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| Titel |
Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| VerfasserIn |
J. R. Taylor, T. K. Yeoman, Mark Lester, B. A. Emery, D. J. Knipp |
| 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 ; 14, no. 9 ; Nr. 14, no. 9, S.879-887 |
| Datensatznummer |
250012411
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| Publikation (Nr.) |
 copernicus.org/angeo-14-879-1996.pdf |
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| Zusammenfassung |
| The dynamic behaviour of the northern polar
cap area is studied employing Northern Hemisphere electric potential patterns
derived by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE)
procedure. The rate of change in area of the polar cap, which can be defined as
the region of magnetospheric field lines open to the interplanetary magnetic
field (IMF), has been calculated during two intervals when the IMF had an
approximately constant southward component (1100–2200 UT, 20 March 1990 and
1300–2100 UT, 21 March 1990). The estimates of the polar cap area are based on
the approximation of the polar cap boundary by the flow reversal boundary. The
change in the polar cap area is then compared to the predicted expansion rate
based on a simple application of Faraday\'s Law. Furthermore, timings of
magnetospheric substorms are also related to changes in the polar cap area. Once
the convection electric field reconfigures following a southward turning of the
IMF, the growth rate of the observed polar cap boundary is consistent with that
predicted by Faraday\'s Law. A delay of typically 20 min to 50 min is observed
between a substorm expansion phase onset and a reduction in the polar cap area.
Such a delay is consistent with a synthesis between the near Earth neutral line
and current disruption models of magnetospheric substorms in which the
dipolarisation in the magnetotail may act as a trigger for reconnection. These
delays may represent a propagation time between near geosynchronous orbit
dipolarisation and subsequent reconnection further down tail. We estimate, from
these delays, that the neutral X line occurs between ~35RE
and ~75RE downstream in the tail. |
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