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| Titel |
On the occurrence and characteristics of intense low-altitude electric fields observed by Freja |
| VerfasserIn |
G. Marklund, L. Blomberg, C.-G. Fälthammar, P.-A. Lindqvist, L. Eliasson |
| 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 ; 13, no. 7 ; Nr. 13, no. 7, S.704-712 |
| Datensatznummer |
250011912
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| Publikation (Nr.) |
 copernicus.org/angeo-13-704-1995.pdf |
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| Zusammenfassung |
| High-resolution measurements by the double
probe electric field instrument on the Freja satellite are presented. The
observations show that extremely intense (up to 1 V m–1) and
fine-structured (<1 km) electric fields exist at auroral latitudes within the
altitude regime explored by Freja (up to 1700 km). The intense field events
typically occur within the early morning sector of the auroral oval (01–07 MLT)
during times of geomagnetic activity. In contrast to the observations within the
auroral acceleration region characterized by intense converging electric fields
associated with electron precipitation, upward ion beams and upward
field-aligned currents, the intense electric fields observed by Freja are often
found to be diverging and located within regions of downward field-aligned
currents outside the electron aurora. Moreover, the intense fields are observed
in conjunction with precipitating and transversely energized ions of energies
0.5–1 keV and may play an important role in the ion heating. The observations
suggest that the intense electric field events are associated with small-scale
low-conductivity ionospheric regions void of auroral emissions such as east-west
aligned dark filaments or vortex streets of black auroral curls located between
or adjacent to auroral arcs within the morningside diffuse auroral region. We
suggest that these intense fields also exist at ionospheric altitudes although
no such observations have yet been made. This is possible since the
height-integrated conductivity associated with the dark filaments may be as low
as 0.1 S or less. In addition, Freja electric field data collected outside the
auroral region are discussed with particular emphasis on subauroral electric
fields which are observed within the 19–01 MLT sector between the equatorward
edge of the auroral oval and the inner edge of the ring current. |
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