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| Titel |
In-situ observation of ULF wave activities associated with substorm expansion phase onset and current disruption |
| VerfasserIn |
J. Liang, W. W. Liu, E. F. Donovan, E. Spanswick |
| 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 (2009-05-13), S.2191-2204 |
| Datensatznummer |
250016536
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2191-2009.pdf |
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| Zusammenfassung |
| In this paper we present two substorm events with coordinated
ground-based and in-situ THEMIS observations, and focus our interest on the
wave activities in Pi1 and Pi2 bands from minutes before the substorm
expansion phase (EP) onset to minutes after the local current disruption
(CD). We find that Pi2 band (40–100 s) wave appears 1–2 min before the
substorm onset and last over the entire EP interval, while higher-frequency
wave within Pi1 band (10–30 s) emerges within few tens of seconds after the
EP onset, intensifies during the local CD, and fades afterwards. The
pre-onset Pi2 waves are attributed to a ballooning mode which acts as the
seed perturbation to the substorm EP onset process. The azimuthal wavenumber
estimated from the Doppler shift nature of the ballooning mode is consistent
with the longitudinal "wavelength" inferred from the onset auroral
structures. The Pi1 waves appearing within few tens of seconds after the EP
onset are interpreted as supportive of a two-fluid instability mode of thin
current sheet investigated in an accompanying paper (Liu and Liang, 2009).
During the local CD, broadband wave activities from Pi2 band to well above
the ion gyrofrequency are observed, suggesting the coexistence of various
plasma instabilities featuring different frequency ranges. |
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