Electrostatic solitary waves in current layers: from Cluster observations during a super-substorm to beam experiments at the LAPD

Abstract

Abstract. Electrostatic Solitary Waves (ESWs) have been observed by several spacecraft in the current layers of Earth's magnetosphere since 1982. ESWs are manifested as isolated pulses (one wave period) in the high time resolution waveform data obtained on these spacecraft. They are thus nonlinear structures generated out of nonlinear instabilities and processes. We report the first observations of ESWs associated with the onset of a super-substorm that occurred on 24 August 2005 while the Cluster spacecraft were located in the magnetotail at around 18-19 R E and moving northward from the plasma sheet to the lobes. These ESWs were detected in the waveform data of the WBD plasma wave receiver on three of the Cluster spacecraft. The majority of the ESWs were detected about 5 min after the super-substorm onset during which time 1) the PEACE electron instrument Correspondence to: J. S. Pickett (pickett@uiowa.edu) detected significant field-aligned electron fluxes from a few 100 eV to 3.5 keV, 2) the EDI instrument detected bursts of field-aligned electron currents, 3) the FGM instrument detected substantial magnetic fluctuations and the presence of Alfvén waves, 4) the STAFF experiment detected broadband electric and magnetic waves, ion cyclotron waves and whistler mode waves, and 5) CIS detected nearly comparable densities of H+ and O+ ions and a large tailward H+ velocity. We compare the characteristics of the ESWs observed during this event to those created in the laboratory at the University of California-Los Angeles Plasma Device (LAPD) with an electron beam. We find that the time durations of both space and LAPD ESWs are only slightly larger than the respective local electron plasma periods, indicating that electron, and not ion, dynamics are responsible for generation of the ESWs. We have discussed possible mechanisms for generating the ESWs in space, including the beam and kinetic Buneman type instabilities and the acoustic instabilities. Future studies will examine these mechanisms in more detail using Published by Copernicus Publications on behalf of the European Geosciences Union and the American Geophysical Union. 432 J. S. Pickett et al.: Electrostatic solitary waves in current layers the space measurements as inputs to models, and better relate the ESW space measurements to the laboratory through PIC code models.

Arbitrary amplitude ion-acoustic soliton coexistence and polarity in a plasma with two ion species

“…34,35,37 This assumption is needed, because the solitary wave polarity and the direction of propagation could not be disentangled from one another. 38 However, space observations also revealed the presence of large negative potential structures, with the density perturbation, Dn=n, being negative. 23,24 That also agreed with the theory, which predicted that ion-acoustic double layers are typically negative but required the presence of a second electron component.…”

“…senses and on different timescales, implying the possible presence of solitons and double layers of both polarities, for both lower frequency (ion) and higher frequency (electron) structures. 26,33,36,38 The observation of both polarities could follow in a more general plasma, if the satellite passes from one plasma region to another and changes in the plasma parameter values cause the nonlinearity coefficient in the KdV equation to change sign. Furthermore, both polarities could occur if the plasma conditions are fairly similar in two observation periods, but they happen to support coexistence, and the two polarities are excited in neighboring regions due to differences in the local conditions in space and time.…”

“…[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Two major theoretical approaches are used in such investigations. On one hand, small amplitude (weakly nonlinear) solitary waves are found from the Korteweg-de Vries (KdV) family of equations derived from an expansion such as reductive perturbation theory.…”

Soliton model for broadband electrostatic noise

“…Other interpretations put forward for the generation of ESWs are based on electron-acoustic solitary waves [3,4,5]. Recently, the plasma measurements made on the Cluster spacecraft in the PSBL have shown that broadband (∼ 2-6 kHz) electrostatic noise is associated with cold countersteaming electron beams flowing through the hot Maxwellian plasma [6,8]. The observed plasma parameters were (from Ref.…”

Solitary potential structures in presence of non-thermal electrons

“…The velocities of ESWs can vary from ∼ a few hundred to a few thousand km s −1 . Electrostatic solitary structures have been observed in the almost all regions of the Earth's magnetosphere [1][2][3][4][5].…”