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| Titel |
Statistical analysis of ionospheric potential patterns for isolated substorms and sawtooth events |
| VerfasserIn |
X. Cai, C. R. Clauer, A. J. Ridley |
| 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 ; 24, no. 7 ; Nr. 24, no. 7 (2006-08-09), S.1977-1991 |
| Datensatznummer |
250015603
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| Publikation (Nr.) |
 copernicus.org/angeo-24-1977-2006.pdf |
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| Zusammenfassung |
| We present here results which contrast isolated substorms with individual
sawtooth events. Sawtooth events are defined as
quasi-periodic, large-amplitude oscillations in the energetic particle
flux with a periodicity of 2–4 h observed at the geosynchronous orbit.
Sawtooth events have several similarities to isolated substorms leading
therefore, to different opinions about whether sawtooth events are
just an intense periodic form of substorms or if they deserve a category of their own.
To help resolve this, we examine the ionospheric potential
patterns in the northern polar region for isolated substorms and
sawtooth events using the assimilative mapping of ionospheric electrodynamics
(AMIE) technique. First we show a statistical analysis of isolated substorm
potential patterns. In order to examine the seasonal variation,
isolated substorms are identified by mid-latitude positive bay in
the north-south geomagnetic perturbation in each season, respectively. Superposed epoch
analysis (SEA) is applied to obtain the typical polar potential patterns for
each season. By examining the time evolution of the potential
patterns and cross polar cap potential (CPCP) for isolated substorms
during each season, we find only subtle seasonal variations in the
results obtained using the AMIE analysis. This provides a basis for
comparison with sawtooth events in the next step. From the averaged
potential patterns of 213 isolated substorms and those of
184 individual sawtooth events, we find the sawtooth events show
signatures similar to subtorms: the DP 1 potential pattern
develops and dominates the polar region after the onset. However,
the DP 1 potential cell of sawtooth events encompasses a larger
area than that of isolated substorms. Moreover, the CPCP of sawtooth
is stronger than that of isolated substorms. It is also shown that
the sawtooth events displays greater variability between
individual events than isolated substorms. We conclude that in
terms of ionospheric electrodynamics, the sawtoothe events have features
that are similar to those of isolates substorms, though larger in spatial
extent and in magnitude. |
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