Variation of f_oF₂ layer during low solar activity period (2005-2007) in low latitude of China

In this paper, we use the critical frequency of F₂ layer (f_oF₂) data of three ionosonde observations at Chongqing, Guangzhou and Haikou to analyze the diurnal, seasonal and solar variations of f_oF₂, as well as the effects of space weather events such as magnetic storms on f_oF₂. The diurnal variation of f_oF₂ shows a minimum before the sunrise, and in Haikou and Guangzhou the maximum occurs nearby 14:00 to 16:00 local time, while in Chongqing the maximum occurs nearby 12:00 to 14:00 local time. It is found that f_oF₂ value 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).Besides, f_oF₂ at spring equinox is larger than that in autumn which is not obvious in Chongqing. Overall f_oF₂ decreases since 2005, onwards showing a positive correlation with solar activity. f_oF₂ variations during the geomagnetic storm commencing 24 August 2005 with Dst=-184 nT are analysed. f_oF₂ shows a positive ionospheric storm effect on the first day of the storm and negative ionospheric storm effect on the next day. In China low latitudes, it can be divided into equatorial anomaly region and normal region. In these two regions, the change rules of f_oF₂ are similar but still different. We should make a concrete analysis of the two regions combining with solar activity.