Jupiter's Sheared Flow Unstable Magnetopause Boundary Observed by Juno

The interaction between the solar wind and giant magnetospheres (i.e., Jupiter's and Saturn's magnetospheres) is fundamentally important for magnetospheric physics, in which the viscous interaction (presumably driven by the Kelvin-Helmholtz (KH) instability) is often expected to play an important role. Previous simulation and theory studies suggested that Jupiter's low-latitude dawn side flank region is KH unstable due to the large sheared flow between the fast tailward solar wind and magnetospheric sunward corotational flow. The onset of the KH instability can strongly modify the magnetopause boundary layer, which is consistent with the identification of 194 boundary crossings during Juno's first 14 orbits. We applied four different boundary normal analysis methods to illustrate that there is always a wide range of local normal directions, suggesting Jupiter's dawn-side flank region is often highly perturbed. The distribution of local normal directions is insensitive to the upstream solar wind dynamic pressure, Juno's inward/outward boundary crossing direction, and the location along the z direction of the boundary crossing. We also used a 2-D magnetohydrodynamic simulation to demonstrate that such a wide distribution can be formed by the KH instability even at the beginning of the nonlinear stage.