Abstract:
In this paper, we use the critical frequency of F
2 layer (
foF
2) data of three ionosonde observations at Chongqing, Guangzhou and Haikou to analyze the diurnal, seasonal and solar variations of
foF
2, as well as the effects of space weather events such as magnetic storms on
foF
2. The diurnal variation of
foF
2 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
foF
2 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,
foF
2 at spring equinox is larger than that in autumn which is not obvious in Chongqing. Overall
foF
2 decreases since 2005, onwards showing a positive correlation with solar activity.
foF
2 variations during the geomagnetic storm commencing 24 August 2005 with Dst=-184 nT are analysed.
foF
2 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
foF
2 are similar but still different. We should make a concrete analysis of the two regions combining with solar activity.