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Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics  

Anastasios Anastasiadis   Submitted: 2010-09-27 05:17

The universal character of the dynamics of various extreme phenomena is an outstanding scientific challenge. We show that X-ray flux and Dst time series during powerful solar flares and intense magnetic storms, respectively, obey a nonextensive energy distribution function for earthquake dynamics with similar values for the Tsallis entropic index q. Thus, evidence for uni- versality in solar flares, magnetic storms and earthquakes arise naturally in the framework of Tsallis statistical mechanics. The observed similarity sug- gests a common approach to the interpretation of these diverse phenomena in terms of driving physical mechanisms that have the same character. Keywords: universality, solar flare, magnetic storm, earthquake dynamics, Tsallis statistics

Authors: G. Balasis, I. A. Daglis, A. Anastasiadis, C. Papadimitriou, M. Mandea, K. Eftaxias
Projects: None

Publication Status: Accepted for publication in : Physica A (2010)
Last Modified: 2010-09-28 09:57
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Using a new set of space-borne particle monitors to investigate solar-terrestrial relations  

Anastasios Anastasiadis   Submitted: 2010-02-18 02:30

Context. We investigated the solar origin of Solar Particle Events (SPEs) which occurred during four time periods of the 23rd solar cycle with intense solar activity and were detected by the Standard Radiation Environment Monitor (SREM) onboard the INTEGRAL satellite. SREM is a second generation ESA particle radiation monitor, already flying onboard seven spacecraft. Aims. The present study attempts to establish the association of recorded SPEs by INTEGRAL/SREM with their solar sources and hence evaluate the potential of SREM units as an alarm system for hazardous SPEs. Methods. X-ray, optical and radio data of solar flares and coronal mass ejections (CMEs) that were observed by several space-based instruments during the aforementioned solar cycle were reduced and thoroughly analyzed to establish the corresponding solar origin of the selected SPEs. Results. The analysis produced clear associations with X-class solar flares and respective CMEs for the events of the October-November 2003, January 2005 and December 2006 periods, while for the events that occurred during September 2005, associations with X-class flares are possible but not straightforward due to the complexity of the registered solar particle fluxes. Conclusions. SREM proves to be a new valuable asset for a comprehensive study of SPEs and a useful alert instrument for explosive geoe ective solar events.

Authors: K. Tziotziou, I. Sandberg, A. Anastasiadis, I.A. Daglis, and P. Nieminen
Projects: RHESSI

Publication Status: A&A (in press) 2010
Last Modified: 2010-02-18 11:37
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Subject will be restored when possible  

Anastasios Anastasiadis   Submitted: 2008-06-19 06:52

The acceleration of charged particles (electrons and protons) in flaring solar active regions is analyzed by numerical experiments. The acceleration is modelled as a stochastic process taking place by the interaction of the particles with local magnetic reconnection sites via multiple steps. Two types of local reconnecting topologies are studied: the Harris-type and the X-point. A formula for the maximum kinetic energy gain in a Harris-type current sheet, found in a previous work of ours, fits well the numerical data for a single step of the process. A generalization is then given approximating the kinetic energy gain through an X-point. In the case of the multiple step process, in both topologies the particles' kinetic energy distribution is found to acquire a practically invariant form after a small number of steps. This tendency is interpreted theoretically. Other characteristics of the acceleration process are given, such as the mean acceleration time and the pitch angle distributions of the particles.

Authors: A. Anastasiadis, C. Gontikakis, C. Efthymiopoulos
Projects: None

Publication Status: Solar Physics (in press)
Last Modified: 2008-06-19 11:26
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Particle Interactions with Single or Multiple 3D SolarReconnecting Current Sheets  

Anastasios Anastasiadis   Submitted: 2008-06-19 06:52

The acceleration of charged particles (electrons and protons) in flaring solar active regions is analyzed by numerical experiments. The acceleration is modelled as a stochastic process taking place by the interaction of the particles with local magnetic reconnection sites via multiple steps. Two types of local reconnecting topologies are studied: the Harris-type and the X-point. A formula for the maximum kinetic energy gain in a Harris-type current sheet, found in a previous work of ours, fits well the numerical data for a single step of the process. A generalization is then given approximating the kinetic energy gain through an X-point. In the case of the multiple step process, in both topologies the particles' kinetic energy distribution is found to acquire a practically invariant form after a small number of steps. This tendency is interpreted theoretically. Other characteristics of the acceleration process are given, such as the mean acceleration time and the pitch angle distributions of the particles.

Authors: A. Anastasiadis, C. Gontikakis, C. Efthymiopoulos
Projects:

Publication Status: Solar Physics (in press)
Last Modified: 2008-09-09 05:48
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Particle distributions and X-ray spectra in single or multiple solar current sheets  

Anastasios Anastasiadis   Submitted: 2007-04-17 02:31

The acceleration of charged particles in a site of magnetic reconnection is analyzed by detailed numerical simulations. Single or multiple encounters of the particles with Harris-type reconnecting current sheets (RCS) are modelled as an overall stochastic process taking place within an active region. RCS physical parameters are selected in a parameter space relevant to solar flares. Initially, the charged particles form a thermal (Maxwellian) distribution corresponding to coronal temperature 2 imes 106 K. Our main goal is to investigate how the acceleration process changes the shape of the particles? kinetic energy distribution. The evolution of the kinetic energy distribution, calculated numerically after one encounter of the particles with a single RCS, is found to be in good agreement with our previously published analytical formulae (Efthymiopoulos et al. 2005, Gontikakis et al. 2006). In the case of consecutive encounters, we find that the kinetic distribution tends to converge to a practically invariant form after a relatively small number of encounters. We construct a discrete stochastic process that reproduces the numerical distributions and we provide a theoretical interpretation of the asymptotic convergence of the energy distribution. We finally compute the theoretical X-ray spectra that would be emitted by the simulated particles in a thick target model of radiation. Keywords: Sun: flares ? acceleration of particles ? radiation mechanisms: nonthermal ? Sun: X-rays, gamma-rays

Authors: C. Gontikakis, A. Anastasiadis and C. Efthymiopoulos
Projects: None

Publication Status: Mont. Not. R. Astr. Soc., (in press), 2007
Last Modified: 2007-04-18 01:52
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Particle acceleration and radiation in flaring complex solar active regions modeled by cellular automata  

Anastasios Anastasiadis   Submitted: 2007-03-06 02:32

Context. We study the acceleration and radiation of electrons and ions interacting with multiple small-scale dissipation regions resulting from the magnetic energy release process. Aims. We aim to calculate the distribution functions of the kinetic energy of the particles and the X-ray spectra and -ray fluxes produced by the accelerated particles. Methods. The evolution of the magnetic energy released in an active region is mimicked by a cellular automaton model based on the concept of self-organized criticality. Each burst of magnetic energy release is associated with a reconnecting current sheet (RCS) in which the particles are accelerated by a direct electric field. Results. We calculate the energy gain of the particles (ions and electrons) for three different magnetic configurations of the RCS after their interactions with a given number of RCS. We finally compare our results with existing observations. Conclusions. The results of our simulation can reproduce several properties of the observations such as variable electron and ion energy contents and -ray line ratio. Even if very flat X-ray spectra have been reported in a few events, the X-ray spectra produced in this model are too flat when compared to most X-ray observations. Key words. Sun: flares ? Sun: X-rays, gamma-rays ? acceleration of particles

Authors: Dauphin C. , Vilmer N. and Anastasiadis, A.
Projects: None

Publication Status: A&A , (in press), 2007
Last Modified: 2007-03-06 13:53
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Regular and Chaotic Dynamics in 3-D Reconnecting Current Sheets  

Anastasios Anastasiadis   Submitted: 2006-04-18 03:02

We consider the possibility of particles being injected at the interior of a reconnecting current sheet (RCS), and study their orbits by dynamical systems methods. As an example we consider orbits in a 3D Harris type RCS. We find that, despite the presence of a strong electric field, a mirror trapping effect persists to certain extent for orbits with appropriate initial conditions within the sheet. The mirror effect is stronger for electrons than for protons. In summary, three types of orbits are distinguished: a) chaotic orbits leading to escapes by stochastic acceleration, b) regular orbits leading to escapes along the field lines of the reconnecting magnetic component, and c) mirror-type regular orbits that are trapped in the sheet, making mirror oscillations. Dynamically, the latter orbits lie on a set of invariant KAM tori that occupy a considerable measure in the phase space of particles' motion. We also observe the phenomenon of stickiness, namely chaotic orbits that remain trapped in the sheet for a considerable time. A trapping domain, related to the boundary of mirror motions in velocity space, is calculated analytically. Analytical formulae are derived for the kinetic energy gain along regular or chaotic escaping orbits. The analytical results are compared with numerical simulations.

Authors: C. Gontikakis, C. Efthymiopoulos, A. Anastasiadis
Projects: None

Publication Status: Mont. Not. R. Astr. Soc, 368(1), 293 - 304, 2006
Last Modified: 2006-04-19 10:18
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Particle dynamics in 3-D reconnecting current sheets in the solar atmosphere  

Anastasios Anastasiadis   Submitted: 2005-11-08 02:56

The orbits of charged particles (electrons and protons), in a Harris-type 3D field topology of a reconnecting current sheet (RCS), are analyzed by dynamical systems methods. The focus is on values of the magnetic and electric fields relevant to RCSs in the solar atmosphere. First, a perturbative form of the equations of motion is used to determine the stability perpendicularly to the plane of reconnection, which is crucial in the efficiency of the RCS as an accelerator. The problem is shown to correspond to a case of ''parametric resonance''. The orbits are then studied with the complete form of the equations of motion. These can be reduced to a two degrees of freedom Hamiltonian nonlinear system by exploiting the existence of an additional integral of motion besides the energy. The orbits are studied analytically by normal form theory. Regular and chaotic orbits are identified by the use of appropriate Poincaré surfaces of section. The kinetic energy gain for escaping particles is calculated as a function of the initial conditions of injection of an orbit in the sheet. Formulae relating the kinetic energy gain to the physical parameters of the sheet and the initial conditions of the orbits are given both for electrons and protons.

Authors: C. Efthymiopoulos, C. Gontikakis, A. Anastasiadis
Projects: None

Publication Status: A&A 443, 663, 2005
Last Modified: 2005-11-08 02:56
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Electron acceleration and radiation in evolving complex active regions  

Anastasios Anastasiadis   Submitted: 2004-04-06 02:23

We present a model for the acceleration and radiation of solar energetic particles (electrons) in evolving complex active regions. The spatio - temporal evolution of active regions is calculated using a cellular automaton model, based on the self-organized criticality. The acceleration of electrons is due to the presence of randomly placed, localized electric fields produced by the energy release process, simulated by the cellular automaton model. We calculate the resulting kinetic energy distributions of the particles and their emitted X-ray radiation spectra, using the thick target approximation and we perform a parametric study with respect to number of electric fields present and the thermal temperature of the injected distribution. Finally, comparing our results with the existing observations, we find that they are in a good agreement with the observed X-ray spectra of the energy range 100 - 1000 keV.

Authors: A. Anastasiadis, C. Gontikakis, N. Vilmer, L. Vlahos
Projects:

Publication Status: A&A 422, 323-330, 2004.
Last Modified: 2004-07-09 02:34
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Ion heating in an auroral potential structure  

Anastasios Anastasiadis   Submitted: 2004-02-27 03:12

We investigate the interaction of O+ ions with a one-dimensional potential well, using Hamiltonian formulation. Heating of plasma originating in the terrestrial ionosphere plays a catalytic role in solar-driven magnetic storms, which dissipate energy globally within the magnetosphere of the earth. An interesting candidate for ionospheric plasma heating is a potential well located at auroral arcs in the high-latitude magnetosphere. We consider a potential with an exponential form, having a characteristic length L_mathrm{x}. The oxygen ions drift towards the auroral arc in the presence of a constant magnetic field B_mathrm{z} and a constant electric field E_mathrm{y}. The orbits of individual ions for different initial conditions - phase angle and kinetic energy - are traced. Our results show that, depending upon the initial conditions, test particles can be either accelerated or decelerated. Furthermore, we perform a parametric study for the interactions of mono-energetic and Maxwellian type of initial ion distribution - using random phase angle injection of the particles - with respect to our main model parameter, the characteristic length of the potential L_mathrm{x}. We conclude that for characteristic lengths comparable to twice the ion gyroradius, the O+ population is accelerated.

Authors: A. Anastasiadis, I, A, Daglis and C. Tsironis
Projects:

Publication Status: A&A, 419, 793-799 (2004)
Last Modified: 2004-05-10 05:41
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MHD consistent cellular automata (CA) models I:Basic features  

Anastasios Anastasiadis   Submitted: 2003-03-21 03:26

A set-up is introduced which can be superimposed onto the existing solar flare cellular automata (CA) models, and which specifies the interpretation of the model's variables. It extends the CA models, yielding the magnetic field, the current, and an approximation to the electric field, in a way that is consistent with Maxwell's and the MHD equations. Applications to several solar flare CA models during their natural state (self-organized criticality (SOC)) show, among others, that (1) the magnetic field exhibits characteristic large-scale organization over the entire modeled volume; (2) the magnitude of the current seems spatially dis-organized, with no obvious tendency towards large-scale structures or even local organization; (3) bursts occur at sites with increased current, and after a burst the current is relaxed; (4) by estimating the energy released in individual bursts with the use of the current as Ohmic dissipation, it turns out that the power-law distributions of the released energy persist. The CA models, extended with the set-up, can thus be considered as models for energy-release through current-dissipation.The concepts of power-law loading and anisotropic events (bursts) in CA models are generalized to 3-D vector-field models, and their effect on the magnetic field topology is demonstrated.

Authors: H. Isliker, A, Anastasiadis, L. Vlahos
Projects:

Publication Status: A&A 363, 1134, 2000
Last Modified: 2003-03-21 03:26
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MHD consistent cellular automata (CA) models II: Aplications to solar flares  

Anastasios Anastasiadis   Submitted: 2003-03-21 03:21

In Isliker et al. (2000b), an extended cellular automaton (X-CA) model for solar flares was introduced. In this model, the interpretation of the model's grid-variable is specified, and the magnetic field, the current, and an approximation to the electric field are yielded, all in a way that is consistent with Maxwell's and the MHD equations. Here, we reveal which relevant plasma physical processes are implemented by the X-CA model and in what form, and what global physical set-up is assumed by this model when it is in its natural state (SOC). The basic results are: (1) On large-scales, all variables show characteristic quasi-symmetries. (2) The global magnetic topology forms either (i) closed magnetic field lines, or (ii) an arcade of field lines above the bottom plane line, if the model is slightly modified. (3) In case of the magnetic topology (ii), loading can be interpreted as if there were a plasma which flows predominantly upwards, whereas in case of the magnetic topology (i), as if there were a plasma flow expanding from the neutral line. (4) The small-scale physics in the bursting phase represent localized diffusive processes. (5) The local diffusivity usually has a value which is effectively zero, and it turns locally to an anomalous value if a threshold is exceeded, whereby diffusion dominates the quiet evolution (loading). (6) Flares (avalanches) are accompanied by the appearance of localized, intense electric fields. (7) In a variant on the X-CA model, the magnitude of the current is used directly in the instability criterion. First results indicate that the SOC state persists. (8) The current-dissipation during flares is spatially fragmented into a large number of dissipative current-surfaces of varying sizes, which show a highly dynamic temporal evolution.

Authors: H. Isliker, A. Anastasiadis, L. Vlahos
Projects:

Publication Status: A&A 377, 1068, 2001.
Last Modified: 2003-03-21 03:21
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Acceleration of solar energetic particles: The case of solar flares  

Anastasios Anastasiadis   Submitted: 2003-03-21 03:09

Solar energetic particles (SEP) are believed to originate from two different sources, solar flares and coronal mass ejections. These two sources are the most energetic particle accelerators in the heliosphere, as they can accelerate electrons from 10 keV to a few MeV and protons from a few MeV to a few GeV. In this contribution, we restrict our presentation to the case of solar flares, by reviewing the key observations of solar energetic particles, as well as the theoretical acceleration models, such as wave - particle acceleration, DC electric fields, and shock acceleration. Finally, we present a new theoretical approach connecting the acceleration with the energy release during solar flares, which might lead to a global modeling of solar flare energetics.

Authors: A. Anastasiadis
Projects:

Publication Status: J. Atmosph. Solar-Terrestiral Pys., vol 64(5-6), 481, 2002.
Last Modified: 2003-03-21 03:11
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Particle acceratation and radiation in an evolving active region based on a CA model  

Anastasios Anastasiadis   Submitted: 2003-03-21 02:59

We present a model for the acceleration and radiation of solar energetic particles (electrons) in an evolving active region. The spatio - temporal evolution of the active region is calculated using a Cellular Automaton (CA) model for the energy release process. The acceleration of particles is due to the presence of randomly placed, localized electric fields. We calculate the resulting kinetic energy distributions of the particles and the emitted radiation by performing a parametric study with respect to the trapping time of the injected distribution.

Authors: A. Anastasiadis, C. Gontikakis, N. Vilmer, L. Vlahos
Projects:

Publication Status: SPM-10 Conference, ESA Publication SP-506, (Ed. A. Wilson), p. 265, 2002.
Last Modified: 2003-03-24 02:31
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Abstracts by Author
Universality in solar flare, magnetic storm and earthquake dynamics using Tsallis statistical mechanics
Using a new set of space-borne particle monitors to investigate solar-terrestrial relations
Subject will be restored when possible
Particle Interactions with Single or Multiple 3D Solar Reconnecting Current Sheets
Particle distributions and X-ray spectra in single or multiple solar current sheets
Particle acceleration and radiation in flaring complex solar active regions modeled by cellular automata
Regular and Chaotic Dynamics in 3-D Reconnecting Current Sheets
Particle dynamics in 3-D reconnecting current sheets in the solar atmosphere
Electron acceleration and radiation in evolving complex active regions
Ion heating in an auroral potential structure
MHD consistent cellular automata (CA) models I:Basic features
MHD consistent cellular automata (CA) models II: Aplications to solar flares
Acceleration of solar energetic particles: The case of solar flares
Particle acceratation and radiation in an evolving active region based on a CA model

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