Total electron content: Synthesis of past storm studies and needed future work

Prior to the GPS era of global diagnostics for the ionosphere's total electron content (TEC), a remarkable degree of insight into TEC storm effects was achieved using low Earth orbit and geostationary satellite radio beacon observations. Long-term studies at individual stations, networks of stations, and campaign-mode case studies revealed the complex seasonal, local time, and latitude and longitude effects upon TEC during geomagnetic storms. Theory and simulations were used to successfully explain the roles of electrodynamical mechanisms, Joule heating, thermospheric dynamics, and neutral composition changes within the general context of solar wind-magnetosphere-plasmasphere-ionosphere/thermosphere coupling during storms. This paper gives a brief review of the status of past work, presents a new summary of TEC average patterns from pre-GPS data sets, and suggests avenues of research needed to advance the GPS-era yield from TEC storm studies.