A discrete auroral arc is set up by precipitating electrons. Current continuity requires a return current fed by a horizontal current from the arc. In the closing of this current system E-region plasma might escape along the return current, and if the source acts as a constant current generator the horizontal electric field can get enhanced. The existence and relative position of these features can be used to diagnose the state of the magnetospheric generator. ¿ American Geophysical Union 1996