Solar cycle variation and its impact on critical frequency of F layer

20-29The ionosphere exhibits the variability over different time scales. In the present paper we present the long term solar activity variations of mid latitude ionosphere. To accomplish this study we have considered a famous Australian station namely Hobart (42.88°S, 147.32°E), which falls in the mid latitudinal region. The variability has been examined over the previous three solar cycles i.e, 21, 22 and 23 solar cycles. To characterize the long term variability of the solar activity we have used four indices namely sunspot number (Rz), solar radio flux (F 10.7cm), Mg II core to wing ratio and solar flare index. Similarly, for ionospheric variability we have the critical frequency of F2 layer (foF2). From our study, we found that the long term changes in the solar activity indices which are closely and synchronously reflected in the ionospheric foF2. To quantify the magnitude of association between the long term solar activity variations and the ionsopehric variations we have performed the single regression analysis and computed the correlation coefficients between the two types of indicies, and found that there exists an extremely strong correlation between the two types of indices for all the three solar cycles. Hence, it has been concluded that the ionospheric foF2 is strongly influenced by solar activity with an 11-year variability