SIMULATION OF PRESSURE PULSES IN THE BOW SHOCK AND MAGNETOSHEATH DRIVEN BY VARIATIONS IN INTERPLANETARY MAGNETIC-FIELD DIRECTION

Two-dimensional (2-D) hybrid simulations are carried out to study the effects of the variation in the interplanetary magnetic field (IMF) di rection on the bow shock, magnetosheath, and magnetosphere. A curvilin ear coordinate system is used in the simulation. The 2-D simulation is also compared with our one-dimensional simulation results. It is foun d that pressure pulses are generated as a result of the interaction be tween the bow shock (BS) and an interplanetary rotational discontinuit y (RD). First, a structure consisting of a rotational discontinuity an d two slow shocks are present downstream of the bow shock after the BS /RD interaction. The magnetic field and plasma density are anticorrela ted in this structure, The dynamic pressure increases in the structure , leading to a pressure pulse in the magnetosheath. Second, a pressure pulse associated with reflected ions at the bow shock may be generate d in the foreshock when the IMF changes its direction, especially when a local quasi-parallel bow shock becomes a quasi-perpendicular shock. The magnetic field, plasma density, and dynamic pressure are positive ly correlated in the upstream pressure pulse. This pressure pulse conv ects through and interacts with the bow shock, producing; a pressure p ulse in the downstream region. The downstream pressure pulses propagat e to the magnetopause. The amplitude of the downstream pressure pulses can be up to 100% of the background magnetosheath value. It is sugges ted that the pressure pulses impinging on the magnetopause may lead to the magnetic impulse events observed in the high-latitude ionosphere.