The linkage between the ring current and the ionosphere system

The coupling between the ring current and the ionosphere is briefly reviewed and discussed. Given global energetic neutral atom (ENA) observations of the ring current, the three-dimensional current system driven by ring current plasma pressure (the region 2 system) is derived to illustrate where the ring current connects to the ionosphere. Special attention is given to how the ring current and ionospheric conductance set up the sub-auroral polarization streams (SAPS) through the closure of the region 2 current through the ionospheric trough region.