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| Titel |
Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals |
| VerfasserIn |
D. M. Willis, A. C. Holder, C. J. Davis |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 18, no. 1 ; Nr. 18, no. 1, S.11-27 |
| Datensatznummer |
250013877
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| Publikation (Nr.) |
 copernicus.org/angeo-18-11-2000.pdf |
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| Zusammenfassung |
Possible configurations of the magnetic field
in the outer magnetosphere during geomagnetic polarity reversals are
investigated by considering the idealized problem of a magnetic multipole of
order m and degree n located at the centre of a spherical cavity
surrounded by a boundless perfect diamagnetic medium. In this illustrative
idealization, the fixed spherical (magnetopause) boundary layer behaves as a
perfectly conducting surface that shields the external diamagnetic medium from
the compressed multipole magnetic field, which is therefore confined within the
spherical cavity. For a general magnetic multipole of degree n, the
non-radial components of magnetic induction just inside the magnetopause are
increased by the factor {1 + [(n + 1)/n]} relative to their
corresponding values in the absence of the perfectly conducting spherical
magnetopause. An exact equation is derived for the magnetic field lines of an
individual zonal (m = 0), or axisymmetric, magnetic multipole of
arbitrary degree n located at the centre of the magnetospheric cavity.
For such a zonal magnetic multipole, there are always two neutral points and n-1
neutral rings on the spherical magnetopause surface. The two neutral points are
located at the poles of the spherical magnetopause. If n is even, one of
the neutral rings is coincident with the equator; otherwise, the neutral rings
are located symmetrically with respect to the equator. The actual existence of
idealized higher-degree (n>1) axisymmetric magnetospheres would
necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n)
ring currents. Exact equations are also derived for the magnetic field lines of
an individual non-axisymmetric magnetic multipole, confined by a perfectly
conducting spherical magnetopause, in two special cases; namely, a symmetric
sectorial multipole (m = n) and an antisymmetric sectorial
multipole (m = n-1). For both these non-axisymmetric magnetic
multipoles, there exists on the spherical magnetopause surface a set of neutral
points linked by a network of magnetic field lines. Novel magnetospheric
processes are likely to arise from the existence of magnetic neutral lines that
extend from the magnetopause to the surface of the Earth. Finally, magnetic
field lines that are confined to, or perpendicular to, either special meridional
planes or the equatorial plane, when the multipole is in free space, continue to
be confined to, or perpendicular to, these same planes when the perfectly
conducting magnetopause is present.
Key words. Geomagnetism and paleomagnetism
(reversals-process, time scale, magnetostratigraphy) · Magnetospheric physics
(magnetopause, cusp, and boundary layers; magnetospheric configuration and
dynamics) |
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