Tohoku-Oki earthquake caused major ionospheric disturbances at 450 km altitude over Alaska

Ionospheric total electron content (TEC) and atmospheric density perturbations were derived from measurements made from instruments on board the Gravity Recovery and Climate Experiment (GRACE) spacecraft. At the time of the Tohoku‐Oki earthquake on 11 March 2011, the twin spacecraft were orbiting at an altitude of ~450 km over Alaska. Significant TEC fluctuations (up to 0.6 total electron content unit (TECU; 1 TECU = 1016 el m−2), atmospheric density perturbations (~3.6 · 10−14 kg/m3), and sudden changes in GRACE acceleration (~4 · 10−8 m/s2) were observed ~8 min after the arrival of seismic and infrasound waves on the ground in Alaska, ~20 min after the Tohoku‐Oki main shock at 05:46:23 UTC. The results of the three‐dimensional ionospheric‐thermospheric modeling and infrasound ray‐tracing simulations are consistent with the arrival time and physical characteristics of the disturbances at GRACE. This is the first time that ionospheric disturbances associated with an earthquake are clearly attributable to perturbations at such high altitudes. Key Points First coseismic ionospheric and atmospheric perturbations at 450 km altitudeObservations were corroborated with two different model simulationsA novel spaceborne technique is introduced to retrieve atmospheric perturbations