Impacts of Subauroral Polarization Streams on Storm-Enhanced Density Plume and Consequently on Polar Tongue of Ionization

The influences of subauroral polarization streams (SAPS) on storm-enhanced density (SED) plume and consequently on polar tongue of ionization (TOI), an important topic in the field of magnetosphere-ionosphere-thermosphere coupling, however, remain undetermined. The Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) with/without an empirical SAPS model has been used to investigate the impacts of SAPS on local ionosphere-thermosphere system, which in turn affect the SED plume and consequently the TOI. The modeled total electron content and ion drift velocities agree reasonably well with the observations of Global Navigation Satellite System and Defense Meteorological Satellite Program satellites on 17 March 2013. The TIEGCM simulations show that SAPS can significantly affect the electron density of SED plume and consequently of TOI. The ionospheric-thermospheric effect of SAPS can reduce the electron density of the SED plume in the afternoon sector and enhance the SED plume in the noon sector, which moves the SED plume dawnward. SAPS-induced electron depletions in the throat region undergo anti-sunward convection into the polar cap to weaken the TOI. A term-by-term analysis of the O⁺ ion continuity equation in the F-region shows that the electron density depletions on the duskward edge of the SED plume are mainly due to the increased local plasma loss rates because of SAPS elevated plasma-neutral temperatures and O/N₂ reduction because of thermosphere upwelling. The electron density enhancements on the edge of the SED plume near noon are mainly due to the SAPS-induced westward plasma E × B transports and the O/N₂ increment because of thermospheric downwelling.