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| Titel |
Downward auroral currents from the reconnection Hall-region |
| VerfasserIn |
R. A. Treumann, R. Nakamura, W. Baumjohann |
| 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 ; 29, no. 4 ; Nr. 29, no. 4 (2011-04-14), S.679-685 |
| Datensatznummer |
250017004
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| Publikation (Nr.) |
 copernicus.org/angeo-29-679-2011.pdf |
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| Zusammenfassung |
| We present a simple (stationary) mechanism capable of generating the auroral
downward field-aligned electric field that is needed for accelerating the ionospheric
electron component up into the magnetosphere and confining the ionospheric
ions at low latitudes (as is required by observation of an ionospheric cavity
in the downward auroral current region). The lifted ionospheric electrons
carry the downward auroral current. Our model is based on the assumption of
collisionless reconnection in the tail current sheet. It makes use of the
dynamical difference between electrons and ions in the ion inertial region
surrounding the reconnection X-line which causes Hall currents to flow. We
show that the spatial confinement of the Hall magnetic field and flux to the
ion inertial region centred on the X-point generates a spatially variable
electromotive force which is positive near the outer inflow boundaries of the
ion inertial region and negative in the central inflow region. Looked at from
the ionosphere it functions like a localised meso-scale electric potential.
The positive electromotive force gives rise to upward electron flow from the
ionosphere during substorms (causing "black aurorae"). A similar positive
potential is identified on the earthward side of the fast reconnection
outflow region which has the same effect, explaining the observation that
auroral upward currents are flanked from both sides by narrow downward
currents. |
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