Vertical velocity of acoustic wave determined from altitudes of TEC
disturbances after a foreshock
Abstract
We investigate ionospheric disturbances using the total electron content
(TEC) data retrieved by the three satellites after the foreshock of the
2011 Tohoku Earthquake on 9 March 2011. Co-seismic ionospheric
disturbances (CIDs) appeared to extend from an onset point
concentrically in all of the satellite data. We have found, however,
that the geographic coordinates of the onset points did not coincide if
the observed CIDs were assumed to occur at one altitude. Admitting that
the altitudes of the onset points are different, we searched for
coinciding geographic coordinates of the onset points using the two data
sets by changing the altitudes and identified the altitude of the two
onset points at 155.4 and 234.9 km, and the onset time at these
altitudes. As a result, the vertical velocity of acoustic wave is
estimated to be 1.04 km/s from the travel time between the altitudes of
155.4 and 234.9 km. This is 1.4 times higher than the sound velocity
calculated using the empirical model NRLMSISE-00. The present study
provides a method of determining the source location of the acoustic
wave from the ionospheric TEC analysis without using the seismic data.