Pressure balance across the magnetopause during the solar wind event on 5 June 1998

A three-dimensional adaptive magnetohydrodynamic (MHD) model, SWMF, is used to simulate the interaction between the solar wind and magnetosphere for a particular event on 5 June 1998, and the simulated results of this event is used to investigate the balances of the dynamic, thermal and magnetic pressure along the Sun-Earth line for the different conditions of interplanetary magnetic field (IMF). The conclusions are as follows: (1) outside the magnetopause, the total and thermal pressures are clearly correlated with upstream solar wind dynamic pressure and increase with the solar wind dynamic pressure. In contrast, the magnetic pressure decreases with the increasing intensity of the southward IMF due to the magnetic reconnection and is enhanced with the increasing intensity of the northward IMF due to the magnetic accumulation. It is similar to the variation inside the magnetopause; (2) the solar wind pressure coefficient is larger for the northward IMF than that for the southward IMF, but it has no obvious dependence on the upstream solar wind dynamic pressure; (3) the magnetic field compression ratio just inside the magnetopause is larger and more stable in northward IMF than in southward IMF; and (4) along the Sun-Earth line, the thermal pressure is dominant on the magnetopause in southward IMF, while the magnetic pressure is dominant on the magnetopause in northward IMF. The magnetic reconnection easily occurs for southward IMF, and results in magnetic pressure decreasing just inside the magnetopause. This factor plays a crucial role in the earthward displacement of the Earth's magnetopause for southward IMF. And the increasing of thermal pressure just outside the magnetopause also has contribution to this displacement, especially for lower IMF.