Abstract
Abstract. Satellite measurements show that ion beams above the auroral acceleration region are heated to hundreds of eV in a direction perpendicular to the magnetic field. We show that ion acoustic waves may be responsible for much of this heating. Even in the absence of a positive slope in the velocity distribution of the beam ions, ion acoustic waves can be generated by a fan instability. We present analytical estimates of the wave growth rate and ion beam heating rate. These estimates, which are confirmed by particle simulations, indicate that the perpendicular temperature of the beam ions will increase by 30 eV/s, or by 1 eV in 20–25 km. From the simulations we also conclude that the heating saturates at a perpendicular temperature around 200 eV, which is consistent with observations.Key words. Ionosphere (wave-particle interactions) · Magnetospheric Physics (plasma waves and instabilities) · Space plasma physics (wave-particle interactions).
Highlights
Energetic upowing ®eld-aligned ion beams with keV energies are a frequently occurring phenomenon in the auroral zone
Energetic ion beams created only by acceleration of a background ion component in a parallel electric ®eld would show no change in the perpendicular temperature of the beams, and a decrease in the parallel temperature
The growth rate of ion acoustic waves due to the ion fan instability and the rate of perpendicular heating caused by these waves as predicted by quasi-linear theory are con®rmed quantitatively by our simulations
Summary
Energetic upowing ®eld-aligned ion beams with keV energies are a frequently occurring phenomenon in the auroral zone. There are many statistical studies of the ion beam drift energies, composition and occurrence frequencies depending on factors such as solar activity, altitude, magnetic local time and invariant latitude (Kondo et al, 1990; Collin et al, 1987; Yau et al, 1984; Gorney et al, 1981). Vaivads accelerated by a quasi-static electric ®eld parallel to the ambient magnetic ®eld (Rei et al, 1988). The shape of the ion beam distributions cannot be explained by a parallel quasi-static electric ®eld alone. Energetic ion beams created only by acceleration of a background (ionospheric) ion component in a parallel electric ®eld would show no change in the perpendicular temperature of the beams, and a decrease in the parallel temperature (the temperature de®ned from the average energy of beam ions in the beam reference system)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
