Identifying medium-scale traveling ionospheric disturbances driven by atmospheric gravity waves over Japan at sunrise and sunset terminators using high-resolution 3-D GNSS tomography

This study reconstructs the three-dimensional (3-D) structures of medium-scale traveling ionospheric disturbances (MSTIDs) driven by atmospheric gravity waves (GWs) at sunrise and sunset terminators, using computerized ionospheric tomography (CIT) technique based on ultra-dense Global Navigation Satellite System (GNSS) observations over Japan. Two representative events in 2022 summer were analyzed in detail. Reconstruction results suggest that MSTID-induced electron density perturbations predominantly occur at altitudes of 200–400 km, with vertical wavelengths of approximately 250 km. Additionally, the MSTID bands are vertically tilted and exhibit a downward phase progression along their propagation direction. Calculations based on GW dispersion relations show a strong agreement between the theoretical and reconstructed vertical wavelengths. For the first time, the detailed 3-D structures of MSTIDs at sunrise and sunset have been revealed, providing direct observational evidence that these MSTIDs are driven by GWs. These findings suggest the effectiveness of the 3-D CIT technique in resolving ionospheric disturbances with high spatial and temporal resolution, providing a robust tool for identifying disturbance of different sources and improving our understanding of ionospheric dynamics.