Three-dimensional MHD simulations of interplanetary rotational discontinuities impacting the Earth's bow shock and magnetosheath

The first ever fully three-dimensional magnetohydrodynamic (MHD) simulation s of the detailed effects of MHD discontinuities on the magnetosheath have been performed. The simulation results predict that the interaction between a rotational discontinuity (RD) and the bo it shock produces an MHD wave p ulse that propagates downstream from the bow shock to the magnetopause. The main components of this pulse are two slow shocks sandwiched between two t ime-dependent intermediate shocks; in perfectly ideal MHD, these shocks wou ld presumably resolve into slow shocks sandwiched between two RDs. Inside t he pulse, the plasma density, thermal pressure, dynamic pressure (rho v(2)) , and total pressure all increase, while the magnetic field magnitude decre ases; The pulse convects with the downstream flow through the magnetosheath at a speed that is markedly slower than that of the original RD. It comes to rest on the magnetopause, where it raises the total pressure by as much as 75% in some locations. The pulse eventually disappears, as it is convect ed away by the solar wind flow around the magnetopause. The pulse remains i n the magnetosheath for a few Alfven times (i.e., solar wind Alfven velocit y divided by the Earth's radius, perhaps 1-3 min depending on the actual so lar wind parameters) after the initial RD has propagated downstream past th e magnetopause. Comparisons are made with previous one-dimensional and two- dimensional studies of this problem. We conclude that the pulses seen in th ese simulations are possible causes of magnetic impulse events observed in the ionosphere and slow mode structures observed in the inner subsolar magn etosheath.