Modeling total electron content derived from radio occultation measurements by COSMIC satellites over the African region

Abstract

This study developed a model of total electron content (TEC) over the African region. The TEC data were obtained from radio occultation measurements done by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites. Data during geomagnetically quiet time (Kp < 3 and Dst > −20 nT) for the years 2008–2011 and 2013–2017 were binned according to local time, seasons, solar flux level, and geographic longitude and latitude. B splines were fitted to the binned data to obtain model coefficients. The model was validated using actual COSMIC TEC data of the years 2012 and 2018. The validation exercise revealed that approximation of observed TEC data by our model produces a root mean square error of 5.02 TECU (total electron content unit). Moreover, the modeled TEC data correlated highly with the observed TEC data (r=0.93). Due to the extensive input data and the applied modeling technique, we were able to reproduce well-known TEC features such as local time, seasonal, solar activity cycle, and spatial variations over the African region. Further validation of our model using TEC measured by ionosonde stations over South Africa at Hermanus, Grahamstown, and Louisville revealed r values > 0.92 and root mean square error (RMSE) < 5.56 TECU. These validation results imply that our model can estimate TEC fairly well that would be measured by ionosondes over locations which do not have the instrument. Another element of the significance of this study is the fact that it has shown the potential of using basis spline functions for modeling ionospheric parameters such as TEC over the entire African region.