| Summary: | This paper presents a preliminary analysis of the variations of the critical frequency of the F 2 region (f o F 2 ) and the total electron content (TEC) derived from Global Positioning System (GPS) data. Hourly f o F 2 values were scaled from ionograms recorded at San Martin (68.1°S, 293.0°E) and the TEC values were derived from GPS observations at O'Higgins (63.3°S, 302.5 °E). The database includes measurements obtained under different seasonal and solar activity conditions. The study shows that the daily peak of f o F 2 occurs around local noon in winter and fall, and in spring a secondary peak is observed around midnight. In summer (January) f o F 2 reaches its minimum value around the noon sector while the maximum in the diurnal variation of f o F 2 is located in a time sector close to midnight. This behaviour is observed at low and high solar activity. The semiannual anomaly appears around noon at high and low solar activity and the winter anomaly is not observed. The effect of the solar activity is generally observed in every season. The analysis of the GPS TEC measurements in the same region indicates that the diurnal, seasonal and solar activity variations are similar to those observed in the f o F 2 values. An analysis of the performance of the IRI model to predict f o F 2 is also shown using the two IRI options (URSI and CCIR). The comparisons between the experimental values and the IRI predictions show some discrepancies. Facultad de Ciencias Astronómicas y Geofísicas
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