MMS Observations of nonlinear whistler precursor particle acceleration

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. Interestingly, the whistler precursors cause similar disruptions to the backstreaming ions that were previously reflected by the trailing bow shock. 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. That is, the precursors are 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. These results suggest that whistler precursors play an important role in the conversion of bulk flow kinetic energy to other forms in the overall shock energy budget equation.