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  • Other Sources  (11)
  • 1990-1994  (3)
  • 1985-1989  (8)
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  • 1
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    Magnetic field-aligned electric potentials in nonideal plasma flows (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The electric field component parallel to the magnetic field arising from plasma flows which violate the frozen-in field condition of ideal magnetohydrodynamics is discussed. The quantity of interest is the potential U = integral E parallel ds where the integral is extended along field lines. It is shown that U can be directly related to magnetic field properties, expressed by Euler potentials, even when time-dependence is included. These results are applicable to earth's magnetosphere, to solar flares, to aligned-rotator models of compact objects, and to galactic rotation. On the basis of order-of-magnitude estimates, these results support the view that parallel electric fields associated with nonideal plasma flows might play an important role in cosmic particle acceleration.
    Keywords: PLASMA PHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 380; 293-301
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  • 2
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    On the generation of field-aligned plasma flow at the boundary of the plasma sheet (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A possible cause of the large plasma flow velocities parallel to the magnetic field (which were observed in spacecraft experiments) near the boundary of the plasma sheet in the earth's magnetotail is considered in the framework of a magnetohydrodynamic model. It is shown for steady-state configurations that high parallel flow velocities can be expected to exist on field lines connecting to a region of weak magnetic field. The physical mechanism causing large values of the parallel velocity component can be visualized as a strong imbalance of perpendicular mass flux into and out of magnetic flux tubes passing through regions where the magnetic field is weak and inhomogeneous. The value of the parallel velocity component is evaluated, and it is found that it can substantially exceed the perpendicular velocity (by as much as a factor of 40). The results are applied to the earth's magnetotail; it is found that this mechanism is able to explain the parallel flow velocities near the boundary of the plasma sheet in the range of several hundreds of km/s.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 95-107
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  • 3
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    Magnetotail reconnection, MHD theory and simulations (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Magnetotail reconnection leading to plasmoid formation and ejection is discussed, emphasizing three-dimensional structures and deviations from earlier imposed symmetries, based on MHD simulations and topological considerations. In general, the separation of the plasmoid takes a finite amount of time. During this stage the plasmoid is characterized by filamentary structures of interwoven flux tubes with different topological connections.
    Keywords: PLASMA PHYSICS
    Type: ESA, Proceedings of an International School and Workshop on Reconnection in Space Plasma, Volume 2; p 217-221
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  • 4
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    Flux transfer events: Reconnection without separators (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A topological analysis of a simple model magnetic field of a perturbation at the magnetopause modeling an apparent flux transfer event is presented. It is shown that a localized perturbation at the magnetopause can in principle open a closed magnetosphere by establishing magnetic connections across the magnetopause. Although the model field exhibits neutral points, these are not involved in the magnetic connection of the flux tubes. The topological substructure of a localized perturbation is analyzed in a simpler configuration. The presence of both signs of the magnetic field component normal to the magnetopause leads to a linkage of topologically different flux tubes, described as a flux knot, and a filamentary substructure of field lines of different topological types which becomes increasingly complicated for decreasing magnetic shear at the magnetopause.
    Keywords: PLASMA PHYSICS
    Type: ESA, Proceedings of an International School and Workshop on Reconnection in Space Plasma, Volume 2; p 263-268
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  • 5
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    Filamentary structure of a three-dimensional plasmoid (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The changes of the magnetic field topology and the field line connections are examined in detail using a simple explicit magnetic field model of a plasmoid in different stages from its formation, penetration through a separatrix connected with a distant neutral line, to its complete disconnection. It is shown that complications arise from the fact that separatrix surfaces become very complicated, folded, and filamented in the presence of a small but finite magnetic field in the reconnection region. The filamentary mixing of topologically different field lines may lead to a mixing of different plasma populations as well, and thereby possibly to a more efficient dissipation.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 241-251
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  • 6
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    Nonlinear current sheet formation in ideal plasmas (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present a numerical study of the formation of current sheets in ideal plasmas. First we confirm the development of singular current sheets in a one-dimensional model. In a second step we extend the analysis to two-dimensional equilibria. Here it is found that the resulting structures are quiet insensitive to the boundary conditions. For the special case of a magnetotail like equilibrium it will be shown that the resulting current distribution provides a possibility to understand the onset of a localized anomalous resistivity from a macroscopic point of view. Furthermore, the resulting structures provide an explanation for the dramatic decrease of the thickness of the current sheet in the magnetotail prior to the onset of geomagnetic substorms.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; A11; p. 21,241-21,248
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  • 7
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    Analysis of an extended period of earthward plasma sheet flow at about 220 R(E) - CDAW 8 (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The interpretation of the ISEE 3 earthward flow events observed during an extended period on January 29, 1983 is addressed in terms of a neutral line moving beyond roughly 220 earth radii. This concept was tested for consistency with current magnetospheric and solar wind observations. A broad range of additional data including Dynamics Explorer auroral imaging and a wide variety of ground-based measurements from the eighth Coordinated Data Analysis Workshop (CDAW 8) was available. The distant neutral line location within the context of the distant tail, geostationary orbit, auroral zone, and associated solar wind data is analyzed, based on an extended version of the Coraniti and Kennel (1972) flaring tail theory. It is concluded, from known solar wind conditions that, for a typical neutral line location at about 135 earth radii, an increase of about 30 percent of the near-earth lobe field strength would be required to cause the distant neutral line to move tailward beyond 220 earth radii. The question of why substorms did not terminate the growth phase earlier is also addressed.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 15177-15
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  • 8
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    General magnetic reconnection, parallel electric fields, and helicity (1988)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper considers the concept of magnetic reconnection from a general point of view, with special consideration given to magnetic reconnection in nonvanishing magnetic fields, i.e., finite-B reconnection as distinct from zero-B reconnection. It is shown that the electric field component parallel to the magnetic field (E-parallel) plays a crucial physical role in finite-B reconnection. Two theorems involving E-parallel are proposed. The first defines a necessary and sufficient condition of E-parallel for global reconnection to occur. The second theorem is concerned with the change of magnetic helicity to E-parallel for cases where the electric field vanishes at large distances. The general magnetic reconnection concept is tested by applying it to the process of plasmoid formation process.
    Keywords: PLASMA PHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 93; 5547-555
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  • 9
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    Field-aligned plasma flow in MHD simulations of magnetotail reconnection and the formation of boundary layers (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The outflow from a reconnection region in a realistic magnetotail geometry is studied using a two-dimensional time-dependent, compressible, resistive MHD code. Two cases are emphasized: (1) the evolution of near-earth reconnection, which grows in the form of an internal unstable mode after gradual externally forced changes have initiated an anomalous dissipation process, and (2) the evolution of more distant reconnection under influence of a nonuniform inflow that forces reconnection to occur at a given location in the distant tail. In both cases, it is demonstrated that plasma flow is primarily parallel to the magnetic field in regions away from the localized area of reconnection and outside a narrow central layer.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 11116-11
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  • 10
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    On the influence of an external electric field on magnetotail reconnection (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Magnetotail reconnection is studied under the influence of a dawn to dusk electric field applied at the high-latitude tail boundary using a two-dimensional resistive MHD code. It is found that the basic unstable sequence of tearing and plasmoid formation and ejection was not changed if the external electric field was fairly uniform. The externally forced compression, however, could shorten the onset time and the growth time of the evolution. The faster growth can be understood by the fact that the forced compression gradually alters the lobe field strength and the plasma sheet width and reduces thereby the relevant Alfven time. In fact, if the evolution of the cases with imposed electric field is rescaled on the basis of these characteristic parameters, a good quantitative agreement with the case without external electric field is found.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 8817-882
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