Field-aligned magnetohydrodynamic bow shock flows in the switch-on regime Parameter study of the flow around a cylinder and results for the axi-symmetrical flow over a sphere

A parameter study is undertaken for steady symmetrical planar field-aligned MHD bow shock flows around a perfectly conducting cylinder. For sets of values of the inflow plasma β and Alfvénic Mach number (MA) which allow for switch-on shocks, a numerical solution is obtained which exhibits a complex bow shock shape and topology with multiple shock fronts and a dimpled leading front. For parameter values outside the switch-on domain, a classical single-front bow shock flow is obtained. These results show that the β and MA parameter regime for which the complex bow shock topology occurs, corresponds closely to the parameter regime for which switch-on shocks are possible. The axi-symmetrical field-aligned bow shock flow over a perfectly conducting sphere is then calculated for one set of values for β and MA in the switch-on domain, resulting in a complex bow shock topology similar to the topology of the flow around a cylinder. These complex shock shapes and topologies may be encountered in low-β space plasmas. Fast coronal mass ejections moving away from the sun in the low-β inner corona may induce preceding shock fronts with upstream parameters in the switch-on domain. Planetary and cometary bow shocks may have upstream parameters in the switch-on domain when the impinging solar wind occasionally becomes low-β. The simulation results may be important for phenomena in the Earth’s magnetosheath.