Relations Between the Ring Current and Sub-Auroral Electric Fields P.C. Brandt (JHU/APL, Laurel, MD 20723), Y. Ebihara, S. Ohtani, M.-C. Fok, D.G. Mitchell, E.C. Roelof, and R. DeMajistre Sub-auroral electric fields of significant strengths have been observed mostly in the duskside ionosphere. Their strength is sufficient to modify dynamics of the plasmasphere (and perhaps drift trajectories of ring current ions) and are therefore an essential part of the electric field of the inner magnetosphere. Through modeling the electric fields are believed to be produced by the closure of the region 2 current to the region 1 current through the low-conductance gap in the duskside sub-auroral ionosphere. The region 2 currents are in turn driven by plasma pressure gradients in the ring current / plasma sheet region. Model experiments predict that the strength of the electric fields are controlled by the strength of the region 2 currents and the strength and distribution of ionospheric conductance. We will use IMAGE, DMPS, and Iridium data in an attempt to verify what controls the sub-auroral electric fields. ___________ Presentation at the Yosemite Conference of Inner Magnetospheric Interactions, 3 - 6 February 2004, Yosemite, California, USA