Geomagnetic storm effects on the topside ionosphere and plasmasphere: A compact tutorial and new results

The coupled ionosphere-thermosphere-plasmasphere system is very complex. Th e study of its interrelationships during geomagnetically disturbed conditio ns is an especially challenging task. Significant progress has been achieve d during the last few years in developing comprehensive theoretical models to describe its global behaviour. Moreover, more simple, specialized numeri cal modelling of some special aspects of storm behaviour and/or regional mo dels have contributed to the progress in this field. This paper summarizes recent developments in upper ionosphere and plasmasphere storm studies and modelling. From an observational point of view the upper ionosphere/plasmas phere region is well reflected in radio beacon measurements providing the t otal electron content (TEC). The development of space-based radio navigatio n systems such as GPS offers new opportunities to derive TEC on both region al and global scale. Combining TEC with ionosonde data enables the variabil ity of the shape of the electron density distribution during storms to be s tudied. We present some examples of co-ordinated investigation, made during the CEDAR storm study intervals.