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| Titel |
Effect of suprathermal electrons on the intensity and Doppler frequency of electron plasma lines |
| VerfasserIn |
P. Guio, J. Lilensten  |
| 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 ; 17, no. 7 ; Nr. 17, no. 7, S.903-912 |
| Datensatznummer |
250013786
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| Publikation (Nr.) |
 copernicus.org/angeo-17-903-1999.pdf |
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| Zusammenfassung |
In an incoherent scattering radar experiment,
the spectral measurement of the so-called up- and downshifted electron plasma
lines provides information about their intensity and their Doppler frequency.
These two spectral lines correspond, in the backscatter geometry, to two
Langmuir waves travelling towards and away from the radar. In the daytime
ionosphere, the presence of a small percentage of photoelectrons produced by the
solar EUV of the total electron population can excite or damp these Langmuir
waves above the thermal equilibrium, resulting in an enhancement of the
intensity of the lines above the thermal level. The presence of photo-electrons
also modifies the dielectric response function of the plasma from the Maxwellian
and thus influences the Doppler frequency of the plasma lines. In this paper, we
present a high time-resolution plasma-line data set collected on the Eiscat VHF
radar. The analysed data are compared with a model that includes the effect of a
suprathermal electron population calculated by a transport code. By comparing
the intensity of the analysed plasma lines data to our model, we show that two
sharp peaks in the electron suprathermal distribution in the energy range 20-30
eV causes an increased Landau damping around 24.25 eV and 26.25 eV. We have
identified these two sharp peaks as the effect of the photoionisation of N2
and O by the intense flux of monochromatic HeII radiation of wavelength 30.378
nm (40.812 eV) created in the chromospheric network and coronal holes.
Furthermore, we see that what would have been interpreted as a mean Doppler
drift velocity for a Maxwellian plasma is actually a shift of the Doppler
frequency of the plasma lines due to suprathermal electrons.
Key words. Ionosphere (electric fields and currents;
solar radiation and cosmic ray effects) |
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