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| Titel |
Statistical study of high-latitude plasma flow during magnetospheric substorms |
| VerfasserIn |
G. Provan, Mark Lester, S. B. Mende, S. E. Milan |
| 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 ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3607-3624 |
| Datensatznummer |
250015035
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3607-2004.pdf |
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| Zusammenfassung |
| We have utilised the near-global imaging capabilities of the Northern Hemisphere
SuperDARN radars, to perform a statistical superposed epoch
analysis of high-latitude plasma flows during magnetospheric substorms. The
study involved 67 substorms, identified using the IMAGE FUV space-borne
auroral imager. A substorm co-ordinate system was developed, centred on the
magnetic local time and magnetic latitude of substorm onset determined from
the auroral images. The plasma flow vectors from all 67 intervals were
combined, creating global statistical plasma flow patterns and backscatter
occurrence statistics during the substorm growth and expansion phases. The
commencement of the substorm growth phase was clearly observed in the radar
data 18-20min before substorm onset, with an increase in the
anti-sunward component of the plasma velocity flowing across dawn sector of
the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside
backscatter moved to lower latitudes as the growth phase progressed. At
substorm onset a flow suppression region was observed on the nightside, with
fast flows surrounding the suppressed flow region. The dawn-to-dusk
transpolar voltage increased from ~40kV just before substorm onset to
~75kV 12min after onset. The low-latitude return flow started to
increase at substorm onset and continued to increase until 8min after
onset. The velocity flowing across the polar-cap peaked 12-14min after
onset. This increase in the flux of the polar cap and the excitation of
large-scale plasma flow occurred even though the IMF Bz component was
increasing (becoming less negative) during most of this time. This study is
the first to statistically prove that nightside reconnection creates
magnetic flux and excites high-latitude plasma flow in a similar way to
dayside reconnection and that dayside and nightside reconnection, are two
separate time-dependent processes. |
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