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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 9
Ann. Geophys., 18, 1216–1223, 2000
https://doi.org/10.1007/s00585-000-1216-2
© European Geosciences Union 2000

Special issue: IXe EISCAT

Ann. Geophys., 18, 1216–1223, 2000
https://doi.org/10.1007/s00585-000-1216-2
© European Geosciences Union 2000

  30 Sep 2000

30 Sep 2000

Effects of a kappa distribution function of electrons on incoherent scatter spectra

S. Saito1, F. R. E. Forme2, S. C. Buchert1, S. Nozawa1, and R. Fujii1 S. Saito et al.
  • 1Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan
  • 2CETP-Universite Versailles St-Quentin en Yvelines, 10-12, Av. de l'Europe, 78140 Velizy, France

Abstract. In usual incoherent scatter data analysis, the plasma distribution function is assumed to be Maxwellian. In space plasmas, however, distribution functions with a high energy tail which can be well modeled by a generalized Lorentzian distribution function with spectral index kappa (kappa distribution) have been observed. We have theoretically calculated incoherent scatter spectra for a plasma that consists of electrons with kappa distribution function and ions with Maxwellian neglecting the effects of the magnetic field and collisions. The ion line spectra have a double-humped shape similar to those from a Maxwellian plasma. The electron temperatures are underestimated, however, by up to 40% when interpreted assuming Maxwellian distribution. Ion temperatures and electron densities are affected little. Accordingly, actual electron temperatures might be underestimated when an energy input maintaining a high energy tail exists. We have also calculated plasma lines with the kappa distribution function. They are enhanced in total strength, and the peak frequencies appear to be slightly shifted to the transmitter frequency compared to the peak frequencies for a Maxwellian distribution. The damping rate depends on the electron temperature. For lower electron temperatures, plasma lines for electrons with a κ distribution function are more strongly damped than for a Maxwellian distribution. For higher electron temperatures, however, they have a relatively sharp peak.

Key words: Ionosphere (auroral ionosphere; plasma waves and instabilities) – Space plasma physics (kinetic and MHD theory)

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