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| Titel |
Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm |
| VerfasserIn |
T. K. Yeoman, J. A. Davies, N. M. Wade, G. Provan, 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 ; 18, no. 9 ; Nr. 18, no. 9, S.1073-1087 |
| Datensatznummer |
250014058
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| Publikation (Nr.) |
 copernicus.org/angeo-18-1073-2000.pdf |
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| Zusammenfassung |
On August 21st 1998, a sharp southward
turning of the IMF, following on from a 20 h period of northward directed
magnetic field, resulted in an isolated substorm over northern Scandinavia and
Svalbard. A combination of high time resolution and large spatial scale
measurements from an array of coherent scatter and incoherent scatter
ionospheric radars, ground magnetometers and the Polar UVI imager has
allowed the electrodynamics of the impulsive substorm electrojet region during
its first few minutes of evolution at the expansion phase onset to be studied in
great detail. At the expansion phase onset the substorm onset region is
characterised by a strong enhancement of the electron temperature and UV aurora.
This poleward expanding auroral structure moves initially at 0.9 km s-1
poleward, finally reaching a latitude of 72.5°. The optical signature expands
rapidly westwards at ~6 km s-1, whilst the eastward edge also expands
eastward at ~0.6 km s-1. Typical flows of 600 m s-1 and
conductances of 2 S were measured before the auroral activation, which rapidly
changed to ~100 m s-1 and 10-20 S respectively at activation. The
initial flow response to the substorm expansion phase onset is a flow
suppression, observed up to some 300 km poleward of the initial region of
auroral luminosity, imposed over a time scale of less than 10 s. The high
conductivity region of the electrojet acts as an obstacle to the flow, resulting
in a region of low-electric field, but also low conductivity poleward of the
high-conductivity region. Rapid flows are observed at the edge of the
high-conductivity region, and subsequently the high flow region develops,
flowing around the expanding auroral feature in a direction determined by the
flow pattern prevailing before the substorm intensification. The enhanced
electron temperatures associated with the substorm-disturbed region extended
some 2° further poleward than the UV auroral signature associated with it.
Key words: Ionosphere (auroral ionosphere) -
Magnetospheric physics (magnetosphere - ionosphere interactions; storms and
substorms) |
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