A 15-year revisit on seismo-ionospheric precursors associated with the 11 March 2011 M9.0 Tohoku Earthquake observed by the global ionosphere map of total electron content and FORMOSAT-3/COSMIC of electron density profiles

The time series of the total electron content (TEC) extracted from the global ionosphere map (GIM) is useful to detect seismo-ionospheric anomalies at a certain region. When the detected anomalies are similar to those repeatedly appearing before large earthquakes in the same region, it might be considered temporal SIPs (seismo-ionospheric precursors) being observed.  To discriminate the possible SIPs from global effects (such as solar disturbances, magnetic storms, etc.), a global search on anomalies of the GIM TEC is ideal to be employed.  The spatial analysis simultaneously detects anomalies similar to the temporal SIP at each lattice of GIM and finds the distribution or pattern of the detected anomalies of the globe.  When the detected anomalies specifically and continuously appear specifically near the monitoring region, we can declare spatial SIPs of the GIM TEC being observed. The distance between northern and southern crests of equatorial ionization anomaly (EIA) in GIM TEC along the earthquake longitude can be used to estimate electric fields associated with the observed SIPs.  Meanwhile, radio occultation (RO) observations of FORMOSAT-3/COSMIC (F3C) satellites are useful to examine the vertical electron density structures. Results show that GIM TEC and the electron density at the F2-peak, NmF2, of F3C/RO profiles significantly increase specifically over the epicenter 3-4 days before the quake, which suggests SIPs of the Tohoku earthquake being detected. The EIA crests poleward motion and the F3C RO electron density profiles uplift indicate that the eastward electric fields have been enhanced during the SIP days.