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| Titel |
Multi-site observations of the association between aurora and plasma convection in the cusp/polar cap during a southeastward(By ~ |Bz|) IMF orientation |
| VerfasserIn |
P. E. Sandholt, J. Moen, C. J. Farrugia, S. W. H. Cowley, Mark Lester, S. E. Milan, C. Valladares, W. F. Denig, S. Eriksson |
| 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 ; 21, no. 2 ; Nr. 21, no. 2, S.539-558 |
| Datensatznummer |
250014573
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| Publikation (Nr.) |
 copernicus.org/angeo-21-539-2003.pdf |
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| Zusammenfassung |
In a case study we
demonstrate the spatiotemporal structure of aurora and plasma convection in the
cusp/polar cap when the interplanetary magnetic field (IMF) Bz < 0 and By ~
| Bz | (clock angle in GSM Y - Z plane: ~ 135°). This IMF orientation
elicited a response different from that corresponding to strongly northward and
southward IMF. Our study of this "intermediate state" is based on a
combination of ground observations of optical auroral emissions and ionospheric
plasma convection. Utilizing all-sky cameras at NyAlesund, Svalbard and Heiss
Island (Russian arctic), we are able to monitor the high-latitude auroral
activity within the ~10:00–15:00 MLT sector. Information on plasma convection
is obtained from the SuperDARN radars, with emphasis placed on line of sight
observations from the radar situated in Hankasalmi, Finland (Cutlass). A
central feature of the auroral observations in the cusp/polar cap region is a ~
30-min long sequence of four brightening events, some of which consists of
latitudinally and longitudinally separated forms, which are found to be
associated with pulsed ionospheric flows in merging and lobe convection cells.
The auroral/convection events may be separated into different forms/cells and
phases, reflecting a spatiotem-poral evolution of the reconnection process on
the dayside magnetopause. The initial phase consists of a brightening in the
postnoon sector (~ 12:00–14:00 MLT) at ~ 73° MLAT, accompanied by a pulse of
enhanced westward convection in the postnoon merging cell. Thereafter, the
event evolution comprises two phenomena which occur almost simultaneously: (1)
westward expansion of the auroral brightening (equatorward boundary
intensification) across noon, into the ~ 10:00–12:00 MLT sector, where the
plasma convection subsequently turns almost due north, in the convection
throat, and where classical poleward moving auroral forms (PMAFs) are observed;
and (2) auroral brightening at slightly higher latitudes (~ 75° MLAT) in the
postnoon lobe cell, with expansion towards noon, giving rise to a clear cusp
bifurcation. The fading phase of PMAFs is accompanied by a "patch" of
enhanced (~ 1 km/s) poleward-directed merging cell convection at high latitudes
(75–82° MLAT), e.g. more than 500 km poleward of the cusp equatorward
boundary. The major aurora/convection events are recurring at ~ 5–10 min
intervals.
Key words. Magnetospheric physics (auroral
phenomena; magnetopause, cusp, and boundary layers; plasma convection) |
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