Steady State Characteristics of the Terrestrial Geopause

The geopause is a boundary defined by the equal contributions of the solar wind plasma and the ionospheric plasma. This boundary delimits regions where the solar wind is dominant from regions where the ionospheric plasma is dominant. A well known example of the geopause is the magnetopause. It is characterized by the balance of magnetic pressure of the Earth's magnetic field to the solar wind ram pressure. The description of the geopause was first developed by Moore [1991].

We have employed the Space Weather Modeling Framework (SWMF) to model the magnetospheric plasma. We use a two and three fluid MHD approach tracking solar wind and ionospheric plasma (including ionospheric oxygen) under two different solar wind configurations. In both solar wind configurations, the number density, pressure, velocity, and magnetic field intensity are set to be constant through the simulation. In the first solar wind configuration, the IMF is set northward for 8 hours and set southward for the last 4 hours. In the second solar wind configuration, the IMF is set southward for 4 hours and reversed northward for the last 8 hours.

We present results on the influence of the ionospheric composition on the steady state mass density, number density, and pressure geopause. The simulations show an ordering where the magnetopause structure is the largest, then the mass density geopause, number density geopause, and finally the pressure geopause. The geopauses are more extensive with respect to larger mass loading of the magnetosphere.