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| Titel |
Electromagnetic waves and bursty electron acceleration: implications from Freja |
| VerfasserIn |
L. Andersson, J.-E. Wahlund, J. Clemmons, B. Gustavsson, 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 ; 20, no. 2 ; Nr. 20, no. 2, S.139-150 |
| Datensatznummer |
250014350
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| Publikation (Nr.) |
 copernicus.org/angeo-20-139-2002.pdf |
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| Zusammenfassung |
Dispersive Alfvén wave
activity is identified in four dayside auroral oval events measured by the
Freja satellite. The events are characterized by ion injection, bursty electron
precipitation below about 1 keV, transverse ion heating and broadband extremely
low frequency (ELF) emissions below the lower hybrid cutoff frequency (a few
kHz). Large-scale density depletions/cavities, as determined by the Langmuir
probe measurements, and strong electrostatic emissions are often observed
simultaneously. A correlation study has been carried out between the E
and B field fluctuations below 64 Hz and 10 Hz, respectively,
(the DC instruments upper threshold) and the characteristics of the
precipitating electrons. This study revealed that the energisation of electrons
is indeed related to the broadband ELF emissions and that the electrostatic
component plays a predominant role during very active magnetospheric
conditions. Furthermore, the effect of the ELF electromagnetic emissions on the
larger scale field-aligned current systems has been investigated, and it is
found that such an effect cannot be detected. Instead, the Alfvénic activity
creates a local region of field-aligned currents. It is suggested that
dispersive Alfvén waves set up these local field-aligned current regions and,
in turn, trigger more electrostatic emissions during certain conditions. In
these regions, ions are transversely heated, and large-scale density
depletions/cavities may be created during especially active periods.
Key words. Ionosphere (particle
acceleraton; wave-particle interactions) Magnetospheric physics (auroral
phenomena) |
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