Modulated electron plasma waves observed in the tail lobe: Geotail waveform observations

Abstract

Abstract. We present the results of the Geotail waveform observation on the electrostatic plasma waves with their frequency close to the local electron plasma frequency in the tail lobe. Those waves, which we call "electron plasma waves" in the present paper, are strongly modulated in their amplitudes and are very similar to the modulated Lungmuir waves observed by previous spacecraft in the various regions. From the detailed analyses, we conclude that they include• the Lungmuir waves and 5 types of the Electron Cyclotron Harmonic (ECH) waves. Finally, we introduce an interesting event that the observed waves change from the ECH waves to the Lungmuir waves in a short period within one second.

A linear model for amplitude modulation of Langmuir waves in weak electron-beam plasma interaction

“…Characteristic features are the significant amplitude modulation and the formation of Langmuir wave packets with a scale of 5-10 wavelengths of the mode with the largest temporal growth rate, and zero points of the envelope. The field amplitude reaches values in the mV/m range, which is consistent with the order of magnitude seen in observations (Hospodarsky et al, 1994;Kellog et al, 1996;Kojima et al, 1997;Pottelette et al, 1999;Sigsbee et al, 2010). We emphasize that the strong modulation seen here comes about only by the beating of Langmuir waves with different wavenumbers and different amplitudes.…”

“…Among them are Voyager (Gurnett et al, 1981); Galileo (Gurnett et al, 1993;Hospodarsky et al, 1994); Wind (Kellog et al, 1996); Geotail (Kojima et al, 1997); Fast (Pottelette et al, 1999); and Cluster (Sigsbee et al, 2010). The observed Langmuir envelopes are highly structured and have occasionally the form of a chain of wave packets with nearly the same temporal scale.…”

Reconnection and Waves: A Review with a Perspective

“…Therefore polarization is useful information to categorize the wave mode. The parallel-polarization waves reported by Kojima et al (1997b) would indicate the presence of Langmuir waves rather than the upper hybrid waves. The observations by Kojima et al (1997b) and Farrell et al (2002) showed significant difference in the amplitude of the upper hybrid waves.…”

“…The parallel-polarization waves reported by Kojima et al (1997b) would indicate the presence of Langmuir waves rather than the upper hybrid waves. The observations by Kojima et al (1997b) and Farrell et al (2002) showed significant difference in the amplitude of the upper hybrid waves. While the processes for generating the above upper hybrid waves of two different amplitudes may not necessarily be the same, these upper hybrid waves are observed in association with electron heat flux/beam features.…”

“…ESW will be discussed in more detail later. Regarding the upper hybrid waves at the plasma sheet boundary layer, Kojima et al (1997b) observed modulated waveforms that contained a mixture of parallel and perpendicular polarization relative to the ambient magnetic field. In the magnetotail, the upper hybrid frequency is almost equal to the electron plasma frequency because the electron cyclotron frequency is much lower than the electron plasma frequency.…”