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Electromagnetic Sensing and Visualization Technologies

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Concentric waves appear at 300 km altitude after the 2011 Tohoku earthquake

Concentric waves in the ionosphere around 300 km altitude were detected by GPS total electron content (TEC) observation after the 2011 Tohoku earthquake on March 11. This animation of two-dimensional TEC maps was derived using the data of GEONET, a dense GPS receiver network operated by Geospatial Information Authority of Japan. The TEC data are detrended values derived by subtracting 10-minute running average of the data. The star mark represents the epicenter. Amplitudes of TEC variations are designated by colors, that is, red and blue black colors correspond to +0.2 and -0.4 TEC Unit (TECU = 10^16 electrons / m^2), respectively. The concentric waves in the ionosphere began to appear about 7 minutes after the earthquake onset at 05:46:23 UT (14:46:23 JST) near the epicenter (38.322 deg N, 142.369 deg E, according to the U.S. Geological Survey). The center of these ionospheric concentric structures, termed the "ionospheric epicenter", was located about 170 km from the epicenter in the southeast direction. The ionospheric epicenter was closer to the Japan trench than the epicenter and consistent with estimated areas of the tsunami source. These concentric waves appeared in the western part of Japan until around 09:00 UT (18:00 JST). These observational results indicate that this great earthquake caused not only underground waves (seismic wave) and sea waves (tsunami) but also atmospheric waves which propagated upward in the atmosphere and reached the ionosphere. It is the first time to detect all the details of post-seismic ionospheric disturbances by high-resolution and wide-coverage ionospheric observations. This study is important not only to reveal the relationship between the ionosphere and the lower atmosphere, but also to apply the ionospheric observations to monitor tsunami in a wide area.