Ionospheric response over South Africa to the geomagnetic storm of 11-13 April 2001

The mid-latitude ionosphere over South Africa is subject to severe F region ionospheric density perturbations during intense geomagnetic storm activity. Communication and navigation systems relying on trans-ionospheric propagation are adversely affected during strong storms. There is a need to compensate for the effects of the sharp ionospheric total electron content (TEC) gradients associated with the storm time disturbance effects at mid-latitudes. The South African ionosonde and Global Positioning System (GPS) database have been used to examine the spatial extent of the electron density structures during the super storm of 11-13 April, 2001. The ionosonde measurements have supported the observed negative (i.e. decreased electron density) and positive (i.e. increased electron density) storm effects over this region. The hmF2 and h'F ionospheric parameters showed higher and reduced values during the main and recovery storm phases respectively. The ionospheric TEC is a widely used parameter in the studies of the near Earth plasma environment. The derived VTEC and their perturbation components revealed TEC fluctuations of magnitude >= 10 TECU during the storm. The storm-induced TEC perturbations on 11-12 April, 2001 revealed a travelling ionospheric disturbance (TID) phenomenon. The source of the irregularities observed over South Africa during this super storm period has been attributed to TIDs generated by gravity waves due to auroral sub-storm activity. The equatorward propagating waves resulted in an uplift of the F2 layer by pushing the ionospheric plasma along magnetic field lines to higher altitudes where recombination is much lower, which in turn leads to plasma density enhancement. (c) 2012 Elsevier Ltd. All rights reserved.