Large and mid-scale ionospheric perturbation characteristics deduced from GNSS measurements

Large and mid- scale ionospheric perturbations are closely related to complex solar-terrestrial interactions in the course of space weather events. Ground and space based dual frequency measurements of Global Navigation Satellite Systems (GNSS) have been used over more than one solar cycle in order to derive characteristics of ionospheric storms. Whereas the ground based measurements show strong horizontal redistribution of plasma during ionospheric storms, the space borne measurements indicate severe vertical redistribution of the ionospheric plasma during selected space weather events. Storm enhanced spatial gradients are related to strong plasma convection as well as ion outflow in the plasmasphere. Ionization fronts and wavelike perturbation processes propagate predominantly from high to mid-latitudes with a speed ranging from 200-1000 m/s. Spatial gradients may reach values of 50 mm/km which may seriously affect precise and safety-critical GNSS applications. Equatorward Travelling Ionospheric Disturbances (TIDs) are characterized by wavelengths in the order of 2000 km, a mean period of 59 minutes and a mean phase speed of about 680 m/s.