The Thermosphere and Ionosphere System Responses to Subauroral Polarization Streams (SAPS) During the March, 17, 2013 Geomagnetic Storm

During geomagnetic storms, a latitudinally narrow band of strong sunward plasma drifts occurs just equatorward of auroral electron precipitation in the afternoon to pre-midnight sector, which is termed subauroral polarization steams (SAPS). SAPS are produced when the downward Region-2 current is closed through the subauroral region of low ionospheric conductivity and a strong poleward electric field is established to ensure current continuity. SAPS are a manifestation of the strong coupling between the magnetosphere and the ionosphere and thermosphere system. In this study, we employ the high-resolution Multiscale Atmosphere-Geospace Environment (MAGE) model that is developed by the NASA DRIVE Science Center for Geospace Storms (CGS) to simulate the SAPS effects on the global thermosphere-ionosphere system during the March 17 2013 geomagnetic storm. We compare two MAGE model runs, one with SAPS in the entire simulation and the other with the SAPS drifts being turned off when the ionospheric electric fields are used to calculate ion frictional heating, neutral Joule heating, ion drag and plasma transport. By comparing the results from these two runs we quantify the effects of SAPS on the thermosphere and ionosphere system. Our results show that with SAPS ionospheric total electron content (TEC) and electron densities are enhanced in the afternoon sector at middle and high latitudes. This provides a strong source of ionization for the high-latitude convection pattern to transport the plasma into the polar cap to form the polar tongue of ionization (TOI) and patches. Therefore, SAPS facilitate the occurrence and strengthening of TOI. The MAGE simulations also show that the phase and speed of storm-time traveling atmospheric disturbances and neutral circulation are modulated by the SAPS, and the SAPS effects are thus transmitted globally to affect the behavior of the entire thermosphere and ionosphere system during the storm.