Summary
For the low sunspot number period of February 1995 to February 1996, the southern hemisphere mid-latitude trough has been studied using the Global Positioning System (GPS) and TOPEX satellite data. A complete procedure was developed for each technique to reduce the raw satellite data to ionospheric Total Electron Content (TEC) values. The GPS data from the ground stations at Tidbinbilla (35.38ºS; 148.97ºE), Hobart (42.80ºS; 147.43ºE) and Macquarie Island (54.50ºS; 158.94ºE) were plotted in various ways to observe variations in trough characteristics that were related to the current magnetic activity, including magnetic storms. The GPS results were supplemented with the TOPEX data, which were also used to establish diurnal and seasonal trends in the Australian region. The feature of initial build-up of ionisation associated with the development of the trough was also investigated. This feature was compared to observations made previously by other researchers utilising different satellite techniques at Macquarie Island. The effects of auroral activity and magnetic storms on GPS recordings and trough occurrence, respectively, were also investigated. The theoretical TEC generated by PIM 1.4, a complex Parameterised Ionospheric Model (Daniell et al., 1995), was compared directly to the GPS TEC.