Isolated electrostatic structures observed throughout the Cluster orbit: relationship to magnetic field strength

Abstract

Abstract. Isolated electrostatic structures are observed throughout much of the 4 R E by 19.6 R E Cluster orbit. These structures are observed in the Wideband plasma wave instrument's waveform data as bipolar pulses (one positive and one negative peak in the electric field amplitude) and tripolar pulses (two positive and one negative peak, or vice versa). These structures are observed at all of the boundary layers, in the solar wind and magnetosheath, and along auroral field lines at 4.5-6.5 R E . Using the Wideband waveform data from the various Cluster spacecraft we have carried out a survey of the amplitudes and time durations of these structures and how these quantities vary with the local magnetic field strength. Such a survey has not been carried out before, and it reveals certain characteristics of solitary structures in a finite magnetic field, a topic still inadequately addressed by theories. We find that there is a broad range of electric field amplitudes at any specific magnetic field strength, and there is a general trend for the electric field amplitudes to increase as the strength of the magnetic field increases over a range of 5 to 500 nT. We provide a possible explanation for this trend that relates to the structures being Bernstein-GreeneKruskal mode solitary waves. There is no corresponding dependence of the duration of the structures on the magnetic field strength, although a plot of these two quantities reveals the unexpected result that with the exception of the magnetosheath, all of the time durations for all of the other regions are comparable, whereas the magnetosheath time durations clearly are in a different category of much smaller time duration. We speculate that this implies that the structures are much smaller in size. The distinctly different pulse durations for the magnetosheath pulses indicate the possibility that the pulses are generated by a mechanism which is different from the mechanism operating in other regions.

Ion-acoustic solitons in warm magnetoplasmas with super-thermal electrons

“…This is consistent with observvation of these solitons in magnetospheric plasmas [10][11][12][13] . Use the right hand side axis for the case when κ ∼ 3/2, which is very large compared to others.…”

“…In this section, we consider the physical scenario with two-temperature electrons, which is motivated by the experimental observations such as those by the Cluster spacecrafts 10 . We consider two species of electrons -hot and cold one.…”

“…A fullblown analysis of solitary waves where magnetic perturbation is self-consistently considered can be very rigorous 9 . Several space-borne experiments have observed ESWs moving parallel to the ambient magnetic field in various nearearth plasma environments such as the solar wind, magnetosheath and magnetotail regions, and auroral zone [10][11][12][13] . These ESWs are, in general, bipolar structures moving in the direction of the background magnetic field 14 .…”

Plasma waves above the ion cyclotron frequency in the solar wind: a review on observations

“…Since then, they are commonly observed in auroral regions (Ergun et al, 1998; 2001; Pickett et al, 2004) but also in several Earth magnetic environments (Matsumoto et al, 1994;Franz et al, 1998;Cattell et al, 2003;Pickett et al, 2003) and in the Earth bow shock (Bale et al, 1998;Behlke et al, 2004). Evidence for the presence of isolated bipolar electrostatic structures in the solar wind is more recent: Mangeney et al (1999) first reported the observation of such structures in the free solar wind and Williams et al (2006) showed some examples associated to an interplanetary shock.…”

An interpretation for the bipolar electric field structures parallel to the magnetic field observed in the auroral ionosphere

“…The Cluster satellites have observed Electric Field Solitary (EFS) waves, moving parallel to the magnetic field direction, in many space plasma regions, such as the solar wind, magnetosheath, magnetotail, and in the auroral zone (Pickett et al, 2004;Marklund et al, 2004). Indeed, the EFS waves were first observed in the auroral zone by the S3-3 (Temerin et al, 1982) and Viking satellites (Boström et al, 1988).…”