Ionospheric TEC, NmF2 and slab thickness over the Athens region

The data of TEC, f(0)F(2) obtained at the Athens station, from year 2001 to 2005, are used to analyze the diurnal, seasonal, and solar activity variations of TEC, NmF2 and slab thickness tau. The results reveal that TEC and NmF2 have similar diurnal variation patterns, and maximize at 14 : 00LT. The "winter anomalies" of TEC occurred during daytime in year 2001 and 2002, while that of NmF2 occurred between 2001 and 2005. The tau values are about 200 similar to 600 km, and show double-peak structures including predawn and sunset peaks. The predawn peak appeared usually at 5 : 00-6 : 00LT, and the sunset peak began to appear after sunset, reaching the maximum value before midnight. The relationships between ionospheric TEC, NmF2 and solar activity show linear, saturation and amplification features, while tau had positive and negative linear variations or an unremarkable linear relationship. Finally, we suggest that the predawn peak is caused by the increased TEC and decreased NmF2, and the sunset peak can be attributed to the slower decrease for TEC than NmF2.