15:45 〜 16:00
[MIS10-08] The three-dimensional ionospheric tomography related to the Tohoku Earthquake in 2011
★Invited Papers
キーワード：Ionospheric Tomography、Total Electron Content、Ionospheric Disturbances、Atmospheric Gravity Waves
In this study, we reconstructed the three-dimensional (3-D) ionospheric disturbances of electron density (Ne) induced by the M9.0 Tohoku Earthquake in 2011 using the computerized ionospheric tomography (CIT) technique. First, according to the filtered total electron content (TEC) datasets from the GPS Earth Observation Network (GEONET), two patterns of traveling ionospheric disturbances (TIDs) featured by different velocities and wavelengths were detected. The large-scale circular TIDs (CTIDs) with propagating velocity of 2.3 - 3.3 km/s related to the Rayleigh surface waves were observed during 06:00 - 06:25 UT. Following that, the meso-scale CTIDs generated by tsunami-induced atmospheric gravity waves (AGWs) with a slower velocity of 200 - 230 m/s gradually appeared at 06:30 UT.On this basis, an initial input-free algorithm, termed the improved constraint least square fitting (ICLSF) algorithm was adopted in the CIT technique to understand the 3-D evolution of Ne caused by the Tohoku Earthquake.
The reproduced Ne distributions around 06:00 - 06:10 UT exhibited significant uplift with a displacement of ~30 km in the F layer along the longitude of 138° - 141°E, which corresponded to a sudden depletion of Ne when Rayleigh wave-induced TIDs was passing through. With respect to the disturbed Ne (dNe), the values ranged between ±2×1010 e/m3 in 250 - 400 km altitudes. At 06:12 UT, abrupt uplift of the F layer with sharp slope was detected in 137.5°E. Then, it propagated away from the epicenter and appeared in 136°E at 06:24 UT. From then on, the Rayleigh wave-induced ionospheric disturbances became dispersive, and the tsunami-induced disturbed structures became prominent. During 06:34 - 06:52 UT, the meso-scale TIDs associated with tsunami gradually came out from 06:34 UT with a remarkable sinusoidal waveform. Ne mainly distributed in the height of 250 - 400 km, whose values ranged from 2×1011 e/m3 to 8×1011 e/m3. The distribution of detrended Ne presented several prominent negative and positive bands, which were closely following along 132° - 141°E in a similar height interval. Numerically, the amounts approximately ranged between ±2×1011 e/m3.
Further, the downward phase progression with increasing time was significantly detected in the time-height distribution of the filtered Ne related to the tsunami waves generated by offshore earthquake, which strongly indicated the signature of the upward propagation of AGWs in accord with the numerical simulated results. However, this kind of phase progression was not detected during 06: 00 - 06: 30 UT (15 - 45 minutes after the mainshock) because the disturbances during this period were related to the acoustic waves generated by the crust displacement and propagating Rayleigh waves, rather than the tsunami-induced AGWs. Besides, no perturbations were reproduced just after the mainshock from 05:56 UT to 06:00 UT, because the traveling of acoustic waves from the Earth’s surface to the ionosphere takes about 10 - 15 minutes. Finally, by virtue of vertical wavelength reproduced by the ICLSF algorithm and the dispersion equation, we estimated a background neutral wind of -49.3 m/s for the tsunami case (negative values represent northward propagation). The estimated neutral wind velocity is consistent with the usual values ranging from -100 m/s to 100 m/s.
The reproduced Ne distributions around 06:00 - 06:10 UT exhibited significant uplift with a displacement of ~30 km in the F layer along the longitude of 138° - 141°E, which corresponded to a sudden depletion of Ne when Rayleigh wave-induced TIDs was passing through. With respect to the disturbed Ne (dNe), the values ranged between ±2×1010 e/m3 in 250 - 400 km altitudes. At 06:12 UT, abrupt uplift of the F layer with sharp slope was detected in 137.5°E. Then, it propagated away from the epicenter and appeared in 136°E at 06:24 UT. From then on, the Rayleigh wave-induced ionospheric disturbances became dispersive, and the tsunami-induced disturbed structures became prominent. During 06:34 - 06:52 UT, the meso-scale TIDs associated with tsunami gradually came out from 06:34 UT with a remarkable sinusoidal waveform. Ne mainly distributed in the height of 250 - 400 km, whose values ranged from 2×1011 e/m3 to 8×1011 e/m3. The distribution of detrended Ne presented several prominent negative and positive bands, which were closely following along 132° - 141°E in a similar height interval. Numerically, the amounts approximately ranged between ±2×1011 e/m3.
Further, the downward phase progression with increasing time was significantly detected in the time-height distribution of the filtered Ne related to the tsunami waves generated by offshore earthquake, which strongly indicated the signature of the upward propagation of AGWs in accord with the numerical simulated results. However, this kind of phase progression was not detected during 06: 00 - 06: 30 UT (15 - 45 minutes after the mainshock) because the disturbances during this period were related to the acoustic waves generated by the crust displacement and propagating Rayleigh waves, rather than the tsunami-induced AGWs. Besides, no perturbations were reproduced just after the mainshock from 05:56 UT to 06:00 UT, because the traveling of acoustic waves from the Earth’s surface to the ionosphere takes about 10 - 15 minutes. Finally, by virtue of vertical wavelength reproduced by the ICLSF algorithm and the dispersion equation, we estimated a background neutral wind of -49.3 m/s for the tsunami case (negative values represent northward propagation). The estimated neutral wind velocity is consistent with the usual values ranging from -100 m/s to 100 m/s.