scholarly journals Flare particle acceleration in the interaction of twisted coronal flux ropes

2018 ◽  
Vol 611 ◽  
pp. A40 ◽  
Author(s):  
J. Threlfall ◽  
A. W. Hood ◽  
P. K. Browning
Keyword(s):  
Particle Acceleration ◽  
Solar Flares ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Uniform Background ◽  
Energy Gains ◽  
Particle Behaviour

Aim. The aim of this work is to investigate and characterise non-thermal particle behaviour in a three-dimensional (3D) magnetohydrodynamical (MHD) model of unstable multi-threaded flaring coronal loops.Methods. We have used a numerical scheme which solves the relativistic guiding centre approximation to study the motion of electrons and protons. The scheme uses snapshots from high resolution numerical MHD simulations of coronal loops containing two threads, where a single thread becomes unstable and (in one case) destabilises and merges with an additional thread.Results. The particle responses to the reconnection and fragmentation in MHD simulations of two loop threads are examined in detail. We illustrate the role played by uniform background resistivity and distinguish this from the role of anomalous resistivity using orbits in an MHD simulation where only one thread becomes unstable without destabilising further loop threads. We examine the (scalable) orbit energy gains and final positions recovered at different stages of a second MHD simulation wherein a secondary loop thread is destabilised by (and merges with) the first thread. We compare these results with other theoretical particle acceleration models in the context of observed energetic particle populations during solar flares.

scholarly journals Can Multi-threaded Flux Tubes in Coronal Arcades Support a Magnetohydrodynamic Avalanche?

Solar Physics ◽  
2021 ◽  
Vol 296 (8) ◽  
Author(s):  
J. Threlfall ◽  
J. Reid ◽  
A. W. Hood
Keyword(s):  
Magnetic Fields ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Flux Tubes ◽  
Single Thread ◽  
Mhd Instabilities ◽  
Mhd Instability ◽  
Mhd Simulations ◽  
Ideal Mhd ◽  
Model Geometry

AbstractMagnetohydrodynamic (MHD) instabilities allow energy to be released from stressed magnetic fields, commonly modelled in cylindrical flux tubes linking parallel planes, but, more recently, also in curved arcades containing flux tubes with both footpoints in the same photospheric plane. Uncurved cylindrical flux tubes containing multiple individual threads have been shown to be capable of sustaining an MHD avalanche, whereby a single unstable thread can destabilise many. We examine the properties of multi-threaded coronal loops, wherein each thread is created by photospheric driving in a realistic, curved coronal arcade structure (with both footpoints of each thread in the same plane). We use three-dimensional MHD simulations to study the evolution of single- and multi-threaded coronal loops, which become unstable and reconnect, while varying the driving velocity of individual threads. Experiments containing a single thread destabilise in a manner indicative of an ideal MHD instability and consistent with previous examples in the literature. The introduction of additional threads modifies this picture, with aspects of the model geometry and relative driving speeds of individual threads affecting the ability of any thread to destabilise others. In both single- and multi-threaded cases, continuous driving of the remnants of disrupted threads produces secondary, aperiodic bursts of energetic release.

scholarly journals Making Faranoff-Riley I radio sources

2019 ◽  
Vol 621 ◽  
pp. A132 ◽  
Author(s):  
S. Massaglia ◽  
G. Bodo ◽  
P. Rossi ◽  
S. Capetti ◽  
A. Mignone
Keyword(s):  
Low Power ◽  
Constant Pressure ◽  
Three Dimensional ◽  
Stratified Medium ◽  
Radio Sources ◽  
Wide Angle ◽  
Mhd Simulations ◽  
The Universe ◽  
Nonrelativistic Velocity

Radio sources of low power are the most common in the universe. Their jets typically move at nonrelativistic velocity and show plume-like morphologies that in many instances appear distorted and bent. We investigate the role of magnetic field on the propagation and evolution of low-power jets and the connection between the field intensity and the resulting morphology. The problem is addressed by means of three-dimensional magnetohydrodynamic (MHD) simulations. We consider supersonic jets that propagate in a stratified medium. The ambient temperature increases with distance from the jet origin maintaining constant pressure. Jets with low magnetization show an enhanced collimation at small distances with respect to hydrodynamic (HD) cases studied in a previous paper. These jets eventually evolve in a way similar to the HD cases. Jets with higher magnetization are affected by strong nonaxisymmetric modes that lead to the sudden jet energy release. From there on, distorted plumes of jet material move at subsonic velocities. This transition is associated with the formation of structures reminiscent of the “warm spots” observed in wide-angle-tail (WAT) sources.

scholarly journals The role of streamers in the deflection of coronal mass ejections

2011 ◽  
Vol 7 (S286) ◽  
pp. 134-138
Author(s):  
F. P. Zuccarello ◽  
A. Bemporad ◽  
C. Jacobs ◽  
M. Mierla ◽  
S. Poedts ◽  
...  
Keyword(s):  
Current Sheet ◽  
Three Dimensional ◽  
Heliospheric Current Sheet ◽  
Field Of View ◽  
Physical Explanation ◽  
Filament Eruption ◽  
Mhd Simulations ◽  
Radial Evolution ◽  
Mass Ejection

AbstractOn 2009 September 21, a filament eruption and the associated Coronal Mass Ejection (CME) was observed by the STEREO spacecraft. The CME originated from the southern hemisphere and showed a deflection of about 15° towards the heliospheric current sheet (HCS) during its propagation in the COR1 field-of-view (FOV). The aim of this paper is to provide a physical explanation for the strong deflection of the CME. We first use the STEREO observations in order to reconstruct the three dimensional (3D) trajectory of the CME. Starting from a magnetic configuration that closely resembles the potential field extrapolation for that date, we performed numerical magneto-hydrodynamics (MHD) simulations. By applying localized shearing motions, a CME is initiated in the simulation, showing a similar non-radial evolution, structure, and velocity as the observed event. The CME gets deflected towards the current sheet of the larger northern helmet streamer, due to an imbalance in the magnetic pressure and tension forces and finally it gets into the streamer and propagates along the heliospheric current sheet.

scholarly journals Three-dimensional MHD simulations of molecular cloud fragmentation regulated by gravity, ambipolar diffusion, and turbulence

2008 ◽  
Vol 4 (S259) ◽  
pp. 115-116
Author(s):  
Takahiro Kudoh ◽  
Shantanu Basu
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Time Scale ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Three Dimensional ◽  
Core Formation ◽  
Mhd Simulations ◽  
Dimensional Simulation

AbstractWe find that the star formation is accelerated by the supersonic turbulence in the magnetically dominated (subcritical) clouds. We employ a fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally driven fragmentation of molecular clouds. The time-scale of collapsing core formation in subcritical clouds is a few ×107 years when starting with small subsonic perturbations. However, it is shortened to approximately several ×106 years by the supersonic flows in the clouds. We confirm that higher-spacial resolution simulations also show the same result.

A Discussion on the physics of the solar atmosphere - Solar flares

1976 ◽  
Vol 281 (1304) ◽  
pp. 507-513 ◽  
Keyword(s):  
Magnetic Field ◽  
Particle Acceleration ◽  
Observational Data ◽  
Time Scales ◽  
Solar Atmosphere ◽  
Flux Tube ◽  
Solar Flares ◽  
Field Configuration ◽  
Magnetic Field Configuration

A summary is given of some recent observational data on solar flares. Particularly we discuss the flare build-up process and the time scales involved. We suggest as a possible magnetic field configuration a multiply kinked or supertwisted flux tube. The role of plasma turbulence and the Fermi mechanism in particle acceleration is discussed.

scholarly journals Evolution of auroral substorm as viewed from MHD simulations: dynamics, energy transfer and energy conversion

2020 ◽  
Vol 4 (1) ◽  
Author(s):  
Yusuke Ebihara ◽  
Takashi Tanaka
Keyword(s):  
Energy Transfer ◽  
Large Scale ◽  
A Priori ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
The Earth ◽  
Auroral Substorm ◽  
Transient Disturbances ◽  
Global Mhd Simulation

AbstractAn auroral substorm is a visual manifestation of large-scale, transient disturbances taking place in space surrounding the Earth, and is one of the central issues in the space plasma physics. While a number of studies have been conducted, a unified picture of the overall evolution of the auroral substorm has not been drawn. This paper is aimed to overview the recently obtained results of global magnetohydrodynamics (MHD) simulations in a context of a priori presence of anomalous resistivity leading to magnetic reconnection, and to illuminate what the global MHD simulation can sufficiently reproduce the auroral transients during the auroral substorm. Some auroral transients are found to be seamlessly reproduced by the MHD simulation, including complicated auroral structures moving equatorward during the growth phase, auroral brightening starting to appear near the equatorward border of the preexisting auroral arc, and an auroral surge traveling westward. Possible energy transfer and conversion from the solar wind to the Earth are also overviewed on the basis of the MHD simulation. At least, 4 dynamo regions appear sequentially in the course of the development of the auroral substorm. Although the MHD simulation reproduces some transients, further studies are needed to investigate the role of kinetic processes.

scholarly journals Particle acceleration with anomalous pitch angle scattering in 3D separator reconnection

2020 ◽  
Vol 635 ◽  
pp. A63
Author(s):  
A. Borissov ◽  
T. Neukirch ◽  
E. P. Kontar ◽  
J. Threlfall ◽  
C. E. Parnell
Keyword(s):  
Particle Acceleration ◽  
Magnetic Reconnection ◽  
Test Particle ◽  
Pitch Angle ◽  
High Energy ◽  
Energy Spectra ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Angle Scattering ◽  
Particle Orbits

Context. Understanding how the release of stored magnetic energy contributes to the generation of non-thermal high energy particles during solar flares is an important open problem in solar physics. There is a general consensus that magnetic reconnection plays a fundamental role in the energy release and conversion processes taking place during flares. A common approach for investigating how reconnection contributes to particle acceleration is to use test particle calculations in electromagnetic fields derived from numerical magnetohydrodynamic (MHD) simulations of reconnecting magnetic fields. These MHD simulations use anomalous resistivities that are orders of magnitude larger than the Spitzer resistivity that is based on Coulomb collisions. The processes leading to such an enhanced resistivity should also affect the test particles, for example, through pitch angle scattering. This study explores the effect of such a link between the level of resistivity and its impact on particle orbits and builds on a previous study using a 2D MHD simulation of magnetic reconnection. Aims. This paper aims to extend the previous investigation to a 3D magnetic reconnection configuration and to study the effect on test particle orbits. Methods. We carried out orbit calculations using a 3D MHD simulation of reconnection in a magnetic field with a magnetic separator. The orbit calculations use the relativistic guiding centre approximation but, crucially, they also include pitch angle scattering using stochastic differential equations. The effects of varying the resistivity and the models for pitch angle scattering on particle orbit trajectories, final positions, energy spectra, final pitch angle distribution, and orbit duration are all studied in detail. Results. Pitch angle scattering widens highly collimated beams of unscattered orbit trajectories, allowing orbits to access previously unaccessible field lines; this causes final positions to spread along other topological structures which could not be accessed without scattering. Scattered orbit energy spectra are found to be predominantly affected by the level of anomalous resistivity, with the pitch angle scattering model only playing a role in specific, isolated cases. This is in contrast to the study involving a 2D MHD simulation of magnetic reconnection, where pitch angle scattering had a more noticeable effect on the energy spectra. Pitch scattering effects are found to play a crucial role in determining the pitch angle and orbit duration distributions.

scholarly journals Three-Dimensional Simulation Study of Plasmoid Injection into Magnetized Plasma

1998 ◽  
Vol 188 ◽  
pp. 209-210
Author(s):  
Y. Suzuki ◽  
T.-H. Watanabe ◽  
A. Kageyama ◽  
T. Sato ◽  
T. Hayashi
Keyword(s):  
Solar Wind ◽  
Simulation Study ◽  
Solar Flares ◽  
Interplanetary Medium ◽  
Three Dimensional ◽  
Magnetized Plasma ◽  
Important Process ◽  
Plasma Region ◽  
Mhd Simulations ◽  
Dimensional Simulation

Resent observations suggest that, during solar flares, plasmoids are injected into the interplanetary medium (Stewart et al., 1982). It has also been pointed out that solar wind irregularities modeled as plasmoids are penetrated into the magnetosphere (Lemaire, 1977). These plasmoid injections are considered to be an important process because they transfer mass, momentum, and energy into such magnetized plasma regions. Our objective is to investigate the dynamics of a plasmoid, which is injected into a magnetized plasma region and to reveal mechanisms to transfer them. To achieve this, we carried out three-dimensional magnetohydrodynamic (MHD) simulations.

scholarly journals Resistive Processes in the Preflare Phase of Eruptive Flares

1998 ◽  
Vol 188 ◽  
pp. 207-208
Author(s):  
T. Magara ◽  
K. Shibata
Keyword(s):  
Current Sheet ◽  
Current Density ◽  
Solar Flares ◽  
Magnetic Pressure ◽  
Anomalous Resistivity ◽  
Magnetic Island ◽  
Tearing Instability ◽  
Mhd Simulations ◽  
A Current

In this study, we perform 2.5-dimensional MHD simulations and clarify the role of perpendicular magnetic fields (which are perpendicular to the 2D plane) in a preflare current sheet of solar flares. At the first stage, a current sheet formed within a coronal magnetic structure is filled with the perpendicular fields (force-free structure). Then this sheet begins to be dissipated through the tearing instability under a uniform resistivity. As the instability proceeds, the distribution of the perpendicular fields vary in such a way that most of them gather around O-point (magnetic island) instead of X-point. Therefore, the magnetic pressure of these fields weaken in the vicinity of X-point so that they no longer suppress the inflows toward this point. These flows then make the current sheet thinner and thinner, which implies that the current density around X-point becomes high enough to cause an anomalous resistivity whose value is much larger than that of the normal collisional resistivity. In this way, the transition from a uniform resistivity to a locally-enhanced one occurs, which can make the violent energy release observed in solar flares.

scholarly journals Three-dimensional flow near a reconnection site at the dayside magnetopause: analytical solutions coupled with MHD simulations

2007 ◽  
Vol 73 (6) ◽  
pp. 811-819 ◽  
Author(s):  
LARS G. WESTERBERG ◽  
J. VEDIN ◽  
A. EKENBÄCK ◽  
H. O. ÅKERSTEDT
Keyword(s):  
Plasma Flow ◽  
Three Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Three Dimensional Flow ◽  
Mhd Simulation ◽  
Mhd Simulations ◽  
Dayside Magnetopause ◽  
Global Mhd Simulation ◽  
Reconnection Site

AbstractWe present a coupling between an analytical three-dimensional model covering the plasma flow behaviour through the magnetopause transition layer near a reconnection site, with results from a global MHD simulation describing the plasma flow in the magnetosheath. The structure of the plasma flow near a reconnection site at the dayside terrestrial magnetopause is investigated, together with the development of the magnetopause transition region.

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