On the retreat of near-Earth neutral line during substorm expansion phase: a THEMIS case study during the 9 January 2008 substorm

Abstract. The location of magnetic reconnection in the mid-tail during a substorm was studied in many researches. Here we present multi-point THEMIS observations of a reconnection event in the near-Earth magnetotail during substorm. In this event, THEMIS probes stayed in the near-Earth and mid-tail region aligning along the magnetotail. This allows reconnection evolution to be probed simultaneously from about −10 RE to −23 RE down tail. The Hall current related electron streams were observed at the same time by two probes far away from the reconnection site. Before near-Earth reconnection involved the tail lobe magnetic field, the reconnection site was restricted in earthward −23 RE. When reconnection involved into the tail lobe region, the reconnection site started to retreat gradually.

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Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ≠ 0 reconnection

Nonlinear Processes in Geophysics ◽

10.5194/npg-9-139-2002 ◽

2002 ◽

Vol 9 (2) ◽

pp. 139-147 ◽

Cited By ~ 2

Author(s):

T. Wiegelmann ◽

J. Büchner

Keyword(s):

Magnetic Field ◽

Magnetic Reconnection ◽

Hall Current ◽

Neutral Line ◽

Magnetic Helicity ◽

Perpendicular Magnetic Field ◽

Guide Field ◽

Magnetic Neutral Line ◽

Field Lines ◽

The Magnetic Field

Abstract. We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ≠ 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ≠ 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B ≠ 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

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Electron Bernstein waves driven by electron crescents near the electron diffusion region

Nature Communications ◽

10.1038/s41467-019-13920-w ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 3

Author(s):

W. Y. Li ◽

D. B. Graham ◽

Yu. V. Khotyaintsev ◽

A. Vaivads ◽

M. André ◽

...

Keyword(s):

Magnetic Reconnection ◽

Hall Current ◽

Neutral Line ◽

Electron Velocity ◽

Diffusion Region ◽

Electron Diffusion ◽

Field Diffusion ◽

Bernstein Waves ◽

Electron Distributions ◽

Current Reversal

AbstractThe Magnetospheric Multiscale (MMS) spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth’s magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. The EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

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Electron Bernstein Waves driven by Electron Crescents near the Electron Diffusion Region

10.5194/egusphere-egu2020-4295 ◽

2020 ◽

Author(s):

Wenya Li ◽

Daniel Graham ◽

Binbin Tang ◽

Andris Vaivads ◽

Mats Andre ◽

...

Keyword(s):

Magnetic Reconnection ◽

Hall Current ◽

Neutral Line ◽

Electron Velocity ◽

Diffusion Region ◽

Electron Diffusion ◽

Field Diffusion ◽

Bernstein Waves ◽

Electron Distributions ◽

Current Reversal

The Magnetospheric Multiscale spacecraft encounter an electron diffusion region (EDR) of asymmetric magnetic reconnection at Earth's magnetopause. The EDR is characterized by agyrotropic electron velocity distributions on both sides of the neutral line. Various types of plasma waves are produced by the magnetic reconnection in and near the EDR. Here we report large-amplitude electron Bernstein waves (EBWs) at the electron-scale boundary of the Hall current reversal. The finite gyroradius effect of the outflow electrons generates the crescent-shaped agyrotropic electron distributions, which drive the EBWs. The EBWs propagate toward the central EDR. The amplitude of the EBWs is sufficiently large to thermalize and diffuse electrons around the EDR. Our analysis shows that the EBWs contribute to the cross-field diffusion of the electron-scale boundary of the Hall current reversal near the EDR.

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The response of ionospheric convection in the polar cap to substorm activity

Annales Geophysicae ◽

10.1007/s00585-995-0147-3 ◽

1995 ◽

Vol 13 (2) ◽

pp. 147-158 ◽

Cited By ~ 5

Author(s):

M. Lester ◽

M. Lockwood ◽

T. K. Yeoman ◽

S. W. H. Cowley ◽

H. Lühr ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Neutral Line ◽

Flow Reversal ◽

Polar Cap ◽

Substorm Current Wedge ◽

Expansion Phase ◽

Ionospheric Convection ◽

Eiscat Radar ◽

Current Wedge

Abstract. We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.

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Magnetic Curvature Analysis on Reconnection Related Structures at Earth’s Magnetopause

10.5194/egusphere-egu2020-3764 ◽

2020 ◽

Author(s):

Yi Qi ◽

Christopher T. Russell ◽

Robert J. Strangeway ◽

Yingdong Jia ◽

Roy B. Torbert ◽

...

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Magnetic Reconnection ◽

Solar Wind Plasma ◽

Radius Of Curvature ◽

Plasma Properties ◽

Magnetospheric Multiscale ◽

Reconnection Site ◽

Field Lines ◽

The Magnetic Field

Magnetic reconnection is a mechanism that allows rapid and explosive energy transfer from the magnetic field to the plasma. The magnetopause is the interface between the shocked solar wind plasma and Earth&#8217;s magnetosphere. Reconnection enables the transport of momentum from the solar wind into Earth&#8217;s magnetosphere. Because of its importance in this regard, magnetic reconnection has been extensively studied in the past and is the primary goal of the ongoing Magnetospheric Multiscale (MMS) mission. During magnetic reconnection, the originally anti-parallel fields annihilate and reconnect in a thinned current sheet. In the vicinity of a reconnection site, a prominently increased curvature of the magnetic field (and smaller radius of curvature) marks the region where the particles start to deviate from their regular gyro-motion and become available for energy conversion. Before MMS, there were no closely separated multi-spacecraft missions capable of resolving these micro-scale curvature features, nor examining particle dynamics with sufficiently fast cadence.In this study, we use measurements from the four MMS spacecraft to determine the curvature of the field lines and the plasma properties near the reconnection site. We use this method to study FTEs (flux ropes) on the magnetopause, and the interaction between co-existing FTEs. Our study not only improves our understanding of magnetic reconnection, but also resolves the relationship between FTEs and structures on the magnetopause.

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Three-dimensional magnetic reconnection through a moving magnetic null

Nonlinear Processes in Geophysics ◽

10.5194/npg-18-871-2011 ◽

2011 ◽

Vol 18 (6) ◽

pp. 871-882 ◽

Cited By ~ 18

Author(s):

V. S. Lukin ◽

M. G. Linton

Keyword(s):

Magnetic Field ◽

Magnetic Reconnection ◽

Computational Study ◽

Pressure Ratio ◽

Three Dimensional ◽

Field Configuration ◽

Modeling Framework ◽

Reconnection Region ◽

Reconnection Site ◽

Magnetic Null

Abstract. A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

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Cluster magnetotail observations of a tailward-travelling plasmoid at substorm expansion phase onset and field aligned currents in the plasma sheet boundary layer

Annales Geophysicae ◽

10.5194/angeo-23-3667-2005 ◽

2005 ◽

Vol 23 (12) ◽

pp. 3667-3683 ◽

Cited By ~ 5

Author(s):

N. C. Draper ◽

M. Lester ◽

S. W. H. Cowley ◽

J.A. Wild ◽

S. E. Milan ◽

...

Keyword(s):

Boundary Layer ◽

Plasma Sheet ◽

Neutral Line ◽

Current System ◽

Onset Time ◽

Plasma Sheet Boundary Layer ◽

Expansion Phase ◽

Magnetometer Data ◽

Reconnection Site ◽

Substorm Onsets

Abstract. We present data from both ground- and space-based instruments for a substorm event which occurred on 5 October 2002, with an expansion phase onset time of 02:50 UT determined from the ground magnetometer data. During this substorm, the Cluster spacecraft were located around 15 RE downtail, 8 RE from midnight in the pre-midnight sector and just 2 RE above the equatorial plane (in GSM coordinates). At expansion phase onset the Cluster spacecraft were located in the plasma sheet, tailward of a near-Earth neutral line and detected a significant time delay of 6 min between the tail field Bz component becoming negative and the subsequent detection of Earthward flows. This is explained by the formation of a tailward-directed travelling compression region initially Earthward of the spacecraft; 7 min later the Cluster spacecraft entered the plasma sheet boundary layer; they remained in and close to the plasma sheet boundary layer for around 15 min before exiting to the lobe. The spacecraft then re-entered the plasma sheet 30 min after onset. Earthward then tailward directed currents detected in the plasma sheet boundary layer after onset indicate that the Cluster spacecraft encountered the dawnward and duskward portions of the reconnection flow associated current system with Region 1 sense, respectively. The reconnection site and current system were initially skewed towards the pre-midnight sector, consistent with previous observations that found the majority of substorm onsets located in this sector. At later times the reconnection site and current system had moved towards dawn, to be located more centrally in the midnight sector.

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“Diffusion” region of magnetic reconnection: electron orbits and the phase space mixing

Annales Geophysicae ◽

10.5194/angeo-36-731-2018 ◽

2018 ◽

Vol 36 (3) ◽

pp. 731-740

Author(s):

Alexey P. Kropotkin

Keyword(s):

Magnetic Field ◽

Phase Space ◽

Electric Field ◽

Magnetic Reconnection ◽

Neutral Line ◽

Collisionless Plasma ◽

Uniform Electric Field ◽

Diffusion Region ◽

Finite Conductivity ◽

The Magnetic Field

Abstract. The nonlinear dynamics of electrons in the vicinity of magnetic field neutral lines during magnetic reconnection, deep inside the “diffusion” region where the electron motion is nonadiabatic, has been numerically analyzed. Test particle orbits are examined in that vicinity, for a prescribed planar two-dimensional magnetic field configuration and with a prescribed uniform electric field in the neutral line direction. On electron orbits, a strong particle acceleration occurs due to the reconnection electric field. Local instability of orbits in the neighborhood of the neutral line is pointed out. It combines with finiteness of orbits due to particle trapping by the magnetic field, and this should lead to the effect of mixing in the phase space, and the appearance of dynamical chaos. The latter may presumably be viewed as a mechanism producing finite “conductivity” in collisionless plasma near the neutral line. That conductivity is necessary to provide violation of the magnetic field frozen-in condition, i.e., for magnetic reconnection to occur in that region. Keywords. Magnetospheric physics (plasma sheet)

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