Conjugate Effect of the 2011 Tohoku Reflected Tsunami-Driven Gravity Waves in the Ionosphere

This study presents the conjugate ionospheric disturbances triggered by the 2011 Tohoku-Oki reflected tsunami oceanic waves using the ground-based Global Navigation Satellite System (GNSS) total electron content (TEC) observations. We found that the equatorward and westward propagating nighttime medium-scale traveling ionospheric disturbances (MSTIDs) occurred over Japan and Australia simultaneously following the tsunami oceanic waves reflected by the Emperor Seamount Chain in the northern hemisphere. The atmospheric gravity waves driven by reflected tsunami oceanic waves are hypothesized to be the source to trigger the conjugate MSTIDs by transporting the polarization electric fields along the field line to the conjugate hemisphere. Moreover, only the southwestward propagating MSTIDs have this conjugate effect, which could be due to the wavefront orientation. The Perkins instability could also be involved in the interhemispheric coupling process. This study provides the first observational evidence that the reflected tsunami can induce conjugate ionospheric disturbances through electrodynamic forcing. Plain Language Summary The 2011 M 9.1 Tohoku-Oki earthquake occurred near the east coast of Honshu, Japan, unleashing a savage tsunami traveling across the Pacific Ocean and beyond. Some tsunami oceanic waves were reflected by seafloor topography in the Pacific Ocean, thus propagating backward toward Japan. These reflected tsunami oceanic waves also excited gravity waves propagating upward into the upper atmosphere, causing plasma perturbations at the atmosphere-space interaction region above Japan. Gravity wave-driven variations in the neutral wind can move the plasma against the Earth's magnetic field lines, thus generating currents and electric fields. Since the Earth's magnetic field lines are conductive like electric power lines, the generated electric fields can transport along the magnetic field line from Japan to the southern hemisphere, causing plasma disturbances above Australia. This study provides observational evidence that the localized tsunami can also cause space plasma perturbations in the conjugate area.

Automated summary

This study presents observational evidence that the 2011 Tohoku-Oki reflected tsunami can induce conjugate ionospheric disturbances through electrodynamic forcing. The study suggests that the equatorward and westward propagating MSTIDs occurring simultaneously over Japan and Australia are triggered by the atmospheric gravity waves driven by reflected tsunami oceanic waves.