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| Titel |
THEMIS observations of double-onset substorms and their association with IMF variations |
| VerfasserIn |
C.-C. Cheng, C. T. Russell, V. Angelopoulos, I. R. Mann, K.-H. Glassmeier, W. Baumjohann |
| 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 ; 29, no. 3 ; Nr. 29, no. 3 (2011-03-28), S.591-611 |
| Datensatznummer |
250016995
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| Publikation (Nr.) |
 copernicus.org/angeo-29-591-2011.pdf |
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| Zusammenfassung |
| On 16 July 2008, two pairs of consecutive bursts of Pi2 pulsations were
recorded simultaneously across the THEMIS ground-based observatory system.
Wavelet transformation reveals that for each high-latitude pair, the dominant
frequency of the first burst is higher than that of the second. But at low
latitudes, the dominant frequency does not change. It is suggested that both
pairs result from fast magnetospheric cavity waves with the second burst
also containing shear Alfvén waves. INTERMAGNET magnetograms at auroral
latitudes showed magnetic variations affected by two recurrent electrojets
for each pair. The ground-based magnetometers and those at geostationary
orbit sensed magnetic perturbations consistent with the formation of the
substorm current wedge. Four consecutive enhancements of energetic electron
and ion fluxes detected by the THEMIS probes in the dayside magnetosphere
appeared in the later afternoon and then in the early afternoon. The
horizontal magnetic variation vectors had vortex patterns similar to those
induced by the upward and downward field-aligned currents during substorm
times. The hodogram at mid-L stations had a polarization pattern similar to
the one induced by the substorm current wedge for each Pi2 burst. The
mapping of ground Pi2 onset timing to the interplanetary magnetic field
(IMF) observations shows that they appear under two cycles of north-to-south
and then north variation. CLUSTER 4 in the south lobe observed wave-like
magnetic fluctuations, probably driven by near-Earth reconnection, similar
to those on the ground. These two observations are consistent with the link
of double-onset substorms to magnetotail reconnection externally triggered
by IMF variations. |
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