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| Titel |
Statistical visualization of the Earth's magnetotail and the implied mechanism of substorm triggering based on superposed-epoch analysis of THEMIS data |
| VerfasserIn |
S. Machida, Y. Miyashita, A. Ieda, M. Nosé, V. Angelopoulos, J. P. McFadden |
| 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. 2 ; Nr. 32, no. 2 (2014-02-17), S.99-111 |
| Datensatznummer |
250121024
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| Publikation (Nr.) |
 copernicus.org/angeo-32-99-2014.pdf |
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| Zusammenfassung |
| To investigate the physical mechanism responsible for
substorm triggering, we performed a superposed-epoch analysis using plasma
and magnetic-field data from THEMIS probes. Substorm onset timing was
determined based on auroral breakups detected by all-sky imagers at the
THEMIS ground-based observatories. We found earthward flows associated with
north–south auroral streamers during the substorm growth phase. At around
X = −12 Earth radii (RE), the northward magnetic field and its
elevation angle decreased markedly approximately 4 min before substorm
onset. Moreover, a northward magnetic-field increase associated with
pre-onset earthward flows was found at around X = −17 RE. This
variation indicates that local dipolarization occurs. Interestingly, in the
region earthwards of X = −18 RE, earthward flows in the central plasma
sheet (CPS) reduced significantly approximately 3 min before substorm onset,
which was followed by a weakening of dawn-/duskward plasma-sheet
boundary-layer flows (subject to a 1 min time lag). Subsequently,
approximately 1 min before substorm onset, earthward flows in the CPS were
enhanced again and at the onset, tailward flows started at around X = −20
RE. Following substorm onset, an increase in the northward magnetic
field caused by dipolarization was found in the near-Earth region.
Synthesizing these results, we confirm our previous results based on GEOTAIL
data, which implied that significant variations start earlier than both
current disruption and magnetic reconnection, at approximately 4 min before
substorm onset roughly halfway between the two regions of interest; i.e. in
the catapult current sheet. |
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