Sub-Auroral Polarization Stream Observations During Storm and Non-Storm Conditions

A consequence of pressure gradients in the inner magnetosphere and low ionospheric conductivity, sub-auroral polarization streams (SAPS) manifest in the ionosphere as a westward plasma drift (poleward directed electric field) equatorward of the electron precipitation boundary. They can extend over more than 12 hours in MLT with centering on the nightside and maximum velocity in the dusk sector, and occur under all but the quietest geomagnetic conditions. The basic physical mechanism for SAPS appears toinvolve an interplay of field-aligned current, electric field, and conductivity, however, understanding the occurrence and characteristics of SAPS in specific events and the development of a predictive capability require an elaboration of the dynamical aspects of the phenomenon under both storm and non-storm conditions. Ground- and space-based observations, as well as theoretical and modeling capabilities, have improved substantially in recent years and will help answer some of the outstanding questions. Drawing from the recent CEDAR-GEM SAPS Focus Study this talk is an overview of our current state of understanding of the SAPS phenomenon, primarily from an observational perspective, with reference to potential issues and possible studies to resolve them.