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| Titel |
Statistical study on the occurrence of ASAID electric fields |
| VerfasserIn |
S. Liléo, T. Karlsson, G. T. Marklund |
| 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. 2 ; Nr. 28, no. 2 (2010-02-08), S.439-448 |
| Datensatznummer |
250016775
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| Publikation (Nr.) |
 copernicus.org/angeo-28-439-2010.pdf |
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| Zusammenfassung |
The first statistical results on the occurrence of abnormal subauroral ion
drifts (ASAID) are presented based on electric and magnetic field
measurements from the low-altitude Astrid-2 satellite. ASAID are narrow
regions of rapid eastward ion drifts observed in the subauroral ionosphere.
They correspond to equatorward-directed electric fields with peak amplitudes
seen to vary between 45 mV/m and 185 mV/m, and with latitudinal extensions
between 0.2° and 1.2° Corrected Geomagnetic Latitude (CGLat),
reaching in some cases up to 3.0° CGLat.
Opposite to subauroral ion drifts (SAID) that are known to be
substorm-related, ASAID are seen to occur predominantly during extended
periods of low substorm activity. Our results show that ASAID are located in
the vicinity of the equatorward edge of the auroral oval, mainly in the
postmidnight sector between 23:00 and 03:00 magnetic local time. They are
associated with a local current system with the same scale-size as the
corresponding ASAID, composed by a region of downward field-aligned currents
(FACs) flowing in the ASAID poleward side, and a region of upward flowing
FACs in the equatorward side. The FACs have densities between 0.5 and 2.0 μA/m2.
The data suggest that ASAID do not contribute significantly to
the reduction of the ionospheric conductivity. ASAID are seen to have life
times of at least 3.5 h.
A discussion on possible mechanisms for the generation of ASAID is presented.
We speculate that the proximity of the electron to the ion plasma sheet inner
boundaries and of the plasmapause to the ring current outer edge, during
extended quiet times, is an important key for the understanding of the
generation of ASAID electric fields. |
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