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This paper presents a case study of the strong postmidnight bubbles that often occur during magnetically quiet periods primarily in June solstice, along with a 4 year (2009–2012) statistical study that shows strong occurrence peak during June solstice predominantly in the African sector. While the mechanism for producing plasma irregularities in the dusk sector is believed to be fairly well understood, the cause for the formation of irregularities and bubbles during postmidnight sector is still unknown, especially for magnetically quiet periods. For the first time, the presence of Rayleigh-Taylor (RT) instability during postmidnight hours has been confirmed by using the physics-based model for plasma densities and RT growth rates. The question is what cause for the generation of eastward electric field, which is the prime driver of RTI, during postmidnight sector? Several possible sources of the eastward electric fields that permit the RT instability to develop and form bubbles in the postmidnight local time sector has been considered.

Global magnetospheric Ultra Low Frequency (ULF) pulsations with frequencies in the Pc 4–5 range (f = 1.0–8 mHz) have been observed for decades in space and on Earth. ULF pulsations contribute to magnetospheric particle transport and diffusion and play an important role in magnetospheric dynamics. However, only a few studies have been performed on ionospheric observations of ULF wave-related perturbations in the vicinity of the equatorial region. In this paper we report on Pc5 wave related electric field and thus vertical drift velocity oscillations at the equator as observed by ground magnetometers and radar. We show that the magnetometer estimated equatorial ExB drift oscillate with the same frequency as ULF Pc5 waves, creating significant ionospheric density fluctuations. For independent confirmation of the vertical drift velocity fluctuation, we used JULIA 150 km radar drift velocities and found similar fluctuation with the period of 8–10 minutes. We also show ionospheric density fluctuations during the period when we observed ULF wave activities. All these demonstrate that the Pc5 wave can penetrate to the equatorial ionosphere and modulate the equatorial electrodynamics. Finally, in order to detect the ULF activities both on the ground and in space, we use ground-based magnetometer data from African Meridian B-field Education and Research (AMBER) and the South American Meridional B-field Array (SAMBA). From space, we use magnetic field observations from the GOES 12 and the Communication/Navigation Outage and Forecast System (C/NOFS) satellites. Using the WIND spacecraft as the upstream solar wind monitor, we present direct evidence that solar wind number density and ram pressure fluctuations observed far upstream from the terrestrial magnetosphere are the main drivers of ULF wave activity inside the magnetosphere. Finally, we show that the ULF waves in the same frequency range are observed in the magnetosphere by the geosynchronous GOES spacecraft, in the ionosphere by the equatorial C/NOFS satellite, and on the ground by ground-based magnetometers, indicating that the magnetospheric origin ULF wave can penetrate to the ground equatorial region and modulate the equatorial electrodynamics.

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using Global Positioning System (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the quiet-time TEC. Two TEC enhancements were observed at low- and mid-latitudes: the first observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, and the second TEC enhancement associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show that the ionospheric response as seen by ionosondes was different from that of the TEC response during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers existed, i.e., the westward electric field and equatorward neutral wind effects.