Electron-scale nested quadrupole Hall  field in Cluster observations of magnetic reconnection

Abstract. This paper presents the first evidence of a new and unique feature of spontaneous reconnection at multiple sites in electron current sheet, viz. a "nested quadrupole" structure of the Hall field at electron scales, in Cluster observations. The new nested quadrupole is a consequence of electron-scale processes in reconnection. Whistler response of the upstream plasma to the interaction of electron flows from neighboring reconnection sites produces a large-scale quadrupole Hall field enclosing the quadrupole fields of the multiple sites, thus forming a nested structure. Electron-magnetohydrodynamic simulations of an electron current sheet yields a mechanism of the formation of a nested quadrupole.

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Numerical study of the reconnection process between magnetic cloud and heliospheric current sheet

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832951 ◽

2018 ◽

Vol 619 ◽

pp. A82

Author(s):

Man Zhang ◽

Yu Fen Zhou ◽

Xue Shang Feng ◽

Bo Li ◽

Ming Xiong

Keyword(s):

Magnetic Reconnection ◽

Current Sheet ◽

Dynamic Process ◽

Large Scale ◽

Magnetic Cloud ◽

Numerical Study ◽

Three Dimensional ◽

Heliospheric Current Sheet ◽

Reconnection Process ◽

Magnetic Filed

In this paper, we have used a three-dimensional numerical magnetohydrodynamics model to study the reconnection process between magnetic cloud and heliospheric current sheet. Within a steady-state heliospheric model that gives a reasonable large-scale structure of the solar wind near solar minimum, we injected a spherical plasmoid to mimic a magnetic cloud. When the magnetic cloud moves to the heliospheric current sheet, the dynamic process causes the current sheet to become gradually thinner and the magnetic reconnection begin. The numerical simulation can reproduce the basic characteristics of the magnetic reconnection, such as the correlated/anticorrelated signatures in V and B passing a reconnection exhaust. Depending on the initial magnetic helicity of the cloud, magnetic reconnection occurs at points along the boundary of the two systems where antiparallel field lines are forced together. We find the magnetic filed and velocity in the MC have a effect on the reconnection rate, and the magnitude of velocity can also effect the beginning time of reconnection. These results are helpful in understanding and identifying the dynamic process occurring between the magnetic cloud and the heliospheric current sheet.

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Shock heating in numerical simulations of kink-unstable coronal loops

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2014.0266 ◽

2015 ◽

Vol 373 (2042) ◽

pp. 20140266 ◽

Cited By ~ 14

Author(s):

M. R. Bareford ◽

A. W. Hood

Keyword(s):

Magnetic Reconnection ◽

Large Scale ◽

Magnetic Energy ◽

Coronal Loops ◽

Current Sheets ◽

Shock Heating ◽

Strong Current ◽

Coronal Magnetic Fields ◽

Magnetohydrodynamic Simulations ◽

The Magnetic Field

An analysis of the importance of shock heating within coronal magnetic fields has hitherto been a neglected area of study. We present new results obtained from nonlinear magnetohydrodynamic simulations of straight coronal loops. This work shows how the energy released from the magnetic field, following an ideal instability, can be converted into thermal energy, thereby heating the solar corona. Fast dissipation of magnetic energy is necessary for coronal heating and this requirement is compatible with the time scales associated with ideal instabilities. Therefore, we choose an initial loop configuration that is susceptible to the fast-growing kink, an instability that is likely to be created by convectively driven vortices, occurring where the loop field intersects the photosphere (i.e. the loop footpoints). The large-scale deformation of the field caused by the kinking creates the conditions for the formation of strong current sheets and magnetic reconnection, which have previously been considered as sites of heating, under the assumption of an enhanced resistivity. However, our simulations indicate that slow mode shocks are the primary heating mechanism, since, as well as creating current sheets, magnetic reconnection also generates plasma flows that are faster than the slow magnetoacoustic wave speed.

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Filamentary Currents in Turbulent Magnetic Reconnection

10.5194/egusphere-egu2020-12754 ◽

2020 ◽

Author(s):

Meng Zhou ◽

Xiaohua Deng ◽

Zhihong Zhong ◽

Ye Pang

Keyword(s):

Plasma Physics ◽

Magnetic Reconnection ◽

Current Sheet ◽

Coherent Structures ◽

High Speed ◽

Large Scale ◽

Magnetic Energy ◽

Normal Direction ◽

Neutral Sheet ◽

Current Filaments

Magnetic reconnection and turbulence are the two most important energy conversion phenomena in plasma physics. Magnetic reconnection and turbulence are often intertwined. For example, reconnection occurs in thin current layers formed during cascades of turbulence, while reconnection in large-scale current sheet also evolves into turbulence. How energy is dissipated and how particles are accelerated in turbulent magnetic reconnection are outstanding questions in magnetic reconnection and turbulence. Here we report MMS observations of filamentary currents in turbulent outflows in the Earth's magnetotail. We found sub-ion-scale filamentary currents in high-speed outflows that evolved into turbulent states. The normal direction of these current filaments is mainly along the XGSM direction, which is distinct from the neutral sheet. Some filamentary currents were reconnecting, thereby further dissipating the magnetic energy far from the X line. We notice that turbulent reconnection is more efficient in energizing electrons than laminar reconnection. Coherent structures composed of these filaments may be important in accelerating particles during turbulent reconnection. &#160;

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A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet

Annales Geophysicae ◽

10.5194/angeo-27-395-2009 ◽

2009 ◽

Vol 27 (1) ◽

pp. 395-405 ◽

Cited By ~ 2

Author(s):

K. G. Tanaka ◽

K. Haijima ◽

M. Fujimoto ◽

I. Shinohara

Keyword(s):

Electron Temperature ◽

Magnetic Reconnection ◽

Current Sheet ◽

Time Scale ◽

Large Scale ◽

Saturation Level ◽

Small Island ◽

Ion Temperature ◽

Temperature Anisotropy ◽

A Current

Abstract. How to trigger magnetic reconnection is one of the most interesting and important problems in space plasma physics. Recently, electron temperature anisotropy (αeo=Te⊥/Te||) at the center of a current sheet and non-local effect of the lower-hybrid drift instability (LHDI) that develops at the current sheet edges have attracted attention in this context. In addition to these effects, here we also study the effects of ion temperature anisotropy (αio=Ti⊥/Ti||). Electron anisotropy effects are known to be helpless in a current sheet whose thickness is of ion-scale. In this range of current sheet thickness, the LHDI effects are shown to weaken substantially with a small increase in thickness and the obtained saturation level is too low for a large-scale reconnection to be achieved. Then we investigate whether introduction of electron and ion temperature anisotropies in the initial stage would couple with the LHDI effects to revive quick triggering of large-scale reconnection in a super-ion-scale current sheet. The results are as follows. (1) The initial electron temperature anisotropy is consumed very quickly when a number of minuscule magnetic islands (each lateral length is 1.5~3 times the ion inertial length) form. These minuscule islands do not coalesce into a large-scale island to enable large-scale reconnection. (2) The subsequent LHDI effects disturb the current sheet filled with the small islands. This makes the triggering time scale to be accelerated substantially but does not enhance the saturation level of reconnected flux. (3) When the ion temperature anisotropy is added, it survives through the small island formation stage and makes even quicker triggering to happen when the LHDI effects set-in. Furthermore the saturation level is seen to be elevated by a factor of ~2 and large-scale reconnection is achieved only in this case. Comparison with two-dimensional simulations that exclude the LHDI effects confirms that the saturation level enhancement is due to the ion anisotropy effects, while the LHDI effects shorten the overall time scale significantly. The results imply that the ion temperature anisotropy is one of the key properties that enable large-scale magnetic reconnection to develop in a super-ion-scale current sheet.

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Observations of an Electron-only Magnetic Reconnection within a macroscopic Flux Rope in the Magnetotail

10.5194/egusphere-egu2020-2841 ◽

2020 ◽

Author(s):

Hengyan Man ◽

Meng Zhou ◽

Yongyuan Yi ◽

Zhihong Zhong ◽

Xiaohua Deng

Keyword(s):

Electric Field ◽

Magnetic Reconnection ◽

Current Sheet ◽

Large Scale ◽

Energy Transport ◽

Flux Rope ◽

Space Plasmas ◽

Positive Energy ◽

Guide Field ◽

Flux Ropes

It is widely accepted that flux ropes play important roles in the momentum and energy transport in space plasmas. Recent observations found that magnetic reconnection occurs at the interface between two counter flows around the center of flux ropes. In this presentation, we report a novel observation by MMS that reconnection occurs at the edge of a large-scale flux rope, the cross-section of which was about 2.5 Re. The flux rope was observed at the dusk side in Earth&#8217;s magnetotail and was highly oblique with its axis proximity along the XGSM direction. We found an electron-scale current sheet near the edge of this flux rope. The Hall magnetic and electric field, super-Alfv&#233;nic electron outflow, parallel electric field and positive energy dissipation were observed associated with the current sheet. All the above signatures indicate that MMS detected a reconnecting current sheet in the presence of a large guide field. Interestingly, ions were not coupled in this reconnection, akin to the electron-only reconnection observed in the magnetosheath turbulence. We suggest that the electron-scale current sheet was caused by the strong magnetic field perturbation inside the flux rope. This result will shed new lights for understanding the multi-scale coupling associated with flux ropes in space plasmas.

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