The Coronal Heating Paradox

Aschwanden, Markus J.; Winebarger, Amy R.; Tsiklauri, David; Peter, Hardi

doi:10.1086/513070

Cited by 116 publications

(106 citation statements)

References 60 publications

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“…On one hand, one has to realise, that the obtained results are for an X-point configuration, and naturally, the bulk of solar corona is not made of solely of X-points. On the other hand, it is also known that heating of the active regions would provide circa 82 % of the coronal heating budget [34]. In turn, given the fact that X-points are common occurrence in the active regions, our results seem to be of importance for solving the coronal heating problem.…”

Section: Conclusion and Discussionmentioning

confidence: 52%

Magnetic reconnection during collisionless, stressed, X-point collapse using particle-in-cell simulation

Tsiklauri

Haruki

2007

Physics of Plasmas

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Magnetic reconnection during collisionless, stressed, X-point collapse was studied using kinetic, 2.5D, fully electromagnetic, relativistic Particle-in-Cell numerical code. Two cases of weakly and strongly stressed X-point collapse were considered. Here descriptors weakly and strongly refer to 20 % and 124 % unidirectional spatial compression of the X-point, respectively. In the weakly stressed case, the reconnection rate, defined as the out-of-plane electric field in the X-point (the magnetic null) normalised by the product of external magnetic field and Alfvén speeds, peaks at 0.11, with its average over 1.25 Alfvén times being 0.04. During the peak of the reconnection, electron inflow into the current sheet is mostly concentrated along the separatrices until they deflect from the current sheet on the scale of electron skin depth, with the electron outflow speeds being of the order of the external Alfvén speed. Ion inflow starts to deflect from the current sheet on the ion skin depth scale with the outflow speeds about four times smaller than that of electrons. Electron energy distribution in the current sheet, at the high-energy end of the spectrum, shows a power law distribution with the index varying in time, attaining a maximal value of −4.1 at the final simulation time step (1.25 Alfvén times). In the strongly stressed case, magnetic reconnection peak occurs 3.4 times faster and is more efficient. The peak reconnection rate now attains value 2.5, with the average reconnection rate over 1.25 Alfvén times being 0.5. Plasma inflow into the current sheet is perpendicular to it, with the electron outflow seeds reaching 1.4 Alfvén external Mach number and ions again being about four times slower than electrons. The power law energy spectrum for the electrons in the current sheet attains now a steeper index of −5.5, a value close to the ones observed near X-type region in the Earth's magneto-tail. Within about one Alfvén time, 2% and 20% of the initial magnetic energy is converted into heat and accelerated particle energy in the case of weak and strong stress, respectively. In the both cases, during the peak of the reconnection, the quadruple out-of-plane magnetic field is generated, hinting possibly to the Hall regime of the reconnection. These results strongly suggest the importance of the collisionless, stressed X-point collapse as an efficient mechanism of converting magnetic energy into heat and super-thermal particle energy. I. MOTIVATION OF THE STUDYMagnetic reconnection is an important physical process, which serves as one of the possible ways of converting energy stored in the magnetic field into heat and nonthermal, accelerated, motion of plasma particles. This process operates virtually in all extra-galactic, stellar, solar, space and laboratory plasmas with varied degree of importance. For example, in solar and stellar flares magnetic reconnection plays a key role. In addition, it can be one of the main contributing factors to solar coronal heating problem amongst other mechanisms such as wave dissi...

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Section: Conclusion and Discussionmentioning

confidence: 52%

Magnetic reconnection during collisionless, stressed, X-point collapse using particle-in-cell simulation

Tsiklauri

Haruki

2007

Physics of Plasmas

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“…It also implies that discussions (see, e.g. Aschwanden et al 2007) about the true location of a primary energy release (e.g., upper chromosphere, or lower corona) are not so relevant because the subsequent chromospheric evaporation brings about the very same observable consequences.…”

Section: Discussionmentioning

confidence: 99%

Probing nanoflares with observed fluctuations of the coronal EUV emission

Vekstein

2009

A&A

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Context. Recent analysis of the EUV emission of the solar Active Region observed with TRACE (Sakamoto et al. 2008, ApJ, 689, 1421 revealed fluctuations which are significantly larger than the estimated photon noise and other instrumental effects. This was considered as a signature of a multiple-strand structure of coronal loops that originates from numerous sporadic coronal heating events (nanoflares). Aims. The present Letter aims to put these findings into a broader context of the nanoflare heating scenario. Methods. Simultaneous TRACE and Yohkoh/SXT observations were interpreted by using theoretical predictions of the forward modelling of the nanoflare heating. Results. It is estimated that in the coronal active region impulsive heating events have a typical energy of 10 24 erg with the average occurrence rate of 10 −17 events/cm 2 s. These could result in the hot corona with the filling factor as large as 10%. Conclusions. It is demonstrated that analysis of small fluctuations of the coronal emission can provide a useful tool for probing the mechanism of solar coronal heating.

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“…Some observations suggest that the deposition is largely at the base of the loops (Aschwanden 2001), while others suggest a uniform deposition along the loop (Priest et al 2000). If most of the deposition is at the base of the loop, then the predominant heating mechanism occurs at low heights, for example, reconnection with field lines in the magnetic network or carpet (Priest et al 2002;Aschwanden et al 2007). Note that coronal loops will only be observed if they contain a sufficient density of plasma, as emission scales with the square of the density.…”

Section: Introductionmentioning

confidence: 99%

Self-Organized Braiding and the Structure of Coronal Loops

Berger

Asgari-Targhi

2009

ApJ

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The Parker model for heating of the solar corona involves reconnection of braided magnetic flux elements. Much of this braiding is thought to occur at as yet unresolved scales, for example, braiding of threads within an extremeultraviolet or X-ray loop. However, some braiding may be still visible at scales accessible to TRACE or Hinode. We suggest that attempts to estimate the amount of braiding at these scales must take into account the degree of coherence of the braid structure. In this paper, we examine the effect of reconnection on the structure of a braided magnetic field. We demonstrate that simple models of braided magnetic fields which balance the input of topological structure with reconnection evolve to a self-organized critical state. An initially random braid can become highly ordered, with coherence lengths obeying power-law distributions. The energy released during reconnection also obeys a power law. Our model gives more frequent (but smaller) energy releases nearer to the ends of a coronal loop.

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The Coronal Heating Paradox

Cited by 116 publications

References 60 publications

Magnetic reconnection during collisionless, stressed, X-point collapse using particle-in-cell simulation

Magnetic reconnection during collisionless, stressed, X-point collapse using particle-in-cell simulation

Probing nanoflares with observed fluctuations of the coronal EUV emission

Self-Organized Braiding and the Structure of Coronal Loops

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