Effects of High-Latitude Input on Neutral Wind Structure and Forcing During the 17 March 2013 Storm

Journal of Geophysical Research:  This paper presents a quantitative assessment of the thermospheric forcing and its dependence on high-latitude driving is provided. Due to its coupling with the ionosphere via ion-neutral collisions, the simulated neutral wind and the corresponding thermospheric forcing from Global Circulation Models (GCMs) are highly dependent on the model's high-latitude ionospheric input. To study the effects of the different ionospheric inputs, we simulate the thermospheric winds using the Thermosphere-Ionosphere-Electrodynamics GCM (TIE-GCM) and compare them to the observed neutral wind vectors from the Scanning Doppler Imagers located in central Alaska during the St. Patrick’s Day storm in 2013. To assess the model-data discrepancies, the standard root-mean-square error (RMSE) is calculated, as well as the cross-correlation coefficient to better capture the structural differences between the simulated and observed winds. Additionally, individual thermospheric forces are analyzed, providing a full diagnosis of the relative importance of each force on the neutral wind behavior. It was found that the realistic high-latitude input resulted in better simulations of neutral wind structures than the empirical model did, although there was a slightly higher magnitude error. Altering the auroral energy flux mostly affected the resulting neutral wind speeds while the wind structures remained about the same. In the zonal direction, ion-drag is the dominant force, with significant contributions from the horizontal advection force and secondary contributions from the Coriolis and pressure-gradient forces. In the meridional direction, pressure-gradient is the dominant force, with secondary contributions from the ion-drag force and minor contributions from the Coriolis, horizontal advection and viscosity forces.