Estimation of Spatial Gradients and Temporal Variations of the Total Electron Content Using Ground‐Based GNSS Measurements

Precision and safety of life applications of Global Navigation Satellite Systems require key information on space weather conditions in particular on the perturbation degree of the ionosphere. Such systems are particularly vulnerable against severe spatial gradients and rapid changes of the total electron content (TEC) measured along different satellite‐receiver links. To estimate spatial gradients and rapid temporal variations of ionospheric TEC, two approaches are discussed. The Gradient Ionosphere indeX (GIX) and the Sudden Ionospheric Disturbance indeX are able to estimate the perturbation degree of the ionosphere instantaneously without taking into account previous measurements. The capabilities and accuracy of the index approaches are demonstrated by simulations using a 3‐D electron density model of the ionosphere and plasmasphere in conjunction with realistic Global Navigation Satellite Signal constellations. Real data tests confirm the applicability of GIX and the related standard deviation GIX Sigma to monitor spatial gradients. Sudden Ionospheric Disturbance indeX is able to monitor rapid temporal variations of TEC as exemplified by using Global Navigation Satellite Signal measurements carried out during solar flare events. Both approaches could identify enhanced space weather impacts on precise point positioning and the European Geostationary Navigation Overlay Service. More comprehensive studies analyzing ionospheric storms in close dialogue with potential customers are needed to fully utilize the potential of these approaches to serve as objective ionospheric indices for scaling horizontal TEC gradients and rapid TEC variations in space weather services.