KINETIC KELVIN-HELMHOLTZ INSTABILITY AT A FINITE-SIZED OBJECT

Two-dimensional hybrid simulations with particle ions and fluid electr ons are used to calculate the kinetic evolution of the self-consistent flow around a two-dimensional obstacle with zero intrinsic magnetic f ield. Plasma outflow from the obstacle is used to establish a boundary layer between the incoming solar wind and the outgoing plasma. Becaus e the self-consistent flow solution, a velocity shear is naturally set up at this interface, and since the magnetic field for these simulati ons is transverse to this flow, the Kelvin-Helmholtz (K-H) instability can be excited at low-velocity shear. Simulations demonstrate the exi stence of the instability even near the subsolar location, which norma lly is thought to be stable to this instability. The apparent reason f or this result is the overall time dependence at the boundary layer, w hich gives rise to a Rayleigh-Taylor like instability which provides s eed perturbations for the K-R instability. These results are directly applicable to Venus, comets, artificial plasma releases, and laser tar get experiments. This result has potentially important ramifications f or the interpretation of observational results as well as for an estim ation of the cross-field transport. The results suggest that the K-H i nstability may play a role in dayside processes and the Venus ionopaus e, and may exist within the context of more general situations, for ex ample, the Earth's magnetopause.