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

Anastasios Anastasiadis Submitted: 20100927 05:17
The universal character of the dynamics of various extreme phenomena is
an outstanding scientific challenge. We show that Xray 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: 20100928 09:57



Regular and Chaotic Dynamics in 3D Reconnecting Current Sheets 

Anastasios Anastasiadis Submitted: 20060418 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) mirrortype 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: 20060419 10:18



Electron acceleration and radiation in evolving complex active regions 

Anastasios Anastasiadis Submitted: 20040406 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
selforganized 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 Xray 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 Xray spectra of
the energy range 100  1000 keV.
Authors: A. Anastasiadis, C. Gontikakis, N. Vilmer, L. Vlahos
Projects:

Publication Status: A&A 422, 323330, 2004.
Last Modified: 20040709 02:34



Ion heating in an auroral potential structure 

Anastasios Anastasiadis Submitted: 20040227 03:12
We investigate the interaction of O^{+} ions with a
onedimensional potential well, using Hamiltonian formulation.
Heating of plasma originating in the terrestrial ionosphere plays
a catalytic role in solardriven 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 highlatitude
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 monoenergetic 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, 793799 (2004)
Last Modified: 20040510 05:41



MHD consistent cellular automata (CA) models I:Basic features 

Anastasios Anastasiadis Submitted: 20030321 03:26
A setup 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 (selforganized criticality (SOC)) show, among others, that (1) the magnetic field exhibits characteristic largescale organization over the entire modeled volume; (2) the magnitude of the current seems spatially disorganized, with no obvious tendency towards largescale 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 powerlaw
distributions of the released energy persist.
The CA models, extended with the setup, can thus be considered as models for energyrelease through currentdissipation.The concepts of powerlaw loading and anisotropic events (bursts) in CA models are generalized to 3D vectorfield 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: 20030321 03:26



MHD consistent cellular automata (CA) models II: Aplications to solar flares 

Anastasios Anastasiadis Submitted: 20030321 03:21
In Isliker et al. (2000b), an extended cellular automaton (XCA) model for solar flares was introduced. In this model, the interpretation of the model's gridvariable 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 XCA model and in what
form, and what global physical setup is assumed by this model when it is in its natural state (SOC). The basic results are: (1) On largescales, all variables
show characteristic quasisymmetries. (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 smallscale
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 XCA model, the magnitude of the current is used directly in the instability criterion. First results indicate that the SOC state persists. (8) The currentdissipation during flares is spatially fragmented into a large number of dissipative currentsurfaces 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: 20030321 03:21



Acceleration of solar energetic particles: The case of solar flares 

Anastasios Anastasiadis Submitted: 20030321 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. SolarTerrestiral Pys., vol 64(56), 481, 2002.
Last Modified: 20030321 03:11




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