New Formulation for the Topside Ionosphere and Plasmasphere Based on NeQuick

The total electron content (TEC) affecting signal propagation of Global Navigation Satellite Systems (GNSS) is strongly influenced by the topside ionosphere and plasmasphere. This study introduces a new approach in representing the two regions. The developed topside ionosphere and plasmasphere model has been evaluated using TEC data from the COSMIC/FORMOSAT-3 mission, the Swarm-A satellite, and Global Ionospheric Maps (GIMs), covering the period from 2008 to 2024. Van Allen Probes data have also been used as a benchmark for the plasmasphere. All results have been obtained on the basis of a modified version of the NeQuick 2 model, named IonoMAP (Ionospheric Mapping). Although the new formulation for the topside ionosphere and plasmasphere still slightly underestimates TEC, it reduces biases to approximately 1–3 TECU and improves accuracy by 28–40% compared to the NeQuick 2 model formulation. These results suggest that the proposed model is a viable solution to improve current modeling of the topside ionosphere and plasmasphere.