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| Titel |
THEMIS observation of a substorm event on 04:35, 22 February 2008 |
| VerfasserIn |
J. Liu, V. Angelopoulos, H. Frey, J. McFadden, D. Larson, K. Glassmeier, S. Mende, C. T. Russell, I. J. Rae, K. R. Murphy, S. Apatenkov |
| 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 ; 27, no. 5 ; Nr. 27, no. 5 (2009-05-04), S.1831-1841 |
| Datensatznummer |
250016503
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1831-2009.pdf |
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| Zusammenfassung |
| We report on THEMIS in-situ and ground-based observations
during a substorm between 04:30~04:50 UT on 22 February 2008. The
spacecraft (probes) were aligned along the tail between XGSM=−5 RE
to −25 RE. The most distant probe P1 (X=−24.5 RE) detected two
successive tailward moving bipolar magnetic structures. P2 (X=−18 RE),
P3 (X=−11 RE), P4 (X=−10.5 RE) all captured signatures related to
the Earthward movement of a magnetic structure. THEMIS ground stations and
all-sky imagers also recorded Pi2 pulsations and a sudden brightening in a
white-light auroral imager followed by poleward expansion. We perform a
detailed timing analysis of probe and ground-based data and reconstruct the
time sequence of phenomena during this substorm. The earliest sign of
substorm onset was the bipolar perturbation in the northward component of
the magnetic field (interpreted as the result of reconnection onset) at P1
at 04:35:16 UT and corresponding magnetic perturbation at P2 at 04:35:14 UT.
Auroral onset was seen at or before 04:36:55 UT, consistent with the visual
onset of high-latitude magnetic pulsations at around that time. Earthward
flows at P3 and P4 seen at ~04:36:03 UT, and dipolarization onset at
~04:36:50 UT, were observed at almost the same time as the ground onset
signature, implying that near-Earth dipolarization happened in the aftermath
of tail reconnection but not significantly ahead of the auroral
intensification. Reconnection in the tail preceded ground onset and
near-Earth dipolarization (current disruption) by ~2 min. Two
reconnection pulses (the first one weaker than the second one) accompanied
by correlative increases of cumulative magnetic flux transfer into the
reconnection region were observed. A direct association of the reconnection
pulses with two auroral intensifications can be made, suggesting that tail
reconnection, like the auroral expansion, advances in steps rather than
continuously. |
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