![]() Langmuir waves can be generated by both electrons accelerated by parallel electric fields in the auroral acceleration region and scattered into a broad downgoing beam or by concentrated parallel electron beams caused by Alfvénic acceleration. Simultaneous observations of electron distribution functions and plasma waves have been reported by McFadden et al. (1986), Ergun et al. These wave amplitudes can range from a few millivolts per meter ( mV m −1) (McFadden et al., 1986) to greater than 1 V m −1 (Kintner et al., 1995) and have been observed in both under- ( f pe f ce) plasmas, where f pe is the electron plasma frequency and f ce is the electron cyclotron frequency (Beghin et al., 1989 McAdams et al., 1999). ![]() Plasma waves generated at or near the local plasma frequency have been observed in the auroral ionosphere by satellites and rockets ever since there have been instruments capable of measuring them (review by Akbari et al., 2021). The results show that this interpretation is plausible. A dispersion solver, partially informed with measured electron distributions, and associated frequency- and wavevector-matching conditions were employed to determine if the diffuse features could be generated by a nonlinear wave–wave interaction of the plasma line with the lower-frequency auroral hiss waves/lower-hybrid waves. The VLF receiver detected auroral hiss throughout the flight at 5–10 kHz, a frequency matching the difference between the plasma line and the diffuse feature. These angles were found to be comparable to the theoretical Z-infinity angle that these waves would resonate at. The ratio of the parallel to perpendicular components of the plasma line and diffuse feature were used to determine the angle of propagation of these waves with respect to the background magnetic field. ![]() Both of these waves occurred slightly above the local plasma frequency with amplitudes between 1–100 µV m −1. These receivers observed five short-lived Langmuir wave bursts lasting from 0.1–0.2 s, consisting of a thin plasma line with frequencies in the range of 2470–2610 kHz that had an associated diffuse feature occurring 5–10 kHz above the plasma line. The flight was unique in having three high-frequency (HF) receivers using multiple antennas parallel and perpendicular to the ambient magnetic field, as well as very low-frequency (VLF) receivers using antennas perpendicular to the magnetic field. The High-Bandwidth Auroral Rocket (HIBAR) was launched from Poker Flat, Alaska, on 28 January 2003 at 07:50 UT towards an apogee of 382 km in the nightside aurora. ![]()
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