How anomalous resistivity accelerates magnetic reconnection

Che, H.

doi:10.1063/1.5000071

Cited by 26 publications

(32 citation statements)

References 87 publications

(103 reference statements)

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“…Given that the four MMS spacecraft recorded powers between 10 and 30 nW/m 3 , we conclude that fast reconnection of at least 0.1 was observed on 22 October. As discussed by Che (), the reconnection rate undoubtedly has a large variation in time as the spacecraft sample highly variable current sheets and may have been even greater, up to values close to 1, during this encounter.…”

Section: Discussionmentioning

confidence: 95%

“…Given that the four MMS spacecraft recorded powers between 10 and 30 nW/m 3 , we conclude that fast reconnection of at least 0.1 was observed on 22 October. As discussed by Che (2017), the reconnection rate undoubtedly has a large variation in time as the spacecraft sample highly variable current sheets and may have been even greater, up to values close to 1, during this encounter. Some other features reported here are not commonly seen in simulations to our knowledge: the smallscale Hall-like current structure at the EDR, and the very sharp reversal of these currents within the current layer, sometimes resulting in a negative value of E || × J || ; the electromagnetic emission in the EDR above the electron gyrofrequency; the enigmatic diamagnetic cavity which does not resemble O-type flux ropes, as reported for example in , but has been observed at other encounters of the EDR .…”

Section: Discussionmentioning

confidence: 97%

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Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal‐Incidence Magnetopause Crossing

et al. 2017

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On 22 October 2016, the Magnetospheric Multiscale (MMS) spacecraft encountered the electron diffusion region (EDR) when the magnetosheath field was southward, and there were signatures of fast reconnection, including flow jets, Hall fields, and large power dissipation. One rapid, normal‐incidence crossing, during which the EDR structure was almost stationary in the boundary frame, provided an opportunity to observe the spatial structure for the zero guide field case of magnetic reconnection. The reconnection electric field was determined unambiguously to be 2–3 mV/m. There were clear signals of fluctuating parallel electric fields, up to 6 mV/m on the magnetosphere side of the diffusion region, associated with a Hall‐like parallel current feature on the electron scale. The width of the main EDR structure was determined to be ~2 km (1.8 de). Although the MMS spacecraft were in their closest tetrahedral separation of ~8 km, the divergences and curls for these thin current structures could therefore not be computed in the usual manner. A method is developed to determine these quantities on a much smaller scale and applied to compute the normal component of terms in the generalized Ohm's law for the positions of each individual spacecraft (not a barocentric average). Although the gradient pressure term has a qualitative dependence that follows the observed variation of E + Ve × B, the quantitative magnitude of these terms differs by more than a factor of 2, which is shown to be greater than the respective errors. Thus, future research is required to find the manner in which Ohm's law is balanced.

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Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 97%

Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal‐Incidence Magnetopause Crossing

et al. 2017

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“…In collisionless plasmas an appropriate model for resistivity can also be determined from Particle-in-Cell simulations (e.g. Che 2017) or by directly integrating Vlasov's kinetic equation (Büchner & Elkina 2005;Büchner & Elkina 2006). In non-relativistic plasmas the effects of anomalous resistivity have been studied extensively, concluding that localized resistivity can enable the fast Petschek (1964) reconnection mechanism (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Relativistic resistive magnetohydrodynamic reconnection and plasmoid formation in merging flux tubes

Ripperda

Porth

Sironi

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We apply the general relativistic resistive magnetohydrodynamics code BHAC to perform a 2D study of the formation and evolution of a reconnection layer in between two merging magnetic flux tubes in Minkowski spacetime. Small-scale effects in the regime of low resistivity most relevant for dilute astrophysical plasmas are resolved with very high accuracy due to the extreme resolutions obtained with adaptive mesh refinement. Numerical convergence in the highly nonlinear plasmoid-dominated regime is confirmed for a sweep of resolutions. We employ both uniform resistivity and nonuniform resistivity based on the local, instantaneous current density. For uniform resistivity we find Sweet-Parker reconnection, from η = 10 −2 down to η = 10 −4 , for a reference case of magnetisation σ = 3.33 and plasma-β = 0.1. For uniform resistivity η = 5 × 10 −5 the tearing mode is recovered, resulting in the formation of secondary plasmoids. The plasmoid instability enhances the reconnection rate to v rec ∼ 0.03c compared to v rec ∼ 0.01c for η = 10 −4 . For non-uniform resistivity with a base level η 0 = 10 −4 and an enhanced current-dependent resistivity in the current sheet, we find an increased reconnection rate of v rec ∼ 0.1c. The influence of the magnetisation σ and the plasma-β is analysed for cases with uniform resistivity η = 5 × 10 −5 and η = 10 −4 in a range 0.5 ≤ σ ≤ 10 and 0.01 ≤ β ≤ 1 in regimes that are applicable for black hole accretion disks and jets. The plasmoid instability is triggered for Lundquist numbers larger than a critical value of S c ≈ 8000.

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“…Since the scale on which these effects operate is not captured in fluid models, we cannot know the 'correct' values of the parameters. However, since resistivity sets the timescale on which the reconnection unfolds, we can fit the parameters to the timescales observed in the corona (∼ 10s -100s) (Che 2017). As a practical convenience, it sets a lower limit on the thickness of any current sheets which form, hence the threshold current j crit is chosen to be higher than that which would occur in a grid-scale current sheet.…”

Section: Lare2dmentioning

confidence: 99%

Forced magnetic reconnection and plasmoid coalescence

Potter

Browning

Gordovskyy

2019

A&A

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Context. Forced magnetic reconnection, a reconnection event triggered by external perturbation, should be ubiquitous in the solar corona. Energy released during such cases can be much greater than that which was introduced by the perturbation. The exact dynamics of magnetic reconnection events are determined by the structure and complexity of the reconnection region: the thickness of reconnecting layers, the field curvature; the presence, shapes and sizes of magnetic islands. It is unclear how the properties of the external perturbation and the initial current sheet affect the reconnection region properties, and thereby the reconnection dynamics and energy release profile. Aims. We investigate the effect of the form of the external perturbation and initial current sheet on the evolution of the reconnection region and the energy release process. Chiefly we explore the non-linear interactions between multiple, simultaneous perturbations, which represent more realistic scenarios. Future work will use these results in test particle simulations to investigate particle acceleration over multiple reconnection events. Methods. Simulations are performed using Lare2d, a 2.5D Lagrangian-remap solver for the visco-resistive MHD equations. The model of forced reconnection is extended to include superpositions of sinusoidal driving disturbances, including localised Gaussian perturbations. A transient perturbation is applied to the boundaries of a region containing a force-free current sheet. The simulation domain is sufficiently wide to allow multiple magnetic islands to form and coalesce. Results. Island coalescence contributes significantly to energy release and involves rapid reconnection. Long wavelength modes in perturbations dominate the evolution, without the presence of which reconnection is either slow, as in the case of short wavelength modes, or the initial current sheet remains stable, as in the case of noise perturbations. Multiple perturbations combine in a highly non-linear manner: reconnection is typically faster than when either disturbance is applied individually, with multiple low-energy events contributing to the same total energy release.

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How anomalous resistivity accelerates magnetic reconnection

Cited by 26 publications

References 87 publications

Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal‐Incidence Magnetopause Crossing

Structure and Dissipation Characteristics of an Electron Diffusion Region Observed by MMS During a Rapid, Normal‐Incidence Magnetopause Crossing

Relativistic resistive magnetohydrodynamic reconnection and plasmoid formation in merging flux tubes

Forced magnetic reconnection and plasmoid coalescence

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