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| Titel |
Intermediate-m ULF waves generated by substorm injection: a case study |
| VerfasserIn |
T. K. Yeoman, D. Yu. Klimushkin, P. N. Mager |
| 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 ; 28, no. 8 ; Nr. 28, no. 8 (2010-08-05), S.1499-1509 |
| Datensatznummer |
250016865
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1499-2010.pdf |
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| Zusammenfassung |
| A case study of SuperDARN observations of Pc5 Alfvén ULF wave activity
generated in the immediate aftermath of a modest-intensity substorm expansion
phase onset is presented. Observations from the Hankasalmi radar reveal that
the wave had a period of 580 s and was characterized by an intermediate
azimuthal wave number (m=13), with an eastwards phase propagation. It had a
significant poloidal component and a rapid equatorward phase propagation
(~62° per degree of latitude). The total equatorward phase
variation over the wave signatures visible in the radar field-of-view
exceeded the 180° associated with field line resonances. The wave
activity is interpreted as being stimulated by recently-injected energetic
particles. Specifically the wave is thought to arise from an eastward
drifting cloud of energetic electrons in a similar fashion to recent
theoretical suggestions (Mager and Klimushkin, 2008; Zolotukhina
et al., 2008; Mager et al., 2009). The
azimuthal wave number m is determined by the wave eigenfrequency and the
drift velocity of the source particle population. To create such an
intermediate-m wave, the injected particles must have rather high energies
for a given L-shell, in comparison to previous observations of wave
events with equatorward polarization. The wave period is somewhat longer than
previous observations of equatorward-propagating events. This may well be a
consequence of the wave occurring very shortly after the substorm expansion,
on stretched near-midnight field lines characterised by longer
eigenfrequencies than those involved in previous observations. |
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