Simultaneous observations of ionospheric irregularities in the African low-latitude region

Ionospheric storms represent large global disturbances of the ionospheric F-region electron density in response to geomagnetic storms. This study investigates the ionospheric response during a minor geomagnetic storm that occurred on 13–15 September 2004. In particular, we use total electron content (TEC) measurements (rate of TEC change, ROT) to examine the presence of ionospheric irregularities over four low-latitude stations in the African sector, a region that has been less studied. Ionospheric irregularities are known to cause fading and phase fluctuation of L-band radio navigation signals such as those used by the Global Navigation Satellite Systems (GNSS), and are a common feature in the equatorial and low-latitude ionosphere. In the present study, the storm began with a sudden commencement at approximately 20:00 UT on 13 September, while the peak of the main phase occurred on 14 September with an SYM-H index value around −59 nT. On 13 September, the storm did not appear to hinder the development of irregularities as they were observed over all the stations. In contrast, irregularities were rarely observed at two of the 4 stations under study and were absent over the other two stations on 14 September. The DSMP F15 satellite post-sunset flight over the African region observed deep density depletions on 13 September that can be associated with the presence of ionospheric plasma bubble irregularities. Furthermore, an analysis of ΔHΔH (horizontal geomagnetic component corrected for ring current effects) shows that there was a strong positive ΔHΔH perturbation observed in the post-sunset hours on 13 September, which suggests the presence of an eastward penetration electric field, while a negative perturbation of ΔHΔH, which is associated with the equatorial counter-electrojet, was observed on 14 September.

► Ionospheric irregularities in African sector, a region that has less been studied.
► Irregularities associated with deep plasma depletions.
► DMSP observations show plasma depletions linked to plasma bubbles.
► Discuss equatorial electric impact on the occurrence of irregularities.
► Discuss local time dependence of irregularities occurrence.