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This paper presents the diurnal, seasonal, and solar activity impacts on the variability of ionospheric foF2 over the Southeast Asian sector. Data from three ionosonde stations, namely, Manila (14.7°N, 121.1°E, dip 14.7°N), Okinawa (26.3°N, 127.8°E, dip 36.8°N), and Vanimo (2.7°S, 141.3°E, dip 22.5°S), were used for the investigation via the standard deviation approach. The diurnal analysis revealed that foF2 is more susceptible to variability during the nighttime than the daytime. The observed variability is characterized by two peaks: a postsunset peak (15%–50%; corresponding to 3–14 MHz for the mean foF2 values) and a postmidnight peak (18%–68%; corresponding to 2–9 MHz for the mean foF2 values). Seasonally, the trend of the foF2 variability maximum does not follow any typical pattern (no particular season has a leading edge over others) for all levels of solar activity. On average the foF2 variability maximum was observed at the Vanimo station during low‐ and high‐solar‐activity years (1986 and 1989, respectively). During the moderate‐solar‐activity year (1983), the foF2 variability maximum was observed at the Manila station. With the exception of the Okinawa data, where little or no difference in the foF2 variability peaks during the low‐ and moderate‐solar‐activity years was noticed, foF2 variability increases with decreasing solar activity at all stations.

This article presents the first results regarding the investigation of the response of the equatorial ionospheric F region in the African sector during geomagnetic storm periods between April 2000 and November 2007 using GPS‐derived vertical total electron content observed at Libreville, Gabon (0.35°N, 9.67°E, dip latitude −8.05°S). We performed a superposed epoch analysis of the storms by defining the start time of the epoch as the storm onset time. During geomagnetic storms, the altered electric fields contribute significantly to the occurrence of negative and positive ionospheric storm effects. Our results showed that the positive storm effects are more prevalent than the negative storm effects and generally last longer irrespective of storm onset times. Also, the positive storm effects are most pronounced in the daytime than in the premidnight and postmidnight periods.

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