On the significance of extreme plasma dynamics in the subauroral region

The subauroral region is located equatorward of the auroral oval, where important magnetosphere-ionosphere-thermosphere dynamical processes take place. Historically, low-Earth orbit satellites as well as ground-based imagers and radars have provided important information about the region. However, in recent years it has become increasingly clear that there are several unexplored aspects of the region that remain elusive in part due to instrumental and observational limitations. Furthermore, the most commonly used large-scale “state of the art” models and theoretical frameworks of the region rely on a quasi steady-state approach which does not accurately represent the rich subauroral electrodynamics underway. Recent ground-based and in-situ measurements have revealed new and compelling dynamics taking place in the subauroral region and reinvigorated the community’s interest there. Optical signatures with unexpected spectrographic properties, such as SAR arcs, STEVE, and the picket fence, have been associated with extreme and unusual subauroral plasma conditions, including large ion flow velocities ( ∼ 3–10 km/s) and extreme electron temperatures (>6000 K). Additionally, recent observations have revealed that the transformation of the subauroral region into these extreme conditions occurs within minutes. These new measurements pose a significant challenge to our existing theories and available instrumentation, and demonstrate the necessity of new development and deployment of in-situ and remote measurements of the subauroral ionosphere. This paper highlights some of the open questions in the subauroral region that have arisen recently.