Subauroral Polarization Streams (SAPS) within the dusk-premidnight subauroral sector are associated with closure of region 2 field-aligned current (R2 FAC) through the low conductivity region. Although SAPS have often been studied from a magnetosphere-ionosphere (M-I) coupling perspective, recent observations suggest strong interaction also exists between SAPS and the thermosphere (T). We focuse on thermospheric wind driving and its impact on SAPS and R2 FAC during the March 17, 2013 geomagnetic storm using both observations and the physics-based RCM-CTIPe model that self-consistently couples the M-I-T system. DMSP-18 and GOCE satellite observations show that, as the storm progresses, sunward ion flows intensify and expand equatorward, and are accompanied by strengthening of subauroral neutral winds with some delay. Our model successfully reproduces time evolution and overall structure of the sunward ion drift and neutral wind. A force term analysis is performed to investigate the momentum transfer to the neutrals from the ions. Contrary to previous studies showing that Coriolis force is the main driver of neutrals, we find that the ion drag is the largest force driving westward neutral wind in the SAPS region where the ion density is low in the trough region. Furthermore, simulations with and without the neutral wind dynamo effect are compared to quantify the effect of the neutral to plasma flow. The comparison shows that the self-consistent active I-T coupling increases the R2 FAC, via the flywheel effect, and the westward ion drift equatorward of the SAPS region, via an increase in overshielding, by 20% and 40%, respectively.
Ferdousi, Banafsheh; Nishimura, Yukitoshi; Maruyama, Naomi; and Lyons, Larry, "Subauroral Neutral Wind Driving and its Feedback to SAPS during the March 17, 2013 Geomagnetic Storm" (2019). Cooperative Institute for Research in Environmental Sciences Faculty Contributions. 78.