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| Titel |
Method of characteristics in spherical geometry applied to a Harang-discontinuity situation |
| VerfasserIn |
O. Amm |
| 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 ; 16, no. 4 ; Nr. 16, no. 4, S.413-424 |
| Datensatznummer |
250013243
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| Publikation (Nr.) |
 copernicus.org/angeo-16-413-1998.pdf |
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| Zusammenfassung |
The method of characteristics for obtaining
spatial distributions of ionospheric electrodynamic parameters from ground-based
spatial observations of the ground magnetic disturbance and the ionospheric
electric field is presented in spherical geometry. The method includes tools for
separation of the external magnetic disturbance, its continuation to the
ionosphere, and calculation of ionospheric equivalent currents. Based on these
and the measured electric field distribution, the ionospheric Hall conductance
is calculated as the primary output of the method. By estimating the Hall-
to-Pedersen conductance ratio distribution, the remaining ionospheric
electrodynamic parameters are inferred. The method does not assume ∇×E=0
to allow to study time-dependent situations. The application of this method to a
Harang discontinuity (HD) situation on 27 October 1977, 17:39 UT, reveals the
following: (1) The conductances at and north of the HD are clearly reduced as
compared to the eastern electrojet region. (2) Plasma flow across the HD is
observed, but almost all horizontal current is diverted into upward-flowing
field-aligned currents (FACs) there. (3) The FACs connected to the Hall currents
form a latitudinally aligned sheet with a magnitude peak between the
electrically and magnetically defined HD, where break-up arcs are often
observed. Their magnitude is larger than that of the more uniformly distributed
FACs connected to the Pedersen currents. They also cause the southward shift of
the magnetically defined HD with respect to the electrically defined one. (4) A
tilt of the HD with respect to geomagnetic latitude as proposed by an earlier
study on the same event, which used composite vector plot technique, and by
statistical studies, is not observed in our single time-step analysis.
Key words. Ionosphere · Electric fields and currents
· Instruments and techniques · Magnetospheric physics · Current systems |
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