Subauroral Neutral Wind Driving and Its Feedback to SAPS During the 17 March 2013 Geomagnetic Storm

Abstract

AbstractSubauroral Polarization Streams (SAPS) 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 coupling perspective, recent observations suggest strong interaction also exists between SAPS and the thermosphere. Our study focuses on thermospheric wind driving and its impact on SAPS and R2 FAC during the 17 March 2013 geomagnetic storm using both observations and the physics‐based Rice Convection Model‐Coupled Thermosphere, Ionosphere, Plasmasphere, electrodynamics (RCM‐CTIPe) model that self‐consistently couples the magnetosphere‐ionosphere‐thermosphere system. Defense Meteorological Satellite Program (DMSP)‐18 and Gravity Field and Steady‐State Ocean Circulation Explorer (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 during storm time, 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 ionosphere thermosphere coupling increases the R2 FAC and the westward ion drift equatorward of the SAPS region by 20% and 40% by the flywheel effect, respectively.