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| Titel |
The electric field response to the growth phase and expansion phase onset of a small isolated substorm |
| VerfasserIn |
R. V. Lewis, M. P. Freeman, A. S. Rodger, G. D. Reeves, D. K. Milling |
| 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 ; 15, no. 3 ; Nr. 15, no. 3, S.289-299 |
| Datensatznummer |
250012665
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| Publikation (Nr.) |
 copernicus.org/angeo-15-289-1997.pdf |
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| Zusammenfassung |
| We capitalise on the very large field of view
of the Halley HF radar to provide a comprehensive description of the electric
field response to the substorm growth phase and expansion phase onset of a
relatively simple isolated substorm ( |AL| < 250 nT) which occurred on 13
June 1988. The substorm phases are identified by their standard ground magnetic
and spacecraft energetic particle signatures, which provide a framework for the
radar measurements. The substorm is preceded by a prolonged period (>12 h) of
magnetic quiescence, such that prior to the start of the growth phase, the
apparent latitudinal motion of the radar backscatter returns is consistent with
the variation in latitude of the quiet-time auroral oval with magnetic local
time. The growth phase is characterised by an increasing, superimposed
equatorward motion of the equatorward edge of the radar backscatter as the
auroral oval expands. Within this backscatter region, there is a poleward
gradient in the Doppler spectral width, which we believe to correspond to
latitudinal structure in auroral emissions and magnetospheric precipitation.
During the growth phase the ionospheric convection is dominated by a relatively
smooth large-scale flow pattern consistent with the expanding DP2 (convection)
auroral electrojets. Immediately prior to substorm onset the ionospheric
convection observed by the radar in the midnight sector has a predominantly
equatorward flow component. At substorm onset a dramatic change occurs and a
poleward flow component prevails. The timing and location are quite remarkable.
The timing of the flow change is within one minute of the dispersionless
injection observed at geostationary orbit and the Pi2 magnetic signature on the
ground. The location shows that this sudden change in flow is due to the effect
of the upward field aligned current of the substorm current wedge imposed
directly within the Halley radar field of view. |
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