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| Titel |
Observational evidence for an inside-out substorm onset scenario |
| VerfasserIn |
M. G. Henderson |
| 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 (2009-05-08), S.2129-2140 |
| Datensatznummer |
250016531
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2129-2009.pdf |
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| Zusammenfassung |
| We present observations which provide strong support for a substorm
expansion phase onset scenario in which a localized inner magnetospheric
instability developed first and was later followed by the development of a Near
Earth Neutral Line (NENL) farther down-tail. Specifically, we find that the
onset began as a localized brightening of an intensified growth phase arc which
developed as a periodic series of arc-aligned (i.e. azimuthally arrayed) bright
spots. As the disturbance grew, it evolved into vortical structures that
propagated poleward and eventually morphed into an east-west aligned arc system
at the poleward edge of the auroral substorm bulge. The evolution of the
auroral intensity is consistent with an exponential growth with an e-folding
time of around 188 s (corresponding to a linear growth rate, γ of
5.33×10−3 s−1). During the initial breakup, no obvious
distortions of auroral forms to the north were observed. However, during the
expansion phase, intensifications of the poleward boundary of the expanding
bulge were observed together with the equatorward ejection of auroral streamers
into the bulge. A strong particle injection was observed at geosynchronous
orbit, but was delayed by several minutes relative to onset. Ground
magnetometer data also shows a two phase development of mid-latitude positive
H-bays, with a quasi-linear increase in H between the onset and the injection.
We conclude that this event provides strong evidence in favor of the so-called
"inside-out" substorm onset scenario in which the near Earth region activates
first followed at a later time by the formation of a near-to-mid tail substorm
X-line. The ballooning instability is discussed as a likely mechanism for the
initial onset. |
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