  In this paper, two-dimensional (2-D) hybrid simulations are performed to
investigate ion dynamics at a rippled quasi-parallel shock. The results show
that the ripples around the shock front are inherent structures of a
quasi-parallel shock, and the reformation of the shock is not synchronous along
the surface of the shock front. By following the trajectories of the upstream
ions, we find that these ions behave differently when they interact with the
shock front at different positions along the shock surface. The upstream
particles are easier to transmit through the upper part of a ripple, and the
bulk velocity in the corresponding downstream is larger, where a high-speed jet
is formed. In the lower part of the ripple, the upstream particles tend to be
reflected by the shock. For the reflected ions by the shock, they may suffer
multiple stage acceleration when moving along the shock surface, or trapped
between the upstream waves and the shock front. At last, these ions may escape
to the further upstream or enter the downstream, therefore, the superthermal
ions can be found in both the upstream and downstream.
