A study of intense ionospheric scintillation observed during a quiet day in the East African low-latitude region

[1] Ionospheric plasma density irregularities are a common feature of the equatorial and low-latitude ionosphere. These irregularities are known to cause fading and phase fluctuation (scintillation) of L-band radio navigation signals such as those used by Global Navigation Satellite Systems. This study investigates the occurrence of intense ionospheric scintillation in the postsunset period during a geomagnetically quiet day on 8 April 2011. In particular, we use Global Positioning System (GPS) derived observations, i.e., total electron content (TEC) and amplitude scintillation intensity index, S4, to examine the occurrence of intense scintillations at two low-latitude stations in the East African sector. Deep TEC depletions, in some cases roughly 40 TECU, are observed consistently with the occurrence of intense scintillations. In addition, we compare the GPS-based observations to the Communication/Navigation Outage Forecasting System (C/NOFS) satellite plasma data. The intense scintillation events also correspond well with plasma depletion structures present on the C/NOFS observations and can be attributed to strong plasma bubble activity. The C/NOFS data also provide evidence of strong upward drift velocities (> 60 m/s) associated with the depletions, which may have contributed to the generation of the strong irregularities.