Analysis of traveling ionospheric disturbances (TIDs) in GPS TEC launched by the 2011 Tohoku earthquake

Traveling ionospheric disturbances (TIDs) have been detected using various measurement techniques, including HF sounders, incoherent scatter radars, in situ measurements, and optical techniques. However, observations of TIDs have tended to be sparse and there is a need for additional observations to provide new scientific insight into the geophysical source phenomenology and wave propagation physics. The dense network of GPS receivers around the globe offers a relatively new data source to observe and monitor TIDs. In this paper, we use total electron content (TEC) measurements from ~4000 GPS receivers throughout the continental United States to observe TIDs associated with the 11 March 2011 Tohoku tsunami. The tsunami propagated across the Pacific to the U.S. west coast over several hours, and we show that corresponding TIDs were observed in the US. Using this network of GPS receivers we present a 2D imaging of TEC perturbations and calculate various TID parameters, including horizontal wavelength, speed, and period. Well-formed, planar TIDs were detected over the west coast of the U.S. ~10 h after the earthquake. Fast Fourier transform analysis of the observed waveforms revealed that the period of the wave was 15.1 min with a horizontal wavelength of 194.8 km, phase velocity of 233.0 m/s, and an azimuth of 105.2° (propagating nearly due east in the direction of the tsunami wave). These results are consistent with the TID observations in airglow measurements from Hawaii earlier in the day and with other GPS TEC observations.