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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 21, issue 7
Ann. Geophys., 21, 1393–1403, 2003
https://doi.org/10.5194/angeo-21-1393-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 21, 1393–1403, 2003
https://doi.org/10.5194/angeo-21-1393-2003
© Author(s) 2003. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Jul 2003

31 Jul 2003

Interaction of suprathermal solar wind electron fluxes with sheared whistler waves: fan instability

C. Krafft1 and A. Volokitin2 C. Krafft and A. Volokitin
  • 1Laboratoire de Physique des Gaz et des Plasmas, Université Paris Sud, 91405 Orsay Cedex, France
  • 2Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, Academy of Sciences, Troitsk, Moscow Region, 142190, Russia

Abstract. Several in situ measurements performed in the solar wind evidenced that solar type III radio bursts were some-times associated with locally excited Langmuir waves, high-energy electron fluxes and low-frequency electrostatic and electromagnetic waves; moreover, in some cases, the simultaneous identification of energetic electron fluxes, Langmuir and whistler waves was performed. This paper shows how whistlers can be excited in the disturbed solar wind through the so-called "fan instability" by interacting with energetic electrons at the anomalous Doppler resonance. This instability process, which is driven by the anisotropy in the energetic electron velocity distribution along the ambient magnetic field, does not require any positive slope in the suprathermal electron tail and thus can account for physical situations where plateaued reduced electron velocity distributions were observed in solar wind plasmas in association with Langmuir and whistler waves. Owing to linear calculations of growth rates, we show that for disturbed solar wind conditions (that is, when suprathermal particle fluxes propagate along the ambient magnetic field), the fan instability can excite VLF waves (whistlers and lower hybrid waves) with characteristics close to those observed in space experiments.

Key words. Space plasma physics (waves and instabilities) – Radio Science (waves in plasma) – Solar physics, astrophysics and astronomy (radio emissions)

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