A Review Of Electrostatic Solitary Wave Research From The Cluster Mission

A review of the advancements in the knowledge of electrostatic solitary waves (ESWs) made with data obtained by the four satellite Cluster mission, after 20 years in orbit, is presented. ESWs are nonlinear solitary waves or structures observed in high time resolution waveform data. The ESW pulses are the wave data representation of electron or ion phase-space holes, or density/acoustic structures, and are observed throughout the Cluster orbit, particularly at boundary layers, in turbulent plasmas, and wherever there is mixing of plasmas, such as in the magnetotail with the onset of a super-substorm. Much of the research reviewed here involves ESWs involved in the magnetic reconnection processes of Earth, with their mapping across the separatrix region. One of the major advancements in ESW knowledge came from investigating propagation from one spacecraft to another, thus addressing the issue of lifetime and stability of these structures which cannot be adequately addressed with single spacecraft propagation studies. Knowing how stable the ESWs are can help determine their generation mechanism, which was also addressed in many of the papers discussed herein through observations and theory. The ESWs were found to be generated through a mix of instabilities and processes, namely two-stream, Buneman, bump-on-tail, electron-ion, beam-plasma, electron and ion acoustic instabilities, and out of turbulence.