Ion behaviors in the meso-scale 3-D Kelvin–Helmholtz instability

Abstract:

Over three decades of in-situ observations illustrate that the Kelvin–Helmholtz (KH) instability driven by the sheared flow between the magnetosheath’s and magnetospheric plasma often occurs at the Earth’s and other planet’s magnetopauses under various IMF conditions. It has been well demonstrated that the KH instability plays an important role for energy, momentum, and mass transport during the solar-wind-magnetosphere coupling process. Particularly, the KH instability is an important mechanism to trigger secondary small scale (i.e., often kinetic-scale) physical processes, such as magnetic reconnection, kinetic Alfven waves, ion-acoustic waves, and turbulence, providing the bridge for the coupling of cross scale physical processes. From the simulation perspective, to fully investigate the role of the KH instability to the cross-scale process requires the numerical modeling that can describe the physical scales from a few Earth radii to a few ion (even electron) inertial lengths in three dimensions, which is often computationally expensive. Thus, it is useful to use different simulation methods to explore physical processes on different length scales, and cross validate the physical processes which occur on the overlapping length scales. This presentation will provide a comparison study of the 3-D KH instability simulation between the Hall MHD simulations with test particles and hybrid (ion particle and electron fluid treatment) simulations. This study will mainly focus on the behavior of different ion species (i.e., H+, He+, O+, and super-thermal species), which include particle distributions, mixing, acceleration, and heating, and corresponding physical mechanisms. We will also discuss the simulation results with newly reported in-situ KH observation events by MMS, and potential application to Cassini and JUNO data analysis.