Electron plasma oscillations in the Venus foreshock

Abstract

Plasma waves are observed in the solar wind upstream of the Venus bow shock by the Pioneer Venus Orbiter. These wave signatures occur during periods when the interplanetary magnetic field through the spacecraft position intersects the bow shock, thereby placing the spacecraft in the foreshock region. The electron foreshock boundary is clearly evident in the data as a sharp onset in wave activity and a peak in intensity. Wave intensity is seen to drop rapidly with incresing penetration into the foreshock. The peak wave electric field strength at the electron foreshock boundary is found to be similar to terrestrial observations. A normalized wave spectrum was constructed using measurements of the electron plasma frequency and the spectrum was found to be centered about this value. These results, along with polarization studies showing the wave electric field to be field aligned, are consistent with our interpretation of the waves as electron plasma oscillations.

Statistical imaging of the Venus foreshock using VLF wave emissions

“…In brief, these waves also consist of parallel polarized emissions observed near local ft,, (here -30 kHz) and evidence of crossing the electron foreshock boundary is clearly observable as a sharp onset in such wave activity. The waves have peak amplitude (10 mV/m; the same as at the Earth) at the foreshock boundary (tangent field line, Figure 1) then decrease in amplitude with penetration into the foreshock [Crawford et al, 1990[Crawford et al, , 1993a. There is also some evidence ] that the emissions first increase then decrease in intensity with distance along the foreshock boundary from the shock.…”

“…The VLF characteristics of the Venus electron foreshock have been discussed in detail by Crawford et al [ 1990Crawford et al [ , 1991Crawford et al [ , 1993a. More recently, the major results from these papers and highlights of the present work (namely a brief overview of our statistical imaging results) have been reviewed by Strangeway and Crawford [1995a, b].…”

Microphysics of the Venusian and Martian mantles

“…3c) Before closing, we point out that a great deal of work still remains. Future studies will need to consider such topics as injection (as opposed to the initial-value simulation considered here), the relative importance of the MTSI, LHSI, and ion-acoustic modes [Crawford et al, 1993;Huba, 1993], the importance of magnetic shear, the importance of electron kinetic effects on wave stability, and the effect of multiple spatial dimensions and non-periodic boundary conditions.…”

The Martian bow shock: Wave observations in the upstream region

“…The trend for the signal to increase is rather modest is comparison with the scatter of the measurements, which makes the result less conclusive. However, this feature is also observed at Earth [Filbert and Kellogg, 1979;Etcheto and Faucheux, 1984] and Venus [Crawford et al, 1990]. The present analysis can only be qualitative because of the limitation of the data base, the broad bandwidth of the filters, and the relatively high and variable level of instrument background noise.…”

“…It is known that wave measurements performed upstream of planetary bow shocks depend on spacecraft location and magnetic field orientation [Filbert and Kellogg, 1979;Etcheto and Faucheux, 1984;Crawford et al, 1990]. For this reason, calculations involving a model bow shock, magnetic field measurements, and spacecraft orbital data are carried out to determine the time periods during which the Phobos 2 spacecraft is magnetically connected to the Martian bow shock.…”