Observations of Traveling Ionospheric Disturbances (TIDs) Over the United States Associated With the Tsunami Generated by the 2011 Tohoku Earthquake

Abstract:

The March 11, 2011 Tohoku earthquake generated a massive tsunami off the Pacific coast of Japan which in turn forced intense atmospheric gravity waves (AGW) that were seen in GPS Total Electron Content (TEC) data and airglow measurements as traveling ionospheric disturbance (TID) signatures as far away as Hawaii. What is unknown is how far these TIDs traveled after being launched by the tsunami and the role of the underlying neutral atmosphere on their propagation characteristics. For the first time, we show that TIDs associated with the Tohoku tsunami were observed in GPS TEC data for several hours over the west coast of the US and as far inland as Colorado. The results presented here show a range of TIDs generated by gravity wave packets propagating into the ionosphere from below. We present results indicating the presence of TIDs with periods ranging from 15 to 30 minutes, and horizontal wavelengths from 150 km to 400 km. The azimuth of the observed TID wave train was 121.8 ± 1.8° (angle measured in degrees east of north), which matches the azimuth of the tsunami near the Pacific coast of the US. The observed period of the TIDs was one of the spectral components of the tsunami wave packet as it approached the Pacific coast of the US. These results suggest that the tsunami was the source of the TIDs over the US. Additionally, the TID periods and horizontal wavelengths clearly vary in longitude. These variations agree with theoretical gravity wave results concerning propagation and dissipation in the thermosphere.