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| Titel |
M-I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs) |
| VerfasserIn |
P. E. Sandholt, C. J. Farrugia, W. F. Denig |
| 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 ; 32, no. 4 ; Nr. 32, no. 4 (2014-04-09), S.333-351 |
| Datensatznummer |
250121045
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| Publikation (Nr.) |
 copernicus.org/angeo-32-333-2014.pdf |
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| Zusammenfassung |
| We study substorms from two perspectives, i.e., magnetosphere–ionosphere
coupling across the auroral oval at dusk and at midnight magnetic local
times. By this approach we monitor the activations/expansions of basic
elements of the substorm current system (Bostrøm type I centered at
midnight and Bostrøm type II maximizing at dawn and dusk) during the
evolution of the substorm activity. Emphasis is placed on the R1 and R2 types
of field-aligned current (FAC) coupling across the Harang reversal at dusk.
We distinguish between two distinct activity levels in the substorm expansion
phase, i.e., an initial transient phase and a persistent phase. These
activities/phases are discussed in relation to polar cap convection which is
continuously monitored by the polar cap north (PCN) index. The substorm
activity we selected occurred during a long interval of continuously strong
solar wind forcing at the interplanetary coronal mass ejection passage on
18 August 2003. The advantage of our scientific approach lies in the
combination of (i) continuous ground observations of the ionospheric
signatures within wide latitude ranges across the auroral oval at dusk and
midnight by meridian chain magnetometer data, (ii) "snapshot" satellite
(DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii)
observations of current disruption/near-Earth magnetic field dipolarizations
at geostationary altitude. Under the prevailing fortunate circumstances we
are able to discriminate between the roles of the dayside and nightside
sources of polar cap convection. For the nightside source we distinguish
between the roles of inductive and potential electric fields in the two
substages of the substorm expansion phase. According to our estimates the
observed dipolarization rate (δ Bz/δt) and the inferred large
spatial scales (in radial and azimuthal dimensions) of the dipolarization
process in these strong substorm expansions may lead to 50–100 kV
enhancements of the cross-polar-cap potential due to inductive electric field
coupling. |
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