MAGE Simulations of Thermosphere and Ionosphere Responses to Subauroral Polarization Streams (SAPS)

Subauroral polarization streams (SAPS) are a latitudinally narrow band of intense westward plasma flows just equatorward of the auroral oval in the dusk-to-midnight ionosphere. SAPS are frequently observed by radars and satellites during geomagnetically active times. 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 ionosphere and thermosphere. In this study, we employ the high-resolution Multiscale Atmosphere-Geospace Environment (MAGE) model developed by the NASA DRIVE Science Center for Geospace Storms (CGS) to simulate the SAPS effects on the global thermosphere-ionosphere system during the 17 March 2013 geomagnetic storm. MAGE can self-consistently generate SAPS and simulate their effects. In the SAPS channel, two processes occur to affect the thermosphere and ionosphere state, the first one is the intense frictional heating to the ionospheric plasma and atmospheric neutrals and the other one is the strong ion drag that changes the neutral winds. Our MAGE numerical experiments show that thermospheric temperature and wind circulation are modulated by the SAPS, and the SAPS effects are transmitted globally to affect the behavior of the entire thermosphere and ionosphere system during the storm. With SAPS included in MAGE simulations ionospheric total electron content 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 facilitate the occurrence and strengthening of polar cap tongue of ionization.