Thermosphere and ionosphere response to subauroral polarization streams (SAPS): Model simulations

An empirical model of subauroral polarization streams (SAPS) has been incorporated into the Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM). This SAPS driven TIEGCM is used to simulate the effect of SAPS on the global thermosphere and ionosphere during a moderate geomagnetically active period between day of year (DOY) 329 and 333 in 2008. Model results show: (1) SAPS caused an increase in global thermospheric temperature which became stronger with time. This neutral temperature increase was more significant in subauroral and auroral regions. Joule heating by the SAPS and the redistribution of this heat by dynamic processes were the primary mechanisms for the simulated global neutral temperature changes. (2) In the SAPS driven TIEGCM, the strong ion drag effect in the subauroral SAPS channel drove large changes in thermospheric winds. Zonal neutral winds had either an extra, separate channel of westward flow in the subauroral region in the afternoon-midnight sector or a broad westward wind jet that merged with the regular duskside auroral westward zonal neutral wind driven by the high latitude convection pattern. The exact latitudinal profile of the zonal winds depended on local time. (3) The response of neutral temperature and wind to SAPS was more significant at higher altitudes and exhibited seasonal/hemispheric asymmetry. (4) The heating to the thermosphere by SAPS also resulted in changes in thermospheric composition with upwelling of molecular rich air in subauroral and auroral regions and downwelling of atomic oxygen rich air at other latitudes. These changes in thermospheric composition contributed to the deeper and more extended ionospheric electron density depletions in subauroral middle latitude regions, as well as electron density increases along the equatorward edge of the SAPS channel in the afternoon sector.