Subauroral Polarization Streams Effects on the Low-Latitude Ionosphere During the Geomagnetic Storm on 17 March 2015

The equatorial ionization anomaly (EIA) is the salient feature of the low-latitude ionosphere, characterized by two crests around magnetic latitudes ±15° and one trough around the dip equator. The effects of the subauroral polarization streams (SAPS) on EIA are rarely studied, impairing our understanding of high- and low-latitude ionospheric coupling during geomagnetic storms. In this work, we deploy the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) with an empirical SAPS model and GPS observed total electron content (TEC) to identify the SAPS effects on the EIA during the geomagnetic storm on 17 March 2015. Our results show that the low-latitude TEC (∼±20° magnetic latitudes and 12–16 LT) is enhanced by 5 TECU (∼5%) due to SAPS effects. This enhancement is found at both the crests and trough of EIA. A term-by-term analysis of the ion continuity equation is performed in TIEGCM. The SAPS-induced equatorward winds (∼30 m/s) are the most important in producing electron density enhancement at the topside ionosphere. The ionosphere is lifted to higher altitudes where the chemical recombination is slower, causing the TEC and electron density enhancement. However, at the bottomside F-layer ionosphere, the electron density enhancement is dominated by the downward E × B drifts (∼5 m/s) driven by SAPS.