Vela 4 plasma observations near the Earth’s bow shock

Abstract

Concurrent measurements of electron and proton differential energy spectrums (each spectrum measurement requiring from 0.1 to 0.3 sec) have been obtained near the earth’s bow shock with the Vela 4B electrostatic analyzer. The following results have been derived from an analysis of 26 shock crossings during May and June 1967: (1) The jump in proton temperature is 2 to 4 times greater than the jump in electron temperature. (2) In the magnetosheath the proton temperature is nearly always greater than the electron temperature. (3) Te/Tp, upstream from the shock ranges between 0.6 and 4, and the shock remains well defined over this range. (4) Electron thermalization usually occurs in much less than 3 sec and has been observed to occur in ≈ 0.03 sec. (5) The magnetosheath electron velocity distribution is flat‐topped or sometimes somewhat concave in shape within at least a few RE of the shock. (6) Evidence has been found that electrons are thermalized in a thin region upstream from the region in which most of the proton thermalization occurs. The observed increase in Te/Tp resulting from electron preheating may account for destabilization of electrostatic ion waves that may then produce strong ion heating by nonlinear Landau damping. Representative proton and electron velocity distributions from which the above results were derived are presented.

Magnetospheric Plasma Flow and the Nature of the Magnetospheric Boundary Layer

“…A complete energy spectrum (at 20 to 24 logarithmicallyspaced energy levels) is measured every four seconds (every 22.5 degrees of rotation) when the satellites are operated in the real-time (high bit-rate) mode. More detailed descriptions of these instruments have been given by Montgomery et al (1970), by Bame et al (1971) and by Hones et al (1972).…”

Observations of low-energy electrons upstream of the Earth's bow shock

“…This intermixing of distribution functions was originally discussed by Mott-Smith [1951] in connection with classical gas shocks and a discussion applicable to collisionless plasma shocks may be found in Tidman and Krall [1971]. The upstream component of the downstream ion distribution has been observed experimentally by Montgomery et al [1970].…”

“…To emphasize this last point, in Figure 3 we have plotted a superposition of a typical solar wind electron energy spectrum -3 as reported by Montgomery et al [1970] with n = 5.5 cm and Te = 1.6 x 1050K and the spectrum fitted to the data of Figure 2. The bow shock electrons appear essentially as a small highenergy tail upon the main spectrum.…”

“…In their model the ions on both sides of the shock were at zero temperature (thus disposing of the need for an additional dissipation mechanism) while the post-shock electrons were treated as a sum of free and trapped distributions. An estimate of the potential drop across the shock can be obtained by using the measured electron spectrum ( Figure 2) and a typical magnetosheath distribution [Montgomery et al, 1970] and by assuming that the Liouville Theorem applies.…”

Shocks in collisionless plasmas

“…Moreover, this instrument is microprocessor controlled and the highvoltage (HV) sweeps only near the peak of the SW distribution and data from each of the 64 h; / directions can be examined separately. This capability allows us to identify presence of the reflected, gyrating, and leaked MS particles that permeate the vicinity of the bow shock which contaminate the SW measurements (Montgomery et al 1970;Thomsen et al 1983;Sckopke 1995;Parks et al 2016). Although these particles represent a small fraction of the SW (up to 20%), they have energies higher than the SW and affect the values of the bulk parameters calculated from the moments of the measured distribution.…”