Reconnection in solar flares: Outstanding questions

Isobe, Hiroaki; Shibata, Kazunari

doi:10.1007/s12036-009-0007-8

Cited by 13 publications

(5 citation statements)

References 52 publications

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“…(The terms "large" and "small" amplitude are defined later in this Section.) The exciters identified thus far include Moreton or EIT waves (Eto et al 2002;Okamoto et al 2004;Gilbert et al 2008;Asai et al 2012), EUV waves (Liu et al 2012;Shen et al 2014a;Xue et al 2014;Takahashi et al 2015), shock waves (Shen et al 2014b), nearby jets, subflares and flares (Jing et al 2003(Jing et al , 2006Vršnak et al 2007;, and the eruption of the filament (Isobe & Tripathi 2006;Isobe et al 2007;Pouget 2007;Chen et al 2008;Foullon et al 2009;Bocchialini et al 2011).…”

Section: Introductionmentioning

confidence: 99%

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

Luna

Karpen

Ballester

et al. 2018

ApJS

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We have catalogued 196 filament oscillations from the GONG Hα network data during several months near the maximum of solar cycle 24 (January -June 2014). Selected examples from the catalog are described in detail, along with our statistical analyses of all events. Oscillations were classified according to their velocity amplitude: 106 small-amplitude oscillations (SAOs), with velocities < 10 km s −1 , and 90 large-amplitude oscillations (LAOs), with velocities > 10 km s −1 . Both SAOs and LAOs are common, with one event of each class every two days on the visible side of the Sun. For nearly half of the events we identified their apparent trigger. The period distribution has a mean value of 58±15 min for both types of oscillations. The distribution of the damping time per period peaks at τ /P = 1.75 and 1.25 for SAOs and LAOs respectively. We confirmed that LAO damping rates depend nonlinearly on the oscillation velocity. The angle between the direction of motion and the filament spine has a distribution centered at 27 • for all filament types. This angle agrees with the observed direction of filament-channel magnetic fields, indicating that most of the catalogued events are longitudinal (i.e., undergo field-aligned motions). We applied seismology to determine the average radius of curvature in the magnetic dips, R ≈ 89 Mm, and the average minimum magnetic-field strength, B ≈ 16 G. The catalog is available to the community online, and is intended to be expanded to cover at least 1 solar cycle.

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Section: Introductionmentioning

confidence: 99%

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

Luna

Karpen

Ballester

et al. 2018

ApJS

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“…4(a) that the heat conduction in the physical environment similar to the solar corona will make the reconnection rate higher up to a value that exceeds 0.003 during the plasmoid instability process. On the other hand, according to the observational evidence (Nagashima & Yokoyama 2006;Isobe & Shibata 2009), the estimated reconnection rate is in the range 0.001 − 0.07. Therefore, the global reconnection rate measured from our simulations should be fast enough to explain the solar flares observed in the solar corona.…”

Section: Numerical Results and Discussionmentioning

confidence: 97%

Impact of Temperature-Dependent Resistivity and Thermal Conduction on Plasmoid Instabilities in Current Sheets in the Solar Corona

Roussev

Lin

et al. 2012

ApJ

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In this paper, we investigate, by means of two-dimensional magnetohydrodynamic simulations, the impact of temperature-dependent resistivity and thermal conduction on the development of plasmoid instabilities in reconnecting current sheets in the solar corona. We find that the plasma temperature in the current-sheet region increases with time and it becomes greater than that in the inflow region. As secondary magnetic islands appear, the highest temperature is not always found at the reconnection X-points, but also inside the secondary islands. One of the effects of anisotropic thermal conduction is to decrease the temperature of the reconnecting X-points and transfer the heat into the O-points, the plasmoids, where it gets trapped. In the cases with temperature-dependent magnetic diffusivity, η ∼ T −3/2 , the decrease in plasma temperature at the X-points leads to (1) an increase in the magnetic diffusivity until the characteristic time for magnetic diffusion becomes comparable to that of thermal conduction, (2) an increase in the reconnection rate, and (3) more efficient conversion of magnetic energy into thermal energy and kinetic energy of bulk motions. These results provide further explanation of the rapid release of magnetic energy into heat and kinetic energy seen during flares and coronal mass ejections. In this work, we demonstrate that the consideration of anisotropic thermal conduction and Spitzer-type, temperature-dependent magnetic diffusivity, as in the real solar corona, are crucially important for explaining the occurrence of fast reconnection during solar eruptions.

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“…Sweet-Parker reconnection is extremely slow, even when kinetic effects are accounted for (Comisso & Asenjo, 2014), and it is well known that the solar flares in the sun require reconnection rates orders of magnitude faster than the Sweet-Parker value (e.g. Isobe & Shibata, 2009;Kagan et al, 2015;Galtier, 2016). Therefore, one of the fundamental questions relating to magnetic reconnection is how fast reconnection can take place, which is generally thought to happen via tearing/plasmoid instabilities that cause the current sheet to fragment into a series of magnetic islands (e.g.…”

Section: Magnetic Reconnectionmentioning

confidence: 99%

Particle acceleration in astrophysical jets

Matthews,

Bell,

Blundell

2020

Preprint

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In this chapter, we review some features of particle acceleration in astrophysical jets. We begin by describing four observational results relating to the topic, with particular emphasis on jets in active galactic nuclei and parallels between different sources. We then discuss the ways in which particles can be accelerated to high energies in magnetised plasmas, focusing mainly on shock acceleration, second-order Fermi and magnetic reconnection; in the process, we attempt to shed some light on the basic conditions that must be met by any mechanism for the various observational constraints to be satisfied. We describe the limiting factors for the maximum particle energy and briefly discuss multimessenger signals from neutrinos and ultrahigh energy cosmic rays, before describing the journey of jet plasma from jet launch to cocoon with reference to the different acceleration mechanisms. We conclude with some general comments on the future outlook.

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Reconnection in solar flares: Outstanding questions

Cited by 13 publications

References 52 publications

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

GONG Catalog of Solar Filament Oscillations Near Solar Maximum

Impact of Temperature-Dependent Resistivity and Thermal Conduction on Plasmoid Instabilities in Current Sheets in the Solar Corona

Particle acceleration in astrophysical jets

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