The research on critical frequency of F2 layer variations during low solar activity period near the equatorial anomaly crest region in China

In this paper, we use the critical frequency of F2 layer (foF2) data of two ionosonde observation stations in Guangzhou and Haikou to analyze the variation of foF2 during the low solar activity period from January 2005 to December 2007. In this study, we analyzed the daily variation, seasonal variation and its variation with low solar activity, and the effects of space weather events such as magnetic storm on foF2. The diurnal variation of foF2 shows a minimum before the sunrise, then rises steadily with time, and the maximum occurs near 16:00 local time in the afternoon. The mean diurnal variations during different seasons are brought out. It is found that foF2 is at its maximum during Equinoctial months (March, April, May, September, October, November), and minimum during the summer months (June, July, August), with intermediate values during Winter months (December, January, February), showing a semi-annual variation. Besides, foF2 at spring equinox is larger than it at autumn. Overall foF2 decreases since 2005, onwards showing a positive correlation with solar activity. foF2 variations during the geomagnetic storm commencing 24 August 2005 with Dst=-184nT are analysed. foF2 shows a positive ionospheric storm effect on the first day of the storm and negative ionospheric storm effect on the next day.