Ionospheric response to the July 29, 2025 Kamchatka tsunami from multi-instrument measurements

The ionospheric response to the 29 July 2025 Mw 8.8 Kamchatka earthquake–generated tsunami is investigated using a coordinated set of ground-based and space-based observations. Tsunami signals are analysed using 1-min NOAA tide-gauge data across the Pacific Ocean and compared with ionospheric perturbations derived from GNSS total electron content (TEC), Digisonde ionograms and ionospheric tilt measurements, and in-situ electron density observations from the Swarm-B satellite. Near-field observations show that tsunami-driven ionospheric disturbances first appear over Alaska approximately 30 min after the initial oceanic arrival, consistent with upward-propagating atmospheric gravity waves. In the mid- and far-field, coherent TEC oscillations with dominant periods of 10–15 min are detected over equatorial and low-latitude stations, including Kiritimati, Pohnpei, and Hawaii, with amplitudes up to ∼1 TECU. Combined Digisonde and Swarm-B observations over Hawaii reveal tilted F-region structures and electron density perturbations that are temporally consistent with GNSS-TEC signatures, confirming vertical coupling between the ocean surface and the ionosphere. A distance–time (hodochrone) analysis demonstrates that near- to mid-field ionospheric disturbances propagate in lockstep with the tsunami at speeds of ∼295 m s⁻ 1 , while basin-scale observations exhibit multiple propagation branches (≈165–235 m s⁻ 1 ) associated with bathymetric effects and dispersive tsunami modes. These results provide robust multi-instrument evidence of tsunami–ionosphere coupling and demonstrate the potential of ionospheric monitoring to complement conventional tsunami detection systems, particularly in regions with sparse ocean-based instrumentation.