Paper Title
Day - to - Day Variability of the Critical Frequency of F1 Layer

The characterization of the day – to – day variability (VR) of the critical frequency of F1 (foF1) layer on diurnal and seasonal scale is undertaken at Ibadan (7.40 N, 3.90 E, 60 S dip ) in the African sector during low solar activity (LSA) and moderate solar activity (MSA). The latitudinal effect on foF1 VR is also investigated by combining data from Singapore (1.30N, 103.80 E, 17.60S dip) in the East Asian sector and Slough (51.50 N, 359.40 E, 66.50 N dip) in the European sector. The variability of foF1 is found to be of order (1-3.8%) during LSA and (2-9%) during MSA. On the seasonal scale foF1 VR is greater during March Equinox for both epochs. Comparison of foF1 VR with foE VR and foF2 VR shows that foF1 VR is of the same order of magnitude (0.5 to 4%) during LSA and slightly greater than foE VR (1.5 - 6%) during MSA, in general. It is less than foF2 VR (2-15%) during both epochs. Daytime (10:00 h -16:00 h) foF1 VR is greater at Singapore (1.8 - 5.8%) and at Ibadan (1.8 -5.8%) than at Slough (2.2 - 4.0%), on a general note. While pre-sunrise and postsunset peaks are apparent at Slough, they are not at Singapore and Ibadan. Keywords— F1 layer, foF1variability, latitude, solar activity.