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| Titel |
Excitation of Alfvén waves by modulated HF heating of the ionosphere, with application to FAST observations |
| VerfasserIn |
E. Kolesnikova, T. R. Robinson, J. A. Davies, D. M. Wright, Mark Lester |
| 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. 1 ; Nr. 20, no. 1, S.57-67 |
| Datensatznummer |
250014342
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| Publikation (Nr.) |
 copernicus.org/angeo-20-57-2002.pdf |
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| Zusammenfassung |
During the operation of
the EISCAT high power facility (heater) at Tromsø, Norway, on 8 October 1998,
the FAST spacecraft made electric field and particle observations in the inner
magnetosphere at 0.39 Earth radii above the heated ionospheric region.
Measurements of the direct current electric field clearly exhibit oscillations
with a frequency close to the modulated frequency of heater ( ~ 3 Hz) and an
amplitude of ~ 2 - 5 mV m-1. Thermal electron data from the
electrostatic analyser show the modulation at the same frequency of the
downward electron fluxes. During this period the EISCAT UHF incoherent scatter
radar, sited also at Tromsø, measured a significant enhancement of the
electron density in E-layer up to 2 · 1012 m-3. These
observations have prompted us to make quantitative estimates of the expected
pulsations in the inner magnetosphere caused by the modulated HF heating of
lower ionosphere. Under the conditions of the strong electron precipitation in
the ionosphere, which took place during the FAST observations, the primary
current caused by the perturbation of the conductivity in the heated region is
closed entirely by the parallel current which leaks into the magnetosphere. In
such circumstances the conditions at the ionosphere-magnetosphere boundary are
most favourable for the launching of an Alfvén wave: it is launched from the
node in the gradient of the scalar potential which is proportional to the
parallel current. The parallel electric field of the Alfvén wave is
significant in the region where the electron inertial length is of order of the
transverse wavelength of the Alfvén wave or larger and may effectively
accelerate superthermal electrons downward into the ionosphere.
Key words. Ionosphere (active
experiments; ionosphere – magnetosphere interactions; particle acceleration) |
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