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| Titel |
Response of the auroral electrojet indices to abrupt southward IMF turnings |
| VerfasserIn |
J. W. Gjerloev, R. A. Hoffman, S. Ohtani, J. Weygand, R. Barnes |
| 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 ; 28, no. 5 ; Nr. 28, no. 5 (2010-05-26), S.1167-1182 |
| Datensatznummer |
250016835
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1167-2010.pdf |
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| Zusammenfassung |
We present results from a study of the behavior of the auroral electrojet
indices following abrupt southward turnings of the IMF Bz. The auroral
electrojet indices are calculated from observations made by more than 100
ground based stations provided by the SuperMAG collaborators. Based on three
simple criteria we selected 73 events. In each event the interval of
analysis started at the time of the IMF Bz southward turning and ended 45
minutes later or at the onset of any abrupt energy unloading event in the
magnetosphere, regardless of size. We refer to this period as the
"pre-unloading phase". To isolate the dependence of the auroral
electrojets on the solar induced ionospheric conductivity during this phase
we separated the standard AU/AL indices into two new sets of indices defined
by the upper and lower envelope of the north-south component for all sunlit
stations (AUs/ALs) and for all stations in darkness (AUd/ALd). Based on
events and statistical analyses we can conclude that following a southward
turning of the IMF Bz the AUd/ALd indices show no measurable response while
the AUs/ALs indices clearly intensify. The intensifications of AUs/ALs are
dependent on the intensity of the solar wind driver (as measured by IMF Bz
or the Akasofu ε parameter). The lack of AUd/ALd response does
not depend on the intensity of any subsequent substorm.
We find that during these isolated events the ionospheric current system is
primarily confined to the sunlit ionosphere. This truncated version of the
classical global DP-2 current system suggests that auroral electrojet
continuity is not maintained across the terminator. Because of its
conductivity dependence on the solar zenith angle, this truncated global
current pattern is expected to be highly dependent on UT and season and thus
can be asymmetric between hemispheres. Thus we argue that the global
two-cell DP-2 current system is not a consequence only of a southward
turning of the IMF but requires also the reduction of the conductivity
gradient at the terminator. |
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