An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

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.