Coupling Between Subauroral Neutral Wind and Extended Sunward Ion Flow During the 17 March 2013 Storm

Subauroral Polarization Streams (SAPS) are strong westward flow enhancements in the pre-midnight sector equatorward of the electron aurora oval. They are closely associated with region-2 field-aligned currents in the region of low conductivity below the electron equatorward boundary. While SAPS are usually regarded as a magnetosphere-ionosphere (M-I) coupling phenomenon, recent studies have suggested a strong interaction of SAPS with the thermosphere. The March 17, 2013 storm was studied by using the near-simultaneous observations of plasma velocity and neutral wind made by the DMSP-18 and GOCE satellites to investigate the subauroral neutral wind responses to storm time sunward ion flows in the dusk local time sector, as well as the role of the thermosphere in SAPS M-I coupling. Sunward ion flows intensified and shifted equatorward as the storm progressed, and the duskside subauroral neutral wind showed a strong correlation with the sunward ion flow with 2 hours delay. Our simulation results from a coupled Magnetosphere-Ionosphere-Thermosphere (M-I-T) model that includes the self-consistent electrodynamic coupling reproduced the temporal and spatial evolution of the observed ion and neutral flow patterns fairly well with some discrepancies. The model auroral conductivity calculation has been improved by including the RCM aurora precipitation to achieve better agreement between model results and observation. The force terms in the neutral momentum equation have been analyzed to understand the cause of the observed correlation between the neutral wind and ion flow. By comparing runs with and without self-consistent I-T coupling, we found that coupling to the neutral wind increases sunward ion flows by 20% and drives ion-flow penetration to lower latitudes, suggesting that neutral wind can drive the plasma flow where the magnetospheric forcing does not exist at mid and low latitude. Furthermore, we will also address the impact of the frictional heating arising from ion-neutral collisions on changing the conductivity within the SAPS region.