Total electron content measurements in the southern hemisphere using GPS satellites, 1991 to 1995

The seasonal, diurnal, and latitudinal variations of total electron content (TEC) were determined using Global Positioning System (GPS) satellite sign als over approximately 5 days per month during almost half a sunspot cycle (July 1991 to June 1995) at Salisbury (latitude 34.77 degrees S, longitude 138.63 degrees E), South Australia. These are the only such extensive south ern hemisphere data till 1995 that have been recorded and analyzed. A selec tion of the data is presented, discussed, and compared with other workers' observations. Examples of Australian Surveying and Land Information Group ( AUSLIG) data in the Australian region are presented. Some model predictions for northern hemisphere ionospheric TEC are compared with the GPS southern hemisphere observations of the combined TEC of the ionosphere and protonos phere. (The two models employed are the international reference ionosphere (IRI-90) and the paramaterized ionospheric model (PIM)(version 1.4, Februar y 1996)). They are considered to be global models, even though the IRT mode l is based primarily, but not exclusively, on northern hemisphere TEC data, and PIM is based on a theoretical model and is thus not directly based on TEC data.