Search for the magnetic neutral line in the near-Earth plasma sheet 2. Systematic study of Imp 6 magnetic field observations

1977 ◽  
Vol 82 (10) ◽  
pp. 1547-1565 ◽  
Author(s):  
A. T. Y. Lui ◽  
C. -I. Meng ◽  
S. -I. Akasofu
Keyword(s):  
Magnetic Field ◽  
Systematic Study ◽  
Plasma Sheet ◽  
Neutral Line ◽  
Field Observations ◽  
Magnetic Neutral Line

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

2002 ◽  
Vol 9 (2) ◽  
pp. 139-147 ◽  
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.

scholarly journals Observations of flux rope − associated particle bursts with GEOTAIL in the distant tail

1997 ◽  
Vol 15 (12) ◽  
pp. 1515-1531 ◽  
Author(s):  
A. Belehaki ◽  
E. T. Sarris ◽  
G. Tsiropoula ◽  
R. W. McEntire ◽  
S. Kokubun ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Plasma Sheet ◽  
Energetic Particle ◽  
Neutral Line ◽  
Flux Rope ◽  
Closed Field ◽  
The North ◽  
Magnetospheric Configuration And Dynamics ◽  
Substorm Onsets ◽  
Suprathermal Ions

Abstract. Geotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120Re<|XGSM|< 130 Re), associated with moving magnetic field structures, following substorm onsets. The features obtained from this data analysis are consistent with the distant magnetotail dynamics determined first by ISEE3 observations and explained in terms of the neutral line model. At the onset of the bursts, before plasma sheet entrance, energetic electrons appear as a field-aligned beam flowing in the tailward direction, followed by anisotropic ions. Within the flux rope region, suprathermal ions exhibit a convective anisotropy, which allows determination of the plasma flow velocity, assuming that the anisotropy arises from the Compton-Getting effect. The velocities thus determined in the plasma sheet are estimated to be 200–650 km/s, and compare favourably with the velocities derived from the CPI electron and proton experiment. The estimated length of magnetic field structures varies between 28 and 56 Re and depends on the strength of the westward electrojet intensification. Finally, the three structures reported here show clear magnetic field signatures of flux rope topology. The existence of a strong magnetic field aligned approximately along the Y-axis and centred on the north-to-south excursion of the field, and the bipolar signature in both By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure.Key words. Magnetospheric configuration and dynamics · Magnetotail

scholarly journals Planar charged-particle trajectories in multipole magnetic fields

1997 ◽  
Vol 15 (2) ◽  
pp. 197-210 ◽  
Author(s):  
D. M. Willis ◽  
A. R. Gardiner ◽  
V. N. Davda ◽  
V. J. Bone
Keyword(s):  
Magnetic Field ◽  
Charged Particle ◽  
Magnetic Dipole ◽  
Equatorial Plane ◽  
Legendre Function ◽  
Neutral Line ◽  
Radial Distance ◽  
Radius Of Curvature ◽  
Particle Trajectories ◽  
Magnetic Neutral Line

Abstract. This paper provides a complete generalization of the classic result that the radius of curvature (ρ) of a charged-particle trajectory confined to the equatorial plane of a magnetic dipole is directly proportional to the cube of the particle's equatorial distance (ϖ) from the dipole (i.e. ρ ∝ ϖ3). Comparable results are derived for the radii of curvature of all possible planar charged-particle trajectories in an individual static magnetic multipole of arbitrary order m and degree n. Such trajectories arise wherever there exists a plane (or planes) such that the multipole magnetic field is locally perpendicular to this plane (or planes), everywhere apart from possibly at a set of magnetic neutral lines. Therefore planar trajectories exist in the equatorial plane of an axisymmetric (m = 0), or zonal, magnetic multipole, provided n is odd: the radius of curvature varies directly as ϖn+2. This result reduces to the classic one in the case of a zonal magnetic dipole (n =1). Planar trajectories exist in 2m meridional planes in the case of the general tesseral (0 < m < n) magnetic multipole. These meridional planes are defined by the 2m roots of the equation cos[m(Φ – Φnm)] = 0, where Φnm = (1/m) arctan (hnm/gnm); gnm and hnm denote the spherical harmonic coefficients. Equatorial planar trajectories also exist if (n – m) is odd. The polar axis (θ = 0,π) of a tesseral magnetic multipole is a magnetic neutral line if m > 1. A further 2m(n – m) neutral lines exist at the intersections of the 2m meridional planes with the (n – m) cones defined by the (n – m) roots of the equation Pnm(cos θ) = 0 in the range 0 < θ < π, where Pnm(cos θ) denotes the associated Legendre function. If (n – m) is odd, one of these cones coincides with the equator and the magnetic field is then perpendicular to the equator everywhere apart from the 2m equatorial neutral lines. The radius of curvature of an equatorial trajectory is directly proportional to ϖn+2 and inversely proportional to cos[m(Φ – Φnm)]. Since this last expression vanishes at the 2m equatorial neutral lines, the radius of curvature becomes infinitely large as the particle approaches any one of these neutral lines. The radius of curvature of a meridional trajectory is directly proportional to rn+2, where r denotes radial distance from the multipole, and inversely proportional to Pnm(cos θ)/sin θ. Hence the radius of curvature becomes infinitely large if the particle approaches the polar magnetic neutral line (m > 1) or any one of the 2m(n – m) neutral lines located at the intersections of the 2m meridional planes with the (n – m) cones. Illustrative particle trajectories, derived by stepwise numerical integration of the exact equations of particle motion, are presented for low-degree (n ≤ 3) magnetic multipoles. These computed particle trajectories clearly demonstrate the "non-adiabatic'' scattering of charged particles at magnetic neutral lines. Brief comments are made on the different regions of phase space defined by regular and irregular trajectories.

Liquid instability and energy transformation near a magnetic neutral line: a soluble non-linear hydromagnetic problem

1963 ◽  
Vol 271 (1347) ◽  
pp. 435-448 ◽  
Keyword(s):  
Magnetic Field ◽  
Electric Current ◽  
Neutral Line ◽  
Cylinder Axis ◽  
Permanent Magnetic Field ◽  
Stagnation Line ◽  
Small Motion ◽  
Magnetic Neutral Line ◽  
Non Linear ◽  
The Magnetic Field

Hydromagnetic flow of a conducting fluid has a special character near a magnetic neutral line. This is investigated with reference to the two-dimensional motion of a cylinder of perfectly conducting liquid in a permanent magnetic field, of which the axis of the cylinder is a neutral line. Electric current is induced in the liquid by its irrotational motion in the magnetic field. The liquid is uniform, incompressible and frictionless. The surface is elliptically cylindrical, infinitely long, free and in vacuo. The motion is governed by the force exerted on the electric current by the magnetic field, permanent and induced. The stream lines are constant rectangular hyperbolas, in planes normal to the cylinder axis. The permanent magnetic field lines are orthogonal rectangular hyperbolas. The cylinder axis is a stagnation line and a magnetic neutral line. If the liquid is initially at rest, with circular cross-section, and no electric current, its state is unstable. A small motion imparted to it, of the kind indicated, will grow indefinitely, magnetic energy being converted into kinetic energy. The initial motion, however, need not be small. This non-linear hydromagnetic problem is completely soluble. The initial conditions may be chosen in more than one way. The bearing of the solution on the theories of solar flares and the aurora is briefly considered.

scholarly journals Statistical visualization of the Earth's magnetotail based on Geotail data and the implied substorm model

2009 ◽  
Vol 27 (3) ◽  
pp. 1035-1046 ◽  
Author(s):  
S. Machida ◽  
Y. Miyashita ◽  
A. Ieda ◽  
M. Nosé ◽  
D. Nagata ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Plasma Sheet ◽  
Neutral Line ◽  
Substorm Onset ◽  
Start Time ◽  
Superposed Epoch Analysis ◽  
Central Plasma ◽  
Magnetic Neutral Line

Abstract. We investigated the temporal and spatial development of the near-Earth magnetotail during substorms based on multi-dimensional superposed-epoch analysis of Geotail data. The start time of the auroral break-up (t=0) of each substorm was determined from auroral data obtained by the Polar and IMAGE spacecraft. The key parameters derived from the plasma, magnetic-field, and electric-field data from Geotail were sorted by their meridional X(GSM)–Z(proxy) coordinates. The results show that the Poynting flux toward the plasma-sheet center starts at least 10 min before the substorm onset, and is further enhanced at X~−12 RE (Earth radii) around 4 min before the onset. Simultaneously, large-amplitude fluctuations occurred, and earthward flows in the central plasma sheet between X~−11 RE and X~−19 RE and a duskward flow around X=−10 RE were enhanced. The total pressure starts to decrease around X=−16 RE about 4 min before the onset of the substorm. After the substorm onset, a notable dipolarization is observed and tailward flows commence, characterised by southward magnetic fields in the form of a plasmoid. We confirm various observable-parameter variations based on or predicted by the relevant substorm models; however, none of these can explain our results perfectly. Therefore, we propose a catapult (slingshot) current-sheet relaxation model, in which an earthward convective flow produced by catapult current-sheet relaxation and a converted duskward flow near the Earth are enhanced through flow braking around 4 min before the substorm onset. These flows induce a ballooning instability or other instabilities, causing the observed current disruption. The formation of the magnetic neutral line is a natural consequence of the present model, because the relaxation of a highly stretched catapult current-sheet produces a very thin current at its tailward edge being surrounded by intense earthward and tailward magnetic fields which were formerly the off-equatorial lobe magnetic fields. This location is the boundary between a highly stressed catapult current sheet and a Harris-type current sheet characterized by little stress. In addition, the flows induced around the boundary toward the current-sheet center may enhance the formation of the magnetic neutral line and the efficiency of magnetic reconnection. After magnetic reconnection is induced, it plays a significant role in driving the substorm.

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