Variability of TEC at mid latitude with solar activity during the solar cycle 23 and 24

The ionospheric behavior is controlled by the solar output, therefore the ionospheric variability follows a synchronous variation with the solar activity. The solar activity follows a periodic long term variability, which therefore can be expected to be reflected in the ionospheric behavior. We investigated the variability of ionosphere by using the GPS derived Total Electron Content (TEC) at a mid latitude station Usuda (36.13N, 138.36E), Japan during the sunspot cycle 23 and 24. The solar activity is characterized by a number of activity indices, however for the present study we have used five solar activity indices relevant to the ionospheric studies namely, Sunspot Number (Rz), Solar radio Flux (F 10.7 cm), EUV Flux (26-34 nm), Flare Index and CME Occurrences. The long term variation of the solar activity indices were compared with the variability of ionospheric TEC, and it was found that ionospheric TEC and solar activity variations occur synchronously. The correlation analysis was performed to access the magnitude of correlation between the long term solar cycle variations and the ionospheric behavior. From the analysis we found that GPS derived TEC follows a strong correlation with the solar activity indices. The correlation was found to be remarkably strongest during the deep minimum of the cycle 24 i.e 2007-2008.