  The effect of the main phase of two intense geomagnetic storm events which
occurred on August 5 - 6 and September 26 - 27, 2011 on the equatorial
ionosphere have been investigated using Global Positioning System (GPS) data
obtained from an Ile-Ife station (geomagnetic lat. \ang{9.84}N, long. 77.25
degree E, Dip \ang{7.25}N). Total Electron Content (TEC) profiles during the
main phase of the two geomagnetically disturbed days were compared with quiet
time average profiles to examine the response of the equatorial ionosphere. The
results showed that the intensity of both storm events during the main phase
which occurred at night-time correlated well with a strong southward direction
of the z-component of the Interplanetary Magnetic Field (IMF-Bz) and Solar Wind
Speed (Vsw), with the Disturbance storm time (Dst) profile showing multiple
step development. TEC depletion was observed during the main phase of the
August 5 - 6, 2011 storm event with TEC recording a maximum value of 9.31 TECU.
A maximum TEC value of 55.8 TECU was recorded during the main phase of the
September 26 - 27, 2011 storm event depicting TEC enhancement. Significant
scintillation index value of 0.57 was observed when the main phase started on
August 5 - 6, 2011 followed by a prolonged suppression while there was less
significant scintillation impact on September 26 - 27, 2011 with a maximum
value of 0.33. The present study show that rapid energy input from solar wind
during geomagnetic storm events effect large variations in TEC and significant
scintillation phenomenon in the equatorial ionosphere over Ile-Ife, Nigeria.
