Response of the Magnetosphere and Ionosphere to Solar Wind Dynamic Pressure Pulse

The interaction of the solar wind with Earth's magnetosphere produces various phenomena, such as substorms and aurora, in polar region. When the IMF turns southward, the energy of the solar wind is efficiently transferred to the magnetosphere by reconnection, and convection and currents within in the magnetosphere increase. Some of observation results show that the polar cap potential are saturated and dayside magnetic reconnection are enhanced due to the increase of solar wind dynamic pressure. However, the effects of solar wind dynamic pressure variation were not systematically studied by using a global simulation. We have investigated the effects of sudden enhancement of dynamic pressure with a constant IMF value in the ideal case on the magnetosphere and ionosphere by using a global MHD simulation. For sudden enhancement of the density (from 5 /cc to 10 /cc) with a small value of Bz (-2 nT), large viscous cells appear near the magnetopause region but the convection is very small in the tail. The location of dayside magnetopause is at 14 Re. Tail reconnection occurs after 20 min of the pulse arrival with earthward flow (~40 km/s). For case with a strong IMF Bz (= -10 nT), the location of the dayside magnetopause is at 13 Re. Tail reconnection occurs at 11 Re with a strong earthward flow (~300 km/s) after 10 min and tail current increases about 3 times. In addition, pressure gradient is very high near the inner magnetopause in the tail.