During the development of large-scale magnetospheric substorm expansive phase activity, the auroral oval may become very wide. During such episodes, clear discrete arc structures appear from time to time in the equatorward portion of the evening sector oval in a region of space normally thought to feature structureless diffuse auroras. On occasion, these discrete auroral forms acquire a north-south orientation and remain as identifiable forms for up to several minutes. Most auroral theories attempt to describe the origin of the normally east-west aligned features. In this paper we propose that the particles responsible for north-south aligned arc structures originate as plasma blobs injected into the central plasma sheet (CPS) from the adjacent low-latitude boundary layer, as a result of enhanced wave activity at the interface between the two regions during active times. We show that the characteristics geometric forms of the CPS auroral structures follow from tracking the drift paths of the particles in the injected plasma blob as they convect earthward, heating adiabatically in the process. We also outline outstanding issues pertaining to the proposal as motivation for a continued study. ¿ American Geophysical Union 1993