The use of GPS (Global Positioning System) in studies of the Earth's atmosphere has increased significantly in recent years. In this paper, the behavior of Earth's upper atmosphere, called the ionosphere has been studied over a period of high solar activity (year 2001) using data from dual-frequency GPS receivers located in the Brazilian region, belonging to RBMC (Brazilian Network of Continuous Monitoring). Using the GPS data the ionospheric TEC (Total Electron Content) was calculated. Additionally, data of critical frequency of F2 layer were included in the study, derived from Digisondes located in São Luís/MA (3ºS; 44ºW) and Cachoeira Paulista/SP (22ºS; 45ºW), Brazil, for comparison purposes. In general, the results showed higher values of TEC during the equinoxes and lower during the winter months. Regarding the daily variation, the lowest TEC values were observed at around 4-6 HL and higher values occurred in the afternoon, with values slightly higher in São Luís. The second peak of the equatorial anomaly was observed at Cachoeira Paulista during the equinoxes and summer months. In most case, the comparison between critical frequency and TEC showed high linear correlation, especially in São Luís.
ionosphere; GPS; TEC; digisonde; ionosphere critical frequency
