Mass Flux in Corkscrew Flow Vortices in the Venus Plasma Wake

Abstract

Measurements conducted with the Venus Express spacecraft (VEX) around Venus have provided evidence for the presence of a vortex structure in its wake. A configuration of the form of a corkscrew flow with a cross-section comparable to the planet’s radius has been inferred from those measurements and exhibits a rotation in the counterclockwise sense when viewed from the wake back to Venus. Such structure is generated by the solar wind and also by planetary ions driven along the wake as inferred from the analysis of data obtained in several orbits of that spacecraft. It has also been learned that the width of the corkscrew structure gradually decreases with distance along the wake and its position varies along the solar cycle occurring closer to the planet during minimum solar cycle conditions. Measurements also show that the flow speed of the planetary ions driven from the nightside ionosphere is modified as they move through the corkscrew flow structure and become accelerated as the width of a corkscrew structure decreases with increasing distance downstream from Venus. Measurements also show that the mass flux of the planetary ions increases at high altitudes above the planet when they are conducted across the narrow part of a corkscrew shape in the particle distribution along the wake.