[M-TT43] Brand-new scope of coupling geophysics being established by infrasound and associated waves

[MTT43-02] An estimation of acoustic velocity in lower thermosphere using GNSS TEC after the foreshock of the 2011 Tohoku Earthquake

*Yoshihiro Kakinami¹, Hiroaki Saito², Tetsuo Yamamoto², Chia-Hung Chen³, Masa-yuki Yamamoto⁴, Kensuke Nakajima⁵, Jann-Yenq LIU⁶, Shigeto Watanabe¹ (1.Hokkaido Information University, 2.Hokkaido University, 3.National Cheng Kung University, 4.Kochi University of Technology, 5.Kyushu University, 6.National Central University)

Keywords:the foreshock of the 2011 Tohoku Earthquake, velocity of acoustic wave in the thermosphere, GNSS Total electron content, an estimation of altitude of total electron content

An acoustic wave emitted by earthquake reaches thermosphere and disturb ionospheric plasma through the collision. These disturbances are often observed in GNSS total electron content (TEC) observations. However, since TEC is the integrated plasma density, it is hard to investigate the propagation of acoustic in principle when we use a single satellite data. We found that concentrically propagating disturbance retrieved by three satellites after the foreshock of the 2011 Tohoku Earthquake on 9 March 2011. When the observed altitude is fixed an altitude, the onset points did not coincide. When we relaxed the assumption of the fix altitude, we found that the onset points coincide and altitude and geographic coordinates of the onset points are determined simultaneously. The altitudes are found to be 107.8, 131.8 and 133.3 km, and the onset time at these altitudes. As a result, the vertical velocity of acoustic wave is estimated to be 448 m/s from the travel time between the altitudes of 107.8 and 131.8 km and 370 m/s between the altitude of 107.8 and 133.3 km. These velocities are comparable to those estimated from the neutral temperature given by the empirical model NRLMSISE-00. The proposed method can determine the location of ionospheric disturbance detected in TEC independently of the seismic data and gives the information of propagation of acoustic wave in the thermosphere.