Quasi-perpendicular to quasi-parallel shock transitions

One-dimensional hybrid simulations are performed in order to study the response of a collisionless shock to a sudden change of the upstream magnetic field direction, such that the shock, which has been quasi-perpendicular, becomes quasi-parallel. Immediately after the transition from quasiperpendicular to quasi-parallel the shock specularly reflects a large percentage of the incoming solar wind. These ions can subsequently get scattered and become diffuse. At later times, when the quasi-parallel shock is well developed, the reflection rate decreases to 1 - 3%. At this state backstreaming ions are not specularly reflected but already accelerated at the shock to superthermal energies. Leakage of downstream heated ions is only a minor contribution to upstream diffuse ions.