MHD simulations of the Kelvin-Helmholtz instability near the ionopause of Venus across a range of density ratios and magnetic Reynolds numbers

Abstract

The Kelvin–Helmholtz instability on the ionopause of Venus with different density ratios and magnetic Reynolds numbers has been simulated numerically by using the magnetohydrodynamics equations. For the special case of a Venus-like planet, the plasma density increases from the magnetosheath to the ionosphere. The numerical simulation shows that the density increasing toward the planet has more important effects than the magnetic Reynolds number on the Kelvin–Helmholtz instability. And during the evolution of the Kelvin–Helmholtz instability, there are three different phases, the linear growth phase, followed by a nonlinear phase with vortex-like structure, and finally, the turbulent phase. During the nonlinear evolution of the Kelvin–Helmholtz instability, the spatial scale of the vortex has a width of about $\sim 12a$, where $a$ is the half width of the shear layer located at the Venusian ionopause. For each phase, the vorticity of the system also has different characteristics. Supersonic flow could appear at the position where the vorticity is stronger in both nonlinear and turbulent phases.