Characterization of ionospheric irregularities over the equatorial and low latitude Nigeria region

Abstract

Ionospheric irregularity poses severe challenges to the highly dynamic satellite communication, navigation and tracking operations that rely on transionospheric satellite services like the operation of the Global Navigation Satellite System (GNSS). Although numerous studies on the effect of geomagnetic storms on the inhibition or suppression of irregularities across different longitudes have been documented, the prediction of equatorial ionospheric irregularities/scintillation over the Nigerian region still remains an unsolved scientific problem. Hence, this study characterizes storm-time ionospheric irregularities and comparison with the quiet-time baseline over the Nigerian equatorial region during the maximum phase (2012–2014) of the solar cycle 24. The ionospheric Total Electron Content (TEC) data from five geodetic GNSS stations across the equatorial region in Nigeria are considered to investigate the regional rate of change of TEC (ROT) and the rate of change of TEC index (ROTI). We also exploited the E×B vertical plasma drift (Vz) measurements from C/NOFS satellite and solar wind parameters from Advanced Composition Explorer (ACE) satellites in conjunction with the disturbance ionospheric electric currents (Diono) proxies from ground-based magnetometers to demonstrate the role of electrodynamics on development and modulation of ionospheric irregularities. In brief, we focused on regional ionospheric response characteristics during the initial phase, main phase and recovery phase of selected important storm events through comparison with the quiet-time ionospheric reference level over the region. The results show almost equal intensity of post-sunset ionospheric irregularities during quiet and disturbed geomagnetic days at most of the stations whereas the drift velocity was slightly higher during the quiet period. Moreover, the enhancement or suppression of ionospheric irregularities during the geomagnetic storm period demonstrates dependence on the local time of the storm commencement when the IMF-Bz and Dst southward orientation is at its minimum level. We emphasize the combined effect of the nominal quiet-time ionospheric electric field and storm-time Prompt Penetration Electric Field (PPEF) responsible for altering the E×B drift during the storm-time to modulate the pre-reversal enhancement (PRE) for the occurrence of ionospheric irregularities over the equatorial region, particularly when the storm onset local time, IMF-Bz southward flipping coincides with the post-sunset hours.