Particle acceleration by nonlinear whistler precursors and possible reformation

An examination reveals the disruption, deceleration, and heating of the incident solar wind ion core population by nonlinear whistler precursor waves at a high Mach number, quasi-perpendicular shock observed by the four MMS spacecraft. The precursors propagate obliquely to the quasi-static magnetic field, the shock normal unit vector, and the incident bulk flow velocity vector, consistent with previous work. These large amplitude oscillations are not consistent with shock ripples -- Alfven-like oscillations on the surface of a shock that are linearly polarized and propagate along the shock surface. The oscillations examined here are elliptically-to-circularly polarized, not propagating along the shock surface, and have durations roughly seven times shorter than expected for shock ripples from theory. Their spatial scales range from a few 100 km down to several 10s of km, which corresponds to spatial scales spanning from from several upstream averaged ion inertial lengths to electron scales. The magnitude of the disruption and profile of the reduced ion distributions may suggest these nonlinear waves are causing the shock to reform; at the very least they induce local nonstationarity.