Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields

Kowal, Grzegorz; Lazarían, A.; Vishniac, Ethan T.; Otmianowska-Mazur, K.

doi:10.1088/0004-637x/700/1/63

Cited by 357 publications

(559 citation statements)

References 98 publications

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“…b, Magnified view of the ion diffusion region and the reconnection jet. Secondary islands and turbulence around the X-line have been found in simulations 18,20,28,29 . Changes in the inflow speed may produce the two reconnection jets 22 that have been observed by Cluster in the downstream region at [−17.2, −6.9, 0.0] R E .…”

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confidence: 76%

“…2c) inside the FPR are attributed to unsteady reconnection, which may be externally driven, for example by perturbations near the magnetopause 22,27 , or internally driven by turbulence and instabilities inside the ion diffusion region 28,29 . A perturbation near the magnetopause can lead to a time-varying inflow speed near the X-line ( Fig.…”

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confidence: 99%

“…1) and then a significant change of the local Alfvén speed 22 that defines the outflow jet speed. Also intrinsic instabilities may cause transient changes in the reconnection rate 29 , leading to drastic changes in the jet speed 28 and the formation of dipolarization fronts.…”

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confidence: 99%

“…Changes in the inflow speed may produce the two reconnection jets 22 that have been observed by Cluster in the downstream region at [−17.2, −6.9, 0.0] R E . Turbulence and secondary islands can also affect the reconnection process 28,29 , and then produce the two reconnection jets as well. c, Schematic showing the speeds of the two reconnection jets.…”

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confidence: 99%

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Energetic electron acceleration by unsteady magnetic reconnection

Fu¹,

Khotyaintsev²,

Vaivads³

et al. 2013

Nature Phys

245

246

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The mechanism that produces energetic electrons during magnetic reconnection is poorly understood. This is a fundamental process responsible for stellar flares 1,2 , substorms 3,4 , and disruptions in fusion experiments 5,6 . Observations in the solar chromosphere 1 and the Earth's magnetosphere 7-10 indicate significant electron acceleration during reconnection, whereas in the solar wind, energetic electrons are absent 11 . Here we show that energetic electron acceleration is caused by unsteady reconnection. In the Earth's magnetosphere and the solar chromosphere, reconnection is unsteady, so energetic electrons are produced; in the solar wind, reconnection is steady 12 , so energetic electrons are absent 11 . The acceleration mechanism is quasi-adiabatic: betatron and Fermi acceleration in outflow jets are two processes contributing to electron energization during unsteady reconnection. The localized betatron acceleration in the outflow is responsible for at least half of the energy gain for the peak observed fluxes.

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confidence: 76%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Energetic electron acceleration by unsteady magnetic reconnection

Fu¹,

Khotyaintsev²,

Vaivads³

et al. 2013

Nature Phys

245

246

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“…Kowal et al (2009) studied numerically the effects of turbulence on magnetic reconnection using three-dimensional direct numerical simulations, and tested the model of fast magnetic reconnection developed by Lazarian and Vishniac (1999). The numerical simulations duplicated the Sweet-Parker CS in the absence of turbulence.…”

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confidence: 99%

Review on Current Sheets in CME Development: Theories and Observations

et al. 2015

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We introduce how the catastrophe model for solar eruptions predicted the formation and development of the long current sheet (CS) and how the observations were used to recognize the CS at the place where the CS is presumably located. Then, we discuss the direct measurement of the CS region thickness by studying the brightness distribution of the CS region at different wavelengths. The thickness ranges from 10 4 km to about 10 5 km at heights between 0.27 and 1.16 R from the solar surface. But the traditional theory indicates that the CS is as thin as the proton Larmor radius, which is of order tens of meters in the corona. We look into the huge difference in the thickness between observations and theoretical expectations. The possible impacts that affect measurements and results are studied, and physical causes leading to a thick CS region in which reconnection can still occur at a reasonably fast rate are analyzed. Studies in both theories and observations suggest that the difference between the true value and the apparent value of the CS thickness is not significant as long as the CS could be recognised in observations. We review observations that show complex structures and flows inside the CS region and present recent numerical modelling results on some aspects of these structures. Both observations and numerical experiments indicate that the downward reconnection outflows are usually slower than the upward ones in the same eruptive event. Numerical simulations show that the complex structure inside CS and its temporal behavior as a result of turbulence and the Petschek-type slow-mode shock could probably account for the thick CS and fast reconnection. But whether the CS itself is that thick still remains unknown since, for the time being, we cannot measure the electric current directly in that region. We also review the most recent laboratory experiments of reconnection driven by energetic laser beams, and discuss some important topics for future works.

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Detection of small‐scale folds at a solar wind reconnection exhaust

2015

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Observations of reconnection in the solar wind over the last few years appear to indicate that the majority of large-scale reconnecting current sheets are roughly planar, and that reconnection itself is quasi-steady. Most studies of solar wind exhausts have used spacecraft with large separations and relatively low time cadence ion measurements. Here we present multipoint Cluster observations of a reconnection exhaust and the associated current sheet at ACE and Wind, enabling it to be studied on multiple length scales and at high time resolution. While analysis shows that on large scales the current sheet is planar, detailed measurements using the four closely spaced Cluster spacecraft show that the trailing edge of the reconnection jet is nonplanar with folds orthogonal to the reconnection plane, with length scales of approximately 230 ion inertial lengths. Our findings thus suggest that while solar wind current sheets undergoing reconnection may be planar on large scales, they may also exhibit complex smaller-scale structure. Such structure is difficult to observe and has rarely been detected because exhausts are rapidly convected past the spacecraft in a single cut; there is therefore a limited set of spacecraft trajectories through the exhaust which would allow the nonplanar features to be intercepted. We consider how such nonplanar reconnection current sheets can form and the processes which may have generated the 3-D structure that was observed.

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Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields

Cited by 357 publications

References 98 publications

Energetic electron acceleration by unsteady magnetic reconnection

Energetic electron acceleration by unsteady magnetic reconnection

Review on Current Sheets in CME Development: Theories and Observations

Detection of small‐scale folds at a solar wind reconnection exhaust

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