Correlation of auroral hiss and upward electron beams near the polar cusp

Abstract

Simultaneous plasma and wave data obtained by the DE-I satellite are used to study a correlation between electrostatic auroral hiss emissions at several kilohertz and upward electron beams at altitudes between 2 and 4 R e near the dayside polar cusp. Among five randomly selected DE-I passes, intense electrostatic hiss emissions at frequencies below the electron plasma frequency are found to be associated with strong upward electron beams for every pass. The frequency-time spectrum of auroral hiss near the polar cusp is sometimes characterized by a funnel shape, suggesting that the radiation is emitted from a wave source below the spacecraft. At the center of the enhanced wave region, the electron distribution function above 20 eV is characterized by two components: a hot Maxwellian component and an upward electron beam. The bqams generally have a peak energy around 50 eV, a temperature around 20 eV and a density of the order of I cm -3. The observed distribution functions are fitted by a drifting Maxwellian function for the electron beam and an isotropic Maxwellian function for the hot component. The empirically fitted plasma parameters are then used to solve the linear dispersion equation of electrostatic waves. The instability analyses indicate that whistler waves propagating with wave normal angles near a small resonance cone can be easily excited by low energy (<100 eV) upward electron beams. The frequencies of large growth rates are found below the electron plasma frequency, in agreement with the observations. On the basis of the model that cusp auroral hiss emissions are whistler waves propagating near the resonance cone, ray phth studies indicate that the low altitude boundary of the wave source of cusp hiss is located at about I R e. ß oo o ß ß ß 6 Oct 1981 o ß o ß o ß ß o ßo ß o o o 0o oß ß ß ß ß ßo ßo ß o o o ß ß ß o o ß :-ß ß .• o ß ß ß ß o o ß ß ß ß ß o ß 10:48 10:49

The relationship between auroral hiss at high altitudes over the polar caps and the substorm dynamics of aurora

“…Only the example of the auroral hiss correlation with upgoing 50 eV electrons in the dayside polar cusp was shown (Lin et al, 1984). However, this result contradicts with results by Morgan et al (1994), who investigated the role of Landau damping for upward propagating auroral hiss.…”

Whistler-Langmuir oscillitons and their relation to auroral hiss

“…In contrast to the purely electrostatic Langmuir waves well studied in past, analogous investigations in magnetized plasmas at oblique propagation, however, require the full apparatus of electromagnetic plasma dispersion theory and less work on this has appeared in the literature (see e.g. Kennel, 1966;Maggs, 1976;Lin et al, 1984;Morgan et al, 1994;Willes and Cairns, 2000;Kopf et al, 2010).…”

Experimental observation of electron-acoustic wave propagation in laboratory plasma

“…Furthermore, EAW in nonlinear regime form solitary structures 11 and also provides a decay channel for the long wavelength Langmuir waves through nonlinear wave interactions 12 . In space plasma, analysis of the broadband electrostatic noise (BEN) in the terrestrial cusp of the magnetosphere and the hiss (high frequency field fluctuations) in the polar cusp region were found to corroborate to the generation of EAW [13][14][15][16] . As mentioned before, in typical laboratory plasmas EAW is highly damped.…”