Intermediate shocks in three-dimensional magnetohydrodynamic bow-shock flows with multiple interacting shock fronts

摘要

Previous MHD simulations predict that when switch-on shock conditions obtain in the solar wind, the bow shock produced in front of an ellipsoidal obstacle will produce a unique bow shock configuration that includes a concave intermediate shock region at the nose of the shock. These simulations have been carried out with hard shell inner boundary conditions. We extend these studies by investigating the configuration of the bow shock when the obstacle is a terrestrial magnetic dipole field. It is found that, in contrast to the typical fast shock, reconnection at the magnetosphere affects the structure of the upstream magnetosheath and bow shock considerably. Asymmetry in magnetic reconnection rates between the northern and southern hemispheres changes the bow shock configuration notably. In the hemisphere where the dipole field is largely antiparallel to the interplanetary magnetic field, the intermediate shock is eliminated in favor of a standard fast shock. In the other hemisphere, however, the intermediate shock still forms as an important, stable element of the overall shock configuration. We also launch a solar wind MHD fast shock into the simulation domain and observe how the resulting waves transmit and reflect in the magnetosheath and magnetosphere and how the general morphology of the bow shock changes.