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| Titel |
Polar observations of electron density distribution in the Earth’s magnetosphere. 2. Density profiles |
| VerfasserIn |
H. Laakso  , R. Pfaff, P. Janhunen |
| 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 ; 20, no. 11 ; Nr. 20, no. 11, S.1725-1735 |
| Datensatznummer |
250014487
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| Publikation (Nr.) |
 copernicus.org/angeo-20-1725-2002.pdf |
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| Zusammenfassung |
Using spacecraft potential measurements of
the Polar electric field experiment, we investigate electron density variations
of key plasma regions within the magnetosphere, including the polar cap, cusp,
trough, plasmapause, and auroral zone. The statistical results were presented
in the first part of this study, and the present paper reports detailed
structures revealed by individual satellite passes. The high-altitude (> 3 RE)
polar cap is generally one of the most tenuous regions in the magnetosphere,
but surprisingly, the polar cap boundary does not appear as a steep density
decline. At low altitudes (1 RE) in summer, the polar
densities are very high, several 100 cm-3 , and interestingly, the
density peaks at the central polar cap. On the noonside of the polar cap, the
cusp appears as a dense, 1–3° wide region. A typical cusp density above 4 RE
distance is between several 10 cm-3 and a few 100 cm-3 .
On some occasions the cusp is crossed multiple times in a single pass,
simultaneously with the occurrence of IMF excursions, as the cusp can instantly
shift its position under varying solar wind conditions, similar to the
magnetopause. On the nightside, the auroral zone is not always detected as a
simple density cavity. Cavities are observed but their locations, strengths,
and sizes vary. Also, the electric field perturbations do not necessarily
overlap with the cavities: there are cavities with no field disturbances, as
well as electric field disturbances observed with no clear cavitation. In the
inner magnetosphere, the density distributions clearly show that the
plasmapause and trough densities are well correlated with geomagnetic activity.
Data from individual orbits near noon and midnight demonstrate that at the
beginning of geomagnetic disturbances, the retreat speed of the plasmapause can
be one L-shell per hour, while during quiet intervals the plasmapause can
expand anti-earthward at the same speed. For the trough region, it is found
that the density tends to be an order of magnitude higher on the day-side (~1
cm-3) than on the nightside (~0.1–1 cm-3), particularly
during low Kp.
Key words. Magnetospheric physics (auroral phenomena;
plasmasphere; polar cap phenomena) |
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