Modelling Sub-Auroral Polarization Streams Equatorward of the Plasmapause Footprints.

Recent results from the ESA Cluster satellite constellation, the NASA IMAGE satellite, and from global Total Electron Content (TEC) measurements, have demonstrated that both the plasmapause and its coupling footprint in the ionosphere can have dynamic features whose analysis requires a deeper understanding of the processes involved. The effects on the mid-latitude ionosphere in particular, and the consequences for Global Positioning Satllite (GPS) signals are particularly relevant. We present a modelling study on the effects of SAPS events equatorward of the plasmapause footprints using the Sheffield Coupled Thermosphere-Ionosphere-Plasmasphere model (CTIP). Three SAPS potentials (-20 kV, -40 kV and -60 kV) are imposed for two hours in the pre-midnight sector, 18 to 24 MLT, between 50° and 59° magnetic latitude. During the SAPS events, oxygen ions are rapidly recombined due to a combination of the increased temperatures from ion-neutral frictional heating and the elevated N2 and O2 densities due to enhanced Joule heating of the thermosphere. The decrease in F-region ion density is found to be dependent on SAPS potential. There is also an associated decrease in the vertical total electron count (VTEC) and increase in the height of the F-region.