Abstrakt: |
In this study, we report the persistent impacts of the 2011 Tohoku earthquake/tsunami on the ionosphere using the ground‐based Global Navigation Satellite System and FORMOSAT‐3/COSMIC total electron content. Multiple unusual ionospheric phenomena, such as ionospheric irregularities, nighttime medium‐scale traveling ionospheric disturbances (MSTIDs), and planar traveling ionospheric disturbances (TIDs), were observed after the emergence of tsunami‐induced concentric gravity waves. The ionospheric irregularities initially developed over the Hokkaido region following the interference of gravity waves at ~8:45 UT. Remarkably, the Perkins‐type nighttime MSTIDs accompanying the planar TIDs were discernible over Japan following the irregularities. By comparing with the tsunami model simulation and ocean buoy observations, it is determined that these planar TIDs, lasting for about 10 hr, were likely related to tsunami ocean waves reflected by seamounts, ridges, islands, and seafloor topography in the Pacific Ocean. Due to the absence of sporadic E layers, we suggest that the coupling between the tsunami‐generated gravity waves and the Perkins instability plays an essential role in initiating the equinoctial nighttime MSTIDs. The long‐lasting tsunami can continuously impact the ionosphere, affecting the nighttime ionospheric electrodynamics and making the conditions conducive for the development of midlatitude nighttime ionospheric irregularities and instabilities. Plain Language Summary: On 11 March 2011, a magnitude 9.0 earthquake occurred near the east coast of Honshu, Japan, unleashing a savage tsunami as well as unprecedented plasma ripples at the space‐atmosphere interaction region. Although the earthquake was a transient local event, the tsunami ocean waves backscattered by seafloor topography in the Pacific Ocean continuously excited gravity waves and planar traveling ionospheric disturbances (TIDs) propagating toward Japan for more than 10 hr. Unusual ionospheric band structures referred to the midlatitude nighttime medium‐scale TIDs (MSTIDs) and plasma irregularities developed following the planar TIDs over Japan. It is common to observe the nighttime MSTIDs traveling along the Japan island during the summer; however, they are rarely seen in March. What drove the appearance of MSTIDs and ionospheric irregularities in March was likely the reflected tsunami wave‐induced gravity waves. Such space weather phenomena have an adverse impact on Global Navigation Satellite System navigation and applications. Therefore, understanding how natural hazards impact our upper atmosphere and cause variations in the space environment around Earth is crucial. Key Points: The Tohoku earthquake/tsunami stimulated unstable plasma structures in the midlatitude nighttime ionospherePlanar TIDs related to reflected tsunami‐excited gravity waves are observed along the coastline direction of JapanReflected tsunami‐excited gravity wave seeding may contribute to the formation of the ionospheric irregularities and nighttime MSTIDs [ABSTRACT FROM AUTHOR] |