Effects of decreasing ionospheric pressure on the solar wind interaction with non-magnetized planets

Abstract

The large-scale solar wind interaction with the ionosphere of non-magnetized planets is numerically simulated in the framework of three-dimensional (3-D) magnetohydrodynamics (MHD) with a two-component plasma. The finite-volume total variation diminishing (TVD) scheme is used to solve this problem. Numerical results are given for two cases of different solar extreme ultraviolet (EUV) flux values. In case 1, solar EUV ionization is set so the peak ionospheric plasma pressure is below the incident solar wind dynamic pressure. In case 2, on the other hand, it is set so the peak ionospheric pressure exceeds the solar wind dynamic pressure. While the formation of the bow shock and the magnetic barrier in the upstream region is seen in both cases, a clear formation of the ionopause is seen only in case 2. In case 1, the interplanetary magnetic field (IMF) penetrates from the magnetosheath to the dayside ionosphere so as to adjust the ionospheric total pressure. Penetrating IMF affects the vertical motion of the ionospheric plasma to cause anomalous stratifications of the terminator ionosphere. However, formation process of the ionotail is little affected by the penetrating IMF. Another important process predicted from the present study is partial penetration of the IMF from the magnetic barrier to the terminator ionosphere. This nonideal MHD process characterized by the penetration of flowing magnetized plasma into non-magnetized plasma plays a principal role in the mixing interaction between the solar wind and the planetary ionosphere.