Mechanisms of field‐aligned current formation in magnetic reconnection

Ma, Xuanye; Otto, A.

doi:10.1002/jgra.50457

Cited by 17 publications

(23 citation statements)

References 29 publications

(44 reference statements)

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“…Examination of conditional PDFs in the MHD runs (not shown), reveals that, while there may be some association between strong currents and highly-aligned σ jb , the association tends to be stronger in HMHD. Evidence has also been found that the inclusion of the Hall term can generate magnetic field-aligned currents in laminar reconnection [79,80]. the Earth's magnetotail.…”

Section: B Behavior In Real Spacementioning

confidence: 99%

Small-scale behavior of Hall magnetohydrodynamic turbulence

Stawarz

Pouquet

2015

Phys. Rev. E

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Decaying Hall magnetohydrodynamic (HMHD) turbulence is studied using three-dimensional (3D) direct numerical simulations with grids up to 768 3 points and two different types of initial conditions. Results are compared to analogous magnetohydrodynamic (MHD) runs and both Laplacian and Laplacian squared dissipative operators are examined. At scales below the ion inertial length, the ratio of magnetic to kinetic energy as a function of wave number transitions to a magnetically dominated state. The transition in behavior is associated with the advection term in the momentum equation becoming subdominant to dissipation. Examination of autocorrelation functions reveals that, while current and vorticity structures are similarly sized in MHD, HMHD current structures are narrower and vorticity structures are wider. The electric field autocorrelation function is significantly narrower in HMHD than in MHD and is similar to the HMHD current autocorrelation function at small separations. HMHD current structures are found to be significantly more intense than in MHD and appear to have an enhanced association with strong alignment between the current and magnetic field, which may be important in collisionless plasmas where field-aligned currents can be unstable. When hyperdiffusivity is used, a longer region consistent with a k −7/3 scaling is present for right polarized fluctuations when compared to Laplacian dissipation runs.

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Section: B Behavior In Real Spacementioning

confidence: 99%

Small-scale behavior of Hall magnetohydrodynamic turbulence

Stawarz

Pouquet

2015

Phys. Rev. E

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“…The basic mechanism is already present in two-dimensional reconnection [La Belle-Hamer et al, 1995]. It is important to realize that the accumulation of B y flux generates a significant field-aligned current [Ma and Otto, 2013], which in turn can cause reconnection. For instance, the magenta and orange lines in Figure 2 show a moderate field-aligned potential difference (see the Figure 6 (right)).…”

Section: Overall Dynamicsmentioning

confidence: 99%

Interaction of magnetic reconnection and Kelvin‐Helmholtz modes for large magnetic shear: 1. Kelvin‐Helmholtz trigger

Otto

Delamere

2014

JGR Space Physics

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At the Earth's magnetopause, both magnetic reconnection and the Kelvin-Helmholtz (KH) instability can operate simultaneously for southward interplanetary magnetic field conditions. The dynamic evolution of such a system can be expected to depend on the importance of KH wave evolution versus reconnection and therefore on the respective initial perturbations. In this study, a series of local three-dimensional MHD and Hall MHD simulations are carried out to investigate the situation where the Kelvin-Helmholtz instability is initially the primary process. It is demonstrated that magnetic reconnection is driven and strongly modified by nonlinear KH waves. The highest reconnection rate is close to the Petschek rate, but the total open flux is limited by the size of the nonlinear KH wave. Most of the total open magnetic flux has no flux rope structure and originates from reconnection at thin current layers which connect adjacent vortices. In contrast, complex flux ropes generated by patchy reconnection within the KH vortices dominate the vicinity of the equatorial plane; however, the associated open flux with flux ropes is a minor contribution to the total open flux. Although the presence of Hall physics leads to a fast early increase of the reconnection rate, the maximum reconnection rate and the total amount of open magnetic flux at saturation are the same as in the MHD case.

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“…In the presence of plasma flow, magnetic reconnection is associated with the generation of field‐aligned currents (FACs), which play a critical role in the coupling between the magnetosphere and ionosphere [ Ma and Otto , ]. The generation is basically one‐dimensional [ Lin and Lee , ] and has also been demonstrated in two‐dimensional geometry [ La Belle‐Hamer et al , ].…”

Section: Simulation Resultsmentioning

confidence: 99%

“…Field-aligned electric potential difference at t = 20, 48, 90, 104, and 144 for the reference case in a cut at z = 1 close to the equatorial plane. [Ma and Otto, 2013]. The generation is basically one-dimensional [Lin and Lee, 1993] and has also been demonstrated in two-dimensional geometry [La Belle-Hamer et al, 1995].…”

Section: Overall Dynamicsmentioning

confidence: 96%

Interaction of magnetic reconnection and Kelvin‐Helmholtz modes for large magnetic shear: 2. Reconnection trigger

Otto

Delamere

2014

JGR Space Physics

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Citation:Ma, X., A. Otto, and P. A. Delamere (2014) Abstract A typical property of magnetopause reconnection is a significant perpendicular shear flow due to the fast streaming magnetosheath plasma. Therefore, the magnetopause represents a large magnetic and flow shear boundary during periods of southward interplanetary magnetic field, which can be unstable to Kelvin-Helmholtz (KH) modes and to magnetic reconnection. A series of local three-dimensional MHD and Hall MHD simulations is carried out to investigate the interaction of reconnection and nonlinear KH waves considering magnetic reconnection as the primary process. It is demonstrated that the onset reconnection causes a thinning of the shear flow layer, thereby generating small wavelength KH modes. In turn, the growing KH modes modify the current layer width, which modulate the diffusion regions, increase the local reconnection rates, and generate field-aligned currents. The simulation results imply a limitation of total amount of open flux likely caused by nonlinear saturation of KH growth and the associated diffusion. It is also demonstrated that the reconnection rate maximizes for conditions that allow a strong nonlinear evolution of KH waves, i.e., fast shear flow and limited guide magnetic field. The presence of Hall physics increases the reconnection rate in the early stage; however, the maximum reconnection rate and the total amount of open flux at saturation are the same as in the MHD case.

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Mechanisms of field‐aligned current formation in magnetic reconnection

Cited by 17 publications

References 29 publications

Small-scale behavior of Hall magnetohydrodynamic turbulence

Small-scale behavior of Hall magnetohydrodynamic turbulence

Interaction of magnetic reconnection and Kelvin‐Helmholtz modes for large magnetic shear: 1. Kelvin‐Helmholtz trigger

Interaction of magnetic reconnection and Kelvin‐Helmholtz modes for large magnetic shear: 2. Reconnection trigger

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