Relationship between F2 layer critical frequency and solar activity indices during different solar epochs

This paper aims at investigating the relationship between F2 layer critical frequency (foF2) and solar activity indices viz. smoothed twelve-month running mean of the sunspot number (R12) and the solar radio flux of 10.7cm wavelength (F10.7) during three different solar epochs. Data from Ouagadougou, an African low latitude station (latitude 12.4[degrees]N, longitude 1.5[degrees]W, dip 5.7), and the National Geophysical Data Centre were used for this study. Distinct characteristics were observed during different solar epochs and during each season. Sunspot number and solar radio flux agreed better during the year of moderate solar activity than during the year of low solar activity. The average correlation coefficients between foF2 and F10.7 obtained for high, moderate and low solar activity were 0.17, 0.67, and 0.44, respectively; while correlation coefficients between foF2 and R12 obtained were 0.05, 0.66, and 0.49, respectively. Irrespective of solar epochs and the trend of the indices, a trough in foF2 value was observed towards the end of June solstice. Relationship between foF2 and the solar activity indices agreed reasonably for the three solar epochs during December solstice. A strong solar activity dependence of foF2 around equinoxes than solstices was also observed. Factors that could cause the F2 layer variation were discussed.