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| Titel |
EISCAT observations of unusual flows in the morning sector associated with weak substorm activity |
| VerfasserIn |
N. J. Fox, M. Lockwood, S. W. H. Cowley, M. P. Freeman, E. Friis-Christensen, D. K. Milling, M. Pinnock, G. D. Reeves |
| 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 ; 12, no. 6 ; Nr. 12, no. 6, S.541-553 |
| Datensatznummer |
250010911
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| Publikation (Nr.) |
 copernicus.org/angeo-12-541-1994.pdf |
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| Zusammenfassung |
| A discussion is given of plasma flows in the
dawn and nightside high-latitude ionospheric regions during substorms occurring
on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment.
Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET
magnetometers and geostationary satellites are compared to the EISCAT
observations. On 4 October 1989 a weak substorm with initial expansion phase
onset signatures at 0030 UT, resulted in the convection reversal boundary
observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band
of elevated ionospheric ion temperatures and a localised plasma density
depletion. This polar cap contraction event is shown to be associated with
various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in
the midnight sector and particle injections at geosynchronous orbit. A similar
event was observed on the following day around 0230 UT (~0515 MLT) with the
unusual and significant difference that two convection reversals were observed,
both contracting poleward. We show that this feature is not an ionospheric
signature of two active reconnection neutral lines as predicted by the
near-Earth neutral model before the plasmoid is "pinched off", and
present two alternative explanations in terms of (1) viscous and lobe
circulation cells and (2) polar cap contraction during northward IMF. The
voltage associated with the anti-sunward flow between the reversals reaches a
maximum of 13 kV during the substorm expansion phase. This suggests it to be
associated with the polar cap contraction and caused by the reconnection of open
flux in the geomagnetic tail which has mimicked "viscous-like"
momentum transfer across the magnetopause. |
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