Ionospheric disturbances
after the 2011 Tohoku earthquake

 

 

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Ionospheric disturbances were observed by GPS total electron content (TEC) and ionosonde observations after the 2011 off the Pacific coast of Tohoku Earthquake at 05:46 on March 11, 2011.

 

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Animation of TEC variation derived with GEONET data.


Animation file : MPEG format [12.6MB] / MOV format [7.9MB]

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Figure 1. Two-dimensional maps of total electron content (TEC) variation derived with GEONET data. Star and cross marks represent the epicenter and "ionospheric epicenter", respectively. Gray circles represent concentric circles with the ionospheric epicenter.

Figure 1 shows two-dimensional maps of total electron content (TEC) variation 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. Star and cross marks represent the epicenter and "ionospheric epicenter", respectively. Gray circles represent concentric circles with the ionospheric epicenter.
Several minutes after the earthquake, concentric waves appeared to propagate away from the ionospheric epicenter. The ionospheric epicenter was located around 37.5 deg N of latitude and 144.0 deg E of longitude, 170km far from the epicenter to the southeast direction.

 

(a)Ionograms at Kokubunji (left) just after the earthquake and (right) at the same time one day before.

(a)Ionograms at Yamagawa (left) just after the earthquake and (right) at the same time one day before.

 

Figure 2. Ionograms from ionosonde observations at (a) Kokubunji and (b) Yamagawa. The horizontal and vertical axies represent the frequency from 1 to 15 MHz and the virtual height from 0 to 600 km, respectively.

Figure 2 shows the ionograms from ionosonde observations at Kokubunji (35.71 deg N, 139.49 deg E) and Yamagawa (31.20 deg N, 130.62 deg E). The horizontal and vertical axies represent the frequency from 1 to 15 MHz and the virtual height from 0 to 600 km, respectively. The ionospheric echo traces in the ionograms correspond to the vertual height of the ionosphere. As indicated by red circles, the irregular distortion of echo trace is observed at virtual height of 200-300 km at both Kokubunji and Yamagawa after the earthquake. The 200-300 km virtual height corresponds to the real height of 150-250 km. These irregular echo traces would be caused by the modulation of ionoshperic height due to the atmospheric waves associated with the earthquake.

 

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The GPS data of GEONET are provided by the Geospatial Information Authority of Japan. GPS-TEC Data analysis is carried out under the collaboration among NICT, Kyoto University, and Nagoya University. For further information, please refer to the following papers:

 

 

Tsugawa, T., A. Saito, Y. Otsuka, M. Nishioka, T. Maruyama, H. Kato, T. Nagatsuma, and K. T. Murata(2011), Ionospheric disturbances detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake, Earth, Planets, and Space, 63, 875-879.

Maruyama, T., T. Tsugawa, H. Kato, A. Saito, Y. Otsuka, and M. Nishioka(2011), Ionospheric multiple stratifications and irregularities induced by the 2011 off the Pacific coast of Tohoku Earthquake, Earth, Planets, and Space,63, 869-873.

Chen, C. H., A. Saito, C. H. Lin, J. Y. Liu, H. F. Tsai, T. Tsugawa, Y. Otsuka, M. Nishioka, and M. Matsumura(2011), Long-distance propagation of ionospheric disturbance generated by the 2011 off the Pacific coast of Tohoku Earthquake, Earth, Planets, and Space, 63, 881-884.

Saito, A., T. Tsugawa, Y. Otsuka, M. Nishioka, T. Iyemori, M. Matsumura, S. Saito, C. H. Chen, Y. Goi, and N. Choosakul (2011), Acoustic resonance and plasma depletion detected by GPS total electron content observation after the 2011 off the Pacific coast of Tohoku Earthquake, Earth, Planets, and Space, 63, 863-867.

Matsumura, M., A. Saito, T. Iyemori, H. Shinagawa, T. Tsugawa, Y. Otsuka, M. Nishioka, and C. H. Chen(2011), Numerical simulations of atmospheric waves excited by the 2011 off the Pacific coast of Tohoku Earthquake, Earth, Planets, and Space, 63, 885-889.

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