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  • 1
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical models of magnetic reconnection are reviewed with a critical view of their suitability for astrophysical plasmas, with a focus on those sampled plasmas near the magnetopause. Frequently the approximations are more those of convenience than physically justified. It is concluded that magnetic reconnection cannot be qualitatively or quantitatively addressed with any one fluid MHD picture unless the Hall, ambipolar and inertial emfs are included in the Generalized Ohm's Law. The observed size of electron pressure anisotropies ensures that the thawing of magnetic flux is almost always determined by the often neglected ambipolar term of the Generalized Ohm's Law. Thus resistive MHD or even resistive Hall MHD cannot possibly give a correct structural picture of the reconnection current carrying layer at the magnetopause. In the magnetotail the ion inertial "resistivity" is much larger than coulomb resistivity with a similar structural form as the coulomb emf. However, until recently the ambipolar contributions there have not been considered. This change in viewpoint of the controlling factors for thawing of magnetic flux parallels the recent evolution of understanding of collisionless shocks, where initially stochastic wave-resistivities were thought to substitute for the coulomb dissipation of high density shock waves. Now these shocks are known to be controlled by coherent agents that can modify emf's such as the ambipolar electric field, the Hall contributions of the gyrating ions, and the electric electron drift in the shock layer to support the current without thawing flux and without any requirement of ohmic dissipation per se. The observational tests that reconnection is a viable process for plasma entry in the magnetosphere are briefly reviewed. Sites where these conservation laws are said to be approximately fulfilled are discussed with an eye toward systematic experimental issues of these tests. That magnetic shear poorly indexes "good" Walén testing layers may be an indication that the resistive dissipation is either not uniformly important across the data set or resistive emf's are not the appropriate agent for the thawing of flux. The ambipolar scale length clearly exceeds the resistive or electron skin depth regime with layers that pass the "good" Walén test layers which have β 〈 5; this may indicate the importance of the ambipolar violations to the frozen field description.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Space science reviews 23 (1979), S. 123-133 
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A survey, using results from the first 25 orbits of ISEE-1, has been made of some aspects of electrons in the dawn magnetosheath. There are indications that the flow of plasma is not uniformly turbulent over this region. The electron heat flux is observed to be directed away from the shock and to have an average value of about twice the interplanetary heat flux. Many magnetopause crossings were observed and usually resemble abrupt transitions from one well-defined plasma state to another. The ejection of plasma from flux tubes converted up against the magnetopause is observed for about half the time, and its thickness and dependence on the solar wind mach number agree with theoretical predictions. A full traversal of the whole forward hemisphere of the magnetosheath is required to fully confirm these deductions.
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  • 3
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Solar Wind Experiment (SWE) on the WIND spacecraft is a comprehensive, integrated set of sensors which is designed to investigate outstanding problems in solar wind physics. It consists of two Faraday cup (FC) sensors; a vector electron and ion spectrometer (VEIS); a strahl sensor, which is especially configured to study the electron ‘strahl’ close to the magnetic field direction; and an on-board calibration system. The energy/charge range of the Faraday cups is 150 V to 8 kV, and that of the VEIS is 7 V to 24.8 kV. The time resolution depends on the operational mode used, but can be of the order of a few seconds for 3-D measurements. ‘Key parameters’ which broadly characterize the solar wind positive ion velocity distribution function will be made available rapidly from the GGS Central Data Handling Facility.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A second encounter took place on September 21 1974 but the spacecraft passed the planet on the Sunward side at too great a distance to permit observations inside the planet's bow shock. The third and last encounter (Mercury III) took place on March 16 1975 at which time the spacecraft passed within ...
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 292 (1981), S. 711-714 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] DURING the Voyager 1 encounter with Saturn, the electron plasma in the energy range 10-5,950 eV was sampled by the plasma science experiment (PLS). The electron distribution function in the vicinity of Saturn is comprised of smoothly joined thermal and suprathermal components; it is not well ...
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  • 6
    Publication Date: 2011-08-19
    Description: Using the results of Scudder et al. (1986) on the bow shock wave observed by ISEE satellites, a quantitative description is presented of the electrodynamics of ion and electron fluids, and phase-standing wave interaction which manifests itself as a supercritical MHD shock. The cross-shock electrical profile was determined in both the normal incidence frame and in the deHoffman-Teller frame by two different methods, and the results were compared with dc electric field measurements.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 11053-11
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  • 7
    Publication Date: 2011-08-19
    Description: Voyager 1 encounter data are used to theoretically examine the interaction of Titan with the solar wind, the Saturn magnetosheath and the Saturn magnetosphere. The spacecraft data comprised magnetometer, plasma wave, radio signal and charged particle measurements. Attention is given to the Alfven (1.9) and Mach (0.57) numbers detected in the Saturn magnetosheath, along with a fast hydrodynamic Mach number of 0.55. Incident plasma interacted with the Titan atmosphere and produced a magnetosphere through mass capture and field-line draping. The tail region was loaded with N(+) and N2(+)/H2CN(+) ions instead of the strong H(+) signals typical of other regions. The magnetotail featured four lobes, and the Titan atmosphere was calculated to lose 10 to the 24th ions/sec. Finally, the Titan internal rotationally aligned magnetic field has an estimated strength of 7 x 10 to the 20th gauss/cu cm.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 8
    Publication Date: 2011-08-19
    Description: A model which is consistent with the solar wind and shock surface boundary conditions for the foreshock electron distribution in the absence of wave-particle effects is formulated for an arbitrary location behind the magnetic tangent to the earth's bow shock. Variations of the gyrophase-averaged velocity distribution are compared and contrasted with in situ ISEE observations. It is found that magnetic mirroring of solar wind electrons is the most important process by which nonmonotonic reduced electron distributions in the foreshock are produced. Leakage of particles from the magnetosheath is shown to be relatively unimportant in determining reduced distributions that are nonmonotonic. The two-dimensional distribution function off the magnetic field direction is the crucial contribution in producing reduced distributions which have beams. The time scale for modification of the electron velocity distribution in velocity space can be significantly influenced by steady state spatial gradients in the background imposed by the curved shock geometry.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 4155-417
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  • 9
    Publication Date: 2011-08-19
    Description: In this paper, an approximate extension of the deHoffmann-Teller (1950) theorem for electrons within layers possessing a normal mass flux is derived. It is shown that the deHoffmann-Teller frame electron bulk velocity is nearly parallel to the magnetic field everywhere through those one-dimensional time-stationary layers which possess a normal mass flux, even though electric field perpendicular to the magnetic field exists throughout such layers. Examples of layers of this class are the fast and slow shocks as well as rotational discontinuities.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 92; 13447-13
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  • 10
    Publication Date: 2011-08-24
    Description: The energy necessary to explain the electron heating in quasi-perpendicular collisionless shocks can be derived either from the electron acceleration in the d.c. cross shock electric potential, or by the interactions between the electrons and the waves existing in the shock. A Monte Carlo simulation has been performed to study the electron distribution function evolution through the shock structure, with and without particle diffusion on waves. This simulation has allowed us to clarify the relative importance of the two possible energy sources; in particular it has been shown that the electron parallel temperature is determined by the d.c. electromagnetic field and not by any wave-particle-induced heating. Wave particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons.
    Keywords: PLASMA PHYSICS
    Type: Nuovo Cimento C, Serie 1 (ISSN 0390-5551); 15 C; 5; p. 607-619.
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