Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns
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 magnet...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
1996-09-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/14/879/1996/angeo-14-879-1996.pdf |
| _version_ | 1818684536675893248 |
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| author | J. R. Taylor T. K. Yeoman M. Lester B. A. Emery D. J. Knipp |
| author_facet | J. R. Taylor T. K. Yeoman M. Lester B. A. Emery D. J. Knipp |
| author_sort | J. R. Taylor |
| collection | DOAJ |
| description | 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 <i>X</i> line occurs between ~35R<sub>E</sub>
and ~75R<sub>E</sub> downstream in the tail. |
| first_indexed | 2024-12-17T10:52:12Z |
| format | Article |
| id | doaj.art-3cc66be80f9f4604ba0d083f18587e7d |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-17T10:52:12Z |
| publishDate | 1996-09-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-3cc66be80f9f4604ba0d083f18587e7d2022-12-21T21:51:55ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05761996-09-011487988710.1007/s00585-996-0879-8Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patternsJ. R. TaylorT. K. YeomanM. LesterB. A. EmeryD. J. KnippThe 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 <i>X</i> line occurs between ~35R<sub>E</sub> and ~75R<sub>E</sub> downstream in the tail.https://www.ann-geophys.net/14/879/1996/angeo-14-879-1996.pdf |
| spellingShingle | J. R. Taylor T. K. Yeoman M. Lester B. A. Emery D. J. Knipp Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns Annales Geophysicae |
| title | Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| title_full | Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| title_fullStr | Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| title_full_unstemmed | Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| title_short | Variations in the polar cap area during intervals of substorm activity on 20-21 March 1990 deduced from AMIE convection patterns |
| title_sort | variations in the polar cap area during intervals of substorm activity on 20 21 march 1990 deduced from amie convection patterns |
| url | https://www.ann-geophys.net/14/879/1996/angeo-14-879-1996.pdf |
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