Ion dynamics at a rippled quasi-parallel shock: 2D hybrid simulations

Two-dimensional hybrid simulations are performed to investigate ion dynamics at a rippled quasiparallelshock. The results show that the ripples around the shock front are inherent structures of a quasi-parallelshock, and the re-formation of the shock is not synchronous along the surface of the shock front. By following thetrajectories of the upstream ions, we find that these ions behave differently when they interact with the shock frontat different positions along the shock surface. The upstream particles are transmitted more easily through the upperpart of a ripple, and the corresponding bulk velocity downstream is larger, where a high-speed jet is formed. In thelower part of the ripple, the upstream particles tend to be reflected by the shock. Ions reflected by the shock maysuffer multiple-stage acceleration when moving along the shock surface or trapped between the upstream wavesand the shock front. Finally, these ions may escape further upstream or move downstream; therefore, superthermalions can be found both upstream and downstream.