non-linear dynamics in driven magnetohydrodynamic turbulent flows [CL]

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http://arxiv.org/abs/1406.3068


Magnetohydrodynamic turbulent flows driven by random mechanical and electromagnetic external forces of zero helicities are investigated by means of direct numerical simulations. It is shown that despite the absence of helicities in the forcing, the system is attracted to self-organized helical states that exhibit laminar behaviour despite the large value of the Reynolds numbers examined. We demonstrate that the correlation time of the external forces is controlling the time spent on these states, i.e. for short correlation times the system remains in the turbulent state while as the correlation time is increased the system spends more and more time in the self-organised states. As a result, time averaged statistics can significantly be affected by the time spent on these states. These results have important theoretical implications for the understanding of the suppression of non-linearities in plasma fusion devises as well as in astrophysical observations.

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V. Dallas and A. Alexakis
Fri, 13 Jun 14
6/46

Comments: 7 pages, 6 figures

The Habitable Zone of Inhabited Planets [EPA]

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http://arxiv.org/abs/1405.4576


In this paper we discuss and illustrate the hypothesis that life substantially alters the state of a planetary environment and therefore, modifies the limits of the HZ as estimated for an uninhabited planet. This hypothesis lead to the introduction of the Habitable Zone for Inhabited planets (hereafter InHZ), defined here as the region where the complex interaction between life and its abiotic environment is able to produce plausible equilibrium states with the necessary physical conditions for the existence and persistence of life itself. We support our hypothesis of an InHZ with three theoretical arguments, multiple evidences coming from observations of the Earth system, several conceptual experiments and illustrative numerical simulations. Conceptually the diference between the InHZ and the Abiotic HZ (AHZ) depends on unique and robust properties of life as an emergent physical phenomenon and not necesarily on the particular life forms bearing in the planet. Our aim here is to provide conceptual basis for the development of InHZ models incorporating consistently life-environment interactions. Although previous authors have explored the effects of life on habitability there is a gap in research developing the reasons why life should be systematically included at determining the HZ limits. We do not provide here definitive limits to the InHZ but we show through simple numerical models (as a parable of an inhabited planet) how the limits of the AHZ could be modified by including plausible interactions between biota and its environment. These examples aim also at posing the question that if limits of the HZ could be modified by the presence of life in those simple dynamical systems how will those limits change if life is included in established models of the AHZ.

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J. Zuluaga, J. Salazar, P. Cuartas-Restrepo, et. al.
Tue, 20 May 14
18/62

Comments: Accepted for publication in Biogeosciences Discussion; 16 pages, 5 figures. Comments and discussion are welcomed at: this http URL

Spatiotemporal organization of energy release events in the quiet solar corona [SSA]

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http://arxiv.org/abs/1404.1086


Using data from STEREO and SOHO spacecraft, we show that temporal organization of energy release events in the quiet solar corona is close to random, in contrast to the clustered behavior of flaring times in solar active regions. The locations of the quiet-Sun events follow the meso- and supergranulation pattern of the underling photosphere. Together with earlier reports of the scale-free event size statistics, our findings suggest that quiet solar regions responsible for bulk coronal heating operate in a driven self-organized critical state, possibly involving long-range Alfv\'{e}nic interactions.

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V. Uritsky and J. Davila
Mon, 7 Apr 14
28/35