The role of the ring current in the dynamics of the electric field of the inner magnetosphere

Analysis of the global proton distributions derived from the IMAGE/HENA energetic neutral atom (ENA) images, implies strong electric fields in the inner magnetosphere. The proton distribution typically shows that the storm main phase ring current is partial and very little is symmetric. The morphology of the partial ring current changes very little in the 10-200 keV range, which implies that the dominating transport mechanism has to be via ExB drift. These conclusions agree with kinetic ring current models that self consistently calculates the magnetospheric electric field by taking into account the closure of the ring current through the ionosphere. The conclusions are also consistent with observations by the CRRES satellite [Wygant et al., J. Geophys. Res., p. 29527, 1998] and radar observations by the Millstone Hill Radar [Foster et al., JGR in press]. While there is a clear general agreement between the build-up of the partial ring current and the electric fields of the inner magnetosphere, it is still not yet understood what role the ring current plays in the dynamics of the electric field of the inner magnetosphere. The shielding of the solar wind electric field from the inner magnetosphere is established by the closue of the region 2 current system which can be disrupted by substorms, magnetospheric compression etc.. A good indicator of the dynamics of the electric fields is the motion of the plasmapause. Global images of the plasmasphere from the IMAGE/EUV camera have revealed erosion (an apparent ``shrinking'') of the plasmasphere about 30 min after the solar wind electric field enhances across the magnetosphere (during a southard turning of the IMF B_z) [Goldstein et al., Geophys. Res. Letters in press]. We will present and discuss different datasets to shed light on the role of the ring current in the dynamics of the electric fields of the inner magnetosphere.