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  • 1985-1989  (4)
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  • 1
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Satellite observations of the heliospheric current sheet indicate that the plasma flow velocity is low at the center of the current sheet and high on the two sides of current sheet. In this paper, we investigate the growth rates and eigenmodes of the sausage, kind, and tearing instabilities in the heliospheric current sheet with the observed sheared flow. These instabilities may lead to the formation of the plasmoids and kink waves in the solar wind. The results show that both the sausage and kink modes can be excited in the heliospheric current sheet with a growth time ∼ 0.05–5 day. Therefore, these modes can grow during the transit of the solar wind from the Sun to the Earth. The sausage mode grows faster than the kink mode for β ∞ 〈 1.5, while the streaming kink instability has a higher growth rate for β ∞ 〉 1.5. Here β ∞ is the ratio between the plasma and magnetic pressures away from the current layer. If a finite resistivity is considered, the streaming sausage mode evolves into the streaming tearing mode with the formation of magnetic islands. We suggest that some of the magnetic clouds and plasmoids observed in the solar wind may be associated with the streaming sausage instability. Furthermore, it is found that a large-scale kink wave may develop in the region with a radial distance greater than 0.5–1.5 AU.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 98 (1985), S. 305-322 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using a one-dimensional electrostatic particle code, we examine processes associated with current interruption in a collisionless plasma when a density depression is present along the current channel. Current interruption due to double layers was suggested by Alfvén and Carlqvist (1967) as a cause of solar flares. At a local density depression, plasma instabilities caused by an electron current flow are accentuated, leading to current disruption. Our simulation study encompasses a wide range of the parameters in such a way that under appropriate conditions, both the Alfvén and Carlqvist (1967) regime and the Smith and Priest (1972) regime take place. In the latter regime the density depression decays into a stationary structure (‘ion-acoustic layer’) which spawns a series of ion-acoustic ‘solitons’ and ion phase space holes travelling upstream. A large inductance of the current circuit tends to enhance the plasma instabilities.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Astrophysics and space science 144 (1988), S. 303-309 
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The presently prevailing theories of solar flares rely on the hypothetical presence of magnetic flux tubes beneath the photosphere and the two subsequent hypotheses, their emergence above the photosphere and explosive magnetic reconnection, converting magnetic energy carried by the flux tubes to solar flare energy. In this paper, we discuss solar flares from an entirely different point of view, namely in terms of power supply by a dynamo process in the photosphere. By this process, electric currents flowing along the magnetic field lines are generated and the familiar ‘force-free’ fields or the ‘sheared’ magnetic fields are produced. Upward field-aligned currents thus generated are carried by downward streaming electrons; these electrons can excite hydrogen atoms in the chromosphere, causing the optical Hα flares or ‘low temperature flares’. It is thus argued that as the ‘force-free’ fields are being built up for the magnetic energy storage, a flare must already be in progress.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper presents the consensus arrived at by the authors with respect to the contributions to the substorm expansive phase of direct energy input from the solar wind and from energy stored in the magnetotail which is released in a sometimes unpredictable manner. Two physical processes, neither of which can be ignored, are considered to be of importance in the dispensation of the energy input from the solar wind. One of these is the ‘driven process’ in which energy, supplied from the solar wind, is directly dissipated in the ionosphere with the only clearly definable delay being due to the inductance of the magnetosphere-ionosphere system. The other is the ‘loading-unloading process’ in which energy from the solar wind is first stored in the magnetotail and then is suddenly released to be deposited in the ionosphere as a consequence of external changes in the interplanetary medium or internal triggering processes. Although the driven process appears to be more dominant on a statistical basis in terms of solar wind-geomagnetic activity relationships, one or the other of the two above processes may dominate for any individual cases. Moreover, the two processes may operate simultaneously during a given phase of the substorm, e.g., the magnetotail may experience loading as the driven system increases in strength. Thus, in our approach, substorms are described in terms of physical processes which we infer to be operative in the magnetosphere and the terminology of the past (e.g., phases) is related to those inferred physical processes. The pattern of substorm development in response to changes in the interplanetary medium is presented for a canonical isolated substorm.
    Type of Medium: Electronic Resource
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