Ionospheric disturbances detected by GPS total electron content observation after the 2011 Tohoku earthquake
Ionospheric disturbances detected by GPS total electron content observation after the 2011 Tohoku earthquake
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2011-12
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通讯作者：
T. Tsugawa;A. Saito;Y. Otsuka;M. Nishioka;T. Maruyama;H. Shinagawa;M. Matsumura;Chia‐Hung Chen;H. Kato;T. Nagatsuma;K. Murata
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作者：
T. Tsugawa;A. Saito;Y. Otsuka;M. Nishioka;T. Maruyama;H. Shinagawa;M. Matsumura;Chia‐Hung Chen;H. Kato;T. Nagatsuma;K. Murata
利用日本的高分辨率GPS总电子含量观测，首次揭示了2011年东北地震后太平洋沿岸电离层扰动开始和演化的全部细节。最初的电离层扰动表现为在05:54UT左右，地震发生后约7分钟，在震中附近，随着小的脉冲TEC增强，突然减少了0.6 TEC单位（20%）。06:00UT， TEC纬向扩展增强出现在日本西部，并向西南方向移动。06:00 ~ 06:15，大尺度双峰圆波沿径向传播，第一峰和第二峰的传播速度分别为3457 m/s和783 m/s。在大尺度波之后，中等尺度同心波似乎以138？06:15 UT后423米/秒。在震中附近，在06:00 UT之后观测到周期为0.4分钟的短周期振荡，持续3小时以上。本文主要研究了圆波和同心波。大、中尺度波的圆形或同心圆结构表明这些电离层扰动有一个点源。这些结构的中心位于北纬37.5度，东经144.0度左右，距离震中东南方向170公里。我们把这个同震电离层变化的中心称为“电离层震中”。从传播速度来看，大尺度波是由瑞利波传播产生的声波引起的，第一个峰值是由瑞利波传播产生的声波引起的，第二个峰值是由震中附近海面产生的声波引起的。中尺度同心波的波长和传播速度随时间的延长而减小。这一特征与同震大气波数值模型的结果一致，表明这些中尺度波是由大气重力波引起的。大、中尺度圆波的振幅随其传播方向的方位角不均匀，北、西方向的振幅比其他方向大得多。这种指向性不能用先前提出的理论来解释。
All the details of the commencement and evolution of ionospheric disturbances after the 2011 off the Pacific coast of Tohoku Earthquake were firstly revealed by the high-resolution GPS total electron content observation in Japan. The initial ionospheric disturbance appeared as sudden depletions by ̃6 TEC unit (20%) following small impulsive TEC enhancements around 05:54UT, about seven minutes after the earthquake onset, near the epicenter. At 06:00UT, zonally extended enhancements of TEC appeared in the west of Japan, and traveled to the southwest direction. From 06:00UT to 06:15UT, large-scale circular waves with two peaks propagated in the radial direction in the propagation velocity of 3,457 m/s and 783 m/s for the first and second peak, respectively. Following the large-scale waves, medium-scale concentric waves appeared to propagate at the velocity of 138?423 m/s after 06:15 UT. In the vicinity of the epicenter, short-period oscillations with period of ̃4 minutes were observed after ̃06:00 UT for 3 hours or more. We focus on the the circular and concentric waves in this paper. The circular or concentric structures of the largeand medium-scale waves indicate that these ionospheric disturbances had a point source. The center of these structures was located around 37.5 deg N of latitude and 144.0 deg E of longitude, 170 km far from the epicenter to the southeast direction. We termed this center of the coseismic ionospheric variations as ”ionospheric epicenter”. According to the propagation velocities, the large-scale waves would be caused by the acoustic waves generated from the propagating Rayleigh wave for the first peak and from the sea surface near the epicenter for the second peak. The wavelength and the propagation velocity of the medium-scale concentric waves tended to decrease with time. This characteristic is consistent with the result of a numerical model of the coseismic atmospheric wave, indicating that these medium-scale waves were caused by the atmospheric gravity waves. The amplitude of the largeand medium-scale circular waves were not uniform depending on azimuth of their propagation direction, much larger in the north and west directions than other directions. This directivity could not be explained by the previously proposed theory.