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| Titel |
Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event |
| VerfasserIn |
S. Kasahara, Y. Miyashita, T. Takada, M. Fujimoto, V. Angelopoulos, H. U. Frey, J. Bonnell, J. P. McFadden, D. Larson, K. H. Glassmeier, H. U. Auster, W. Magnes, I. Mann |
| 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. 10 ; Nr. 27, no. 10 (2009-10-09), S.3825-3840 |
| Datensatznummer |
250016672
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3825-2009.pdf |
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| Zusammenfassung |
| We report multi-spacecraft and ground-based observations of
a "sawtooth" event on 20 November 2007.
For this event, data from three THEMIS,
two GOES, and four LANL spacecraft are available
as well as those from extensively distributed ground magnetometers
and all-sky imagers.
In the present paper we focus on
the spatial extents of the electromagnetic and particle
signatures of the first "tooth".
In this event, auroral images and ground magnetic bays
showed two activations: a pseudo onset
and a major onset
(we use the term pseudo onset since the former auroral brightening
did not significantly expand poleward).
Ground magnetic bay observations indicate that
the substorm current wedge (SCW) developed after the major
onset in an azimuthally wide region of
~14–3 h MLT. Similarly, broad magnetic bay distribution
was observed also for the pseudo onset prior to the major
onset. Furthermore, around the pseudo onset,
magnetic dipolarisations were observed
from 0.5 to 5 h MLT.
These observations illustrate that,
during sawtooth events, activities following
not only the major onset but also
the pseudo onset can extend more widely than those during
usual substorms.
Remarkable electromagnetic field fluctuations
embedded in the dipolarisation trend
were seen at 0.5 and 2.5 h MLT.
In particular, comprehensive plasma and field data
from THEMIS showed the presence of a long-excited weak
magnetosonic wave and an impulsive
large-amplitude Alfvén wave with an earthward Poynting
flux at around the eastward edge of
the SCW;
the latter was sufficiently strong for powering
aurora (140 mW/m2 when mapped to the ionosphere).
These two activations of the electromagnetic wave
were identified, corresponding to the pseudo onset
and the major onset.
On the other hand, the dipolarisation at geosynchronous
0 h MLT was observed only
after the major onset, despite its closer location
to the centre of the auroral activity in terms of the MLT;
this indicates that the inner radial limit of the dipolarisation
region at the pseudo onset was tailward of geosynchronous
altitude at 0 h MLT.
The outer radial limit of the electron injection
region was also found at ~10 RE
by conjunction measurements with THEMIS satellites.
These radial distributions are not significantly different
to those expected for usual substorms. |
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