Characterising ionospheric TEC gradients over Nigerian longitudes during increasing phase of solar cycle #24

Abstract

Over the last decades, there has been growing interest in the characterization of ionospheric total electron content (TEC) for the effective planning, implementation and optimum performance of the satellite-based technology applications. This paper essentially examines the ionospheric TEC gradients using Global Navigation Satellite Systems (GNSS) data during the increasing phase of solar cycle 24, years 2011-2013. The data used were mined from the African GNSS Network of stations (AFREF, www.afrefdata.org) and Nigeria GNSS ground-based Network Observation Stations (NIGNET) located within the belt of the Equatorial Ionization Anomaly (EIA) region. The ionospheric TEC gradients were analysed during distinct geomagnetic conditions. The monthly mean results have shown that the magnitude of ionospheric TEC gradients are higher at equinoctial months and December solstices when compared with other solstices months and also during the disturbed conditions when the ionospheric storm has positive phase leading to an increase in the ionization, while the ionospheric TEC gradients are lower during the quiet conditions when the ionospheric storm is in the negative phase and this is evidenced in the decreased ionization at the disturbed conditions. The study records that the magnitude of ionospheric gradients increases with solar activities and could be as high as 300 mm/km within the Nigeria longitudes during the high of solar activity and the conjugate distance is not ono-to-one relation to the magnitude ionospheric gradient observe spatially. The results of the bounding errors revealed that the ionospheric TEC gradients are not well bounded over the Nigerian longitudes during moderate to high solar activities, which could pose a serious challenge to the seamless GNSS critical applications in terms of navigation and positioning.