Plasma and electric field measurements of the PVO in the Venus ionosheath

A study of the plasma and electric-field measurements of the PVO in the Venus ionosheath near the terminator region is presented. A drastic decrease of the particle-flux intensity measured with the plasma instrument is encountered in the inner ionosheath before the inbound crossing of the ionopause. The outer boundary of the region of weak plasma fluxes is consistent with the presence of a rarefaction wave as reported previously from the Mariner 5 (Bridge et at., 1967), Venera (Verigin et al., 1978) and PVO (Spenner et al., 1980) plasma measurements in the Venus wake. Near that boundary there are, in addition, appreciable changes in the electric field signals detected with the PVO electric-field detectors. These observations suggest the existence of local plasma-wave activity associated with turbulent flow conditions in that region.