Characteristics of electrostatic solitary waves observed in the plasma sheet boundary: Statistical analyses

Abstract

Abstract. We present the characteristics of the Electrostatic Solitary Waves (ESW) observed by the Geotail spacecraft in the plasma sheet boundary layer based on the statistical analyses. We also discuss the results referring to a model of ESW generation due to electron beams, which is proposed by computer simulations. In this generation model, the nonlinear evolution of Langmuir waves excited by electron bump-on-tail instabilities leads to formation of isolated electrostatic potential structures corresponding to "electron hole" in the phase space. The statistical analyses of the Geotail data, which we conducted under the assumption that polarity of ESW potentials is positive, show that most of ESW propagate in the same direction of electron beams, which are observed by the plasma instrument, simultaneously. Further, we also find that the ESW potential energy is much smaller than the background electron thermal energy and that the ESW potential widths are typically shorter than 60 times of local electron Debye length when we assume that the ESW potentials travel in the same velocity of electron beams. These results are very consistent with the ESW generation model that the nonlinear evolution of electron bump-on-tail instability leads to the formation of electron holes in the phase space.

Electron beam-associated symmetric electrostatic solitary waves on the separatrix of magnetic reconnection: multi-spacecraft analysis

“…Their result based on Geotail observation was consistent with the ESW generation mechanism due to the electron beams which resulted from particle simulation performed by Omura et al (1996) and Miyake et al (1998). We also note that in the statistics performed by Kojima et al (1999b), a small portion of the observed ESWs do not travel in the same direction of the electron beam. We suggest that the case in this study corresponds to the small portion of cases in Geotail observation, which only detects that ESWs travel along the magnetic tube with antiparallel electron beam.…”

“…Though it was reported that large-amplitude (on the order of 100 mV/m) ESWs were observed in the magnetopause and bow shock and the cusp region by FAST satellite (Ergun et al 1998) and by Polar in the low-altitude auroral zone and, at high altitudes (~4-8 R E ), during crossings of the plasma sheet boundary and cusp (Cattell et al 1999, however, the amplitude of ESWs observed in the magnetotail is usually on the order of 1~100 uV/m by Geotail (e.g., Matsumoto et al 1994Matsumoto et al , 1999Kojima et al 1997Kojima et al , 1999bLi et al 2009) and on the order of 0.01~1 mV/m by Cluster (Li et al 2010). Cattell et al (2005) had observed largeamplitude (up to 50 mV/m) solitary waves (electron holes) near the outer edge of the plasma sheet, within and on the edge of a density cavity, and at distances on the order of a few ion inertial lengths from the center of the current sheet.…”

“…In observation, Kojima et al (1999b) performed a statistical study on the propagation direction of ESW and the electron beam on the plasma sheet boundary by Geotail observation. Their results suggested that 88 % of the observed ESW traveling direction is almost the same with the electron beam direction.…”

Reconnection and Waves: A Review with a Perspective

“…Such a situation can be realized commonly in the PSBL, which is a corridor for energetic electrons accelerated at a reconnection region. Figure 3 shows a scatter plot showing potential energy versus spatial scale of ESWs observed by Geotail in the geomagnetic tail (Kojima et al 1999). As shown, the ESW potential energies were mostly below 4 eV.…”

Some theoretical models for solitary structures of boundary layer waves

“…They showed that the broadness of the BEN frequency spectra arises from the solitary waveforms. A likely generation mechanism for BEN is based on the nonlinear evolution of the electron beam instabilities, leading to the formation of the isolated Bernstein-Greene-Kruskal (BGK) potential structures, which reproduce well the observed electrostatic solitary waveforms (Omura et al, , 1996Kojima et al, 1997Kojima et al, , 1999). An example of the time evolution of the bump-on-tail instability obtained by the one-dimensional computer simulations is shown in Fig.…”