scholarly journals Current Sheets in Solar Flares

1985 ◽  
Vol 107 ◽  
pp. 233-244
Author(s):  
E. R. Priest
Keyword(s):  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Solar Flares ◽  
Tearing Mode ◽  
Mode Instability ◽  
Current Sheets ◽  
Magnetic Arcade

Until recently magnetic reconnection in solar flares was discussed simplistically in terms of either a spontaneous tearing mode instability or a driven Petschek mode. Now the subtle relationship between these two extremes is much better understood. Current sheets may form and reconnection may be initiated in many different ways. There are also a variety of nonlinear pathways from a reconnection instability and several types of driven reconnection.In solar flares current sheets may be important as new flux emerges from below the photosphere and also as a magnetic arcade closes down after being blown open by an eruptive instability. Numerical simulations of these sheets will be described, including new features such as the presence of a fast shock in Petschek's mechanism and impulsive bursty reconnection due to secondary tearing and coalescence.

scholarly journals Three-dimensional magnetic reconnection and its application to solar flares

2017 ◽  
Vol 83 (1) ◽  
Author(s):  
Miho Janvier
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Magnetic Reconnection ◽  
Solar Flares ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Current Layer ◽  
Solar Observations ◽  
The Universe

Solar flares are powerful radiations occurring in the Sun’s atmosphere. They are powered by magnetic reconnection, a phenomenon that can convert magnetic energy into other forms of energy such as heat and kinetic energy, and which is believed to be ubiquitous in the universe. With the ever increasing spatial and temporal resolutions of solar observations, as well as numerical simulations benefiting from increasing computer power, we can now probe into the nature and the characteristics of magnetic reconnection in three dimensions to better understand the phenomenon’s consequences during eruptive flares in our star’s atmosphere. We review in the following the efforts made on different fronts to approach the problem of magnetic reconnection. In particular, we will see how understanding the magnetic topology in three dimensions helps in locating the most probable regions for reconnection to occur, how the current layer evolves in three dimensions and how reconnection leads to the formation of flux ropes, plasmoids and flaring loops.

scholarly journals THE TEARING MODE INSTABILITY OF THIN CURRENT SHEETS: THE TRANSITION TO FAST RECONNECTION IN THE PRESENCE OF VISCOSITY

2015 ◽  
Vol 801 (2) ◽  
pp. 145 ◽  
Author(s):  
Anna Tenerani ◽  
Antonio Franco Rappazzo ◽  
Marco Velli ◽  
Fulvia Pucci
Keyword(s):  
Tearing Mode ◽  
Mode Instability ◽  
Current Sheets ◽  
Fast Reconnection

scholarly journals Probing Current Sheet Instabilities from Flare Ribbon Dynamics

2021 ◽  
Vol 922 (2) ◽  
pp. 117
Author(s):  
Ryan J. French ◽  
Sarah A. Matthews ◽  
I. Jonathan Rae ◽  
Andrew W. Smith
Keyword(s):  
Solar Flare ◽  
Current Sheet ◽  
Solar Flares ◽  
Spatial Scales ◽  
Tearing Mode ◽  
Scale Growth ◽  
Mode Instability ◽  
Field Lines ◽  
Flare Ribbon ◽  
High Cadence

Abstract The presence of current sheet instabilities, such as the tearing mode instability, are needed to account for the observed rate of energy release in solar flares. Insights into these current sheet dynamics can be revealed by the behavior of flare ribbon substructure, as magnetic reconnection accelerates particles down newly reconnected field lines into the chromosphere to mark the flare footpoints. Behavior in the ribbons can therefore be used to probe processes occurring in the current sheet. In this study, we use high-cadence (1.7 s) IRIS Slit Jaw Imager observations to probe for the growth and evolution of key spatial scales along the flare ribbons—resulting from dynamics across the current sheet of a small solar flare on 2016 December 6. Combining analyses of spatial scale growth with Si iv nonthermal velocities, we piece together a timeline of flare onset for this confined event, and provide evidence of the tearing mode instability triggering a cascade and inverse cascade toward a power spectrum consistent with plasma turbulence.

scholarly journals On the Acceleration Processes in Solar Flares

1975 ◽  
Vol 68 ◽  
pp. 427-439
Author(s):  
Z. Švestka
Keyword(s):  
Solar Flares ◽  
Thermal Process ◽  
Second Step ◽  
Relativistic Electrons ◽  
Type Ii ◽  
Tearing Mode ◽  
Mode Instability ◽  
X Ray ◽  
Mev Protons ◽  
Microwave Bursts

The paper summarizes what we know about the acceleration processes on the Sun. Four different instabilities are distinguished: (1) One with purely thermal consequences giving rise to the origin of any flare. (2) A non-thermal process at the flash phase of flares giving rise to ∼ 100 keV electrons and protons, manifested through hard X-ray and impulsive microwave bursts (current interruption?). (3) An instability giving rise to streams of electrons, without accelerating protons, manifested by type III bursts (tearing-mode instability?). When (2) and (3) are linked, flare associated electron events in space are often recorded. (4) Finally an explosive instability produces a shock wave which manifests itself as a type II burst. This instability leads to a second-step acceleration of particles preaccelerated in (2) and gives origin to >10 MeV protons and relativistic electrons (probably stochastic acceleration).

scholarly journals 3D RESISTIVE MHD SIMULATIONS OF MAGNETIC RECONNECTION AND THE TEARING MODE INSTABILITY IN CURRENT SHEETS

2008 ◽  
Vol 17 (10) ◽  
pp. 1715-1721 ◽  
Author(s):  
G. C. MURPHY ◽  
R. OUYED ◽  
G. PELLETIER
Keyword(s):  
Kinetic Energy ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Critical Role ◽  
Temporal Stability ◽  
High Energy ◽  
Linear Regime ◽  
Tearing Mode ◽  
Mode Instability ◽  
Mhd Simulations

Magnetic reconnection plays a critical role in many astrophysical processes where high energy emission is observed, e.g. particle acceleration, relativistic accretion powered outflows, pulsar winds and probably in dissipation of Poynting flux in GRBs. The magnetic field acts as a reservoir of energy and can dissipate its energy to thermal and kinetic energy via the tearing mode instability. We have performed 3D nonlinear MHD simulations of the tearing mode instability in a current sheet. Results from a temporal stability analysis in both the linear regime and weakly nonlinear (Rutherford) regime are compared to the numerical simulations. We observe magnetic island formation, island merging and oscillation once the instability has saturated. The growth in the linear regime is exponential in agreement with linear theory. In the second, Rutherford regime the island width grows linearly with time. We find that thermal energy produced in the current sheet strongly dominates the kinetic energy. Finally preliminary analysis indicates a P(k) 4.8 power law for the power spectral density which suggests that the tearing mode vortices play a role in setting up an energy cascade.

scholarly journals Suppression of neoclassical tearing mode instability at the initial stage by electron cyclotron current drive

AIP Advances ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 035212
Author(s):  
Zhen Yang ◽  
Bin Wu ◽  
Yuanlai Xie ◽  
Yuqing Chen ◽  
Hongming Zhang ◽  
...  
Keyword(s):  
Electron Cyclotron ◽  
Current Drive ◽  
Tearing Mode ◽  
Mode Instability ◽  
Initial Stage ◽  
Neoclassical Tearing Mode
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