Interaction of interplanetary shocks and rotational discontinuities with the Earth's bow shock

The magnetohydrodynamic (MHD) aspects of the interaction between the Earth's bow shock and interplanetary shocks or rotational discontinuities are systematically studied in this paper by MHD simulations. The interplanetary shocks under consideration include forward fast shocks, reverse fast shocks, forward slow shocks, and reverse slow shocks. As an incident forward shock transmits through the bow shock, a fast shock, a slow expansion wave, a slow shock, and a contact discontinuity are generated downstream of the bow shock. At the same time, the bow shock is modified and moves earthward. If the incident shock is a reverse shock, the generated fast shock becomes a fast expansion wave, and the bow shock moves away from the Earth. The generated fast shock or fast expansion wave carries most of the total pressure variation imposed by the incident shock. The contact discontinuity also carries a significant part of the pressure variation. The slow expansion wave and the slow shock are both generated with a small variation in plasma density and pressure but a large variation in magnetic field. When the solar wind Alfven Mach number is small, the density variations associated with the slow shock or slow expansion wave can be significant. Through the interaction between an incident rotational discontinuity and the bow shock, a plateau in the plasma density and thermal pressure is formed. The magnetic pressure is depressed accordingly and anticorrelated with the thermal pressure. If the incident rotational discontinuity propagates toward the Earth (Sun) in the solar wind frame, the leading (trailing) edge of the plateau consists of an intermediate shock or a time-dependent intermediate shock and a slow shock, while the trailing (leading) edge is mainly a slow shock. The generated structure with enhanced plasma density and thermal pressure and a depressed magnetic pressure agrees very well with the observed slow-mode structure in the magnetosheath. Strong dynamic pressure variations associated with this structure may impinge on the magnetopause as a strong pressure pulse.