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  • 1
    Electronic Resource
    Electronic Resource
    Report on the solar physics-plasma physics workshop (1976)
    Springer
    Solar physics 46 (1976), S. 411-431 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This report summarizes the proceedings of a meeting held on 17–20 September 1974, at Stanford University. The purpose was to explore plasma physics problems which arise in the study of solar physics. Sessions were concerned with specific questions including the following: Is the solar plasma thermal or non-thermal? What spectroscopic data are required? What types of magnetic field structures exist? Do MHD instabilities occur? Do resistive or non-MHD instabilities occur? What mechanisms of particle acceleration have been proposed? What information do we have concerning shock waves? Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149863
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    On flares, substorms, and the theory of impulsive flux transfer events (1976)
    Springer
    Solar physics 47 (1976), S. 345-360 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solar flares and magnetospheric substorms are discussed in the context of a general theory of impulsive flux transfer events (IFTE). IFTE theory, derived from laboratory observations in the Double Inverse Pinch Device (DIPD), provides a quantitative extension of “neutral sheet” theories to include nonsteady field line reconnection. Current flow along the reconnection line increases with magnetic flux storage. When flux build-up exceeds the level corresponding to a critical limit on the current, instabilities induce a sudden transition in the mode of conduction. The resulting IFTE, indifferent to the specific modes and instabilities involved, is the more energetic, the lower the initial resistivity. It is the more violent, the greater the resulting resistivity increase and the faster its growth. Violent events can develop very large voltage transients along the reconnection line. Persistent build-up promoting conditions produce relaxation oscillations in the quantity of flux and energy stored (build-up-IFTE cycles). It is difficult to avoid the conclusion: flares and substorms are examples of IFTE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152273
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Conduction mode variation and intertial conductivity (1977)
    Springer
    Astrophysics and space science 49 (1977), S. 473-480 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using separation of variables in space and time we find two-dimensional solutions consistent with simple forms of the inertial Ohm's law, Maxwell's equations, and the equation of momentum transport. conduction mode variation (a temporal change in electrical conductivity due, e.g., to onset of a plasma instability) is frequently found necessary. The result for the effective conductivity shows that either the conduction mode variation or inertial effects may dominate. In the inertial limit and in the absence of conduction mode variation the results are similar to the limiting results of Speiser. However, the important time constant is the inverse growth rate of the current density rather than the lifetime of a particle in the system. Several solutions have magnetic field structures with neutral points.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00641992
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  • 4
    Electronic Resource
    Electronic Resource
    Laboratory solar flare experiments (1976)
    Springer
    Solar physics 47 (1976), S. 331-344 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Several laboratory experiments on magnetic field line reconnection are briefly reviewed. Emphasis is placed on the double inverse pinch device (DIPD) in which magnetic flux is built up during a quiescent reconnection phase and then abruptly transferred during an impulsive reconnection phase. Scaling estimates show that this impulsive phase corresponds to a solar release of 1030 ergs in 102 seconds with the production of GeV potentials. The trigger for the impulsive “flare” is a conduction mode instability (ion-acoustic) which abruptly changes the resistance of the neutral point region when the reconnection current density reaches a critical value. Some results are presented from another reconnection device which has exactly antiparallel fields at the boundaries. This flat plate device develops one x-type neutral point rather than tearing into many neutral points. The reconnection rate is more quiescent than in the DIPD. A mild conduction mode instability occurs. The results suggest that regions with “flattened” boundary fields may not be as conducive to flares as regions with more curved fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152272
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  • 5
    Electronic Resource
    Electronic Resource
    Flux linkages of bipolar sunspot groups: A computer study (1980)
    Springer
    Solar physics 67 (1980), S. 245-258 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Past studies of the structure of solar magnetic fields have used magnetograph data to compute selected field lines for comparison with the morphology of structures seen in various spectral wavelengths. While those analyses examine one of the integral properties of magnetic fields (field lines), they are not complete since they fail to determine the other important integral property: the boundaries of the flux of field lines of given connectivity. In the present analysis we determine such a system of boundaries, called separatrices, for the current free field of two p-f spot pairs so as to exhibit the line of self-intersection, called the separator. The analysis is compared with previous analytical work. These computer results, confirming earlier studies carried out using iron fillings, show that the separatrix has the form of two intersecting ovoids, defining four flux cells. New features which have emerged from this study include the observation that the projections of the separatrix in a plane perpendicular to the separator at its highest point do not intersect at 90° as has been widely believed, but rather closer to 60° in the case studied. The separator is very nearly circular over most of its length. The two neutral points (B = 0) which appear at the photospheric ends of the separator have the mixed radial-hyperbolic form as expected, a feature requiring every field line lying on the separatrix to connect with at least one of the two neutral points. The rotation of line direction with height (shear) is graphically illustrated in the potential field case studied here. We also exhibit a magnetic arcade.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149805
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic flux of colinear bipolar spot pairs (1979)
    Springer
    Solar physics 62 (1979), S. 53-67 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It has been widely conjectured that solar flares are energized by the magnetic energy stored in complex active regions. Paradoxically, however, in attempting to show that magnetic changes cause or characterize flares, solar magnetic observations have produced equivocal results. In previous attempts at resolving the paradox, it has been contended that magnetic measurements are simply imprecise or that magnetic theories of flares are incorrect. We present an alternative explanation: the present use of magnetograms to examine active region structure through numerical integration of miscellaneous field lines (under various force-free assumptions) provides qualitative information only and does not utilize the quantitative information available. Therefore, we propose a new approach to the analysis of magnetograms which is illustrated with a highly symmetrized example that permits integration in closed form. The proposed approach exploits the cellular structure of the flux of field lines present in a complex active region. The various topological connectivities distinguish parent and daughter flux cells. A function F is developed expressing the flux partitioned into the daughter cell of interconnected field lines in a potential field. This F is a function of the location, strength, and relative motions of the photospheric sources. Then dF/dt is used as an EMF in the direct calculation of the stored magnetic energy available for flare production. In carrying out this program the flux partitioning surface (separatrix) is calculated along with its line of self-intersection (separator). The separator is the location of the principal energy release site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00150131
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