Observational support for the current sheet catastrophe model of substorm current disruption

Abstract. Using a fully 3-D particle in-cell simulation, we studied the electrodynamics of a thin current sheet (CS). Starting with a uniform plasma and anti-parallel magnetic field, Harris equilibrium is achieved during the early stage of the simulation. In the processes of reaching the equilibrium, both electrons and ions in the newly formed CS are energized and develop pitch-angle anisotropies. We find two distinct stages of primarily electrostatic instabilities; in the first stage the relative drift between electrons and ions drives the instability in the central regions of the CS. The electrostatic fluctuations scatter electrons causing current disruption in the central region. The associated reduction in the average drift velocity of the current-carrying electrons generates sheared flow. The second stage of the instability begins when the drift velocity develops a minimum in the central plane. Then the shear and the growing electrostatic fluctuations under the condition of the maintained anti-parallel driving magnetic field configuration feed each other making the instability explosive. The growing fluctuations create plasma clumps as the electrons and ions are progressively trapped in the large-amplitude waves. The density clumping also generates clumps in the current. The non-uniform current distribution causes magnetic reconnection, accompanied by heating of electrons and ion at a fast rate and nearly complete bifurcation of the current sheet. Anomalous resistivity during different stages of the evolution of the CS is calculated and compared against theory.

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Ion temperature drop and quasi-electrostatic electric field at the current sheet boundary minutes prior to the local current disruption

Journal of Geophysical Research Atmospheres ◽

10.1029/2009ja014357 ◽

2009 ◽

Vol 114 (A10) ◽

pp. n/a-n/a ◽

Cited By ~ 11

Author(s):

Jun Liang ◽

W. W. Liu ◽

E. F. Donovan

Keyword(s):

Electric Field ◽

Current Sheet ◽

Temperature Drop ◽

Ion Temperature ◽

Current Disruption ◽

Local Current

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Disruption of magnetospheric current sheet by quasi-electrostatic field

Annales Geophysicae ◽

10.5194/angeo-27-1941-2009 ◽

2009 ◽

Vol 27 (5) ◽

pp. 1941-1950 ◽

Cited By ~ 12

Author(s):

W. W. Liu ◽

J. Liang

Keyword(s):

Current Sheet ◽

Drift Velocity ◽

Electrostatic Field ◽

Numerical Solutions ◽

External Perturbation ◽

Ion Drift ◽

Current Disruption ◽

Local Current ◽

Fluid Theory ◽

Two Fluid

Abstract. Recent observational evidence has indicated that local current sheet disruptions are excited by an external perturbation likely associated with the kinetic ballooning (KB) instability initiating at the transition region separating the dipole- and tail-like geometries. Specifically a quasi-electrostatic field pointing to the neutral sheet was identified in the interval between the arrival of KB perturbation and local current disruption. How can such a field drive the local current sheet unstable? This question is considered through a fluid treatment of thin current sheet (TCS) where the generalized Ohm's law replaces the frozen-in-flux condition. A perturbation with the wavevector along the current is applied, and eigenmodes with frequency much below the ion gyrofrequency are sought. We show that the second-order derivative of ion drift velocity along the thickness of the current sheet is a critical stability parameter. In an E-field-free Harris sheet in which the drift velocity is constant, the current sheet is stable against this particular mode. As the electrostatic field grows, however, potential for instability arises. The threshold of instability is identified through an approximate analysis of the theory. For a nominal current sheet half-thickness of 1000 km, the estimated instability threshold is E~4 mV/m. Numerical solutions indicate that the two-fluid theory gives growth rate and wave period consistent with observations.

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Electrodynamics in a very thin current sheet leading to magnetic reconnection

Nonlinear Processes in Geophysics ◽

10.5194/npg-13-509-2006 ◽

2006 ◽

Vol 13 (5) ◽

pp. 509-523 ◽

Cited By ~ 8

Author(s):

N. Singh ◽

C. Deverapalli ◽

G. Khazanov

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Electron Temperature ◽

Magnetic Reconnection ◽

Current Sheet ◽

Electron Mass ◽

Angle Distribution ◽

Current Disruption ◽

Thin Current Sheet ◽

The Magnetic Field

Abstract. We study the formation of a very thin current sheet (CS) and associated plasma electrodynamics using three-dimensional (3-D) particle-in-cell simulations with ion to electron mass ratio M/m=1836. The CS is driven by imposed anti-parallel magnetic fields. The noteworthy features of the temporal evolution of the CS are the following: (i) Steepening of the magnetic field profile Bx(z) in the central part of the CS, (ii) Generation of three-peak current distribution with the largest peak in the CS center as Bx(z) steepens, (iii) Generation of converging electric fields forming a potential well in the CS center in which ions are accelerated. (iv) Electron and ion heating in the central part of the CS by current-driven instabilities (CDI). (v) Re-broadening of the CS due to increased kinetic plasma pressure in the CS center. (vi) Generation of electron temperature anisotropy with temperature perpendicular to the magnetic field being larger than the parallel one. (vii) Current disruption by electron trapping in an explosively growing electrostatic instability (EGEI) and electron tearing instability (ETI). (viii)The onset of EGEI coincides with an increase in the electron temperature above the temperature of the initially hot ions as well as the appearance of new shear in the electron drift velocity. (ix) Bifurcation of the central CS by the current disruption. (x) Magnetic reconnection (MR) beginning near the null in Bx and spreading outward. (xi) Generation of highly energized electrons reaching relativistic speeds and having isotropic pitch-angle distribution in the region of reconnected magnetic fields. We compare some of these features of the current sheet with results from laboratory and space experiments.

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