The high-latitude thermospheric mass density anomaly: A historical review and a semi-empirical model

Recent measurements by the accelerometer on the CHAMP Satellite have confirmed that there are prominent dayside density enhancements at high latitudes at all times. The magnetosphere is the source of the energy which produces these density features. We present a historical review of the observations and a semi-empirical global model which reproduces the observed density increases during geomagnetically quiet times. The parameters in the model were determined over 30 years ago. There is now the opportunity to improve those parameters by using densities measured by the modern accelerometers, as well as by using the latest improvements in describing the UV radiation and the semi-annual density variation. Recent progress in determining physical drag coefficients can enable the model to provide absolute densities.