THE SUBCRITICAL, QUASI-PARALLEL, SWITCH-ON SHOCK

The conditions that lead to subcritical, quasi-parallel bow shocks are very rare. Even more rarely, a subcritical, quasi-parallel shock can also be termed a switch-on shock, where the tangential component of th e magnetic field, which is very small upstream, is said to ''switch on '' downstream. The Rankine-Hugoniot conservation relations predict tha t the jump in the tangential component of the magnetic field across th e shock is very large for these upstream conditions. In this study, we find that the measured jumps in the plasma conditions are in accord w ith predictions made by the Rankine-Hugoniot conservation relations. T he structure of the switch-on shock, not predicted by the Rankine-Hugo niot equations, is very similar to that of the subcritical, quasi-perp endicular shock, with the exception that the precursor wave in front o f the shock ramp damps more slowly.