Multi-fluid simulations of the magnetosphere: The identification of the geopause and its variation with IMF

A new multi‐fluid global treatment is presented that separately tracks the solar wind and ionospheric plasmas in the magnetosphere. The model is used to identify the density and pressure geopauses, i.e. the boundaries where the contributions to the magnetospheric density or pressure from the ionosphere equals that from the solar wind. The density geopause is primarily restricted to the inner magnetosphere and central lobes for northward interplanetary magnetic field (IMF) but during southward IMF it can extend into middle magnetosphere due to enhanced ionospheric outflow and convection. This variation is consistent with recent statistical studies that show that the plasma sheet density is correlated with the solar wind density, particularly during northward IMF.