Solar Activity Variations of Electron Temperature in the Topside Ionosphere

Over the past three decades a large volume of electron temperature (Te) and density (Ne) measurements has been accumulated by satellite insitu instruments as well as ground-based incoherent scatter radars. We have established a data base with the most important of the satellite measurements reaching from the early Explorers to the recent KOMPSAT and DMSP satellites and including close to 7 million data points. Using this database we have studied the variation of Te with solar activity at different altitudes, latitudes, and seasons. Whereas the electron density generally increases with solar activity at all studied altitudes, latitudes and seasons, the electron temperature can either increase, decrease or stay constant depending on the specific altitude, latitude, and season. We have compared these variations patterns with those found with incoherent scatter radar data and with those predicted by the FLIP model. Our comparisons show overall good agreement thus (i) confirming the variation patterns established by this study, (ii) showing the compatibility of the two measurement techniques, and (iii) validating the solar cycle Te predictions of the FLIP model. An important goal of this work is the inclusion of an accurate representation of Te solar cycle variations in the International Reference Ionosphere (IRI) model.