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| Titel |
Radar observations of auroral zone flows during a multiple-onset substorm |
| VerfasserIn |
J. P. Morelli, R. J. Bunting, S. W. H. Cowley, C. J. Farrugia, M. P. Freeman, E. Friis-Christensen, G. O. L. Jones, Mark Lester, R. V. Lewis, H. Lühr, D. Orr, M. Pinnock, G. D. Reeves, P. J. S. Williams, T. K. Yeoman |
| 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 ; 13, no. 11 ; Nr. 13, no. 11, S.1144-1163 |
| Datensatznummer |
250012037
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| Publikation (Nr.) |
 copernicus.org/angeo-13-1144-1995.pdf |
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| Zusammenfassung |
| We present an analysis of ground magnetic
field, ionospheric flow, geosynchronous particle, and interplanetary data during
a multiple-onset substorm on 12 April 1988. Our principal results concern the
modulations of the ionospheric flow which occur during the impulsive electrojet
activations associated with each onset. During the first hour of the disturbance
these take place every ~12.5 min and involve the formation of a new intense
westward current filament in the premidnight sector, just poleward of the pre-existing
extended current system driven by the large-scale flow. These filaments are ~1 h
MLT wide (~600 km), and initially expand poleward to a width of ~300 km before
contracting equatorward and coalescing with the pre-existing current, generally
leaving the latter enhanced in magnitude and/or expanded in latitude. Within the
impulsive electrojets the flow is found to be suppressed to values 50–100 m s–1
or less during the first few minutes, before surging equatorward at 0.5–1.0 km s–1
during the phase of rapid coalescence. The implication is that the
precipitation-induced Hall conductivity within the impulsive electrojet
initially rises to exceed ~100 mho, before decaying over a few minutes. This
value compares with Hall conductivities of ~20 mho in the quasi-steady current
regions, and a few mho or less in the regions poleward of the electrojets and in
the preonset ionosphere. Preliminary evidence has also been found that the flow
surges propagate from midnight to the morning sector where they are associated
with arrested equatorward motion or poleward contractions of the current system.
These observations are discussed in terms of present theoretical paradigms of
the global behaviour of fields and flows which occur during substorms. |
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