Tracking fast-mode wave propagation in Earth’s magnetosphere through GNSS signals

We investigate the magnetospheric response to the 17 March 2015 interplanetary (IP) shock using coordinated ground-based global navigation satellite system (GNSS) total electron content (TEC) observations and global magnetohydrodynamic (MHD) simulations. The TEC measurements reveal distinct perturbations induced by the shock, with the MHD model successfully reproducing the qualitative features of these variations. Our analysis demonstrates: (1) TEC signatures of fast-mode MHD wave propagation from the magnetopause to the inner magnetosphere/plasmasphere within 70 s, generating the strongest TEC enhancements near the subsolar point; (2) subsequent wave reflection between the plasmasphere and magnetopause, producing a secondary TEC peak approximately 2 min after the initial impulse. Comparisons with ground magnetometer data show synchronized two-peak structures, supporting the interpretation of wave reflection dynamics. Although the MHD simulations systematically underestimate TEC magnitudes due to the exclusion of cold plasmaspheric populations, they validate the global patterns and timing of the shock response revealed by the TEC observations. These findings highlight the unique capability of GNSS TEC measurements, with their global coverage and high temporal resolution, to complement in situ observations for studying global-scale magnetospheric wave dynamics and shock impacts. The study underscores the potential of GNSS networks as a powerful tool for probing magnetospheric plasma dynamics, particularly in regions lacking direct satellite instrumentation.