TEC response at two equatorial stations in the African sector to geomagnetic storms

GPS data obtained from two equatorial stations of Ilorin (geographic Lat. 8.53°N, Long. 4.57°E and geomagnetic Lat. 10.57°N, Long. 78.56°E) and Toro (geographic Lat. 10.12°N, Long. 9.12°W and geomagnetic Lat. 11.36°N, Long. 83.35°E) have been used to study the response of vertical TEC to four geomagnetic storms which occurred during 22–23 Jan, 23–26 Jan, 6–8 March and 8–11 March in the year 2012. Three of these events were in the category of moderate storms (−50 > Dst > −100 nT) while the 8–11 March event was in the category of intense storm (−100 > Dst > −200 nT). Results obtained show that TEC response can either be enhancement or depletion irrespective of the category of the storm. While the main and recovery phases of the 23–26 Jan. and 6–8 March, 2012 moderate events produced TEC enhancement at Toro, TEC depletions were observed at Ilorin during the main phases of these two events. The result of the analysis of the 22–23 Jan, 2012 moderate storms with sudden commencement shows that response of TEC to the main phase was depletion at both stations. Percentage deviations in TEC with respect to quiet time averages ranged between −19% and +21% at Toro and −42% to +34% at Ilorin. The moderate storms with gradual commencement (i.e. 23–26 Jan and 6–8 March events) have different effects on TEC at the two stations. While the initial and recovery phases of the 23–24 Jan event produced significant TEC enhancement at both stations (+119% at Toro and +82% at Ilorin), the recovery phase of the 6–8 March event produced enhancement at Toro and depletion at Ilorin. The intense storm of 8–11 March, 2012 produced almost opposite effects on TEC at the two stations. While the effect at Toro was TEC enhancement of 0% to +116% during all the three phases, TEC fluctuations at Ilorin ranged between −36% and +28% during the initial and main phases.